Quantum Key Distribution with a Negatively Charged Quantum Dot Single-Photon Source

TL;DR

This work targets improving QKD by reducing multiphoton emission probabilities $p_2$, $p_3$ and enhancing indistinguishability $I$ and brightness $\beta$ of a negatively charged quantum dot single-photon source embedded in an elliptical micropillar cavity. The authors model a four-level QD coupled to orthogonal cavity modes under resonant and adiabatic rapid passage (ARP) driving, and solve the master equation with Lindblad losses to predict photon statistics and source metrics. They then evaluate secure-key-rate (SKR) for BB84 (with infinite decoy states) and TF-QKD (with infinite decoy states) and compare against Poisson-distributed sources. Results show ARP improves $I$ and reduces $p_2$ relative to resonant driving, that QDS outperform Poisson sources at short to intermediate distances, and that Poisson sources may dominate only at very long distances, providing practical guidance for source design in quantum communication.

Abstract

Various quantum key distribution protocols require bright single-photon sources with a very low probability of multiphoton emission. In this work, we investigate single-photon generation from a negatively charged quantum dot embedded in an elliptical pillar microcavity, driven using either resonant excitation or adiabatic rapid passage (ARP). Our results show that ARP excitation significantly suppresses multiphoton emission probability and improves photon indistinguishability compared to resonant excitation. We further evaluate the secure key rate of both BB84 and twin-field quantum key distribution (TF-QKD) using quantum-dot single-photon sources and compare their performance with that of Poisson-distributed photon sources (PDS) such as weak coherent pulses and down-conversion sources. The analysis reveals that adiabatic excitation offers a modest but consistent enhancement in secure key rate relative to resonant excitation. Moreover, quantum-dot single-photon sources outperform PDS sources over short and intermediate distances; however, at longer distances, PDS sources eventually surpass quantum-dot sources in both infinite decoy-state BB84 and TF-QKD.

Figures (10)

• Figure 1: (a) Illustration of an elliptical pillar microcavity comprising GaAs/AlAs distributed Bragg reflectors with an embedded negatively charged quantum dot (QD). (b) Energy-level diagram and optical transitions of a four-level QD system induced by an externally supplied magnetic field in the Voigt configuration. A description of the different energy levels and optical transitions is provided in the text.
• Figure 2: Evolution of the (a) indistinguishability and (b) brightness as a function of Rabi frequency and pulse duration for resonant excitation with $\Delta_{HV} = 0.6~\mathrm{meV}$.
• Figure 3: Evolution of the (a) indistinguishability and (b) brightness as a function of Rabi frequency and pulse duration for adiabatic excitation with $\Delta_{HV} = 0.6~\mathrm{meV}$.
• Figure 4: Evolution of (a) the indistinguishability and (b) the brightness as functions of the frequency separation between the cavity modes, $\Delta_{HV}$, for $\tau = 2.8~\mathrm{ps}$ and $\Omega_R = 0.4~\mathrm{meV}$ under resonant excitation.
• Figure 5: Evolution of (a) the indistinguishability and (b) the brightness as functions of the frequency separation between the cavity modes, $\Delta_{HV}$, for $\tau = 2.8~\mathrm{ps}$ and $\Omega_R = 0.4~\mathrm{meV}$ under adiabatic excitation.