Superradiance-Mediated Photon Storage for Broadband Quantum Memory

Anindya Rastogi, Erhan Saglamyurek, Taras Hrushevskyi, and Lindsay J. LeBlanc

Phys. Rev. Lett. 129, 120502 – Published 13 September 2022

Abstract

Superradiance, characterized by the collective, coherent emission of light from an excited ensemble of emitters, generates photonic signals on timescales faster than the natural lifetime of an individual atom. The rapid exchange of coherence between atomic emitters and photonic fields in the superradiant regime enables a fast, broadband quantum memory. We demonstrate this superradiance memory mechanism in an ensemble of cold rubidium atoms and verify that this protocol is suitable for pulses on timescales shorter than the atoms’ natural lifetime. Our simulations show that the superradiance memory protocol yields the highest bandwidth storage among protocols in the same system. These high-bandwidth quantum memories provide unique opportunities for fast processing of optical and microwave photonic signals, with applications in large-scale quantum communication and quantum computing technologies.

Received 19 December 2021
Revised 30 July 2022
Accepted 30 August 2022

DOI:https://doi.org/10.1103/PhysRevLett.129.120502

Physics Subject Headings (PhySH)

Light-matter interaction Quantum memories Superradiance & subradiance

Atomic ensemble

Quantum Information, Science & TechnologyAtomic, Molecular & Optical

Authors & Affiliations

Anindya Rastogi ^1,*, Erhan Saglamyurek^1,2, Taras Hrushevskyi¹, and Lindsay J. LeBlanc ^1,†

¹Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
²Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada

^*Corresponding author. rastogi1@ualberta.ca
^†Corresponding author. lindsay.leblanc@ualberta.ca

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Issue

Vol. 129, Iss. 12 — 16 September 2022

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Images

Figure 1
SR memory protocol. (a) A short input probe (pink) with duration $T_{P} ≪ 1 / γ$ is absorbed by an ensemble with $d ≫ 1$ , and, absent the memory control, superradiantly reemits (green) with decay time $T_{SR} ≪ 1 / Γ$ . When a $π$ control (gray) with a duration $T_{C} ≪ T_{SR}$ is applied, it suppresses superradiant emission and induces photonic storage. (b) Reapplying the $π$ -pulse (gray) results in emission of the stored probe. (c) Time evolution of (normalized) photonic (pink), polarization (orange), and spin-wave (blue) coherences at the input face of the medium, showing probe storage. (d) Coherences upon readout, in backward recall. Simulation parameters [ $T_{P}, d, T_{C}, B, Ω_{C}, η$ ] are [ $0.037 / γ, 50, 0.0074 / γ, 13.3 Γ / 2 π, 207 Γ, 0.79$ ].
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Figure 2
Demonstration of SR memory in cold ${}^{87}{Rb}$ atoms. (a) Schematic of the setup. FC: fiber coupler, AOM: acousto-optic-modulator, EOM: electro-optic-modulator, SPD: single-photon-detector, TDC: time-to-digital converter, BD: beam dump. (b) Superradiant emission following an exponential probe. Inset: probe spectral profile (solid red) with bandwidth $B = 1.23 Γ / 2 π$ for linewidth $Γ = 2 π \times 6 MHz$ (shaded blue). (c) Decay of the emission intensity (normalized to its own maximum) for optical depth 9 (red circles), 5 (blue squares), and 3.5 (green diamonds), with solid lines fit to the data. Black dashed line shows spontaneous-emission decay (independent of $d$ ). Inset: superradiant decay time $T_{SR}$ and emission efficiency versus optical depth. Solid black line is fit of measured $T_{SR}$ values using Eq. (1), which matches the probe duration for optimal storage via the SR protocol. (d) Storage and forward retrieval of a $T_{P} = 10 ns$ , $B = 12.7 MHz$ probe containing ${\bar{n}}_{in} ≫ 1$ . Inset: SR emission without control. (e) Variation of memory efficiency with storage time [34]. (f) Storage and recall at the single-photon level with ${\bar{n}}_{in} = 0.18$ . Inset: memory-retrieved signal intensity relative to noise measured in four configurations (other colors) [34].
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Figure 3
Theoretical analysis of SR memory versus ATS and EIT memories for storage of broadband pulses with optimized parameters [ $d, T_{P}, B, Ω_{C} (t)$ ] in backward recall. ATS and EIT protocols are optimized using [56, 57]. (a) Numerically calculated memory efficiency vs optical depth for an exponential probe with $T_{P} = 0.01 / γ$ ( $B = 49.4 Γ / 2 π$ ), showing optimal operation at ( $d = 200$ , $η = 0.93$ ); ( $d = 1400$ , $η = 0.96$ ); and ( $d = 6000$ , $η = 0.93$ ) for the SR, ATS, and EIT protocols, respectively. Universal optimal efficiency $η_{opt}$ is obtained via optimal implementation of any protocol. (b) and (c) Optical depth and control power requirements versus memory bandwidth, where near-optimal operation is maintained ( $η \geq 0.9$ ). Control strength is normalized with respect to the ATS power required for $B = 10$ $Γ / 2 π$ .
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