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arXiv:2205.12762 · Physical Review A

On-demand multimode optical storage in a laser-written on-chip waveguide

Ming-Xu Su, Tian-Xiang Zhu, Chao Liu, Zong‐Quan Zhou, Chuan‐Feng Li, Guang‐Can Guo

Published May 23, 2022• 11 citations
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Abstract

Quantum memory is a fundamental building block for large-scale quantum networks. On-demand optical storage with a large bandwidth, a high multimode capacity, and an integrated structure simultaneously is crucial for practical application. However, this has not been demonstrated yet. Here, we fabricate an on-chip waveguide in a $^{151}\mathrm{Eu}^{3+}:{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ crystal with insertion losses of 0.2 dB, and propose a pumping scheme to enable spin-wave atomic frequency comb (AFC) storage with a bandwidth of 11 MHz inside the waveguide. Based on this, we demonstrate the storage of 200 temporal modes using the AFC scheme and conditional on-demand storage of 100 temporal modes using the spin-wave AFC scheme. The interference visibility between the readout light field and the reference light field is $99.0%\ifmmode\pm\else\textpm\fi{}0.6%$ and $97%\ifmmode\pm\else\textpm\fi{}3%$ for AFC and spin-wave AFC storage, respectively, indicating the coherent nature of this low-loss, multimode, and integrated storage device.

DOI
10.1103/physreva.105.052432

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Quantum memory is a fundamental building block for large-scale quantum networks. On-demand optical storage with a large bandwidth, a high multimode capacity, and an integrated structure simultaneously is crucial for practical application. However, this has not been demonstrated yet. Here, we fabricate an on-chip waveguide in a 151Eu3+:Y2SiO5^{151}\mathrm{Eu}^{3+}:{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}151Eu3+:Y2​SiO5​ crystal with insertion losses of 0.2 dB, and propose a pumping scheme to enable spin-wave atomic frequency comb (AFC) storage with a bandwidth of 11 MHz inside the waveguide. Based on this, we demonstrate the storage of 200 temporal modes using the AFC scheme and conditional on-demand storage of 100 temporal modes using the spin-wave AFC scheme. The interference visibility between the readout light field and the reference light field is 99.099.0%\ifmmode\pm\else\textpm\fi{}0.6%99.0 and 9797%\ifmmode\pm\else\textpm\fi{}3%97 for AFC and spin-wave AFC storage, respectively, indicating the coherent nature of this low-loss, multimode, and integrated storage device.
151 E u 3 + -doped yttrium silicate ( 151 E u 3 + : Y 2 S i O 5 ) crystal is a unique material that possesses hyperfine states with coherence time up to 6 h. Many efforts have been devoted to the development of this material as optical quantum memories based on bulk crystals, but integrable structures (such as optical waveguides) that can promote 151 E u 3 + : Y 2 S i O 5 -based quantum memories to practical applications have not been demonstrated so far. Here we report the fabrication of type II waveguides in a 151 E u 3 + : Y 2 S i O 5 crystal using femtosecond-laser micromachining. The resulting waveguides are compatible with single-mode fibers and have the smallest insertion loss of 4.95 dB. On-demand light storage is demonstrated in a waveguide by employing the spin-wave atomic frequency comb (AFC) scheme and the revival of silenced echo (ROSE) scheme. We implement a series of interference experiments based on these two schemes to characterize the storage fidelity. Interference visibility of the readout pulse is 0.99 ± 0.03 for the spin-wave AFC scheme and 0.97 ± 0.02 for the ROSE scheme, demonstrating the reliability of the integrated optical memory.
Quantum memory is the core device for the construction of large-scale quantum networks. For scalable and convenient practical applications, integrated optical memories, especially on-chip optical memories, are crucial requirements because they can be easily integrated with other on-chip devices. Here, we report the coherent optical memory based on a type-IV waveguide fabricated on the surface of a rare-earth ion-doped crystal (i.e., Eu3+\mathrm{E}{\mathrm{u}}^{3+}Eu3+:Y2SiO5{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}Y2​SiO5​). The properties of the optical transition (${}^{7}{\mathrm{F}}_{0}\ensuremath{\rightarrow}{}^{5}{\mathrm{D}}_{0}$) of the Eu3+{\mathrm{Eu}}^{3+}Eu3+ ions inside the surface waveguide are well preserved compared to those of the bulk crystal. Spin-wave atomic frequency comb storage is demonstrated inside the type-IV waveguide. The reliability of this device is confirmed by the high interference visibility of $97\ifmmode\pm\else\textpm\fi{}1\mathrm{%}$ between the retrieval pulse and the reference pulse. The developed on-chip optical memory paves the way towards integrated quantum nodes.
We report on the coherent and multi-temporal mode storage of light using the full atomic frequency comb memory scheme. The scheme involves the transfer of optical atomic excitations in Pr 3+ :Y 2 SiO 5 to spin waves in hyperfine levels using strong single-frequency transfer pulses. Using this scheme, a total of five temporal modes are stored and recalled on-demand from the memory. The coherence of the storage and retrieval is characterized using a time-bin interference measurement resulting in visibilities higher than 80%, independent of the storage time. This coherent and multimode spin-wave memory is promising as a quantum memory for light.
ABSTRACT Photonic integrated quantum memories are essential for the construction of scalable quantum networks. Spin-wave quantum storage, which can support on-demand retrieval with a long lifetime, is indispensable for practical applications, but has never been demonstrated in an integrated solid-state device. Here, we demonstrate spin-wave quantum storage based on a laser-written waveguide fabricated in a 151Eu3+:Y2SiO5 crystal, using both the atomic frequency comb and noiseless photon-echo protocols. Qubits encoded with single-photon-level inputs are stored and retrieved with a fidelity of 94.9%±1.2%{94.9\%\pm 1.2\%}94.9%±1.2%, which is far beyond the maximal fidelity that can be obtained with any classical device. Our results underline the potential of laser-written integrated devices for practical applications in large-scale quantum networks, such as the construction of multiplexed quantum repeaters in an integrated configuration and high-density transportable quantum memories.
Abstract Optical quantum memories are essential components for realizing the full potential of quantum networks. Among these, rare-earth-doped crystal memories stand out due to their large multimode storage capabilities. To maximize the multimode capacity in the time domain, it is key to simultaneously achieve large memory bandwidth and long optical storage time. Here, we demonstrate an atomic frequency comb optical memory in 171 Yb 3+ :Y 2 SiO 5 , with a memory bandwidth of 250 MHz and a storage time of up to 125 µ s. The efficiency reaches 20% at short storage times, and 5% at 125 µ s. These results were enabled by an optimized optical pumping scheme, guided by numerical modelling. Our approach is specifically designed for future spin-wave storage experiments, with the theoretical bandwidth limit set at 288 MHz by the hyperfine structure of 171 Yb 3+ :Y 2 SiO 5 . Additionally, we introduce an efficient method for synthesizing the optical pumping waveforms required for generating combs with tens of thousands of teeth, as well as a simple yet frequency-agile laser setup for optical pumping across a 10 GHz bandwidth.
Optical quantum memories are essential components for realizing the full potential of quantum networks. Among these, rare-earth-doped crystal memories stand out due to their large multimode storage capabilities. To maximize the multimode capacity in the time domain, it is key to simultaneously achieve large memory bandwidth and long optical storage time. Here, we demonstrate an atomic frequency comb optical memory in 171Yb3+:Y2SiO5 , with a memory bandwidth of 250 MHz and a storage time of up to 125 µs. The efficiency reaches 20% at short storage times, and 5% at 125 µs. These results were enabled by an optimized optical pumping scheme, guided by numerical modelling. Our approach is specifically designed for future spin-wave storage experiments, with the theoretical bandwidth limit set at 288 MHz by the hyperfine structure of 171Yb3+:Y2SiO5 . Additionally, we introduce an efficient method for synthesizing the optical pumping waveforms required for generating combs with tens of thousands of teeth, as well as a simple yet frequency-agile laser setup for optical pumping across a 10 GHz bandwidth.