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Photonics North (PN)

Optical Quantum Memory In Atomic Barium With 880 GHz Bandwidth and 95% Storage Efficiency

Kai Shinbrough, B. D. Hunt, Sehyun Park, Kathleen Oolman, Tegan Loveridge, J. Gary Eden, Virginia O. Lorenz

Published Jun 12, 2023• 0 citations
Publisher

Abstract

We demonstrate quantum memory of single-photon-level coherent pulses of 880 GHz bandwidth with 95.6(3)% storage efficiency in collisionally broadened barium vapor. We measure 26(1)% total efficiency, limited by control field power; 0.49(1) ns memory lifetime, limited by motional dephasing; and a signal-to-noise ratio of ${O}(10^{3})$, limited by two-photon control field scattering. To the best of the authors’ knowledge, this represents the best efficiency, lifetime, and noise performance of atomic quantum memories in the ultrabroadband regime $(\gt100$ GHz bandwidth) to date.

DOI
10.1109/pn58661.2023.10222989

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We demonstrate quantum memory of single-photon-level coherent pulses of 880 GHz bandwidth with 95.6(3)% storage efficiency in collisionally broadened barium vapor. We measure 26(1)% total efficiency, limited by control field power; 0.49(1) ns memory lifetime, limited by motional dephasing; and a signal-to-noise ratio of O(103){O}(10^{3})O(103), limited by two-photon control field scattering. To the best of the authors’ knowledge, this represents the best efficiency, lifetime, and noise performance of atomic quantum memories in the ultrabroadband regime (>100(\gt100(>100 GHz bandwidth) to date.
Optical quantum memory describes the process of on-demand storage and retrieval of single photon-level quantum states, and is a critical enabling technology for many quantum applications. Memory bandwidth plays an important role in these applications, as it determines the pulse durations compatible with the memory and places an upper bound on the clock rate and processing speed of a quantum device. Here we present experimental results of an atomic barium quantum memory that enables storage and retrieval of ultra-broadband(>800(> 800(>800GHz) signal photons with high storage efficiency [95.6(3)%] and low noise [3.8(6)×10−5\times 10^{-5}×10−5noise photons]. Experimental Results.- The quantum memory operation is based on the ground(6s2 1S0)(6s^{2}\ {}^{1}S_{0})(6s2 1S0​), excited(6s6p 1P1)(6s6p \ {}^{1}P_{1})(6s6p 1P1​), and metastable(6s5d 1D2)(6s5d \ {}^{1}D_{2})(6s5d 1D2​)orbital states of atomic barium in aΛ\LambdaΛ-type configuration. The barium vapor is created in an 800–900 °C barium heat pipe oven with 0–1000 torr tunable argon buffer gas pressure. The ground-excited transition at 553.5 nm features large and tunable homogeneous collisional broadening due to the argon buffer gas and a peak optical depth ofd=50d=50d=50. The memory operates in the so-called absorb-then-transfer (ATT) regime, in which the signal field is linearly absorbed along the ground-excited transition, whose collisionally broadened lineshape enables efficient absorption of ultra-broadband photons; the resulting atomic polarization is transferred into a so-called spin wave by application of a strong[O(10 uJ),100 fs][O(10 \ \text{uJ}),100\ \text{fs}][O(10 uJ),100 fs]control pulse along the excited-metastable transition at 1500 nm. The storage state has a 0(0.1) second coherence lifetime in the bare atom [1], but this is reduced to theO(ns)O(\text{ns})O(ns)level due to motional dephasing [0.49(1) ns measured memory lifetime]. The memory experiment is repeated at a repetition rate of 1 kHz. The total end-to-end efficiency of the memory at 900°C is 31(1)%, which is limited by available control field power.
We present a demonstration of simultaneous high-efficiency, high-speed, and low-noise operation of a photonic quantum memory. By leveraging controllable collisional dephasing in a neutral barium atomic vapor, we demonstrate a significant improvement in memory efficiency and bandwidth over existing techniques. We achieve greater than 95% storage efficiency and 26% total efficiency of 880 GHz bandwidth photons, with O(10−5)\mathcal{O}(10^{-5})O(10−5) noise photons per retrieved pulse. These ultrabroad bandwidths enable rapid quantum information processing and contribute to the development of practical quantum memories with potential applications in quantum communication, computation, and networking.
Quantum memories matched to single photon sources will form an important cornerstone of future quantum network technology. We demonstrate such a memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency. With an acceptance bandwidth of δf=0.66 GHz, the memory is suitable for single photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity, and atomic collisions have negligible influence on the optical coherences. Operation of the memory is demonstrated using attenuated laser pulses on the single photon level. For a 50 ns storage time, we measure η_{e2e}^{50 ns}=3.4(3)% end-to-end efficiency of the fiber-coupled memory, with a total intrinsic efficiency η_{int}=17(3)%. Straightforward technological improvements can boost the end-to-end-efficiency to η_{e2e}≈35%; beyond that, increasing the optical depth and exploiting the Zeeman substructure of the atoms will allow such a memory to approach near unity efficiency. In the present memory, the unconditional read-out noise level of 9×10^{-3} photons is dominated by atomic fluorescence, and for input pulses containing on average μ_{1}=0.27(4) photons, the signal to noise level would be unity.
The efficient storage and on-demand retrieval of quantum optical states that are compatible with the telecommunications C-band is a requirement for future terrestrial-based quantum optical networking. Spectrum in the C-band minimises optical fiber-propagation losses, and broad optical bandwidth facilitates high-speed networking protocols. Here we report on a telecommunication wavelength and bandwidth compatible quantum memory. Using the Off-Resonant Cascaded Absorption protocol in hot 87^{87}87Rb vapour, we demonstrate a total memory efficiency of 20.90(1) %20.90(1)\,\%20.90(1)% with a Doppler-limited storage time of 1.10(2) 1.10(2)\,1.10(2)ns. We characterise the memory performance with weak coherent states, demonstrating signal-to-noise ratios greater than unity for mean photon number inputs above 4.5(6)×10−64.5(6)\times10^{-6}4.5(6)×10−6 per pulse.