High-dimensional quantum communication with scalable photonic entanglement in time and frequency

TL;DR

This paper presents a scalable, scan-free method to characterize high-dimensional time-frequency entanglement in photonic systems, achieving record entanglement measures and demonstrating practical quantum communication applications.

Contribution

The authors develop a novel, efficient technique for characterizing high-dimensional entanglement without full tomography, enabling practical quantum communication implementations.

Findings

Achieved 5.70 ebits of entanglement with 1021-dimensional states.

Certified 668-dimensional entanglement in the system.

Demonstrated a secure key rate of 15.6 kB/s in a practical protocol.

Abstract

High-dimensional photonic entanglement holds significant promise for advancing quantum communication, computation, and metrology. For example, large-alphabet quantum communication protocols are known to benefit from enhanced noise resilience and information capacity via multi-bit time-bin encoding. Yet, characterizing high-dimensional entangled states is challenging, as full state tomography becomes prohibitively costly and often requires unrealizable measurements. Here, we demonstrate a scan-free method to characterize high-dimensional entanglement in the time-frequency domain. Our reconstruction achieves a record $5.70\pm0.07$ ebits and a fidelity of $65.4\pm0.4\%$ with the maximally entangled state of local dimension $1021$, certifying the presence of $668$-dimensional entanglement. We further prove the attainability of a secure key rate of $15.6$ kB/s in a composable finite-size, entanglement-based protocol, and show that in continuous operation, the setup can quickly approach asymptotic key rates. Using commercial telecom components and state-of-the-art low-jitter single-photon detectors, our scalable architecture offers a practical path towards high-rate, noise-resilient quantum communication testbeds.