Adaptive spatial filtering of daytime sky noise in a satellite quantum key distribution downlink receiver

Abstract

Abstract. Spatial filtering is an important technique for reducing sky background noise in a satellite quantum key distribution downlink receiver. Atmospheric turbulence limits the extent to which spatial filtering can reduce sky noise without introducing signal losses. Using atmospheric propagation and compensation simulations, the potential benefit of adaptive optics (AO) to secure key generation (SKG) is quantified. Simulations are performed assuming optical propagation from a low-Earth-orbit satellite to a terrestrial receiver that includes AO. Higherorder AO correction is modeled assuming a Shack-Hartmann wavefront sensor and a continuous-face-sheet deformable mirror. The effects of atmospheric turbulence, tracking, and higher-order AO on the photon capture efficiency are simulated using statistical representations of turbulence and a time-domain wave-optics hardware emulator. SKG rates are calculated for a decoy-state protocol as a function of the receiver field of view for various strengths of turbulence, sky radiances, and pointing angles. The results show that at fields of view smaller than those discussed by others, AO technologies can enhance SKG rates in daylight and enable SKG where it would otherwise be prohibited as a consequence of background optical noise and signal loss due to propagation and turbulence effects. Keywords: quantum key distribution; adaptive optics; decoy states; quantum information; cryptography; sky radiance.Paper 151557P received Nov. 5, 2015; accepted for publication Dec. 24, 2015; published online Feb. 2, 2016; corrected Apr. 26, 2016. IntroductionThe threat quantum computing poses to public key cryptography is motivating the development of alternatives to modern key sharing techniques that rely on computational complexity for security.1,2 Presently, there is interest in developing quantum key distribution (QKD), presented by Bennett and Brassard in 1984 (BB84), as a provably secure alternative.2-5 QKD lends itself to mathematical proofs of theoretical security and offers the potential for secure generation of symmetric encryption keys in real time over optical channels.

Characterization of free-space quantum channels

“…where the parameters η (0) n , R n , and λ n are again given by Eqs. (16), (17), and (18), respectively. It is worth to note that in the case when Γ 2 (r; L) significantly deviates from the Gaussian form, the prefactor η 0 in Eq.…”

“…13,14 The successful practical realization of free-space quantum protocols requires the development of advanced preselection, postselection, and adaptive strategies. 15,16,17,18 The main obstacle on the way of high-fidelity quantum communication in free-space is the atmospheric turbulence, random scattering, and absorption losses. The absorption and scattering effects contribute merely to energy losses and the degradation of the signal intensity.…”

Quantum-limited measurements of optical signals from a geostationary satellite

“…Quantum-limited measurements of quantum states traveling through long distances in outer space provide both an offer to test quantum mechanics under such extreme conditions and a prerequisite for its use in quantum technology [7]. To this end satellite quantum communication [8][9][10][11][12][13][14][15] promises to provide the currently missing links for global quantum key distribution (QKD). Important experiments in satellite quantum communication have been reported or are currently being devised and set up [16][17][18][19][20][21][22].This work presents and discusses quantum-limited measurements on optical signals sent from a GEOstationary satellite.…”

Quantum measurements of signals from the Alphasat TDP1 laser communication terminal

“…Existing fiber infrastructure is not suitable for this purpose since classical telecom repeaters cannot relay quantum states [2]. Therefore, optical satellite-to-ground communication [17][18][19][20][21][22] lends itself to bridge intercontinental distances for quantum communication [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. …”