Realistic quantum network simulation for experimental BBM92 key distribution

TL;DR

It is demonstrated that discrete event simulators can meet needs in quantum network simulations which cannot be filled solely by experiment or theory: discrete event simulators can accurately simulate QKD protocols and match experiments in regimes where theoretical models may require more simplifying assumptions.

Abstract

Quantum key distribution (QKD) can provide secure key material between two parties without relying on assumptions about the computational power of an eavesdropper. QKD is performed over quantum links and quantum networks, systems which are resource-intensive to deploy and maintain. To evaluate and optimize performance prior to, during, and after deployment, accurate simulations with attention to physical realism are necessary. Quantum network simulators can simulate a variety of quantum and classical protocols and can assist in quantum network design and optimization by offering realism and flexibility beyond mathematical models which rely on simplifying assumptions and can be intractable to solve as network complexity increases. We use a versatile discrete event quantum network simulator to simulate the entanglement-based QKD protocol BBM92 and compare it to our experimental implementation and to existing theory. We find the discrete event quantum network simulator can match experimental key rates and error rates with a lower mean squared error than analytical theory. Furthermore, we simulate secure key rates in a repeater key distribution scenario for which no experimental implementations exist and find agreement between simulation and analytical theory. Hence, we demonstrate discrete event simulators can meet needs in quantum network simulations which cannot be filled solely by experiment or theory: discrete event simulators can accurately simulate QKD protocols and match experiments in regimes where theoretical models may require more simplifying assumptions, and they can match theoretical models in the opposite scenario where experiments have not yet been performed but theoretical models exist.

Figures (9)

• Figure 1: Schematic of the BBM92 experimental setup used to produce keys, and evaluate key rates and QBER metrics. Detectors are shown in dark blue and are labeled by polarization measurement outcome. BS: beam splitter, PC: polarization control and correction, PBS: polarizing beam splitter.
• Figure 2: Schematic illustrating the discrete event simulation for BBM92 key exchange. An entangled photon pair is emitted from the source. Each photon may be lost during transmission in a loss event or detected by Alice or Bob in a detection event which may be shifted due to detector jitter. Diagonal gray arrows show signal propagation.
• Figure 3: (a) Raw key rates (with relative errors as inset plot) and (b) QBERs (with relative errors as inset plot) for theory, experiment, and AQNSim simulation of BBM92 key exchange. Relevant experimental parameters used in simulations are provided in Table \ref{['tab:parameters']}. The AQNSim key rates and QBERs are obtained from a randomly seeded simulation, re-binned at each coincidence window, averaged over 4,000,000 shots. The experimental key rates and QBERs are obtained from a single experimental run, with the data re-binned at each coincidence window size. Root mean squared errors are displayed for AQNSim and experiment and for theory and experiment for coincidence windows greater than 100 picoseconds.
• Figure 4: Asymptotic BBM92 secure key rate for simulation, theory, and experiment for swept parameters (a) loss per link, (b) detector dead time, (c) detection resolution, (d) dark count rate per communication partner, (e) source brightness, and (f) visibility. The coincidence window for all plots is 2 nanoseconds and all other parameters are given in Table \ref{['tab:parameters']}.
• Figure 5: (a) Entanglement creation using a repeater containing two end nodes (Alice and Bob), one central repeater node with two stored qubits capable of two-qubit gate operations ($r=1)$, and two Bell state measurement stations (BSM). (b) The average entanglement generation rate (in units of $c/L_0$) for different elementary link loss values calculated from simulation (using AQNSim with 1000 shots) and theory for a two-link repeater.