image: The experimental layout of the sender Alice and the receiver Bob. Alice’s setup contains the excitation and collection setup of the single photon source, and a Sagnac-like polarization modulator for fast polarization modulation. Bob’s setup is a two-basis polarization projection based on the Superconducting Nanowire Single Photon Detector.
Credit: ©Science China Press
In a new study published in National Science Review, researchers from the National University of Singapore, Nanyang Technological University, and collaborators report a successful field test of polarization-based quantum key distribution (QKD) using a single-photon source that operates at room temperature and directly emits in the telecom O-band.
Single photons are a fundamental resource in quantum communication. However, most of the single-photon emitters, which “tend” to emit single photons rather than multiple photons at one time, require cryogenic cooling or frequency conversion to match telecom wavelengths. In this work, the team utilizes a GaN-defect based SPS emitting at 1309.5 nm, which is fully compatible with existing fiber networks, operating under ambient conditions without additional temperature control. The QKD protocol was implemented using BB84 encoding with polarization states. In a 3.5 km deployed fiber loop, the setup achieved a quantum bit error rate (QBER) of 5.0% and a secure key rate of 585.9 bps.
One major technical challenge addressed in this work was polarization mode dispersion (PMD), a common impairment in fiber-based quantum communication. By analyzing the PMD and carefully selecting the basis states, the authors minimized the impact of PMD on the QBER, achieving stable operation over extended durations. To show that a channel with lower PMD could permit much longer key distribution, the experiment was further extended to a 32.5 km fiber spool with 11.2 dB attenuation, yielding a lower QBER of 3.2% and a secure key rate of 50.4 bps.
Compared to previous room-temperature SPS-based QKD schemes, this work achieves competitive higher secure key rates, while extending the environment into real-world deployed fibers. The results suggest that GaN-based room-temperature telecom-band SPSs can play a practical role in future secure quantum networks.
Journal
National Science Review