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  • 1. Bavinck, Maaike Bouwes
    et al.
    Jons, Klaus D.
    Zielinski, Michal
    Patriarche, Gilles
    Harmand, Jean-Christophe
    Akopian, Nika
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics. Delft Univ Techno, Netherlands.
    Photon Cascade from a Single Crystal Phase Nanowire Quantum Dot2016In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, no 2, p. 1081-1085Article in journal (Refereed)
    Abstract [en]

    We report the first comprehensive experimental and theoretical study of the optical properties of single crystal phase quantum dots in InP nanowires. Crystal phase quantum dots are defined by a transition in the crystallographic lattice between zinc blende and wurtzite segments and therefore offer unprecedented potential to be controlled with atomic layer accuracy without random alloying. We show for the first time that crystal phase quantum dots are a source of pure single-photons and cascaded photon-pairs from type II transitions with excellent optical properties in terms of intensity and line width. We notice that the emission spectra consist often of two peaks close in energy, which we explain with a comprehensive theory showing that the symmetry of the system plays a crucial role for the hole levels forming hybridized orbitals. Our results state that crystal phase quantum dots have promising quantum optical properties for single photon application and quantum optics.

  • 2.
    Brodu, Annalisa
    et al.
    Univ Utrecht, Debye Inst Nanomat Sci, NL-3584 CC Utrecht, Netherlands..
    Ballottin, Mariana V.
    Radboud Univ Nijmegen, High Field Magnet Lab, HFML EMFL, NL-6525 ED Nijmegen, Netherlands..
    Buhot, Jonathan
    Radboud Univ Nijmegen, High Field Magnet Lab, HFML EMFL, NL-6525 ED Nijmegen, Netherlands..
    van Harten, Elleke J.
    Univ Utrecht, Debye Inst Nanomat Sci, NL-3584 CC Utrecht, Netherlands..
    Dupont, Dorian
    Univ Ghent, Phys & Chem Nanostruct, B-9000 Ghent, Belgium..
    La Porta, Andrea
    Univ Antwerp, EMAT, Electron Microscopy Mat Res, B-2020 Antwerp, Belgium..
    Prins, P. Tim
    Univ Utrecht, Debye Inst Nanomat Sci, NL-3584 CC Utrecht, Netherlands..
    Tessier, Mickael D.
    Univ Ghent, Phys & Chem Nanostruct, B-9000 Ghent, Belgium..
    Versteegh, Marijn A. M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Bals, Sara
    Univ Antwerp, EMAT, Electron Microscopy Mat Res, B-2020 Antwerp, Belgium..
    Hens, Zeger
    Univ Ghent, Phys & Chem Nanostruct, B-9000 Ghent, Belgium..
    Rabouw, Freddy T.
    Univ Utrecht, Debye Inst Nanomat Sci, NL-3584 CC Utrecht, Netherlands..
    Christianen, Peter C. M.
    Radboud Univ Nijmegen, High Field Magnet Lab, HFML EMFL, NL-6525 ED Nijmegen, Netherlands..
    Donega, Celso de Mello
    Univ Utrecht, Debye Inst Nanomat Sci, NL-3584 CC Utrecht, Netherlands..
    Vanmaekelbergh, Daniel
    Univ Utrecht, Debye Inst Nanomat Sci, NL-3584 CC Utrecht, Netherlands..
    Exciton Fine Structure and Lattice Dynamics in InP/ZnSe Core/Shell Quantum Dots2018In: ACS Photonics, E-ISSN 2330-4022, Vol. 5, no 8, p. 3353-3362Article in journal (Refereed)
    Abstract [en]

    Nanocrystalline InP quantum dots (QDs) hold promise for heavy-metal-free optoelectronic applications due to their bright and size tunable emission in the visible range. Photochemical stability and high photoluminescence (PL) quantum yield are obtained by a diversity of epitaxial shells around the InP core. To understand and optimize the emission line shapes, the exciton fine structure of InP core/shell QD systems needs be investigated. Here, we study the exciton fine structure of InP/ZnSe core/shell QDs with core diameters ranging from 2.9 to 3.6 nm (PL peak from 2.3 to 1.95 eV at 4 K). PL decay measurements as a function of temperature in the 10 mK to 300 K range show that the lowest exciton fine structure state is a dark state, from which radiative recombination is assisted by coupling to confined acoustic phonons with energies ranging from 4 to 7 meV, depending on the core diameter. Circularly polarized fluorescence line-narrowing (FLN) spectroscopy at 4 K under high magnetic fields (up to 30 T) demonstrates that radiative recombination from the dark F = +/- 2 state involves acoustic and optical phonons, from both the InP core and the ZnSe shell. Our data indicate that the highest intensity FLN peak is an acoustic phonon replica rather than a zero-phonon line, implying that the energy separation observed between the F = +/- 1 state and the highest intensity peak in the FLN spectra (6 to 16 meV, depending on the InP core size) is larger than the splitting between the dark and bright fine structure exciton states.

  • 3. Cavalli, Alessandro
    et al.
    Wang, Jia
    Zadeh, Iman Esmaeil
    Reimer, Michael E.
    Verheijen, Marcel A.
    Soini, Martin
    Plissard, Sebastien R.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Haverkort, Jos E. M.
    Bakkers, Erik P. A. M.
    High-Yield Growth and Characterization of < 100 > InP p-n Diode Nanowires2016In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, no 5, p. 3071-3077Article in journal (Refereed)
    Abstract [en]

    Semiconductor nanowires are nanoscale structures holding promise in many fields such as optoelectronics, quantum computing, and thermoelectrics. Nanowires are usually grown vertically on (111)-oriented substrates, while (100) is the standard in semiconductor technology. The ability to grow and to control impurity doping of (100) nanowires is crucial for integration. Here, we discuss doping of single-crystalline < 100 > nanowires, and the structural and optoelectronic properties of p-n junctions based on < 100 > InP nanowires. We describe a novel approach to achieve low resistance electrical contacts to nanowires via a gradual interface based on p-doped InAsP. As a first demonstration in optoelectronic devices, we realize a single nanowire light emitting diode in a < 100 >-oriented InP nanowire p-n junction. To obtain high vertical yield, which is necessary for future applications, we investigate the effect of the introduction of dopants on the nanowire growth.

  • 4. Cheng, Y.
    et al.
    Chi, X.
    Gu, C.
    Zou, K.
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Chen, S.
    Liu, H.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Hu, X.
    Experimental demonstration of superconducting nanowire single-photon detectors integrated with current reservoirs2018In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2018Conference paper (Refereed)
    Abstract [en]

    We experimentally demonstrate the superconducting nanowire single-photon detectors integrated with current reservoirs that function as low-noise pre-amplifiers to increase the signal-to-noise ratio of detectors' outputs.

  • 5.
    Chi, Xiaoming
    et al.
    Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin 300072, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin 300072, Peoples R China..
    Zou, Kai
    Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin 300072, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin 300072, Peoples R China..
    Gu, Chao
    Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin 300072, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin 300072, Peoples R China..
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Cheng, Yuhao
    Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin 300072, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin 300072, Peoples R China..
    Hu, Nan
    Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin 300072, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin 300072, Peoples R China..
    Lan, Xiaojian
    Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin 300072, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin 300072, Peoples R China..
    Chen, Shufan
    Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin 300072, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin 300072, Peoples R China..
    Lin, Zuzeng
    KTH, School of Engineering Sciences (SCI), Applied Physics. Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin 300072, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin 300072, Peoples R China..
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Hu, Xiaolong
    Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin 300072, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin 300072, Peoples R China..
    Fractal superconducting nanowire single-photon detectors with reduced polarization sensitivity2018In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 43, no 20, p. 5017-5020Article in journal (Refereed)
    Abstract [en]

    We demonstrate superconducting nanowire single-photon detectors (SNSPDs) based on a fractal design of the nanowires to reduce the polarization sensitivity of detection efficiency. We patterned niobium titanium nitride thin films into Peano curves with a linewidth of 100 nm and integrated the nanowires with optical microcavities to enhance their optical absorption. At a base temperature of 2.6 K, the fractal SNSPD exhibited a polarization-maximum device efficiency of 67% and a polarization-minimum device efficiency of 61% at a wavelength of 1550 nm. Therefore, the polarization sensitivity, defined as their ratio, was 1.1, lower than the polarization sensitivity of the SNSPDs in the meander design. The reduced polarization sensitivity of the detector could be maintained for higher-order spatial modes in multimode optical fibers and could tolerate misalignment between the optical mode and the detector. This fractal design is applicable to both amorphous and polycrystalline materials that are commonly used for making SNSPDs.

  • 6. Chi, Xiaoming
    et al.
    Zou, Kai
    Gu, Chao
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Cheng, Yuhao
    Hu, Nan
    Lan, Xiaojian
    Chen, Shufan
    Lin, Zuzeng
    KTH, School of Engineering Sciences (SCI), Applied Physics. School of Precision Instrument and Optoelectronic Engineering, Tianjin University, Tianjin 300072, China 2 Key Laboratory of Optoelectronic Information Science and Technology, Ministry of Education, Tianjin 300072, China.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Hu, Xiaolong
    Fractal superconducting nanowire single-photon detectors with reduced polarization sensitivity2018In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 43, no 20Article in journal (Refereed)
    Abstract [en]

    We demonstrate superconducting nanowire single-photon detectors (SNSPDs) based on a fractal design of the nanowires to reduce the polarization sensitivity of detection efficiency. We patterned niobium titanium nitride thin films into Peano curves with a linewidth of 100 nm and integrated the nanowires with optical microcavities to enhance their optical absorption. At a base temperature of 2.6 K, the fractal SNSPD exhibited a polarization-maximum device efficiency of 67% and a polarization-minimum device efficiency of 61% at a wavelength of 1550 nm. Therefore, the polarization sensitivity, defined as their ratio, was 1.1, lower than the polarization sensitivity of the SNSPDs in the meander design. The reduced polarization sensitivity of the detector could be maintained for higher-order spatial modes in multimode optical fibers and could tolerate misalignment between the optical mode and the detector. This fractal design is applicable to both amorphous and polycrystalline materials that are commonly used for making SNSPDs.

  • 7.
    Chi, Xiaoming
    et al.
    Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin, Peoples R China..
    Zou, Kai
    Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin, Peoples R China..
    Hu, Nan
    Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin, Peoples R China..
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Hu, Xiaolong
    Tianjin Univ, Sch Precis Instrument & Optoelect Engn, Tianjin, Peoples R China.;Minist Educ, Key Lab Optoelect Informat Sci & Technol, Tianjin, Peoples R China..
    IEEE, GP
    RF-amplifier-free superconducting nanowire single-photon detector system2018In: 2018 ASIA COMMUNICATIONS AND PHOTONICS CONFERENCE (ACP), IEEE , 2018Conference paper (Refereed)
    Abstract [en]

    We used a superconducting nanowire single photon detector integrated th a current reservoir in a closed-cycle cryocooler to demonstrate

  • 8.
    Elshaari, Ali W.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Buyukozer, Efe
    Swiss Fed Inst Technol, Dept Mech & Proc Engn, CH-8092 Zurich, Switzerland..
    Zadeh, Iman Esmaeil
    Delft Univ Technol, Opt Grp, NL-2628 CJ Delft, Netherlands..
    Lettner, Thomas
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zhao, Peng
    Tsinghua Univ, Tsinghua Natl Lab Informat Sci & Technol, Dept Elect Engn, Beijing, Peoples R China..
    Schöll, Eva
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Gyger, Samuel
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Reimer, Michael E.
    Univ Waterloo, Inst Quantum Comp, Waterloo, ON N2L 3G1, Canada.;Univ Waterloo, Dept Elect & Comp Engn, Waterloo, ON N2L 3G1, Canada..
    Dalacu, Dan
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Poole, Philip J.
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Strain-Tunable Quantum Integrated Photonics2018In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 12, p. 7969-7976Article in journal (Refereed)
    Abstract [en]

    Semiconductor quantum dots are crucial parts of the photonic quantum technology toolbox because they show excellent single-photon emission properties in addition to their potential as solid-state qubits. Recently, there has been an increasing effort to deterministically integrate single semiconductor quantum dots into complex photonic circuits. Despite rapid progress in the field, it remains challenging to manipulate the optical properties of waveguide-integrated quantum emitters in a deterministic, reversible, and nonintrusive manner. Here we demonstrate a new class of hybrid quantum photonic circuits combining III V semiconductors, silicon nitride, and piezoelectric crystals. Using a combination of bottom-up, top-down, and nanomanipulation techniques, we realize strain tuning of a selected, waveguide-integrated, quantum emitter and a planar integrated optical resonator. Our findings are an important step toward realizing reconfigurable quantum-integrated photonics, with full control over the quantum sources and the photonic circuit.

  • 9.
    Elshaari, Ali W.
    et al.
    Royal Inst Technol KTH, Dept Appl Phys, Quantum Nano Photon Grp, S-10691 Stockholm, Sweden..
    Buyukozer, Efe
    Swiss Fed Inst Technol, Dept Mech & Proc Engn, CH-8092 Zurich, Switzerland..
    Zadeh, Iman Esmaeil
    Delft Univ Technol, Opt Grp, NL-2628 CJ Delft, Netherlands..
    Lettner, Thomas
    Royal Inst Technol KTH, Dept Appl Phys, Quantum Nano Photon Grp, S-10691 Stockholm, Sweden..
    Zhao, Peng
    Tsinghua Univ, Tsinghua Natl Lab Informat Sci & Technol, Dept Elect Engn, Beijing, Peoples R China..
    Schöll, Eva
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics. Royal Inst Technol KTH, Dept Appl Phys, Quantum Nano Photon Grp, S-10691 Stockholm, Sweden..
    Gyger, Samuel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics. Royal Inst Technol KTH, Dept Appl Phys, Quantum Nano Photon Grp, S-10691 Stockholm, Sweden..
    Reimer, Michael E.
    Univ Waterloo, Inst Quantum Comp, Waterloo, ON N2L 3G1, Canada.;Univ Waterloo, Dept Elect & Comp Engn, Waterloo, ON N2L 3G1, Canada..
    Dalacu, Dan
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Poole, Philip J.
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics. Royal Inst Technol KTH, Dept Appl Phys, Quantum Nano Photon Grp, S-10691 Stockholm, Sweden..
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics. Royal Inst Technol KTH, Dept Appl Phys, Quantum Nano Photon Grp, S-10691 Stockholm, Sweden..
    Strain-Tunable Quantum Integrated Photonics2018In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 12, p. 7969-7976Article in journal (Refereed)
    Abstract [en]

    Semiconductor quantum dots are crucial parts of the photonic quantum technology toolbox because they show excellent single-photon emission properties in addition to their potential as solid-state qubits. Recently, there has been an increasing effort to deterministically integrate single semiconductor quantum dots into complex photonic circuits. Despite rapid progress in the field, it remains challenging to manipulate the optical properties of waveguide-integrated quantum emitters in a deterministic, reversible, and nonintrusive manner. Here we demonstrate a new class of hybrid quantum photonic circuits combining III V semiconductors, silicon nitride, and piezoelectric crystals. Using a combination of bottom-up, top-down, and nanomanipulation techniques, we realize strain tuning of a selected, waveguide-integrated, quantum emitter and a planar integrated optical resonator. Our findings are an important step toward realizing reconfigurable quantum-integrated photonics, with full control over the quantum sources and the photonic circuit.

  • 10.
    Elshaari, Ali W.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Esmaeil Zadeh, I.
    Fognini, A.
    Dalacu, D.
    Poole, P. J.
    Reimer, M. E.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Hybrid quantum photonic integrated circuits2018In: Proceedings - International Conference Laser Optics 2018, ICLO 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, article id 8435508Conference paper (Refereed)
    Abstract [en]

    Quantum photonic integrated circuits require a scalable approach to integrate bright on-demand sources of entangled photon-pairs in complex on-chip quantum photonic circuits. Currently, the most promising sources are based on III/V semiconductor quantum dots. However, complex photonic circuitry is mainly achieved in silicon photonics due to the tremendous technological challenges in circuit fabrication. We take the best of both worlds by developing a new hybrid on-chip nanofabrication approach, allowing to integrate III/V semiconductor nanowire quantum emitters into silicon-based photonics.

  • 11.
    Elshaari, Ali W.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zadeh, I. E.
    Fognini, A.
    Reimer, M. E.
    Dalacu, D.
    Poole, P. J.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Jöns, Klaus
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Hybrid quantum photonics2017In: Optics InfoBase Conference Papers, Optical Society of America, 2017, Vol. Part F43Conference paper (Refereed)
    Abstract [en]

    We deterministically integrate nanowire quantum-emitters in SiN photonic circuits. We generate single-photons, suppress excitation-laser, and isolate specific transitions in the quantumemitter all on-chip with electrically-tunable filter. Finally, we demonstrate a novel Quantum- WDM channel on-chip.

  • 12.
    Elshaari, Ali W.
    et al.
    KTH, School of Electrical Engineering (EES).
    Zadeh, Iman Esmaeil
    Fognini, Andreas
    Reimer, Michael E.
    Dalacu, Dan
    Poole, Philip J.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, School of Electrical Engineering (EES).
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Nano Photonics.
    On-chip single photon filtering and multiplexing in hybrid quantum photonic circuits2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 379Article in journal (Refereed)
    Abstract [en]

    Quantum light plays a pivotal role in modern science and future photonic applications. Since the advent of integrated quantum nanophotonics different material platforms based on III-V nanostructures-, colour centers-, and nonlinear waveguides as on-chip light sources have been investigated. Each platform has unique advantages and limitations; however, all implementations face major challenges with filtering of individual quantum states, scalable integration, deterministic multiplexing of selected quantum emitters, and on-chip excitation suppression. Here we overcome all of these challenges with a hybrid and scalable approach, where single III-V quantum emitters are positioned and deterministically integrated in a complementary metal-oxide-semiconductor-compatible photonic circuit. We demonstrate reconfigurable on-chip single-photon filtering and wavelength division multiplexing with a foot print one million times smaller than similar table-top approaches, while offering excitation suppression of more than 95 dB and efficient routing of single photons over a bandwidth of 40 nm. Our work marks an important step to harvest quantum optical technologies' full potential.

  • 13.
    Elshaari, Ali W.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. Delft Univ Technol, Kavli Inst Nanosci, Netherlands.
    Zadeh, Iman Esmaeil
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. Delft Univ Technol, Kavli Inst Nanosci, Netherlands.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Thermo-Optic Characterization of Silicon Nitride Resonators for Cryogenic Photonic Circuits2016In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 8, no 3, article id 2701009Article in journal (Refereed)
    Abstract [en]

    In this paper, we characterize the Thermo-optic properties of silicon nitride ring resonators between 18 and 300 K. The Thermo-optic coefficients of the silicon nitride core and the oxide cladding are measured by studying the temperature dependence of the resonance wavelengths. The resonant modes show low temperature dependence at cryogenic temperatures and higher dependence as the temperature increases. We find the Thermo-optic coefficients of PECVD silicon nitride and silicon oxide to be 2.51 +/- 0.08 E-5 K-1 and 0.96 +/- 0.09 E-5 K-1 at room temperature while decreasing by an order of magnitude when cooling to 18 K. To show the effect of variations in the thermo-optic coefficients on device performance, we study the tuning of a fully integrated electrically tunable filter as a function of voltage for different temperatures. The presented results provide new practical guidelines in designing photonic circuits for studying low-temperature optical phenomena.

  • 14.
    Fognini, A.
    et al.
    Delft Univ Technol, Kavli Inst Nanosci Delft, NL-2628 CJ Delft, Netherlands..
    Ahmadi, A.
    Univ Waterloo, Inst Quantum Comp, Waterloo, ON N2L 3G1, Canada.;Univ Waterloo, Dept Phys & Astron, Waterloo, ON N2L 3G1, Canada..
    Daley, S. J.
    Univ Waterloo, Inst Quantum Comp, Waterloo, ON N2L 3G1, Canada.;Univ Waterloo, Dept Elect & Comp Engn, Waterloo, ON N2L 3G1, Canada..
    Reimer, M. E.
    Univ Waterloo, Inst Quantum Comp, Waterloo, ON N2L 3G1, Canada.;Univ Waterloo, Dept Elect & Comp Engn, Waterloo, ON N2L 3G1, Canada..
    Zwiller, V
    KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova. KTH, School of Engineering Sciences (SCI), Applied Physics. Delft Univ Technol, Kavli Inst Nanosci Delft, NL-2628 CJ Delft, Netherlands..
    Universal fine-structure eraser for quantum dots2018In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 19, p. 24487-24496Article in journal (Refereed)
    Abstract [en]

    We analyze the degree of entanglement measurable from a quantum dot via the biexciton-exciton cascade as a function of the exciton fine-structure splitting and the detection time resolution. We show that the time-energy uncertainty relation provides means to measure a high entanglement even in presence of a finite fine-structure splitting when a detection system with high temporal resolution is employed. Still, in many applications it would be beneficial if the fine-structure splitting could be compensated to zero. To solve this problem, we propose an all-optical approach with rotating waveplates to erase this fine-structure splitting completely which should allow obtaining a high degree of entanglement with near-unity efficiency. Our optical approach is possible with current technology and is also compatible with any quantum dot showing fine-structure splitting. This bears the advantage that for example the fine-structure splitting of quantum dots in nanowires and micropillars can be directly compensated without the need for further sample processing. 

  • 15.
    Fognini, A.
    et al.
    Delft Univ Technol, Kavli Inst Nanosci Delft, NL-2628 CJ Delft, Netherlands. hmadi, A..
    Ahmadi, A.
    Zeeshan, M.
    Fokkens, J. T.
    Gibson, S. J.
    Sherlekar, N.
    Daley, S. J.
    Dalacu, D.
    Poole, P. J.
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Reimer, M. E.
    Dephasing Free Photon Entanglement with a Quantum Dot2019In: ACS Photonics, E-ISSN 2330-4022, Vol. 6, no 7, p. 1656-1663Article in journal (Refereed)
    Abstract [en]

    Generation of photon pairs from quantum dots with near-unity entanglement fidelity has been a long-standing scientific challenge. It is generally thought that the nuclear spins limit the entanglement fidelity through spin flip dephasing processes. However, this assumption lacks experimental support. Here, we show two-photon entanglement with negligible dephasing from an indium rich single quantum dot comprising a nuclear spin of 9/2 when excited quasi-resonantly. This finding is based on a significantly close match between our entanglement measurements and our model that assumes no dephasing and takes into account the detection system's timing jitter and dark counts. We suggest that neglecting the detection system is responsible for the degradation of the measured entanglement fidelity in the past and not the nuclear spins. Therefore, the key to unity entanglement from quantum dots comprises a resonant excitation scheme and a detection system with ultralow timing jitter and dark counts.

  • 16. Gemmell, Nathan R.
    et al.
    Hills, Matthew
    Bradshaw, Tom
    Rawlings, Tom
    Green, Ben
    Heath, Robert M.
    Tsimvrakidis, Konstantinos
    Dobrovolskiy, Sergiy
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics. Single Quantum B.V., 2628 CH Delft, The Netherlands.
    Dorenbos, Sander N.
    Crook, Martin
    Hadfield, Robert H.
    A miniaturized 4K platform for superconducting infrared photon counting detectors2017In: Superconductors Science and Technology, ISSN 0953-2048, E-ISSN 1361-6668, Vol. 30, no 11, article id 11LT01Article in journal (Refereed)
    Abstract [en]

    We report on a miniaturized platform for superconducting infrared photon counting detectors. We have implemented a fibre-coupled superconducting nanowire single photon detector in a Stirling/Joule-Thomson platform with a base temperature of 4.2 K. We have verified a cooling power of 4 mW at 4.7 K. We report 20% system detection efficiency at 1310 nm wavelength at a dark count rate of 1 kHz. We have carried out compelling application demonstrations in single photon depth metrology and singlet oxygen luminescence detection.

  • 17.
    Gourgues, Ronan
    et al.
    Single Quantum BV, NL-2628 CH Delft, Netherlands..
    Zadeh, Iman Esmaeil
    Single Quantum BV, NL-2628 CH Delft, Netherlands.;Delft Univ Technol, ImPhys Dept, Opt Res Grp, Fac Appl Sci, Lorentzweg 1, NL-2628 CJ Delft, Netherlands..
    Elshaari, Ali W.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Bulgarini, Gabriele
    Single Quantum BV, NL-2628 CH Delft, Netherlands..
    Los, Johannes W. N.
    Single Quantum BV, NL-2628 CH Delft, Netherlands..
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Dalacu, Dan
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Poole, Philip J.
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Dorenbos, Sander N.
    Single Quantum BV, NL-2628 CH Delft, Netherlands..
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Controlled integration of selected detectors and emitters in photonic integrated circuits2019In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 3, p. 3710-3716Article in journal (Refereed)
    Abstract [en]

    Integration of superconducting nanowire single-photon detectors and quantum sources with photonic waveguides is crucial for realizing advanced quantum integrated circuits. However, scalability is hindered by stringent requirements on high-performance detectors. Here we overcome the yield limitation by controlled coupling of photonic channels to pre-selected detectors based on measuring critical current, timing resolution, and detection efficiency. As a proof of concept of our approach, we demonstrate a hybrid on-chip full-transceiver consisting of a deterministically integrated detector coupled to a selected nanowire quantum dot through a filtering circuit made of a silicon nitride waveguide and a ring resonator filter, delivering 100 dB suppression of the excitation laser. In addition, we perform extensive testing of the detectors before and after integration in the photonic circuit and show that the high performance of the superconducting nanowire detectors, including timing jitter down to 23 +/- 3 ps, is maintained. Our approach is fully compatible with wafer-level automated testing in a cleanroom environment. 

  • 18.
    Gu, C.
    et al.
    China.
    Chi, X.
    China.
    Cheng, Y.
    China.
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Hu, N.
    China.
    Lan, X.
    Chona.
    Zou, K.
    China.
    Chen, S.
    China.
    Lin, Z.
    China.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Hu, X.
    China.
    Fractal superconducting nanowire single-photon detectors with low polarization sensitivity2018In: Optics InfoBase Conference Papers, Optical Society of America, 2018Conference paper (Refereed)
    Abstract [en]

    We demonstrated a fractal superconducting nanowire single-photon detector and achieved 42% device efficiency and 1.04 polarization sensitivity. The low polarization sensitivity can be maintained for higher-order spatial modes in few-mode optical fibers.

  • 19. Gu, C.
    et al.
    Chi, X.
    Cheng, Y.
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Hu, N.
    Lan, X.
    Zou, K.
    Chen, S.
    Lin, Zuzeng
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Hu, X.
    Fractal superconducting nanowire single-photon detectors with low polarization sensitivity2018In: 2018 Conference on Lasers and Electro-Optics, CLEO 2018 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2018, article id 8426796Conference paper (Refereed)
    Abstract [en]

    We demonstrated a fractal superconducting nanowire single-photon detector and achieved 42% device efficiency and 1.04 polarization sensitivity. The low polarization sensitivity can be maintained for higher-order spatial modes in few-mode optical fibers.

  • 20.
    Gyger, Samuel
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zeuner, Katharina D.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Jons, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Elshaari, Ali W.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Paul, Matthias
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Hedlund, Carl Reuterskiold
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Hammar, Mattias
    KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.
    Ozolins, Oskars
    KTH, School of Engineering Sciences (SCI), Applied Physics. Rise AB, NETLAB, Isafjordsgatan 22, S-16440 Kista, Sweden.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Reconfigurable frequency coding of triggered single photons in the telecom C-band2019In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 10, p. 14400-14406Article in journal (Refereed)
    Abstract [en]

    In this work, we demonstrate reconfigurable frequency manipulation of quantum states of light in the telecom C-band. Triggered single photons are encoded in a superposition state of three channels using sidebands up to 53 GHz created by an off-the-shelf phase modulator. The single photons are emitted by an InAs/GaAs quantum dot grown by metal-organic vapor-phase epitaxy within the transparency window of the backbone fiber optical network. A cross-correlation measurement of the sidebands demonstrates the preservation of the single photon nature; an important prerequisite for future quantum technology applications using the existing telecommunication fiber network.

  • 21.
    Haffouz, Sofiane
    et al.
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Zeuner, Katharina D.
    KTH.
    Dalacu, Dan
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Poole, Philip J.
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Lapointe, Jean
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Poitras, Daniel
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Mnaymneh, Khaled
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Wu, Xiaohua
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Couillard, Martin
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Korkusinski, Marek
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Schöll, Eva
    KTH.
    Jöns, Klaus D.
    KTH.
    Zwiller, Valery
    KTH.
    Williams, Robin L.
    Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada..
    Bright Single InAsP Quantum Dots at Telecom Wavelengths in Position-Controlled InP Nanowires: The Role of the Photonic Waveguide2018In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 5, p. 3047-3052Article in journal (Refereed)
    Abstract [en]

    We report on the site-selected growth of bright single InAsP quantum dots embedded within InP photonic nanowire waveguides emitting at telecom wavelengths. We demonstrate a dramatic dependence of the emission rate on both the emission wavelength and the nanowire diameter. With an appropriately designed waveguide, tailored to the emission wavelength of the dot, an increase in the count rate by nearly 2 orders of magnitude (0.4 to 35 kcps) is obtained for quantum dots emitting in the telecom O-band, showing high single-photon purity with multiphoton emission probabilities down to 2%. Using emission-wavelength-optimized waveguides, we demonstrate bright, narrow-line-width emission from single InAsP quantum dots with an unprecedented tuning range of 880 to 1550 nm. These results pave the way toward efficient single-photon sources at telecom wavelengths using deterministically grown InAsP/InP nanowire quantum dots.

  • 22. Hu, Xiaolong
    et al.
    Hu, Nan
    Meng, Yun
    Zou, Kai
    Xu, Liang
    Lan, Xiaojian
    Chi, Xiaoming
    Gu, Chao
    Cheng, Yuhao
    Wu, Hao
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Superconducting nanowire single-photon detectors at the infrared spectrum range: detection efficiency and timing jitter2019In: TERAHERTZ, RF, MILLIMETER, AND SUBMILLIMETER-WAVE TECHNOLOGY AND APPLICATIONS XII / [ed] Sadwick, LP Yang, T, 2019Conference paper (Refereed)
    Abstract [en]

    This paper reviews some recent research progress in superconducting nanowire single-photon detectors (SNSPDs) at the infrared spectrum range, with particular emphasis on detection efficiency and timing jitter. For detection efficiency, we present fractal SNSPDs with reduced polarization sensitivity; for timing jitter, we present two mechanisms of device timing jitter - vortex-crossing-induced timing jitter and spatial-inhomogeneity-induced timing jitter.

  • 23.
    Jöns, Klaus D.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Schweickert, Lucas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Versteegh, Marijn A. M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Dalacu, D.
    Poole, P. J.
    Gulinatti, A.
    Giudice, A.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Reimer, M. E.
    Erratum to: Bright nanoscale source of deterministic entangled photon pairs violating Bell’s inequality (Scientific Reports, (2017), 7, 1, (1700), 10.1038/s41598-017-01509-6)2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, no 1, article id 7751Article in journal (Refereed)
  • 24.
    Jöns, Klaus D.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Nano Photonics. Delft University of Technology, Netherlands.
    Schweickert, Lucas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Nano Photonics. Delft University of Technology, Netherlands.
    Versteegh, Marijn A. M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Nano Photonics. Delft University of Technology, Netherlands.
    Dalacu, Dan
    Poole, Philip J.
    Gulinatti, Angelo
    Giudice, Andrea
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Nano Photonics. Delft University of Technology, Netherlands.
    Reimer, Michael E.
    Bright nanoscale source of deterministic entangled photon pairs violating Bell's inequality2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, no 1, article id 1700Article in journal (Refereed)
    Abstract [en]

    Global, secure quantum channels will require efficient distribution of entangled photons. Long distance, low-loss interconnects can only be realized using photons as quantum information carriers. However, a quantum light source combining both high qubit fidelity and on-demand bright emission has proven elusive. Here, we show a bright photonic nanostructure generating polarization-entangled photon pairs that strongly violates Bell's inequality. A highly symmetric InAsP quantum dot generating entangled photons is encapsulated in a tapered nanowire waveguide to ensure directional emission and efficient light extraction. We collect similar to 200 kHz entangled photon pairs at the first lens under 80 MHz pulsed excitation, which is a 20 times enhancement as compared to a bare quantum dot without a photonic nanostructure. The performed Bell test using the Clauser-Horne-Shimony-Holt inequality reveals a clear violation (S-CHSH > 2) by up to 9.3 standard deviations. By using a novel quasi-resonant excitation scheme at the wurtzite InP nanowire resonance to reduce multi-photon emission, the entanglement fidelity (F = 0.817 +/- 0.002) is further enhanced without temporal post-selection, allowing for the violation of Bell's inequality in the rectilinear-circular basis by 25 standard deviations. Our results on nanowire-based quantum light sources highlight their potential application in secure data communication utilizing measurement-device-independent quantum key distribution and quantum repeater protocols.

  • 25.
    Jöns, Klaus D.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. AlbaNova University Center.
    Stensson, Katarina
    KTH, School of Engineering Sciences (SCI), Applied Physics. AlbaNova University Center.
    Reindl, Marcus
    Swillo, Marcin
    KTH, School of Engineering Sciences (SCI), Applied Physics. AlbaNova University Center.
    Huo, Yongheng
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics. AlbaNova University Center.
    Rastelli, Armando
    Trotta, Rinaldo
    Björk, Gunnar
    KTH, School of Engineering Sciences (SCI), Applied Physics. AlbaNova University Center.
    Two-photon interference from two blinking quantum emitters2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 7, article id 075430Article in journal (Refereed)
    Abstract [en]

    We investigate the effect of blinking on the two-photon interference measurement from two independent quantum emitters. We find that blinking significantly alters the statistics in the Hong-Ou-Mandel second-order intensity correlation function g((2))(tau) and the outcome of two-photon interference measurements performed with independent quantum emitters. We theoretically demonstrate that the presence of blinking can be experimentally recognized by a deviation from the g(D)((2))(0) = 0.5 value when distinguishable photons from two emitters impinge on a beam splitter. Our findings explain the significant differences between linear losses and blinking for correlation measurements between independent sources and are experimentally verified using a parametric down-conversion photon-pair source. We show that blinking imposes a mandatory cross-check measurement to correctly estimate the degree of indistinguishability of photons emitted by independent quantum emitters.

  • 26. Kitaygorsky, J.
    et al.
    Slysz, W.
    Shouten, R.
    Dorenbos, S.
    Reiger, E.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI).
    Sobolewski, Roman
    Amplitude distributions of dark counts and photon counts in NbN superconducting single-photon detectors integrated with the HEMT readout2017In: PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ISSN 0921-4534, Vol. 532, p. 33-39Article in journal (Refereed)
    Abstract [en]

    We present a new operation regime of NbN superconducting single-photon detectors (SSPDs) by integrating them with a low-noise cryogenic high-electron-mobility transistor and a high-load resistor. The integrated sensors are designed to get a better understanding of the origin of dark counts triggered by the detector, as our scheme allows us to distinguish the origin of dark pulses from the actual photon pulses in SSPDs. The presented approach is based on a statistical analysis of amplitude distributions of recorded trains of the SSPD photoresponse transients. It also enables to obtain information on energy of the incident photons, as well as demonstrates some photon-number-resolving capability of meander-type SSPDs.

  • 27. Lagoudakis, K. G.
    et al.
    McMahon, P. L.
    Dory, C.
    Fischer, K. A.
    Mueller, K.
    Borish, V.
    Dalacu, D.
    Poole, P. J.
    Reimer, M. E.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Yamamoto, Y.
    Vuckovic, J.
    Ultrafast coherent manipulation of trions in site-controlled nanowire quantum dots2016In: Operator Theory: Advances and Applications, ISSN 1004-4469, E-ISSN 2334-2536, Vol. 3, no 12, p. 1430-1435Article in journal (Refereed)
    Abstract [en]

    Physical implementations of large-scale quantum processors based on solid-state platforms benefit from realizations of quantum bits positioned in regular arrays. Self-assembled quantum dots are well established as promising candidates for quantum optics and quantum information processing, but they are randomly positioned. Site-controlled quantum dots, on the other hand, are grown in pre-defined locations but have not yet been sufficiently developed to be used as a platform for quantum information processing. In this paper, we demonstrate all-optical ultrafast complete coherent control of a qubit formed by the single-spin/trion states of a charged site-controlled nanowire quantum dot. Our results show that site-controlled quantum dots in nanowires are promising hosts of charged-exciton qubits and that these qubits can be cleanly manipulated in the same fashion as has been demonstrated in randomly positioned quantum dot samples. Our findings suggest that many of the related excitonic qubit experiments that have been performed over the past 15 years may work well in the more scalable, site-controlled systems, making them very promising for the realization of quantum hardware.

  • 28. Lagoudakis, Konstantinos G.
    et al.
    McMahon, Peter L.
    Fischer, Kevin A.
    Puri, Shruti
    Mueller, Kai
    Dalacu, Dan
    Poole, Philip J.
    Reimer, Michael E.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Yamamoto, Yoshihisa
    Vuckovic, Jelena
    Initialization of a spin qubit in a site-controlled nanowire quantum dot2016In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 18, article id 053024Article in journal (Refereed)
    Abstract [en]

    A fault-tolerant quantum repeater or quantum computer using solid-state spin-based quantum bits will likely require a physical implementation with many spins arranged in a grid. Self-assembled quantum dots (QDs) have been established as attractive candidates for building spin-based quantum information processing devices, but such QDs are randomly positioned, which makes them unsuitable for constructing large-scale processors. Recent efforts have shown that QDs embedded in nanowires can be deterministically positioned in regular arrays, can store single charges, and have excellent optical properties, but so far there have been no demonstrations of spin qubit operations using nanowire QDs. Here we demonstrate optical pumping of individual spins trapped in site-controlled nanowire QDs, resulting in high-fidelity spin-qubit initialization. This represents the next step towards establishing spins in nanowire QDs as quantum memories suitable for use in a large-scale, fault-tolerant quantum computer or repeater based on all-optical control of the spin qubits.

  • 29.
    Leandro, Lorenzo
    et al.
    Tech Univ Denmark, DTU Dept Photon Engn, DK-2800 Lyngby, Denmark..
    Gunnarsson, Christine P.
    Tech Univ Denmark, DTU Dept Photon Engn, DK-2800 Lyngby, Denmark..
    Reznik, Rodion
    St Petersburg Acad Univ, RAS, St Petersburg 194021, Russia.;ITMO Univ, Kronverkskiy Pr 49, St Petersburg 197101, Russia..
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Shtrom, Igor
    St Petersburg Acad Univ, RAS, St Petersburg 194021, Russia..
    Khrebtov, Artem
    ITMO Univ, Kronverkskiy Pr 49, St Petersburg 197101, Russia..
    Kasama, Takeshi
    Tech Univ Denmark, DTU Dept Photon Engn, DK-2800 Lyngby, Denmark..
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics. Delft Univ Technol, Kavli Inst Nanosci, NL-2628CJ Delft, Netherlands..
    Cirlin, George
    St Petersburg Acad Univ, RAS, St Petersburg 194021, Russia.;ITMO Univ, Kronverkskiy Pr 49, St Petersburg 197101, Russia..
    Akopian, Nika
    Tech Univ Denmark, DTU Dept Photon Engn, DK-2800 Lyngby, Denmark..
    Nanowire Quantum Dots Tuned to Atomic Resonances2018In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 11, p. 7217-7221Article in journal (Refereed)
    Abstract [en]

    Quantum dots tuned to atomic resonances represent an emerging field of hybrid quantum systems where the advantages of quantum dots and natural atoms can be combined. Embedding quantum dots in nanowires boosts these systems with a set of powerful possibilities, such as precise positioning of the emitters, excellent photon extraction efficiency and direct electrical contacting of quantum dots. Notably, nanowire structures can be grown on silicon substrates, allowing for a straightforward integration with silicon-based photonic devices. In this work we show controlled growth of nanowire-quantum-dot structures on silicon, frequency tuned to atomic transitions. We grow GaAs quantum dots in AlGaAs nanowires with a nearly pure crystal structure and excellent optical properties. We precisely control the dimensions of quantum dots and their position inside nanowires and demonstrate that the emission wavelength can be engineered over the range of at least 30 nm around 765 nm. By applying an external magnetic field, we are able to fine-tune the emission frequency of our nanowire quantum dots to the D-2 transition of Rb-87. We use the Rb transitions to precisely measure the actual spectral line width of the photons emitted from a nanowire quantum dot to be 9.4 +/- 0.7 mu eV, under nonresonant excitation. Our work brings highly desirable functionalities to quantum technologies, enabling, for instance, a realization of a quantum network, based on an arbitrary number of nanowire single-photon sources, all operating at the same frequency of an atomic transition.

  • 30.
    Machhadani, Houssaine
    et al.
    Univ Grenoble Alpes, CEA INAC PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Bougerol, Catherine
    Univ Grenoble Alpes, CNRS Inst Neel, 25 Av Martyrs, F-38000 Grenoble, France..
    Lequien, Stephane
    Univ Grenoble Alpes, CEA INAC MEM, 17 Av Martyrs, F-38000 Grenoble, France..
    Thomassin, Jean-Luc
    Univ Grenoble Alpes, CEA INAC PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Mollard, Nicolas
    Univ Grenoble Alpes, CEA INAC MEM, 17 Av Martyrs, F-38000 Grenoble, France..
    Mukhtarova, Anna
    Univ Grenoble Alpes, CEA INAC PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Gerard, Jean-Michel
    Univ Grenoble Alpes, CEA INAC PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Monroy, Eva
    Univ Grenoble Alpes, CEA INAC PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Improvement of the critical temperature of NbTiN films on III-nitride substrates2019In: Superconductors Science and Technology, ISSN 0953-2048, E-ISSN 1361-6668, Vol. 32, no 3, article id 035008Article in journal (Refereed)
    Abstract [en]

    In this paper, we study the impact of using III-nitride semiconductors (GaN, AlN) as substrates for ultrathin (11 nm) superconducting films of NbTiN deposited by reactive magnetron sputtering. The resulting NbTiN layers are (111)-oriented, fully relaxed, and they keep an epitaxial relation with the substrate. The higher critical superconducting temperature (T-c = 11.8 K) was obtained on AIN-on-sapphire, which was the substrate with smaller lattice mismatch with NbTiN. We attribute this improvement to a reduction of the NbTiN roughness, which appears associated with the relaxation of the lattice misfit with the substrate. On AlN-on-sapphire, superconducting nanowire single photon detectors were fabricated and tested, obtaining external quantum efficiencies that are in excellent agreement with theoretical calculations.

  • 31. Machhadani, Houssaine
    et al.
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Bougerol, Catherine
    Lequien, Stéphane
    Thomassin, Jean-Luc
    Mollard, Nicolas
    Mukhtarova, Anna
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Gérard, Jean-Michel
    Monroy, Eva
    Improvement of the critical temeprature of NbTiN films on III-nitride substrates2019In: Superconductors Science and Technology, ISSN 0953-2048, E-ISSN 1361-6668, Vol. 32, no 035008Article in journal (Refereed)
    Abstract [en]

    In this paper, we study the impact of using III-nitride semiconductors (GaN, AlN) as substrates for ultrathin (11 nm) superconducting films of NbTiN deposited by reactive magnetron sputtering. The resulting NbTiN layers are (111)-oriented, fully relaxed, and they keep an epitaxial relation with the substrate. The higher critical superconducting temperature (T c = 11.8 K) was obtained on AlN-on-sapphire, which was the substrate with smaller lattice mismatch with NbTiN. We attribute this improvement to a reduction of the NbTiN roughness, which appears associated with the relaxation of the lattice misfit with the substrate. On AlN-on-sapphire, superconducting nanowire single photon detectors were fabricated and tested, obtaining external quantum efficiencies that are in excellent agreement with theoretical calculations.

  • 32.
    Mukhtarova, Anna
    et al.
    Univ Grenoble Alpes, CEA, INAC, PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Redaelli, Luca
    Univ Grenoble Alpes, CEA, INAC, PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Hazra, Dibyendu
    Univ Grenoble Alpes, CEA, INAC, PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Machhadani, Houssaine
    Univ Grenoble Alpes, CEA, INAC, PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Lequien, Stephane
    Univ Grenoble Alpes, CEA, INAC, MEM, 17 Av Martyrs, F-38000 Grenoble, France..
    Hofheinz, Max
    Univ Grenoble Alpes, CEA, INAC, PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Thomassin, Jean-Luc
    Univ Grenoble Alpes, CEA, INAC, PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Gustavo, Frederic
    Univ Grenoble Alpes, CEA, INAC, PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics. Univ Grenoble Alpes, CEA, INAC, PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France.;Delft Univ Technol, Kavli Inst Nanosci, Lorentzweig 1, NL-2628 CJ Delft, Netherlands..
    Monroy, Eva
    Univ Grenoble Alpes, CEA, INAC, PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Gerard, Jean-Michel
    Univ Grenoble Alpes, CEA, INAC, PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
    Polarization-insensitive fiber-coupled superconducting-nanowire single photon detector using a high-index dielectric capping layer2018In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 13, p. 17697-17704Article in journal (Refereed)
    Abstract [en]

    Superconducting-nanowire single photon detectors (SNSPDs) are able to reach near-unity detection efficiency in the infrared spectral range. However, due to the intrinsic asymmetry of nanowires, SNSPDs are usually very sensitive to the polarization of the incident radiation, their responsivity being maximum for light polarized parallel to the nanowire length (transverse-electric (TE) polarization). Here, we report on the reduction of the polarization sensitivity obtained by capping NbN-based SNSPDs with a high-index SiNx dielectric layer, which reduces the permittivity mismatch between the NbN wire and the surrounding area. Experimentally, a polarization sensitivity below 0.1 is obtained both at 1.31 and 1.55 mu m, in excellent agreement with simulations.

  • 33. Mukhtarova, Anna
    et al.
    Redaelli, Luca
    Hazra, Dibyendu
    Machhadani, Houssaine
    Lequien, Stéphane
    Hofheinz, Max
    Thomassin, Jean-Luc
    Gustavo, Frederic
    Zichi, Julien
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Monroy, Eva
    Gérard, Jean-Michel
    Polarization-insensitive fiber-coupled superconducting-nanowire single photon detector using high-index dielectric capping layer2018In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 13Article in journal (Refereed)
    Abstract [en]

    Superconducting-nanowire single photon detectors (SNSPDs) are able to reach near-unity detection efficiency in the infrared spectral range. However, due to the intrinsic asymmetry of nanowires, SNSPDs are usually very sensitive to the polarization of the incident radiation, their responsivity being maximum for light polarized parallel to the nanowire length (transverse-electric (TE) polarization). Here, we report on the reduction of the polarization sensitivity obtained by capping NbN-based SNSPDs with a high-index SiNx dielectric layer, which reduces the permittivity mismatch between the NbN wire and the surrounding area. Experimentally, a polarization sensitivity below 0.1 is obtained both at 1.31 and 1.55 μm, in excellent agreement with simulations.

  • 34. Redaelli, L.
    et al.
    Bulgarini, G.
    Dobrovolskiy, S.
    Dorenbos, S. N.
    Zwiller, Vall
    KTH, School of Engineering Sciences (SCI), Applied Physics. Univ. Grenoble Alpes, Grenoble, France.
    Monroy, E.
    Gerard, J. M.
    Design of broadband high-efficiency superconducting-nanowire single photon detectors2016In: Superconductors Science and Technology, ISSN 0953-2048, E-ISSN 1361-6668, Vol. 29, no 6, article id 065016Article in journal (Refereed)
    Abstract [en]

    In this paper several designs to maximize the absorption efficiency of superconducting-nanowire single-photon detectors are investigated. Using a simple optical cavity consisting of a gold mirror and a SiO2 layer, the absorption efficiency can be boosted to over 97%: this result is confirmed experimentally by the realization of an NbTiN-based detector having an overall system detection efficiency of 85% at 1.31 mu m. Calculations show that by sandwiching the nanowire between two dielectric Bragg reflectors, unity absorption (>99.9%) could be reached at the peak wavelength for optimized structures. To achieve broadband high efficiency, a different approach is considered: a waveguide-coupled detector. The calculations performed in this work show that, by correctly dimensioning the waveguide and the nanowire, polarization-insensitive detectors absorbing more than 95% of the injected photons over a wavelength range of several hundred nm can be designed. We propose a detector design making use of GaN/AlN waveguides, since these materials allow lattice-matched epitaxial deposition of Nb(Ti)N films and are transparent on a very wide wavelength range.

  • 35. Redaelli, L.
    et al.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, School of Electrical Engineering (EES).
    Monroy, E.
    Gérard, J. M.
    Design of polarization-insensitive superconducting single photon detectors with high-index dielectrics2017In: Superconductors Science and Technology, ISSN 0953-2048, E-ISSN 1361-6668, Vol. 30, no 3, article id 035005Article in journal (Refereed)
    Abstract [en]

    In this paper, the design of superconducting-nanowire single-photon detectors which are insensitive to the polarization of the incident light is investigated. By using high-refractive-index dielectrics, the index mismatch between the nanowire and the surrounding media is reduced. This enhances the absorption of light with electric field vector perpendicular to the nanowire segments, which is generally hindered in these kind of detectors. Building on this principle and focusing on NbTiN nanowire devices, we present several easy-to-realize cavity architectures which allow high absorption efficiency (in excess of 90%) and polarization insensitivity simultaneously. Designs based on ultranarrow nanowires, for which the polarization sensitivity is much more marked, are also presented. Finally, we briefly discuss the specific advantages of this approach in the case of WSi or MoSi nanowires.

  • 36.
    Reindl, Marcus
    et al.
    Johannes Kepler Univ Linz, Inst Semicond & Solid State Phys, A-4040 Linz, Austria..
    Huber, Daniel
    Johannes Kepler Univ Linz, Inst Semicond & Solid State Phys, A-4040 Linz, Austria..
    Schimpf, Christian
    Johannes Kepler Univ Linz, Inst Semicond & Solid State Phys, A-4040 Linz, Austria..
    da Silva, Saimon F. Covre
    Johannes Kepler Univ Linz, Inst Semicond & Solid State Phys, A-4040 Linz, Austria..
    Rota, Michele B.
    Johannes Kepler Univ Linz, Inst Semicond & Solid State Phys, A-4040 Linz, Austria.;Sapienza Univ Rome, Dept Phys, I-00185 Rome, Italy..
    Huang, Huiying
    Johannes Kepler Univ Linz, Inst Semicond & Solid State Phys, A-4040 Linz, Austria..
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Rastelli, Armando
    Johannes Kepler Univ Linz, Inst Semicond & Solid State Phys, A-4040 Linz, Austria.;Johannes Kepler Univ Linz, Linz Inst Technol, A-4040 Linz, Austria..
    Trotta, Rinaldo
    Johannes Kepler Univ Linz, Inst Semicond & Solid State Phys, A-4040 Linz, Austria.;Sapienza Univ Rome, Dept Phys, I-00185 Rome, Italy..
    All-photonic quantum teleportation using on-demand solid-state quantum emitters2018In: Science Advances, E-ISSN 2375-2548, Vol. 4, no 12, article id eaau1255Article in journal (Refereed)
    Abstract [en]

    All-optical quantum teleportation lies at the heart of quantum communication science and technology. This quantum phenomenon is built up around the nonlocal properties of entangled states of light that, in the perspective of real-life applications, should be encoded on photon pairs generated on demand. Despite recent advances, however, the exploitation of deterministic quantum light sources in push-button quantum teleportation schemes remains a major open challenge. Here, we perform an important step toward this goal and show that photon pairs generated on demand by a GaAs quantum dot can be used to implement a teleportation protocol whose fidelity violates the classical limit (by more than 5 SDs) for arbitrary input states. Moreover, we develop a theoretical framework that matches the experimental observations and that defines the degree of entanglement and indistinguishability needed to overcome the classical limit independently of the input state. Our results emphasize that on-demand solid-state quantum emitters are one of the most promising candidates to realize deterministic quantum teleportation in practical quantum networks.

  • 37. Reindl, Marcus
    et al.
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Nano Photonics.
    Huber, Daniel
    Schimpf, Christian
    Huo, Yongheng
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, School of Electrical Engineering (EES).
    Rastelli, Armando
    Trotta, Rinaldo
    Phonon-Assisted Two-Photon Interference from Remote Quantum Emitters2017In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, no 7, p. 4090-4095Article in journal (Refereed)
    Abstract [en]

    Photonic quantum technologies are on the verge of finding applications in everyday life with quantum cryptography and quantum simulators on the horizon. Extensive research has been carried out to identify suitable quantum emitters and single epitaxial quantum dots have emerged as near-optimal sources of bright, on demand, highly indistinguishable single photons and entangled photon-pairs. In order to build up quantum networks, it is essential to interface remote quantum emitters. However, this is still an outstanding challenge, as the quantum states of dissimilar "artificial atoms" have to be prepared on-demand with high fidelity and the generated photons have to be made indistinguishable in all possible degrees of freedom. Here, we overcome this major obstacle and show an unprecedented two-photon interference (visibility of 51 +/- 5%) from remote strain-tunable GaAs quantum dots emitting on-demand photon-pairs. We achieve this result by exploiting for the first time the full potential of a novel phonon-assisted two-photon excitation scheme, which allows for the generation of highly indistinguishable (visibility of 71 +/- 9%) entangled photon-pairs (fidelity of 90 +/- 2%), enables push-button biexciton state preparation (fidelity of 80 +/- 2%) and outperforms conventional resonant two-photon excitation schemes in terms of robustness against environmental decoherence. Our results mark an important milestone for the practical realization of quantum repeaters and complex multiphoton entanglement experiments involving dissimilar artificial atoms.

  • 38.
    Schweickert, Lucas
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Lettner, Thomas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Zeuner, Katharina
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Elshaari, Ali W.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Fognini, A.
    Zadeh, I. E.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Generating, manipulating and detecting quantum states of light at the nanoscale2018In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2018Conference paper (Refereed)
    Abstract [en]

    We generate, manipulate and detect light at the single photon level with semiconducting and superconducting nanowires.

  • 39.
    Schweickert, Lucas
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Zeuner, Katharina D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    da Silva, Saimon Filipe Covre
    Huang, Huiying
    Lettner, Thomas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Reindl, Marcus
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Trotta, Rinaldo
    Rastelli, Armando
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    On-demand generation of background-free single photons from a solid-state source2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 9, article id 093106Article in journal (Refereed)
    Abstract [en]

    True on-demand high-repetition-rate single-photon sources are highly sought after for quantum information processing applications. However, any coherently driven two-level quantum system suffers from a finite re-excitation probability under pulsed excitation, causing undesirable multi-photon emission. Here, we present a solid-state source of on-demand single photons yielding a raw second-order coherence of g((2)) (0) = (7.5 +/- 1.6) x 10(-5) without any background subtraction or data processing. To this date, this is the lowest value of g((2)) (0) Peported for any single-photon source even compared to the previously reported best background subtracted values. We achieve this result on GaAs/AlGaAs quantum dots embedded in a low-Q planar cavity by employing (i) a two-photon excitation process and (ii) a filtering and detection setup featuring two superconducting single-photon detectors with ultralow dark-count rates of (0.0056 +/- 0.0007) s(-1) and (0.017 +/- 0.001) s(-1), respectively. Re-excitation processes are dramatically suppressed by (i), while (ii) removes false coincidences resulting in a negligibly low noise floor.

  • 40.
    Schöll, Eva
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Hanschke, Lukas
    Tech Univ Munich, Walter Schottky Inst, D-85748 Garching, Germany.;Tech Univ Munich, Phys Dept, D-85748 Garching, Germany..
    Schweickert, Lucas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Zeuner, Katharina D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Reindl, Marcus
    Johannes Kepler Univ Linz, Inst Semicond & Solid State Phys, A-4040 Linz, Austria..
    da Silva, Saimon Filipe Covre
    Johannes Kepler Univ Linz, Inst Semicond & Solid State Phys, A-4040 Linz, Austria..
    Lettner, Thomas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Trotta, Rinaldo
    Sapienza Univ Roma, Dipartimento Fis, Piazzale A Moro 1, I-00185 Rome, Italy..
    Finley, Jonathan J.
    Tech Univ Munich, Walter Schottky Inst, D-85748 Garching, Germany.;Tech Univ Munich, Phys Dept, D-85748 Garching, Germany..
    Mueller, Kai
    Tech Univ Munich, Walter Schottky Inst, D-85748 Garching, Germany.;Tech Univ Munich, Phys Dept, D-85748 Garching, Germany..
    Rastelli, Armando
    Johannes Kepler Univ Linz, Inst Semicond & Solid State Phys, A-4040 Linz, Austria..
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Resonance Fluorescence of GaAs Quantum Dots with Near-Unity Photon Indistinguishability2019In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 19, no 4, p. 2404-2410Article in journal (Refereed)
    Abstract [en]

    Photonic quantum technologies call for scalable quantum light sources that can be integrated, while providing the end user with single and entangled photons on demand. One promising candidate is strain free GaAs/A1GaAs quantum dots obtained by aluminum droplet etching. Such quantum dots exhibit ultra low multi-photon probability and an unprecedented degree of photon pair entanglement. However, different to commonly studied InGaAs/GaAs quantum dots obtained by the Stranski-Krastanow mode, photons with a near-unity indistinguishability from these quantum emitters have proven to be elusive so far. Here, we show on-demand generation of near-unity indistinguishable photons from these quantum emitters by exploring pulsed resonance fluorescence. Given the short intrinsic lifetime of excitons and trions confined in the GaAs quantum dots, we show single photon indistinguishability with a raw visibility of V-raw = (95.0(-6.1)(+5.0))%, without the need for Purcell enhancement. Our results represent a milestone in the advance of GaAs quantum dots by demonstrating the final missing property standing in the way of using these emitters as a key component in quantum communication applications, e.g., as quantum light sources for quantum repeater architectures.

  • 41.
    Wengerowsky, Soeren
    et al.
    Austrian Acad Sci, Inst Quantum Opt & Quantum Informat Vienna, A-1090 Vienna, Austria.;Vienna Ctr Quantum Sci & Technol, A-1090 Vienna, Austria..
    Joshi, Siddarth Koduru
    Austrian Acad Sci, Inst Quantum Opt & Quantum Informat Vienna, A-1090 Vienna, Austria.;Vienna Ctr Quantum Sci & Technol, A-1090 Vienna, Austria.;HH Wills Phys Lab, Quantum Engn Technol Labs, Bristol BS8 1FD, Avon, England.;Univ Bristol, Dept Elect & Elect Engn, Bristol BS8 1UB, Avon, England..
    Steinlechner, Fabian
    Austrian Acad Sci, Inst Quantum Opt & Quantum Informat Vienna, A-1090 Vienna, Austria.;Vienna Ctr Quantum Sci & Technol, A-1090 Vienna, Austria.;Fraunhofer Inst Appl Opt & Precis Engn IOF Jena, D-07745 Jena, Germany.;Friedrich Schiller Univ Jena, Abbe Ctr Photon, D-07745 Jena, Germany..
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics. Single Quantum BV, NL-2628 CJ Delft, Netherlands..
    Dobrovolskiy, Sergiy M.
    Single Quantum BV, NL-2628 CJ Delft, Netherlands..
    van der Molen, Rene
    Single Quantum BV, NL-2628 CJ Delft, Netherlands..
    Los, Johannes W. N.
    Single Quantum BV, NL-2628 CJ Delft, Netherlands..
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics. Single Quantum BV, NL-2628 CJ Delft, Netherlands..
    Versteegh, Marijn A. M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Mura, Alberto
    Ist Nazl Ric Metrol, I-10135 Turin, Italy..
    Calonico, Davide
    Ist Nazl Ric Metrol, I-10135 Turin, Italy..
    Inguscio, Massimo
    European Lab Nonlinear Spect LENS, I-50019 Sesto Fiorentino, Italy.;Univ Florence, Dept Phys & Astron, I-50019 Sesto Fiorentino, Italy.;CNR, I-00185 Rome, Italy..
    Huebel, Hannes
    Austrian Inst Technol, Ctr Digital Safety & Secur, A-1210 Vienna, Austria..
    Bo, Liu
    Austrian Acad Sci, Inst Quantum Opt & Quantum Informat Vienna, A-1090 Vienna, Austria.;Vienna Ctr Quantum Sci & Technol, A-1090 Vienna, Austria.;Natl Univ Def Technol, Coll Adv Interdisciplinary Studies, Changsha 410073, Hunan, Peoples R China..
    Scheidl, Thomas
    Austrian Acad Sci, Inst Quantum Opt & Quantum Informat Vienna, A-1090 Vienna, Austria.;Univ Vienna, Quantum Opt Quantum Nanophys & Quantum Informat, A-1090 Vienna, Austria..
    Zeilinger, Anton
    Austrian Acad Sci, Inst Quantum Opt & Quantum Informat Vienna, A-1090 Vienna, Austria.;Univ Vienna, Quantum Opt Quantum Nanophys & Quantum Informat, A-1090 Vienna, Austria..
    Xuereb, Andre
    Univ Malta, Dept Phys, MSD-2080 Msida, Malta..
    Ursin, Rupert
    Austrian Acad Sci, Inst Quantum Opt & Quantum Informat Vienna, A-1090 Vienna, Austria.;Vienna Ctr Quantum Sci & Technol, A-1090 Vienna, Austria..
    Entanglement distribution over a 96-km-long submarine optical fiber2019In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 116, no 14, p. 6684-6688Article in journal (Refereed)
    Abstract [en]

    Quantum entanglement is one of the most extraordinary effects in quantum physics, with many applications in the emerging field of quantum information science. In particular, it provides the foundation for quantum key distribution (QKD), which promises a conceptual leap in information security. Entanglement-based QKD holds great promise for future applications owing to the possibility of device-independent security and the potential of establishing global-scale quantum repeater networks. While other approaches to QKD have already reached the level of maturity required for operation in absence of typical laboratory infrastructure, comparable field demonstrations of entanglement-based QKD have not been performed so far. Here, we report on the successful distribution of polarization-entangled photon pairs between Malta and Sicily over 96 km of submarine optical telecommunications fiber. We observe around 257 photon pairs per second, with a polarization visibility above 90%. Our results show that QKD based on polarization entanglement is now indeed viable in long-distance fiber links. This field demonstration marks the longest-distance distribution of entanglement in a deployed telecommunications network and demonstrates an international submarine quantum communication channel. This opens up myriad possibilities for future experiments and technological applications using existing infrastructure.

  • 42. Zadeh, Iman Esmaeil
    et al.
    Elshaari, Ali W.
    KTH, School of Electrical Engineering (EES). Delft Univ Technol, Netherlands.
    Jöns, Klaus D.
    KTH, School of Electrical Engineering (EES). Delft Univ Technol, Netherlands.
    Fognini, Andreas
    Dalacu, Dan
    Poole, Philip J.
    Reimer, Michael E.
    Zwiller, Val
    KTH, School of Electrical Engineering (EES). Delft Univ Technol, Netherlands.
    Deterministic Integration of Single Photon Sources in Silicon Based Photonic Circuits2016In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, no 4, p. 2289-2294Article in journal (Refereed)
    Abstract [en]

    A major step toward fully integrated quantum optics is the deterministic incorporation of high quality single photon sources in on-chip optical circuits. We show a novel hybrid approach in which preselected III-V single quantum dots in nanowires are transferred and integrated in silicon based photonic circuits. The quantum emitters maintain their high optical quality after integration as verified by measuring a low multiphoton probability of 0.07 +/- 0.07 and emission line width as narrow as 3.45 +/- 0.48 GHz. Our approach allows for optimum alignment of the quantum dot light emission to the fundamental waveguide mode resulting in very high coupling efficiencies. We estimate a coupling efficiency of 24.3 +/- 1.7% from the studied single-photon source to the photonic channel and further show by finite-difference time-domain simulations that for an optimized choice of material and design the efficiency can exceed 90%.

  • 43. Zadeh, Iman Esmaeil
    et al.
    Los, Johannes W. N.
    Gourgues, Ronan B. M.
    Steinmetz, Violette
    Bulgarini, Gabriele
    Dobrovolskiy, Sergiy M.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Nano Photonics. Single Quantum BV, Netherlands.
    Dorenbos, Sander N.
    Single-photon detectors combining high efficiency, high detection rates, and ultra-high timing resolution2017In: APL PHOTONICS, ISSN 2378-0967, Vol. 2, no 11, article id 111301Article in journal (Refereed)
    Abstract [en]

    Single-photon detection with high efficiency, high time resolution, low dark counts, and high photon detection rates is crucial for a wide range of optical measurements. Although efficient detectors have been reported before, combining all performance parameters in a single device remains a challenge. Here, we show a broadband NbTiN superconducting nanowire detector with an efficiency exceeding 92%, over 150 MHz photon detection rate, and a dark count rate below 130 Hz operated in a Gifford-McMahon cryostat. Furthermore, with careful optimization of the detector design and readout electronics, we reach an ultra-low system timing jitter of 14.80 ps (13.95 ps decoupled) while maintaining high detection efficiencies (>75%).

  • 44.
    Zeuner, Katharina D.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Paul, Matthias
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Lettner, Thomas
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Reuterskiold Hedlund, Carl
    KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.
    Schweickert, Lucas
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Steinhauer, Stephan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Yang, Lily
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Hammar, Mattias
    KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    A stable wavelength-tunable triggered source of single photons and cascaded photon pairs at the telecom C-band2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 17, article id 173102Article in journal (Refereed)
    Abstract [en]

    The implementation of fiber-based long-range quantum communication requires tunable sources of single photons at the telecom C-band. Stable and easy-to-implement wavelength-tunability of individual sources is crucial to (i) bring remote sources into resonance, (ii) define a wavelength standard, and (iii) ensure scalability to operate a quantum repeater. So far, the most promising sources for true, telecom single photons are semiconductor quantum dots, due to their ability to deterministically and reliably emit single and entangled photons. However, the required wavelength-tunability is hard to attain. Here, we show a stable wavelength-tunable quantum light source by integrating strain-released InAs quantum dots on piezoelectric substrates. We present triggered single-photon emission at 1.55 mu m with a multi-photon emission probability as low as 0.097, as well as photon pair emission from the radiative biexciton-exciton cascade. We achieve a tuning range of 0.25 nm which will allow us to spectrally overlap remote quantum dots or tuning distant quantum dots into resonance with quantum memories. This opens up realistic avenues for the implementation of photonic quantum information processing applications at telecom wavelengths. 

  • 45.
    Zichi, Julien
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Gyger, Samuel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Baghban, Mohammad Amin
    Elshaari, Ali W.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Gallo, Katia
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    An NbTiN superconducting single photon detector implemented on a LiNbO3 nano-waveguide at telecom wavelength2019In: Poster session T.Po2, 2019Conference paper (Refereed)
    Abstract [en]

    Fiber-coupled superconducting nanowire single photon detectors are a ubiquitous tool for quantum optics experiments as they offer near unity detection efficiency over a broad wavelength range, low dark count rate, excellent time resolution and high saturation rate. Nevertheless, advancing quantum optics experiments and applications beyond the few-photon limit requires large scale integrated systems of quantum sources and detectors. In recent years there has been a tremendous progress with integrating single photon detectors with a variety of photonic platforms. This includes attempts on ion-diffused waveguides in LiNbO3, a non-linear and electro-optic material with widespread use for signal processing, frequency conversion, and quantum optics devices. However the realization of superconducting detectors on single mode waveguides remains elusive. Here we present an NbTiN superconducting single photon detector integrated directly on a LiNbO3 single mode nanophotonic waveguide at telecom wavelength, with a high critical current density and a dark count rate of 3 mHz at 99% of its critical current.

  • 46.
    Zichi, Julien
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Yang, Lily
    Gyger, Samuel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Lettner, Thomas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Errando-Herranz, Carlos
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Baghban, Mohammad Amin
    Gallo, Katia
    Steinhauer, Stephan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Heterogeneous integration of NbTiN by universal room temperature depositionManuscript (preprint) (Other academic)
    Abstract [en]

    Being the Nb-based compound with the highest known critical temperature, NbTiN is of particular interest for many applications. It is used in Josephson junctions for single flux quantum logic gates, as a superconducting electrode to contact semiconductor devices, and one important use is in superconducting nanowire single photon detectors. These detectors are the ideal candidate for on-chip integration in photonic circuits, offering near-unity detection efficiency, low noise and excellent time resolution, therefore it is desirable to implement them on a wide variety of platforms. However, it remains a challenge to deposit the superconducting material with a process suitable for heterogeneous integration, as the most widespread material, NbN, is associated with a deposition at a high temperature. Taking advantage of the possibility to deposit superconducting NbTiN with various stoichiometries by co-sputter deposition at room temperature, we demonstrate growth on six different substrates – silicon dioxide, silicon nitride, gallium arsenide, lithium niobate, [Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] or PMN-PT, and aluminum nitride – in the same deposition run, and show that all the films exhibit superconducting properties with similar critical temperatures. We fabricated waveguide-compatible superconducting nanowire single photon detectors on five substrates, report short dead times for all devices with a narrow spread of performances, and discuss their different photon detection saturation behavior. Our method simplifies the fabrication of superconducting devices on a wide range of materials.

  • 47.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, School of Electrical Engineering (EES).
    Quantum optics with nanowires (Conference Presentation)2017In: QUANTUM DOTS AND NANOSTRUCTURES: GROWTH, CHARACTERIZATION, AND MODELING XIV / [ed] Huffaker, DL Eisele, H, SPIE-INT SOC OPTICAL ENGINEERING , 2017, article id UNSP 101140IConference paper (Refereed)
  • 48.
    Zwiller, Val
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Nano Photonics.
    Zadeh, I. E.
    Los, J. W. N.
    Gourgues, R. B. M.
    Steinmetz, V.
    Dobrovolskiy, S. M.
    Dorenbos, S. N.
    Single-photon detection with near unity efficiency, ultrahigh detection-rates, and ultra-high time resolution2017In: CLEO: Science and Innovations part of CLEO: 2017 : 4-19 May 2017, San Jose, California, United States, Optical Society of America, 2017Conference paper (Refereed)
    Abstract [en]

    Single-photon detectors with high efficiency, high time resolution, low dark counts and high photon detection-rates are vital for most demanding quantum optics experiments. Combining all performances in a single device has been challenging. Here, we demonstrate a broadband detector with efficiency higher than 92%, over 150 MHz photon detection-rate and dark counts below 130 Hz operated in a conventional Gifford-McMahon cryostat. Furthermore, using our custom made cryogenic amplifiers and optimized detector, we reach a record low jitter of 14.80 ps while maintaining high efficiency.

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