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Physica Scripta

A theoretical approach for quantum memory based on modified superradiance lattice

Atif Shabbir, Sajid Qamar

Published Dec 2, 2022• 4 citations
Publisher

Abstract

Abstract We propose modified superradiance lattice (MSL) based scheme to realize quantum memory where intensity of the control field plays an important role in achieving high storage efficiency. We report that via proposed scheme one can store light with 96% storage efficiency having corresponding fidelity of 99% and group delay 1 μs. We notice that the group delay can be enhanced to 10 μs via manipulation of the control field, however, the storage efficiency is reduced to 87%. The benefit of considering MSL for the quantum memory is that one can obtain directional light. The main advantage of the proposed scheme is that it does not require large optical depth to obtain high storage efficiency, which makes it experimentally more viable.

DOI
10.1088/1402-4896/aca845

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Abstract We propose modified superradiance lattice (MSL) based scheme to realize quantum memory where intensity of the control field plays an important role in achieving high storage efficiency. We report that via proposed scheme one can store light with 96% storage efficiency having corresponding fidelity of 99% and group delay 1 μs. We notice that the group delay can be enhanced to 10 μs via manipulation of the control field, however, the storage efficiency is reduced to 87%. The benefit of considering MSL for the quantum memory is that one can obtain directional light. The main advantage of the proposed scheme is that it does not require large optical depth to obtain high storage efficiency, which makes it experimentally more viable.
Abstract We propose an efficient light-storage scheme based on a modified superradiance lattice that achieves high storage efficiency with a significantly reduced dependence on optical depth (OD). Our results demonstrate storage efficiencies in the ranges of 25 % − 79 % , 66 % − 84 % , and 80 % − 86 % for ODs of 20, 156, and 500, respectively, under identical parameters with a fixed group delay of 10 μ s . Notably, the largest efficiency change is observed for the small OD of 20, highlighting the scheme’s robustness against variations in OD. Fidelity approaches near unity at optimized parameters, particularly at higher storage efficiency, i.e. greater than 80%. These results demonstrate that high-performance quantum memory can be realized without requiring excessively large ODs. Additionally, the difference in storage efficiency across ODs decreases with increasing group delay, making the scheme more independent of OD. The scheme also enables highly directional emission, improving experimental feasibility, and can be implemented using rubidium ( 87 Rb) atoms. Overall, this approach provides robust and scalable light storage, offering a promising platform for practical quantum memory and photonic information-processing applications.
The effects of high optical depth phenomena, such as superradiance, are investigated in potential quantum memory materials. The results may have relevance for several schemes, including controlled reversible inhomogeneous broadening, atomic frequency combs, and quantum memories based on electromagnetically induced transparency, which are based on using ensembles as storage media. It is shown that strong superradiant effects manifested as decay rates larger than $1/{T}_{2}^{\ensuremath{\ast}}$ are present even for moderate values of $\ensuremath{\alpha}L\ensuremath{\le}5$ and increases as a function of $\ensuremath{\alpha}L$. For even higher $\ensuremath{\alpha}L$, effects such as off-resonant slow light is demonstrated and discussed and, finally, the efficiency of time-reversed optimized input pulses is tested. A maximum retrieval efficiency of $\ensuremath{\sim}20%$ is reached and agreement with the theoretically expected result is discussed.
Quantum memory is an important component in the long-distance quantum communication system based on the quantum repeater protocol. To outperform the direct transmission of photons with quantum repeaters, it is crucial to develop quantum memories with high fidelity, high efficiency and a long storage time. Here, we achieve a storage efficiency of 96\% for a photonic memory based on the electromagnetically induced transparency (EIT) scheme in cold atomic media with an optical depth of near 1000. At a storage efficiency of 50\%, we also obtain a fractional delay of 1200. Both are the best record to date in all kinds of the schemes for the realization of quantum memory. Our work significantly advances the pursuit of a high-performance photonic memory and should have important applications in quantum information science.
We develop a three-dimensional theory for quantum memories based on light storage in ensembles of $\ensuremath{\Lambda}$-type atoms, where two long-lived atomic ground states are employed. We consider light storage in an ensemble of finite spatial extent and we show that within the paraxial approximation the Fresnel number of the atomic ensemble and the optical depth are the only important physical parameters determining the quality of the quantum memory. We analyze the influence of these parameters on the storage of light followed by either forward or backward read-out from the quantum memory. We show that for small Fresnel numbers the forward memory provides higher efficiencies, whereas for large Fresnel numbers the backward memory is advantageous. The optimal light modes to store in the memory are presented together with the corresponding spin waves and outcoming light modes. We show that for high optical depths such $\ensuremath{\Lambda}$-type atomic ensembles allow for highly efficient backward and forward memories even for small Fresnel numbers $F\ensuremath{\gtrsim}0.1$.
Controlled manipulation, storage, and retrieval of quantum information is essential for quantum communication and computing. Quantum memories for light, realized with cold atomic samples as the storage medium, are prominent for their high storage efficiencies and lifetime. We demonstrate the controlled transport of stored light over 1.2 mm in such a storage system and show that the transport process and its dynamics only have a minor effect on the coherence of the storage. Extending the presented concept to longer transport distances and augmenting the number of storage sections will allow for the development of novel quantum devices such as optical racetrack memories or optical quantum registers.
Quantum memory is an important component in the long-distance quantum communication based on the quantum repeater protocol. To outperform the direct transmission of photons with quantum repeaters, it is crucial to develop quantum memories with high fidelity, high efficiency and a long storage time. Here, we achieve a storage efficiency of 92.0 (1.5)% for a coherent optical memory based on the electromagnetically induced transparency scheme in optically dense cold atomic media. We also obtain a useful time-bandwidth product of 1200, considering only storage where the retrieval efficiency remains above 50%. Both are the best record to date in all kinds of schemes for the realization of optical memory. Our work significantly advances the pursuit of a high-performance optical memory and should have important applications in quantum information science.