Proposal for a long-lived quantum memory using matter-wave optics with Bose-Einstein condensates in microgravity

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Proposal for a long-lived quantum memory using matter-wave optics with Bose-Einstein condensates in microgravity

Elisa Da Ros, Simon Kanthak, Erhan Sağlamyürek, Mustafa Gündoğan, and Markus Krutzik

Phys. Rev. Research 5, 033003 – Published 5 July 2023

Abstract

Bose-Einstein condensates are a promising platform for optical quantum memories but suffer from several decoherence mechanisms, leading to short memory lifetimes. While some of these decoherence effects can be mitigated by conventional methods, density-dependent atom-atom collisions ultimately set the upper limit of the quantum memory lifetime to timescales of seconds in trapped Bose-Einstein condensates. We propose a quantum memory technique that utilizes microgravity as a resource to minimize such density-dependent effects. We show that by using optical atom lenses to collimate and refocus the freely expanding atomic ensembles, in a semi-ideal environment, the expected memory lifetime is only limited by the quality of the background vacuum. We anticipate that this method can be experimentally demonstrated in Earth-bound microgravity platforms or space missions, eventually leading to storage times of minutes and unprecedented time-bandwidth products of $10^{10}$ .

Received 21 December 2022
Accepted 24 April 2023

DOI:https://doi.org/10.1103/PhysRevResearch.5.033003

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Cold atoms & matter waves Effects of atomic coherence on light propagation Quantum information processing Quantum memories

Atomic ensemble Bose gases Bose-Einstein condensates Trapped atoms

Coherent control Optical lattices & traps

Atomic, Molecular & OpticalQuantum Information, Science & Technology

Authors & Affiliations

Elisa Da Ros ^1,*, Simon Kanthak ^1,*, Erhan Sağlamyürek^2,3,†, Mustafa Gündoğan ^1,‡, and Markus Krutzik^1,4,§

¹Institut für Physik and IRIS Adlershof, Humboldt-Universität zu Berlin, Newtonstraße 15, 12489 Berlin, Germany
²Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada T2N 1N4
³Department of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2E1
⁴Ferdinand-Braun-Institut (FBH), Gustav-Kirchoff-Straße 4, 12489 Berlin, Germany

^*These authors contributed equally to this work.
^†Present address: Lawrence Berkeley National Laboratory and Department of Physics, University of California, Berkeley, California, 94720, USA.
^‡mustafa.guendogan@physik.hu-berlin.de
^§markus.krutzik@physik.hu-berlin.de

Article Text

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Issue

Vol. 5, Iss. 3 — July - September 2023

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Images

Figure 1
Protocol for a long-lived quantum memory utilizing interaction-driven expansion and delta kick collimation (DKC) of a Bose-Einstein condensate (BEC) in microgravity. (a) $Λ らむだ$ -type three-level structure together with the light fields employed during (b) different stages of the size evolution of the BEC. The quantum state of single-photon pulses is imprinted into an internal excitation of a BEC shortly after its release from an optical dipole trap (ODT). Brief exposure of the BEC to two consecutive optical lensing potentials allows us to stop and subsequently reverse the interaction-driven expansion via DKC. This protocol allows for transition between the complementary density regimes needed for an efficient write-in and readout of the memory at high optical depths (ODs) and large coherence times for long-time storage at low atomic densities, respectively.
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Figure 2
BEC dynamics and intrinsic memory efficiency. Time evolution of (a) the BEC size $σ しぐま$ and (b) the corresponding decay rates ${γ がんま}_{2-body}$ and its effect on (c) the intrinsic memory efficiency (i.e., not including write-in and readout efficiencies) due to only two-body collisions (dashed lines) and a combination of two- and one-body collisions (solid lines). We compare our protocol with storage times ${τ たう}_{mem} \approx 5 s$ (blue) and ${τ たう}_{mem} \approx 100 s$ (orange) together with the trapped case (yellow). The insets show a zoom of the respective changes during the focus of the BEC for the case ${τ たう}_{mem} \approx 5 s$ , in linear scaling. The black vertical lines indicate the timing of the DKC pulses for the case with ${τ たう}_{mem} \approx 5 s$ . See Appendix pp1 for simulation details.
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Figure 3
Intrinsic memory efficiency for different initial BEC sizes ${σ しぐま}_{0}$ and common initial peak density ${ρ ろー}_{0} (0) = 2.3 \times 10^{14} {cm}^{- 3}$ . The black lines indicate the timing of the DKC pulses to collimate and refocus the BEC. The inset shows the evolution of the two-body decay rate shortly after release and during refocusing, in linear scaling. See Appendix pp1 for simulation details.
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Figure 4
Calculated overall efficiency as a function of ${τ たう}_{mem}$ . For each data point, the readout is performed after refocusing, i.e., at high density. The inset shows a comparison between the overall retrieval efficiency ${η いーた}_{tot}$ , the efficiency factor ${η いーた}_{ATS}$ , and the intrinsic memory efficiency ${η いーた}_{1} \cdot {η いーた}_{2}$ as a function of time for $T_{C} = 3 s$ (i.e., ${τ たう}_{mem} \approx 5 s$ ) during the focus of the BEC.
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Figure 5
Comparison of (a) the atomic density distribution during the DKC pulses (presented in Fig. 2 in the main text); (b) the optical intensity distribution needed for a harmonic-shaped DKC potential of (c) trap frequencies leading to (d) differential AC-Stark shifts between the two hyperfine ground states for different characteristic sizes $h_{0}$ .
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