Single-emitter quantum key distribution over 175 km of fibre with optimised finite key rates

Abstract

Quantum key distribution with solid-state single-photon emitters is gaining traction due to their rapidly improving performance and compatibility with future quantum networks. Here we emulate a quantum key distribution scheme with quantum-dot-generated single photons frequency-converted to 1550 nm, achieving count rates of 1.6 MHz with $${g}^{\left(2\right)}\left(0\right)=3.6\%$$ g 2 0 = 3.6 % and asymptotic positive key rates over 175 km of telecom fibre. We show that the commonly used finite-key analysis for non-decoy state QKD drastically overestimates secure key acquisition times due to overly loose bounds on statistical fluctuations. Using the tighter multiplicative Chernoff bound to constrain the estimated finite key parameters, we reduce the required number of received signals by a factor 108. The resulting finite key rate approaches the asymptotic limit at all achievable distances in acquisition times of one hour, and at 100 km we generate finite keys at 13 kbps for one minute of acquisition. This result is an important step towards long-distance single-emitter quantum networking.

High-rate intercity quantum key distribution with a semiconductor single-photon source

“…For the case of a finite block size of the keys, we evaluate the SKBs per pulse using the multiplicative Chernoff bound 45 , 46 , Here, R is the CR, t is the acquisition time, the lower bound of non-multiphoton emissions in the receiver module for X and Z bases, the upper bound of the phase error rate, λ E C the lower bound of information leakage 47 and ϵ c o r are the bits used for verification during the error correction process. ϵ P A is the failure probability of privacy amplification.…”

“…In this experiment, the MTL for both the asymptotic and finite-key block cases are limited by the blinking-corrected g 2 (0), since the multi-photon emission probability is detrimental for generating high SKRs with single-photon states in the high-loss regime. The SKR and MTL can be improved by employing adequate pre-attenuation 46 and employing time gating on the histograms of second-order correlation and truth table during post-processing 44 , 50 .…”

“…Recent QKD implementations have reported two noteworthy approaches, both utilising SPSs. The first involves QDs in photonic crystal waveguides 37 , while the second employs a QD contained in an oxide-apertured micropillar 46 . Both SPS were not directly emitting into the telecom C-band, and therefore frequency conversion techniques were employed, introducing additional losses.…”

Quantum Key Distribution Using a Quantum Emitter in Hexagonal Boron Nitride

“…Furthermore, recent experiments have performed QKD with frequency-converted quantum dot SPSs over longer distances, achieving 1-689 kbits/s depending on fiber length at 160 MHz clock rate in Ref. [20] and 5-6 kbits/s at 72.6 MHz clock rate in Ref. [35].…”

“…Over the last few decades, significant effort has been put forward to develop such sources, with the prime challenges being their purity (i.e., minimization of multiphoton events) and extraction of light (i.e., collection efficiencies). [15,16] While semiconductor quantum dots are a great choice for a bright and pure source, [17][18][19][20][21] their operation is limited to cryogenic temperatures. For wide deployment and practical implementation of QKD in real-world settings, compact, room temperature, sources are required.…”