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  • 101. Soderholm, J.
    et al.
    Björk, Gunnar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Hessmo, B.
    Inoue, S.
    Quantum limits on phase-shift detection using multimode interferometers2003Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 67, nr 5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fundamental phase-shift detection properties of optical multimode interferometers are analyzed. Limits on perfectly distinguishable phase shifts are derived for general quantum states of a given average energy. These bounds are found to be independent of the number of interfering modes, and are consistent with the Heisenberg limit. A short discussion on the concept of well-defined relative phase is also included.

  • 102. Soderholm, J.
    et al.
    Björk, Gunnar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Trifonov, A.
    Unpolarized light in quantum optics2001Inngår i: Optics and Spectroscopy, ISSN 0030-400X, E-ISSN 1562-6911, Vol. 91, nr 4, s. 532-534Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a new derivation of the unpolarized quantum states of light, whose general form was first derived by Prakash and Chandra [6]. Our derivation makes use of some basic group theory, is straightforward, and offers some new insights.

  • 103.
    Stensson, Katarina
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Björk, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Measurement of the two-time intensity-correlation function of arbitrary states2018Inngår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, nr 3, artikkel-id 033812Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For light-intensity-correlation measurements, different methods are used in the high-photon-number or high-intensity regime and in the single- and two-photon regime. Hence, there is an unfortunate measurement "gap" primarily for multiphoton, quantum states. These states, for example, multiphoton Fock states, will be increasingly important in the realization of quantum technologies and in exploring the boundaries between quantum and classical optics. We show that a naive approach based on attenuation, state splitting, and two-detector correlation can give the correct two-time intensity correlation for any state. We analyze how added losses decrease the measurement systematic error. The price to be paid is that the losses increase the measurement statistical error or, alternatively, increase the acquisition time for a given tolerable level of statistical error. We have experimentally demonstrated the feasibility of the method for a coherent state and a quasithermal state. The method is easy to implement in any laboratory and will simplify characterization of medium and highly excited nonclassical states as they become experimentally available.

  • 104.
    Stensson, Katarina
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantelektronik och -optik, QEO.
    Björk, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantelektronik och -optik, QEO.
    Gallo, Katia
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantelektronik och -optik, QEO.
    Green-pumped parametric downconversion in hexagonally poled MgO:LiTaO32014Inngår i: Advanced Solid State Lasers, ASSL 2014, 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We demonstrate multi-beam optical parametric generation in the 800-1550 nm spectral range sustained by concurrent nonlinear processes in hexagonally poled MgO-doped LiTaO<inf>3</inf>. Experiments performed with a nanosecond pump at 532 nm yield good agreement with theoretical predictions and hold promise for novel coherent parametric sources based on 2D nonlinear lattices.

  • 105.
    Sudirman, Azizahalhakim
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Kvantelektronik och -optik, QEO.
    Björk, Gunnar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Kvantelektronik och -optik, QEO.
    Margulis, Walter
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Reflectometry, ablation and fluid retrieval with an optical fiber2010Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, nr 1, s. 134-140Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A technique combining low-coherence reflectometry, laser ablation and microfluidics in a single microstructured fiber is developed. Experimental results demonstrate the possibility to ablate thin aluminum foil samples with fiber-guided Nd:YAG laser light, to collect liquid in the holes of the fiber and to simultaneously monitor the positioning of fiber for ablation and the fluid collection process with low-coherence reflectometry. Potential applications of the technique include minimally invasive retrieval of liquid samples with low contamination risk.

  • 106.
    Swillo, Marcin
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik (Stängd 20120101), Halvledarmaterial, HMA (Stängd 20120101).
    Ivarsson, M.
    Neubeck, A.
    Holm, N. G.
    Broman, C.
    Björk, Gunnar G.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik (Stängd 20120101), Kvantelektronik och -optik, QEO (flyttad till SCI 2011-07-01).
    Laser ablation in selected minerals for extracting fluid in inclusions2011Inngår i: Conf. Lasers Electro-Opt. Europe Eur. Quantum Electron. Conf., CLEO EUROPE/EQEC, 2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Fluid inclusions are naturally formed micro-containers in minerals that have been sealed since the mineral was formed. Analysis of inorganic and organic fluids from various inclusions is of particular interest for geologists, who are investigating environmental information and sometimes organic content. The inclusions are to a large extent prevented from contamination and many temporal changes as they are embedded within minerals. However, an essential part of the investigation procedure is the method of extracting fluids from such minerals. Since mechanical drilling or polishing involves a high risk for contamination of the sample, it is suggested to use a laser ablation technique to isolate the samples. In order to assess the potential of this technique, we have studied the parameters for laser ablation in quartz, calcite and apatite (the most common minerals containing fluid inclusions).

  • 107. Sánchez-Soto, L. L.
    et al.
    Klimov, A. B.
    Björk, Gunnar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik (Stängd 20120101), Kvantelektronik och -optik, QEO (flyttad till SCI 2011-07-01).
    Söderholm, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik (Stängd 20120101), Kvantelektronik och -optik, QEO (flyttad till SCI 2011-07-01). Max Planck Institut für die Physik des Licht, Germany.
    Andersen, U. L.
    Marquardt, C.
    Leuchs, G.
    Polarization correlations in quantum optics2011Inngår i: Opt.InfoBase Conf. Papers, 2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The standard degree of polarization involves exclusively first-order moments of the Stokes variables. This may be sufficient for most classical problems, but for quantum fields higher-order correlations are crucial. We claim that a complete polarization characterization must involve a whole hierarchy of polarization degrees constructed order by order, as it happens in coherence theory. We present here a second-order degree and determine it experimentally.

  • 108. Söderholm, J.
    et al.
    Björk, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Klimov, A. B.
    Sanchez-Soto, L. L.
    Leuchs, G.
    Quantum polarization characterization and tomography2012Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 14, s. 115014-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a complete polarization characterization of any quantum state of two orthogonal polarization modes and give a systematic measurement procedure to collect the necessary data. Full characterization requires measurements of the photon number in both modes and linear optics. In the case where only the photon-number difference can be determined, a limited but useful characterization is obtained. The characteristic Stokes moment profiles are given for several common quantum states.

  • 109. Trifonov, A.
    et al.
    Björk, Gunnar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Soderholm, J.
    Simultaneous minimum-uncertainty measurement of discrete-valued complementary observables2001Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 86, nr 20, s. 4423-4426Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have made the first experimental demonstration of the simultaneous minimum uncertainty product between two complementary observables for a two-state system (a qubit). A partially entangled two-photon state, where each of the photons carries (partial) information of the initial state, was used to perform such a measurement.

  • 110. Trifonov, A.
    et al.
    Björk, Gunnar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Soderholm, J.
    Tsegaye, T.
    Comprehensive experimental test of quantum erasure2002Inngår i: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 18, nr 2, s. 251-258Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In an interferometer, path information and interference visibility are incompatible quantities. Complete determination of the path will exclude any possibility of interference, rendering zero visibility. However, it is, under certain conditions, possible to trade the path. information for improved (conditioned) visibility. This procedure is called quantum erasure. We have performed such experiments with polarization-entangled photon pairs. Using a partial polarizer, we could vary the degree of entanglement between the object and the probe. We could also vary the interferometer splitting ratio and thereby vary the a priori path predictability. This allowed us to test quantum erasure under a number of different experimental conditions. All experiments were in good agreement with theory.

  • 111. Trifonov, A.
    et al.
    Tsegaye, T.
    Björk, Gunnar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Soderholm, J.
    Goobar, E.
    Atature, N.
    Sergienko, A. V.
    Experimental demonstration of the relative phase operator2000Inngår i: Journal of Optics B-Quantum and Semiclassical Optics, ISSN 1464-4266, E-ISSN 1741-3575, Vol. 2, nr 2, s. 105-112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have experimentally demonstrated a realization of the two-mode relative phase operator introduced by Luis and Sanchez-Soto (Luis A and Sanchez-Soto L L 1993 Phys. Rev. A 48 4702). The relative phase distribution function was measured for a weakly excited relative phase eigenstate and weakly excited two-mode coherent states. The experiment is also (using the eigenstates) a demonstration of Heisenberg-limited interferometry.

  • 112. Tsegaye, T.
    et al.
    Björk, Gunnar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Atature, M.
    Sergienko, A. V.
    Saleh, B. E. A.
    Teich, M. C.
    Complementarity and quantum erasure with entangled-photon states2000Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 62, nr 3, s. art. no.-32106Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A quantum-erasure experiment was performed on superposition states of two photons in either of two spatiotemporal modes. Symmetrical tapping of energy from the two-mode state creates a four-mode entangled state. A direct measurement of one photon in two of the modes reveals the path of the second one, thereby eliminating the possibility of observing interference between the two remaining modes. It is shown that a unitary rotation of one of the two-mode states erases the path information; as a consequence, the visibility of the other two-mode state can be resurrected.

  • 113. Tsegaye, T.
    et al.
    Soderholm, J.
    Atature, M.
    Trifonov, A.
    Björk, Gunnar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Sergienko, A. V.
    Saleh, B. E. A.
    Teich, M. C.
    Experimental demonstration of three mutually orthogonal polarization states of entangled photons2000Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 85, nr 24, s. 5013-5017Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Linearly polarized classical light can be expressed in a vertical and a horizontal component. Geometrically rotating vertically polarized light by 90 degrees will convert it to the orthogonal horizontal polarization. We have experimentally generated a two-photon state of light which evolves into an orthogonal state upon geometrical rotation by 60 degrees. Rotating this state by an additional 60 degrees will yield a state which is mutually orthogonal to the first two states. Generalizing this procedure, one can generate N + 1 mutually orthogonal N-photon states that cyclicly evolve from one to another upon a geometric rotation by 180/(N + 1) degrees.

  • 114. Usachev, P.
    et al.
    Soderholm, J.
    Björk, Gunnar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Trifonov, A.
    Experimental verification of differences between classical and quantum polarization properties2001Inngår i: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 193, nr 06-jan, s. 161-173Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have carried out polarization measurements on a two-photon quantum state generated by spontaneous parametric down conversion. Our measurements show that the state is unpolarized in the classical theory, but they also show that the state is not invariant under geometric rotation. Therefore, it is not unpolarized in the quantum theory. This is another example of a rather simple experiment that clearly shows the effects of quantum interference. It also confirms the theoretical investigation by Klyshko [Phys. Lett. A 163 (1992) 349]. The experiment is explained theoretically and a systematic treatment of polarization in quantum theory is outlined.

  • 115. Wang, Q.
    et al.
    Wang, X. B.
    Björk, Gunnar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Karlsson, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik.
    Improved practical decoy state method in quantum key distribution with parametric down-conversion source2007Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 79, nr 4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, a new decoy state scheme for quantum key distribution with parametric down-conversion source is proposed. We use both three-intensity decoy states and their triggered and nontriggered components to estimate the fraction of single-photon counts and the quantum bit-error rate of single-photon pulses, and then deduce a more accurate value of the key generation rate. The final key rate over transmission distance is simulated, which shows that we can obtain a higher key rate than that of the existing methods, including our own earlier work.

  • 116.
    Yuntian, Chen
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Björk, Gunnar
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    Generation and detection of photonic qutrits2007Inngår i: 2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, CLEO, 2007, s. 4386921-Konferansepaper (Fagfellevurdert)
  • 117. Zwiller, V.
    et al.
    Björk, Gunnar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Improved light extraction from emitters in high refractive index materials using solid immersion lenses2002Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 92, nr 2, s. 660-665Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Solid immersion lenses (SILs) are optically transparent, truncated spheres, brought in contact with a sample to be imaged. The combination of a conventional optical microscope and a SIL results in a highly effective numerical aperture of the imaging system that can improve the resolution. In addition, when imaging high refractive index samples, such as semiconductors, the light collection efficiency can be increased drastically. We investigate the collection efficiency as a function of the SILs geometry and refractive index, using an analytical expression for the light dispersion through an arbitrarily truncated sphere. The theoretical results are compared to experimental measurements obtained on single quantum dots and are found to be in good agreement.

  • 118. Zwiller, V.
    et al.
    Falth, S.
    Persson, J.
    Seifert, W.
    Samuelson, L.
    Björk, Gunnar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Fabrication and time-resolved studies of visible microdisk lasers2003Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, nr 4, s. 2307-2309Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the fabrication and characterization of microdisk lasers emitting at around 650 nm. The structures were grown by metalorganic vapor phase epitaxy and processed using electron beam lithography and wet etching. Time-resolved photoluminescence measurements done at low temperature show a lasing threshold of 60 muW average power. A redshift in the whispering modes energy is observed.

  • 119. Zwiller, Valéry
    et al.
    Blom, Hans
    KTH, Tidigare Institutioner, Elektronik.
    Jonsson, Per
    KTH, Tidigare Institutioner, Elektronik.
    Panev, Nikolay
    Jeppesen, Sören
    Tsegaye, Tedros
    Goobar, Edgard
    Pistol, Mats-Erik
    Samuelson, Lars
    Björk, Gunnar
    KTH, Tidigare Institutioner, Elektronik.
    Single quantum dots emit single photons at a time: Antibunching experiments2001Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 78, nr 17, s. 2476-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied the photoluminescence correlation from a single InAs/GaAs self-assembled Stranski–Krastanow quantum dot under continuous, as well as under pulsed excitation. Under weak continuous excitation, where the single dot luminescence is due primarily to single exciton recombinations, antibunching is observed in the single dot emission correlation. Under weak pulsed excitation, the number of photons emitted by the quantum dot per pulse is close to one. We present data obtained under both conditions and are able to show that devices based on single quantum dots can be used to generate single photons.

  • 120. Zwiller, Valéry
    et al.
    Jonsson, Per
    Blom, Hans
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Jeppesen, Sören
    Pistol, Mats-Erik
    Samuelson, Lars
    Katznelson, A. A.
    Kotelnikov, E. Yu.
    Evtikhiev, Vadim
    Björk, Gunnar
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Correlation spectroscopy of excitons and biexcitons on a single quantum dot2002Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 66, nr 2, s. 053814-053814-7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report the observation of antibunched emission from single self-assembled InAs quantum dots under various conditions. We have measured the correlation function of the photon emission pertaining to single emission lines from single quantum dots under continuous and pulsed laser excitation, as well as under continuous white light excitation. The measurements were performed under different excitation intensities at liquid helium temperatures on two samples with distinct structures. At higher temperatures ~30 K!, an antibunching dip was still observed. We have also observed antibunching on a second emission line in the quantum dot spectrum, attributed to the biexciton, demonstrating the possibility of generating photon pairs with a single quantum dot. Polarization correlations on the biexciton and exciton line were also measured in an attempt to generate entangled photon pairs.

123 101 - 120 of 120
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