Passively stable distribution of polarisation entanglement over 192 km of deployed optical fibre

Abstract

Quantum key distribution (QKD) based on entangled photon pairs holds the potential for repeater-based quantum networks connecting clients over long distance. We demonstrate longdistance entanglement distribution by means of polarisation-entangled photon pairs through two successive deployed 96 km-long telecommunications fibres in the same submarine cable. One photon of each pair was detected directly after the source, while the other travelled the fibre cable in both directions for a total distance of 192 km and attenuation of 48 dB. The observed two-photon Bell state exhibited a fidelity 85%±2 % and was stable over several hours. We employed neither active stabilisation of the quantum state nor chromatic dispersion compensation for the fibre.

Strategies for achieving high key rates in satellite-based QKD

“…Quantum key distribution (QKD) allows to generate symmetric keys between distant parties, with a level of privacy that can be lower bounded from the very laws of physics. Flying qubits encoded in photons can be distributed up to distances of a few hundred kilometers in fibers [1][2][3] , while longer distances can be achieved by employing quantum repeaters 4,5 . Alternatively, optical satellite links have been proposed to overcome the distance limitations of groundbased transmission of photons 6,7 .…”

Polarization Scramblers to Solve Practical Limitations of Frequency Transfer

“…It also attracts much attention in offering the possibility to implement long-distance quantum communication protocols like quantum key distribution (QKD). By applying quantum entanglement to pairs of photons, these QKD systems can be naturally integrated into existing wavelength-division-multiplexed (WMD) networks, thereby taking advantage of the vast fiber-optic infrastructure, which is ubiquitously deployed around the globe [5]- [13].…”

“…In the frequency metrology domain, it can be simply compensated with optical amplifiers and optical repeater techniques with automatic polarization control [14]- [16]. In the quantum communication domain, QKD system has been verified over distances up to 100 km in combination with existing fiber telecommunication networks using polarizationentangled photons [13]. In addition, recent developments relying on active fiber noise stabilisation to lock two independent laser wavelengths and with a single photon detector, demonstrate twin field quantum key distribution (TF-QKD) over 300 km optical fiber spools [17].…”

Metrology Perspective of Single‐Photon Detectors: Review on Global Calibration Methods

“…Single or few photon technologies have paved their way beyond research and are utilized in many applications. A few of them are quantum cryptography, quantum key distribution, [ 1–4 ] long‐distance communication, [ 5 ] single‐molecule detection, [ 6 ] quantum computing, [ 7 ] quantum imaging, [ 8–10 ] and medical care. [ 11 ] Figure provides a glimpse of single‐photon device applications.…”

“…[ 31,32,34–37 ] over conventional detectors and is used for multiple applications. [ 4,5,38–43 ] Despite having advantages, superconducting detectors require cryogenic temperature for their operation as low as around 2.5 K (WSi SNSPD). [ 44 ] This requirement further introduces the cost factor, size, power requirements, to develop the operational setup of SNSPD.…”