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Acta Physica Sinica

Multimode solid-state quantum memory

Tian-Shu Yang, Zong‐Quan Zhou, Chuan‐Feng Li, Guang‐Can Guo

Published Jan 1, 2019• 2 citations
Publisher

Abstract

The faithful storage and coherent manipulation of single photon state in a matter-system are crucial for linear-optical quantum computation, long-distance quantum communication, and quantum networking.To reach useful data rate in a large-scale quantum network, highly multimode quantum memories are required to build a multiplexed quantum repeater.Rare-earth-ion doped crystal (REIC) is very promising material as a candidate for multimode quantum storage due to the wide inhomogeneous broadening and long optical coherence time.In this article, we review the recent advances in multimode quantum memories based on REICs.First, we briefly introduce the properties of REIC and the atomic frequency comb protocol based on REIC.Next, we review the achievements of multimode quantum memories based on REIC in recent years, including frequency, temporal and spatial multimode storage.Afterwards, we review our experimental work on multiplexed storage based on a multiple degree-of-freedom quantum memory.Finally, we introduce the quantum mode converter and real-time arbitrary manipulations based on the multiple degree-of-freedom quantum memory. The combination of storage and real-time manipulation in a device should enable the construction of a versatility quantum repeater.This review highlights that multimode quantum memories based on REIC can be found to possess some practical applications in developing the optical quantum information processing in the near future.

DOI
10.7498/aps.68.20182207

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The faithful storage and coherent manipulation of single photon state in a matter-system are crucial for linear-optical quantum computation, long-distance quantum communication, and quantum networking.To reach useful data rate in a large-scale quantum network, highly multimode quantum memories are required to build a multiplexed quantum repeater.Rare-earth-ion doped crystal (REIC) is very promising material as a candidate for multimode quantum storage due to the wide inhomogeneous broadening and long optical coherence time.In this article, we review the recent advances in multimode quantum memories based on REICs.First, we briefly introduce the properties of REIC and the atomic frequency comb protocol based on REIC.Next, we review the achievements of multimode quantum memories based on REIC in recent years, including frequency, temporal and spatial multimode storage.Afterwards, we review our experimental work on multiplexed storage based on a multiple degree-of-freedom quantum memory.Finally, we introduce the quantum mode converter and real-time arbitrary manipulations based on the multiple degree-of-freedom quantum memory. The combination of storage and real-time manipulation in a device should enable the construction of a versatility quantum repeater.This review highlights that multimode quantum memories based on REIC can be found to possess some practical applications in developing the optical quantum information processing in the near future.
The faithful storage and coherent manipulation of quantum states with matter-systems would enable the realization of large-scale quantum networks based on quantum repeaters. To achieve useful communication rates, highly multimode quantum memories are required to construct a multiplexed quantum repeater. Here, we present a demonstration of on-demand storage of orbital-angular-momentum states with weak coherent pulses at the single-photon-level in a rare-earth-ion-doped crystal. Through the combination of this spatial degree-of-freedom (DOF) with temporal and spectral degrees of freedom, we create a multiple-DOF memory with high multimode capacity. This device can serve as a quantum mode converter with high fidelity, which is a fundamental requirement for the construction of a multiplexed quantum repeater. This device further enables essentially arbitrary spectral and temporal manipulations of spatial-qutrit-encoded photonic pulses in real time. Therefore, the developed quantum memory can serve as a building block for scalable photonic quantum information processing architectures.
Abstract Ensemble-based quantum memories are key to developing multiplexed quantum repeaters, able to overcome the intrinsic rate limitation imposed by finite communication times over long distances. Rare-earth ion doped crystals are main candidates for highly multimode quantum memories, where time, frequency and spatial multiplexing can be exploited to store multiple modes. In this context the atomic frequency comb (AFC) quantum memory provides large temporal multimode capacity, which can readily be combined with multiplexing in frequency and space. In this article, we derive theoretical formulas for quantifying the temporal multimode capacity of AFC-based memories, for both optical memories with fixed storage time and spin-wave memories with longer storage times and on-demand read out. The temporal multimode capacity is expressed in key memory parameters, such as AFC bandwidth, fixed-delay storage time, memory efficiency, and control field Rabi frequency. Current experiments in europium- and praseodymium-doped Y2SiO5 are analyzed within this theoretical framework, which is also tested with newly acquired data, as prospects for higher temporal capacity in these materials are considered. In addition we consider the possibility of spectral and spatial multiplexing to further increase the mode capacity, with examples given for praseodymium doped Y2SiO5.
Abstract Quantum memory is a core enabling device for large-scale quantum networks, serving as the fundamental building block for quantum repeaters and transportable quantum memories. Among various physical platforms, rare-earth-ion-doped crystals stand out as one of the most promising solid-state candidates for long-lived photonic quantum memories, owing to their exceptionally long spin coherence time and their compatibility with integration. In this review, we first introduce the physical mechanisms underlying long-lived spin coherence in rare-earth systems, with particular emphasis on the zero-first-order-Zeeman transition and dynamical decoupling techniques. We then review the experimental progress in this field, highlighting three distinct lifetimes—the spin coherence time, the light storage time, and the quantum storage time—and covering experiments that have achieved hour-scale spin coherence, minute- to hour-scale light storage, and minute-scale single-photon-level quantum storage. Finally, we discuss the remaining challenges that hinder the realization of practical long-lived quantum memories, explore potential strategies to overcome these obstacles, and outline the prospects for their future applications in quantum networks.
An efficient multimode quantum memory is a crucial resource for long-distance quantum communication based on quantum repeaters. We propose a quantum memory based on spectral shaping of an inhomogeneously broadened optical transition into an atomic frequency comb (AFC). The spectral width of the AFC allows efficient storage of multiple temporal modes without the need to increase the absorption depth of the storage material, in contrast to previously known quantum memories. Efficient readout is possible thanks to rephasing of the atomic dipoles due to the AFC structure. Long-time storage and on-demand readout is achieved by use of spin states in a lambda-type configuration. We show that an AFC quantum memory realized in solids doped with rare-earth-metal ions could store hundreds of modes or more with close to unit efficiency, for material parameters achievable today.
The process of storing information carried by single photons demands strong light-matter interaction. While interfacing single photon sources with quantum memories is still challenging, a possible short-cut by combining source and memory in the same ensemble was proposed by Duan, Lukin, Cirac, and Zoller (DLCZ) [1]. It is already a quite common protocol in cold atomic ensemble QMs, however it is very demanding to realize in solid state systems. Here we demonstrate for the first time a DLCZ-type memory with a rare-earth ion-doped crystal (REIC) with photon counting, directly applicable to the well-known quantum repeater schemes which works with QMs. We find second order cross correlation values up to 21±4 and violate Cauchy-Schwarz equality by R = 44 ± 20. Although the original DLCZ protocol does not support temporal multi-modality, we store 11 temporal modes thanks to a modified scheme in which we combine the DLCZ and the Atomic Frequency Comb protocols. Generating and storing non-classical multiplexed photon pairs with a single scheme in a REIC paves the way of making scalable, solid-state quantum repeater architectures.
The process of storing information carried by single photons demands strong light-matter interaction. While interfacing single photon sources with quantum memories is still challenging, a possible short-cut by combining source and memory in the same ensemble was proposed by Duan, Lukin, Cirac, and Zoller (DLCZ) [1]. It is already a quite common protocol in cold atomic ensemble QMs, however it is very demanding to realize in solid state systems. Here we demonstrate for the first time a DLCZ-type memory with a rare-earth ion-doped crystal (REIC) with photon counting, directly applicable to the well-known quantum repeater schemes which works with QMs. We find second order cross correlation values up to 21±4 and violate Cauchy-Schwarz equality by R = 44 ± 20. Although the original DLCZ protocol does not support temporal multi-modality, we store 11 temporal modes thanks to a modified scheme in which we combine the DLCZ and the Atomic Frequency Comb protocols. Generating and storing non-classical multiplexed photon pairs with a single scheme in a REIC paves the way of making scalable, solid-state quantum repeater architectures.