Entanglement-based quantum key distribution with a blinking-free quantum dot operated at a temperature up to 20 K

Abstract

Entanglement-based quantum key distribution (QKD) promises enhanced robustness against eavesdropping and compatibility with future quantum networks. Among other sources, semiconductor quantum dots (QDs) can generate polarization-entangled photon pairs with near-unity entanglement fidelity and a multiphoton emission probability close to zero even at maximum brightness. These properties have been demonstrated under resonant two-photon excitation (TPE) and at operation temperatures below 10 K. However, source blinking is often reported under TPE conditions, limiting the maximum achievable photon rate. In addition, operation temperatures reachable with compact cryocoolers could facilitate the widespread deployment of QDs, e.g., in satellite-based quantum communication. We demonstrate blinking-free emission of highly entangled photon pairs from GaAs QDs embedded in a p-i-n diode. High fidelity entanglement persists at temperatures of at least 20 K, which we use to implement fiber-based QKD between two buildings with an average raw key rate of 55 bits∕s and a qubit error rate of 8.4%. We are confident that by combining electrical control with already demonstrated photonic and strain engineering, QDs will keep approaching the ideal source of entangled photons for real world applications.

Beyond the Four-Level Model: Dark and Hot States in Quantum Dots Degrade Photonic Entanglement

“…We evaluate concurrence and fidelity at every temperature for a time bin of 2 ns, as shown in Figure (f). At low temperatures the concurrence [fidelity] is equal to 0.94(1) [0.969(4)], comparable to former investigations. ,, The degree of entanglement stays approximately constant up to about 15 K and then decreases with increasing temperature. The slight increase in g (2) (0) mentioned above does not explain the observed steep entanglement degradation shown in Figures (d–f) since the g (2) (0) values are still in the range typically observed at T = 5 K. ,, …”

“…21,30,31 The degree of entanglement stays approximately constant up to about 15 K and then decreases with increasing temperature. The slight increase in g (2) (0) mentioned above does not explain the observed steep entanglement degradation shown in Figures 1(d−f) since the g (2) (0) values are still in the range typically observed at T = 5 K. 30,32,33 To gain further insights into the origin of the entanglement degradation, we study the decay dynamics of the XX and X For purely heavy-hole excitons we would expect two bright and two dark states, similar to the ground-state exciton. In ref 36 a triplet was instead observed, which we ascribe to the high light-hole contribution of almost 40% (with ∼25% of bright admixture) to "p-shell" holes.…”

“…At low temperatures the concurrence [fidelity] is equal to 0.94(1) [0.969(4)], comparable to former investigations. 21,30,31 The degree of entanglement stays approximately constant up to about 15 K and then decreases with increasing temperature. The slight increase in g (2) (0) mentioned above does not explain the observed steep entanglement degradation shown in Figures 1(d−f) since the g (2) (0) values are still in the range typically observed at T = 5 K. 30,32,33 To gain further insights into the origin of the entanglement degradation, we study the decay dynamics of the XX and X to "p-shell" holes.…”

Continuous entanglement distribution over a transnational 248 km fiber link

“…Here, with amounts to the number of bits from the raw key used for parameter estimation, and s , which we set following ref. 47 , is the security parameter giving a failure probability of for the whole protocol. We numerically find the parameter values 0.0964, 0.0127, and 0.0116 to allow for the longest key, with 0.1711 and 258,231 bits.…”

Collective Excitation of Spatio-Spectrally Distinct Quantum Dots Enabled by Chirped Pulses

“…Entangled photon pairs that are encoded in polarization [1][2][3][4][5] or time-bins [6,7], are key to testing the foundations of quantum mechanics [8] and implementing secure quantum key distribution protocols [9]. To construct a scalable quantum photonic architecture for such purposes, it is desirable to have an ensemble of quantum emitters that can be collectively manipulated [10,11].…”