Full daylight quantum-key-distribution at 1550 nm enabled by integrated silicon photonics

Abstract

The future envisaged global-scale quantum-communication network will comprise various nodes interconnected via optical fibers or free-space channels, depending on the link distance. The free-space segment of such a network should guarantee certain key requirements, such as daytime operation and the compatibility with the complementary telecom-based fiber infrastructure. In addition, space-to-ground links will require the capability of designing light and compact quantum devices to be placed in orbit. For these reasons, investigating available solutions matching all the above requirements is still necessary. Here we present a full prototype for daylight quantum key distribution at 1550 nm exploiting an integrated silicon-photonics chip as state encoder. We tested our prototype in the urban area of Padua (Italy) over a 145 m-long free-space link, obtaining a quantum bit error rate around 0.5% and an averaged secret key rate of 30 kbps during a whole sunny day (from 11:00 to 20:00). The developed chip represents a cost-effective solution for portable free-space transmitters and a promising resource to design quantum optical payloads for future satellite missions.

Advances in Space Quantum Communications

“…The effects of daylight operations on QKD has been investigated for more than two decades and several demonstrations of free space QKD in daylight have been realised [253][254][255]. More recently, by exploiting single mode fibre coupling as spatial filtering and by using telecommunication wavelength to minimise the external noise, it has become possible to demonstrate QKD in daylight with the potential to reach satellite to ground communication [256,257]. Previous demonstrations used near-IR, narrow wavelength filtering and baffles around the receiving telescope [255].…”

“…Previous demonstrations used near-IR, narrow wavelength filtering and baffles around the receiving telescope [255]. In particular, in [257], the authors proposed an integrated photonic circuit as a source of quantum states. This is an interesting technology for space application, as it might drastically reduce the size, weight and power (SWaP) of the payload.…”

Experimental secure quantum key distribution in presence of polarization-dependent loss

“…Quantum key distribution (QKD) has received great interest as it is an information-theoretic security communication technology [1]. With much effort, QKD has been experimentally demonstrated over fiber-based [2][3][4][5][6][7][8][9], free-space [10][11][12], and underwater channels [13]. Various quantum field networks have been reported worldwide [14][15][16][17][18].…”

Near-Maximal Two-Photon Entanglement for Optical Quantum Communication at 2.1μm

“…A critical challenge for satellite-to-ground QKD is the limited operability in daylight due to excess background in the telecom and visible bands [13]. As a result, most demonstrations to date rely on nighttime operation, with only a few exceptions [14]. Moreover, entanglement-based or device-independent approaches in daylight are still to be demonstrated.…”