Ultralow-Noise Room-Temperature Quantum Memory for Polarization Qubits

Mehdi Namazi, Connor Kupchak, Bertus Jordaan, Reihaneh Shahrokhshahi, and Eden Figueroa

Phys. Rev. Applied 8, 034023 – Published 25 September 2017

Abstract

Here, we show an ultralow-noise regime of operation in a simple quantum memory in warm ${}^{87}{Rb}$ atomic vapor. By modeling the quantum dynamics of four-level room-temperature atoms, we achieve fidelities $> 90 %$ for single-photon-level polarization qubits, surpassing any classical strategies exploiting the nonunitary memory efficiency. Additionally, we show experimental techniques capable of producing fidelities close to unity. Our results demonstrate the potential of simple, resource-moderate experimental room-temperature quantum devices.

Received 27 July 2016

DOI:https://doi.org/10.1103/PhysRevApplied.8.034023

Physics Subject Headings (PhySH)

Electromagnetically induced transparency Quantum communication Quantum information with atoms & light Quantum memories Quantum optics

Atomic ensemble

Polarization

Quantum Information, Science & TechnologyAtomic, Molecular & Optical

Authors & Affiliations

Mehdi Namazi, Connor Kupchak, Bertus Jordaan, Reihaneh Shahrokhshahi, and Eden Figueroa

Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800, USA

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Vol. 8, Iss. 3 — September 2017

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Images

Figure 1
(a) Dual-rail quantum-memory setup. Probe, red beam paths; control, yellow beam paths; BD, polarization beam displacer; GLP, Glan-Laser polarizer; SPCM, single-photon counter module. The color-code bar depicts the strength of the collective atomic excitation. (b) Rubidium $D 1$ line four-level scheme describing the transitions used in the description of the efficiency and background response. $| 1 ⟩$ and $| 2 ⟩$ , ground states; $| 3 ⟩$ , excited state; $| 4 ⟩$ , off-resonant virtual state; and $Δ$ , one-photon laser detuning.
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Figure 2
(a) Measured transmission profile $T_{RT} (Δ)$ . (b) Cold atom storage bandwidths $η_{1} (Δ)$ and $η_{2} (Δ)$ for the two excited states of the rubidium $D 1$ line manifold (the blue line is a master equation prediction of the storage bandwidth) and room-temperature storage bandwidth $η_{RT} (Δ)$ (the solid red line is the result of the convolution with a velocity distribution). (c) Overall efficiency response $\propto [η_{RT} (Δ)] [T_{RT} (Δ)]$ (solid red line) and storage experiments over a 4-GHz scan region with a central frequency at the $F = 1$ to $F^{'} = 1$ $D 1$ line rubidium transition (blue dots). The error bars are statistical.
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Figure 3
(a) Cold atom background response $Q (Δ)$ (dashed red line) featuring the contributions of incoherent scattering and Stokes fields; etalon transmission profile (dashed blue line); convoluted response indicating the background transmission through the filtering elements (solid blue line); experimental background measurement for $Δ = - 500 MHz$ (green dots), 0 MHz (purple dots), and $+ 500 MHz$ (black dots); technical background (brown dotted line). (b) Cold atom background bandwidths $Q_{1} (Δ)$ and $Q_{2} (Δ)$ for the two excited states of the rubidium $D 1$ line manifold (the purple dotted line is a master equation prediction of the background bandwidth); warm atom background response $Q_{RT} (Δ)$ (the solid red line is the result of the convolution with a velocity distribution); background measurements vs $Δ$ (blue dots). (c) Predicted room-temperature signal-to-background ratio ${SBR}_{RT} \propto [η_{RT} (Δ)] [T_{RT} (Δ)] / [Q_{RT} (Δ)]$ (solid red line); SBR experimental measurements (blue dots). The error bars are statistical.
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Figure 4
(a) Single rail storage with SBR of about six where the histogram of photon counts shows the retrieved signal (dark blue bars) compared with background counts (light blue bars); the original pulse is shown by the dotted black line. Inset: SBR vs storage time (black dots) and experimental fit (redline). (b) Storage efficiencies for six different input polarizations using the dual rail system.
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Figure 5
(a) Noise reduction by introducing an auxiliary field (dashed red), the interaction between dark-state polaritons creates a background-free region. Retrieving the probe within this interval results in a $SBR > 25$ for the retrieved probe field. (b) Storage of light at the few-photon level with storage times $τ = 1 μ s$ ( $η = 11 %$ , blue), $τ = 14 μ s$ ( $η = 5.6 %$ , red), $τ = 28 μ s$ ( $η = 3.1 %$ , orange), and $τ = 42 μ s$ ( $η = 1.1 %$ , purple).
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