Highly Efficient and Broadband Optical Delay Line towards a Quantum Memory

• URL: http://arxiv.org/abs/2509.02096v1
• Date: Tue, 02 Sep 2025 08:50:53 GMT
• Title: Highly Efficient and Broadband Optical Delay Line towards a Quantum Memory
• Abstract summary: We demonstrate a high-efficiency, free space optical delay line utilizing a nested multipass cell architecture.<n>The cell is characterized using polarization-entangled photon pairs, with signal photons routed through the delay line and idler photons used as timing reference.<n>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.
• Score: 40.95138262420604
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: 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 $\sim12.6$~ns increments. The longest delay and wide spectral bandwidth result in a time-bandwidth product of $3.87\times 10^7$. These results position this delay line as a strong candidate for all-optical quantum memories and synchronization modules for scalable quantum networks.

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