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arXiv:1803.07122 · Science Advances

A hybrid quantum memory–enabled network at room temperature

Xiao-Ling Pang, Ai-Lin Yang, Jian-Peng Dou, Hang Li, Chao-Ni Zhang, Eilon Poem, D. J. Saunders, Hao Long Tang, Joshua Nunn, Ian A. Walmsley, Xian-Min Jin

Published Feb 7, 2020• 48 citations
arXivHTMLPDF

Abstract

Quantum memory capable of storage and retrieval of flying photons on demand is crucial for developing quantum information technologies. However, the devices needed for long-distance links are different from those envisioned for local processing. We present the first hybrid quantum memory-enabled network by demonstrating the interconnection and simultaneous operation of two types of quantum memory: an atomic ensemble-based memory and an all-optical Loop memory. Interfacing the quantum memories at room temperature, we observe a well-preserved quantum correlation and a violation of Cauchy-Schwarz inequality. Furthermore, we demonstrate the creation and storage of a fully-operable heralded photon chain state that can achieve memory-built-in combining, swapping, splitting, tuning, and chopping single photons in a chain temporally. Such a quantum network allows atomic excitations to be generated, stored, and converted to broadband photons, which are then transferred to the next node, stored, and faithfully retrieved, all at high speed and in a programmable fashion.

DOI
10.1126/sciadv.aax1425

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Quantum memory capable of storage and retrieval of flying photons on demand is crucial for developing quantum information technologies. However, the devices needed for long-distance links are different from those envisioned for local processing. We present the first hybrid quantum memory-enabled network by demonstrating the interconnection and simultaneous operation of two types of quantum memory: an atomic ensemble-based memory and an all-optical Loop memory. Interfacing the quantum memories at room temperature, we observe a well-preserved quantum correlation and a violation of Cauchy-Schwarz inequality. Furthermore, we demonstrate the creation and storage of a fully-operable heralded photon chain state that can achieve memory-built-in combining, swapping, splitting, tuning, and chopping single photons in a chain temporally. Such a quantum network allows atomic excitations to be generated, stored, and converted to broadband photons, which are then transferred to the next node, stored, and faithfully retrieved, all at high speed and in a programmable fashion.
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Abstract Quantum memory capable of stopping flying photons and storing their quantum coherence is essential for scalable quantum technologies. A room-temperature broadband quantum memory will enable the implementation of large-scale quantum systems for real-life applications. Due to either intrinsic high noises or short lifetime, it is still challenging to find a room-temperature broadband quantum memory beyond conceptual demonstration. Here, we present a far off-resonance Duan–Lukin–Cirac–Zoller (FORD) protocol and demonstrate the broadband quantum memory in room-temperature atoms. We observe a low unconditional noise level of 10−4 and a cross-correlation up to 28. A strong violation of Cauchy–Schwarz inequality indicates high-fidelity generation and preservation of non-classical correlation. Furthermore, the achieved cross-correlation in room-temperature atoms exceeds the key boundary of 6, above which quantum correlation is able to violate Bell’s inequality. Our results open up the door to an entirely new realm of memory-enabled quantum applications at ambient conditions.
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Abstract Non-classical photon sources are a crucial resource for distributed quantum networks. Photons generated from matter systems with memory capability are particularly promising, as they can be integrated into a network where each source is used on-demand. Among all kinds of solid state and atomic quantum memories, room-temperature atomic vapours are especially attractive due to their robustness and potential scalability. To-date room-temperature photon sources have been limited either in their memory time or the purity of the photonic state. Here we demonstrate a single-photon source based on room-temperature memory. Following heralded loading of the memory, a single photon is retrieved from it after a variable storage time. The single-photon character of the retrieved field is validated by the strong suppression of the two-photon component with antibunching as low as gRR∣W=1(2)=0.20±0.07{g}_{{\rm{RR| W = 1}}}^{(2)}=0.20\pm 0.07gRR∣W=1(2)​=0.20±0.07 g RR∣W=1 ( 2 ) = 0.20 ± 0.07 . Non-classical correlations between the heralding and the retrieved photons are maintained for up to τNCR=(0.68±0.08) ms{\tau }_{{\rm{NC}}}^{{\mathcal{R}}}=(0.68\pm 0.08)\ {\rm{ms}}τNCR​=(0.68±0.08) ms τ NC R = ( 0.68 ± 0.08 ) ms , more than two orders of magnitude longer than previously demonstrated with other room-temperature systems. Correlations sufficient for violating Bell inequalities exist for up to τBI = (0.15 ± 0.03) ms.
Quantum memories capable of storing single photons are essential building blocks for quantum information processing, enabling the storage and transfer of quantum information over long distances. Devices operating at room temperature can be deployed on a large scale and integrated into existing photonic networks, but so far warm quantum memories have been susceptible to noise at the single photon level. Using a fundamentally different approach to quantum memories, i.e. the recently developed far off-resonant Raman memory scheme, the authors present a highly efficient room-temperature memory that is able to operate with a low unconditional noise floor in the quantum regime, something that no other room-temperature memory has been able to demonstrate before.
This thesis is about the experimental implementation of a high-speed and robust quantum memory for light. A novel far off-resonant Raman approach to ensemble-based quantum memories in a room-temperature environment is developed and demonstrated. Storage and retrieval of sub-nanosecond, weak coherent light pulses at the single-photon-level with total efficiencies exceeding 30% and storage times of up to 4 μs are achieved. The coherence of the memory is shown by directly interfering a copy of the incident signal with the retrieved signal from the memory. The unconditional noise floor of the memory is found to be low enough to operate the memory in the quantum regime at room temperature. Multiple readout of a single stored excitation is demonstrated, suggesting that 100% readout is possible in different temporal modes. Furthermore, first results regarding the storage and retrieval of polarisation encoded qubits are obtained. This and the memory’s ability to operate in the quantum regime at room temperature with a low unconditional noise floor illustrate its potential usefulness for real world applications.