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arXiv:2008.12901 · Physical Review Applied

Coherent Optical Memory Based on a Laser-Written On-Chip Waveguide

Tian-Xiang Zhu, Chao Liu, Liang Zheng, Zong‐Quan Zhou, Chuan-Feng Li, Guang-Can Guo

Published Nov 30, 2020• 24 citations
arXivHTMLPDF

Abstract

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., $\mathrm{E}{\mathrm{u}}^{3+}$:${\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$). The properties of the optical transition (${}^{7}{\mathrm{F}}_{0}\ensuremath{\rightarrow}{}^{5}{\mathrm{D}}_{0}$) of the ${\mathrm{Eu}}^{3+}$ 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.

DOI
10.1103/physrevapplied.14.054071

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•Apr 20, 2022•2 citations
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 (7F0\ensuremath→5D0{}^{7}{\mathrm{F}}_{0}\ensuremath{\rightarrow}{}^{5}{\mathrm{D}}_{0}7F0​\ensuremath→5D0​) 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.
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.
Quantum memories are a key building block for optical quantum computers and quantum networks. Rare-earth ion-doped crystals are a promising material to achieve quantum memory using an atomic frequency comb protocol. However, current atomic frequency comb memories typically use bulk materials or waveguides with large cross sections or rely on fabrication techniques not easily adaptable to wafer scale processing. Here, we demonstrate a compact chip-integrated atomic frequency comb in rare-earth-doped thin-film lithium niobate. Our optical memory exhibits a broad storage bandwidth exceeding 100 MHz and optical storage time as long as 250 ns. The enhanced optical confinement in this device leads to three orders of magnitude reduction in optical power required for a coherent control as compared to ion-diffused waveguides. These compact atomic frequency comb memories pave the way toward scalable, highly efficient, electro-optically tunable quantum photonic systems that can store and manipulate light on a compact chip.
Quantum memory is an essential building block for applications in quantum information science, where scalability and integrability are needed for progress toward large-scale architectures. The authors present a platform for integrated photonic memory, based on laser-written waveguides in rare-earth-doped crystals. The coherence properties of the optically active ions persist after micromachining, enabling proof-of-principle light storage using the full atomic-frequency-comb protocol. This is a pioneering demonstration of on-demand optical memory on a chip.
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.
Photonic quantum memory is the core element in quantum information processing (QIP). For the scalable and convenient practical applications, great efforts have been devoted to the integrated quantum memory based on various waveguides fabricated in solids. However, on-demand storage of qubits, which is an essential requirement for QIP, is still challenging to be implemented using such integrated quantum memory. Here we report the on-demand storage of time-bin qubits in an on-chip waveguide memory fabricated on the surface of a ^{151}Eu^{3+}:Y_{2}SiO_{5} crystal, utilizing the Stark-modulated atomic frequency comb protocol. A qubit storage fidelity of 99.3%±0.2% is obtained with single-photon-level coherent pulses, far beyond the highest fidelity achievable using the classical measure-and-prepare strategy. The developed integrated quantum memory with the on-demand retrieval capability represents an important step toward practical applications of integrated quantum nodes in quantum networks.
Abstract Atomic frequency combs memories that coherently store optical signals are a key building block for optical quantum computers1 and quantum networks2. Current atomic frequency combs typically use bulk materials or waveguides with large cross-sections3–5, or rely on fabrication techniques not easily adaptable to wafer scale processing6. Integrating such memories into compact and chip-scale devices is essential for scalable quantum technology. We demonstrate a compact chip-integrated atomic frequency comb in rare earth doped thin-film lithium niobate. Our optical memory exhibits a broad storage bandwidth exceeding 100 MHz, and optical storage time of over 250 ns. The enhanced optical confinement in this device leads to three orders of magnitude reduction in optical power required for coherent control as compared to ion-diffused waveguides 7. These compact atomic frequency comb memories pave the way towards scalable, highly efficient, electro-optically tunable quantum photonic systems that can store and manipulate light on a compact chip3.