2025/09/02 by Guo, Yu, Banerji, Anindya, Chin, Jia Boon +2 · 2 citations
#FOS: Physical sciences #Optics (physics.optics) #Quantum Physics (quant-ph)
paper · doi:10.48550/arxiv.2509.02096
We demonstrate a high-efficiency, free space optical delay line utilizing a nested multipass cell architecture. This design supports extended optical paths with low loss, aided by custom broadband dielectric coating that provides high reflectivity across a wide spectral bandwidth. The cell is characterized using polarization-entangled photon pairs, with signal photons routed through the delay line and idler photons used as timing reference. Quantum state tomography performed on the entangled pair reveals entanglement preservation with a fidelity of 99.6(9)% following a single-transit delay of up to 687~ns, accompanied by a photon retrieval efficiency of 95.390(5)%. The delay is controllable and can be set between 1.8~ns to 687~ns in ∼12.6~ns increments. The longest delay and wide spectral bandwidth result in a time-bandwidth product of 3.87× 107. These results position this delay line as a strong candidate for all-optical quantum memories and synchronization modules for scalable quantum networks.