Quantum cryptography with highly entangled photons from semiconductor quantum dots

TLDR

Current quantum key distribution relies on laser-generated single photons and suffers from limited range and security loopholes, but polarization‑entangled photon pairs from semiconductor quantum dots offer ultra‑low multi‑pair emission and promise secure, long‑distance communication. The study implements the BBM92 protocol with a semiconductor quantum‑dot source achieving an entanglement fidelity of 0.97(1). The experiment produced a 135‑bit/s key over 350 m of fiber with a 1.9 % error rate, proving that quantum‑dot sources enable entanglement‑based QKD and, with photonic integration, could reach gigabit‑per‑second rates.

Abstract

State-of-the-art quantum key distribution systems are based on the BB84 protocol and single photons generated by lasers. These implementations suffer from range limitations and security loopholes, which require expensive adaptation. The use of polarization entangled photon pairs substantially alleviates the security threads while allowing for basically arbitrary transmission distances when embedded in quantum repeater schemes. Semiconductor quantum dots are capable of emitting highly entangled photon pairs with ultra-low multi-pair emission probability even at maximum brightness. Here we report on the first implementation of the BBM92 protocol using a quantum dot source with an entanglement fidelity as high as 0.97(1). For a proof of principle, the key generation is performed between two buildings, connected by 350 metre long fiber, resulting in an average key rate of 135 bits/s and a qubit error rate of 0.019 over a time span of 13 hours, without resorting to time- or frequency-filtering techniques. Our work demonstrates the viability of quantum dots as light sources for entanglement-based quantum key distribution and quantum networks. By embedding them in state-of-the-art photonic structures, key generation rates in the Gbit/s range are at reach.