Nicolas Perlot

We present a quantum key distribution (QKD) platform targeting mid-range fiber, free-space and hybrid links. With its interfaces for third-party post-processing, commercial key management, encryptors and QRNG, the modular and flexible system enables easy integration into existing telecom infrastructures. Recent experiments demonstrate its seamless operation over fiber and free-space links.

When wavelength multiplexing a large number of quantum communication channels and time-phase coding is used, it’s desired in terms of cost and complexity to minimize the number of interferometers. Here, we demonstrate that a visibility sufficiently high to enable QKD operation can be maintained with only a single interferometer at the receiver and without the need for additional high frequency phase modulation.

Emerging quantum technologies, such as quantum key distribution, increase the demand for reliable tools that enable single-photon generation, manipulation and sensing on an increasingly large scale. In the framework of integrated photonics, these needs can be fulfilled by patterning highly stable photonic devices on monolithic silicon chips in CMOS compatible processes. In this work we show how advanced single-photon detection capabilities are achieved on a silicon chip, realizing a 4x4 array of waveguide-integrated superconducting nanowire single-photon detectors (SNSPDs). Our detectors are fabricated from highly uniform superconducting NbTiN thin films in a U-shape geometry atop of silicon nitride strip waveguides [1]. The nanophotonic circuitry is interfaced with scalable 3D polymeric out-of-plane fiber-to-chip couplers [2] featuring high broadband transmission in the telecom regime. In order to address each detector individually via a separate fiber-optic channel, we precisely align a 16-channel 2D fiber array to the 4x4 coupler matrix. We evaluate the performance of our waveguide-integrated SNSPD array in a cost-efficient closed-cycle cryostat at 3.5 K. We find dark count rates below 10 Hz combined with a superior system detection efficiency of up to 50 % at 30 MHz count rate for telecom-wavelength photons. In addition, we achieve 120 ps timing jitter with a simple two-stage room-temperature amplification approach. Our detector arrays pave the way for parallelized multi-channel single-photon detection and will therewith enable ultra-fast quantum key distribution. Furthermore, our approach allows for integrating sophisticated nanophotonic devices with waveguide-coupled single-photon detectors providing additional variability and functionality.