Abstract
Advances in single-photon sources (SPSs) and single-photon detectors (SPDs) promise unique applications in the field of quantum information technology. In this paper, we report long-distance quantum key distribution (QKD) by using state-of-the-art devices: a quantum-dot SPS (QD SPS) emitting a photon in the telecom band of 1.5 μm and a superconducting nanowire SPD (SNSPD). At the distance of 100 km, we obtained the maximal secure key rate of 27.6 bps without using decoy states, which is at least threefold larger than the rate obtained in the previously reported 50-km-long QKD experiment. We also succeeded in transmitting secure keys at the rate of 0.307 bps over 120 km. This is the longest QKD distance yet reported by using known true SPSs. The ultralow multiphoton emissions of our SPS and ultralow dark count of the SNSPD contributed to this result. The experimental results demonstrate the potential applicability of QD SPSs to practical telecom QKD networks.
Highlights
Over the past decade, advances in sources, operational devices, and detectors have attracted the attention of many researchers in the field of quantum information technology
The g(2)(0) is assumed to be ~10−4, which is lower than the current quantum-dot single-photon sources (SPSs) (QD SPS) by one order of magnitude
The distance is comparable to the record of phase-encoding quantum key distribution (QKD) system using decoy states[38]
Summary
Transmission of secure keys over 50 km of in-lab fiber is the record of standard QKD based on a true SPS; that experiment used a telecom-band InAs/InP quantum dot (QD) SPS and conventional InGaAs avalanche SPD (ASPD)[15]. The transmission distance was limited by the residual multiphoton emission of the SPS and dark count of the SPD. A high-purity SPS was needed, i.e., one having a small probability of emitting more or fewer than 1 photon. This is a challenging problem, because the goals of enhancing single-photon efficiency and suppressing multiphoton emission are incompatible in many SPSs16–21. We demonstrate secure key distribution up to 120 km by using an ultrahigh purity QD SPS and a superconducting nanowire SPD (SNSPD)[22,23,24,25]. We demonstrate that our true SPS has the potential to extend the transmission distance over 200 km by accounting for the additional improvement of g(2)(0) and source efficiencies
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