Quantum communication networks are used for QKD and metrological applications. We present research connecting two nodes ≈ 20 kilometers apart over the municipal fiber network using semiconductor quantum dots emitting at 1550 nm.

Quantum communication networks are used for QKD and metrological applications. We present research connecting two nodes ˜ 20 kilometers apart over the municipal fiber network using semiconductor quantum dots emitting at 1550 nm.

Quantum communication networks are used for QKD and metrological applications. We present research connecting two nodes ≈ 20 kilometers apart over the municipal fiber network using semiconductor quantum dots emitting at 1550 nm.

Quantum communication networks will connect future generations of quantum processors, enable metrological applications, and provide security through quantum key distribution. We present a testbed that is part of the municipal fiber network in the greater Stockholm metropolitan area for quantum resource distribution through a 20 km long fiber based on semiconductor quantum dots emitting in the telecom C-band. We utilize the service to generate random numbers passing the NIST test suite SP800-22 at a subscriber 8 km outside of the city with a bit rate of 23.4 kbit/s.

Herein, the fabrication of InP photonic-crystal surface-emitting lasers (PCSELs) using a buried airhole/InP photonic-crystal (PC) layer based on an epitaxial regrowth process is reported. The formation of PC voids in the InP crystal structure requires a precise tuning of the metal-organic vapor-phase epitaxy (MOVPE) growth parameters, where the regrowth evolution is a function of temperature, V/III ratio, and growth rate. With precise control of these parameters, it is possible to alter the airhole shape from complete infilling to perfect encapsulation. Low-threshold lasing is demonstrated from these encapsulated airhole regrown PCSELs using optical pumping.

Entangled photons are an integral part in quantum optics experiments and a key resource in quantum imaging, quantum communication, and photonic quantum information processing. Making this resource available on-demand has been an ongoing scientific challenge with enormous progress in recent years. Of particular interest is the potential to transmit quantum information over long distances, making photons the only reliable flying qubit. Entangled photons at the telecom C-band could be directly launched into single-mode optical fibers, enabling worldwide quantum communication via existing telecommunication infrastructure. However, the on-demand generation of entangled photons at this desired wavelength window has been elusive. Here, we show a photon pair generation efficiency of 69.9 +/- 3.6% in the telecom C-band by an InAs/GaAs semiconductor quantum dot on a metamorphic buffer layer. Using a robust phonon-assisted two-photon excitation scheme we measure a maximum concurrence of 91.4 +/- 3.8% and a peak fidelity to the Phi(+) state of 95.2 +/- 1.1%, verifying on-demand generation of strongly entangled photon pairs and marking an important milestone for interfacing quantum light sources with our classical fiber networks.

Entangled photon generation at 1550 nm in the telecom C-band is of critical importance as it enables the realization of quantum communication protocols over long distance using deployed telecommunication infrastructure. InAs epitaxial quantum dots have recently enabled on-demand generation of entangled photons in this wavelength range. However, time-dependent state evolution, caused by the fine-structure splitting, currently limits the fidelity to a specific entangled state. Here, we show fine-structure suppression for InAs quantum dots using micromachined piezoelectric actuators and demonstrate generation of highly entangled photons at 1550 nm. At the lowest fine-structure setting, we obtain a maximum fidelity of 90.0 +/- 2.7% (concurrence of 87.5 +/- 3.1%). The concurrence remains high also for moderate (weak) temporal filtering, with values close to 80% (50%), corresponding to 30% (80%) of collected photons, respectively. The presented fine-structure control opens the way for exploiting entangled photons from quantum dots in fiber-based quantum communication protocols.

We demonstrate a surface emitting 1.5 mu m multi-quantum well (MQW) light-emitting diode (LED) on a 3-inch epitaxial lateral overgrowth (ELOG) InP/Si wafer. The enhanced crystalline quality of ELOG InP/Si is revealed by various characterization techniques, which gives rise to a MQW with high photoluminescence intensity at 1.5 mu m and interference fringes arising from the vertical Fabry-Perot cavity. The LED devices exhibited strong electroluminescence intensity that increased with pump current. Moreover, transparency current measurements indicate optical gain in the 1.5 mu m MQW on InP/Si. The results are encouraging for obtaining wafer scale 1.5 mu m surface emitting laser structures on silicon with further optimization.

Herein, the design, metal-organic vapor-phase epitaxial growth, fabrication, and characterization of buried-tunnel junction (BTJ) current injection structures for InP/Si hybrid nanomembrane photonic crystal surface emitting lasers (PCSELs) are reported. Corresponding BTJ-light-emitting diodes on InP substrate show low series resistance and uniform carrier injection over square-shaped device areas with side length ranging from 15 up to 250 mu m, whereas BTJ-PCSEL structures with similar current injection configuration fabricated on photonic-crystal silicon-on-insulator substrate using transfer print technology show significant linewidth narrowing at low current density.