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Optica

Full-bandwidth quantum memory of squeezed light

Jinxian Guo, Meihong Wang, Zeliang Wu, Chenyu Qiao, Fengyi Xu, Xiaoran Zhang, Xiaolong Su, L. Q. Chen, Weiping Zhang

Published Apr 8, 2026• 1 citation
Publisher

Abstract

Achieving high end-to-end efficiency and broadband quantum memory of squeezed light is crucial for continuous-variable quantum information processing. Existing demonstrations fail to store squeezed states across their full squeezing bandwidth. Here, we present a full-bandwidth quantum memory of squeezed light with up to 24 MHz bandwidth, which is at least 12 times that of previous narrowband resonant memory systems, via a far-off resonant Raman process. We achieve output squeezing as high as 1.0±0.29dB, with fidelity above 92±0.5% and a memory efficiency of 80%, corresponding to an end-to-end efficiency of 64.2±0.7% when input squeezing is 1.6±0.23dB. The lowest excess noise of 0.025 shot-noise unit in the memory system is estimated by the noisy model, which benefits from optimizing quantum memory performance with a backward-retrieval strategy. Our results show high-performance memory for squeezed states within tens of MHz-level bandwidth, which has potential applications in high-speed quantum information processing.

DOI
10.1364/optica.578380

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Achieving high end-to-end efficiency and broadband quantum memory of squeezed light is crucial for continuous-variable quantum information processing. Existing demonstrations fail to store squeezed states across their full squeezing bandwidth. Here, we present a full-bandwidth quantum memory of squeezed light with up to 24 MHz bandwidth, which is at least 12 times that of previous narrowband resonant memory systems, via a far-off resonant Raman process. We achieve output squeezing as high as 1.0±0.29dB, with fidelity above 92±0.5% and a memory efficiency of 80%, corresponding to an end-to-end efficiency of 64.2±0.7% when input squeezing is 1.6±0.23dB. The lowest excess noise of 0.025 shot-noise unit in the memory system is estimated by the noisy model, which benefits from optimizing quantum memory performance with a backward-retrieval strategy. Our results show high-performance memory for squeezed states within tens of MHz-level bandwidth, which has potential applications in high-speed quantum information processing.
In continuous-variable quantum information processing, it is crucial to develop high-efficiency and broadband quantum memory of squeezed light, which enables the storage of full-bandwidth information. Here, we present a quantum memory of squeezed light with up to 24 MHz bandwidth, which is at least 12 times that of previous narrowband resonant memory systems, via a far-off resonant Raman process. We achieve output squeezing of as high as 1.0 dB with fidelity above 92% and a memory efficiency of 80%, corresponding to an end-to-end efficiency of 64.2%, when input squeezing is 1.6 dB. The lowest excess noise of 0.025 shot-noise-unit in the memory system is estimated by the noisy channel model which is benefited from optimizing quantum memory performance with a backward retrieval strategy. Our results represent a breakthrough in high-performance memory for squeezed states within tens of MHz-level bandwidth, which has potential applications in high-speed quantum information processing.
Photonic quantum information processing has emerged as a powerful platform for realising quantum-enhanced technologies. In order to be scalable, many of these technologies depend on the availability of a suitable quantum memory for the coherent storage and on-demand retrieval of photonic quantum states. In this thesis, I investigate broadband light storage in a room-temperature Raman memory, implemented both in free space and, for the first time, inside a low-finesse optical cavity designed for low-noise operation. The ability of the Raman memory to preserve phase coherence was tested by storing coherent polarisation states in two spatially separate atomic ensembles. Polarisation storage with a fidelity of up to 97 ± 1% was demonstrated by performing full process tomography on the system. The Raman memory was then interfaced for the first time with a spontaneous parametric downconversion (SPDC) source of heralded, GHz-bandwidth single photons. The memory performance was characterised by measuring the second-order autocorrelation of the retrieved fields. While the SPDC input photon statistics showed a clear influence on the statistics of the retrieved field, four-wave mixing (FWM) noise, stimulated by spontaneous Raman scattering, prevented the preservation of non-classical photon statistics during read-out. Suppressing this source of noise represents the last remaining challenge for realising a broadband single-photon Raman memory suitable for quantum information applications. To this end, I demonstrate a novel cavity implementation of the Raman memory which reduces the FWM contribution relative to the signal field by re-distributing the density of states into which the noise photons can be scattered. Cavity-enhanced memory operation was investigated using weak coherent input states, showing a significant improvement of the signal-to-noise ratio compared to the free-space memory implementation. This proof-of-principle demonstration suggests that cavity Raman memories may offer a practical route towards low-noise, high-bandwidth quantum storage at room temperature.
We have developed a quantum memory that is completely compatible with current quantum information processing for continuous variables of light, where arbitrary frequency sidebands of a squeezed vacuum can be stored and retrieved using bichromatic electromagnetic induced transparency. The 2 MHz sidebands of squeezed vacuum pulses with temporal widths of 470 ns and a squeezing level of -1.78±0.02 dB were stored for 3 μs in laser-cooled 87Rb atoms. Squeezing of -0.44±0.02 dB, which is the highest squeezing reported for a retrieved pulse, was achieved.
We have developed a quantum memory that is completely compatible with current quantum information processing for continuous variables of light, where arbitrary frequency sidebands of a squeezed vacuum can be stored and retrieved using bichromatic electromagnetic induced transparency. The 2 MHz sidebands of squeezed vacuum pulses with temporal widths of 470 ns and a squeezing level of $\ensuremath{-}1.78\ifmmode\pm\else\textpm\fi{}0.02$ dB were stored for 3 $\ensuremath{\mu}$s in laser-cooled 87Rb^{87}\mathrm{Rb}87Rb atoms. Squeezing of $\ensuremath{-}0.44\ifmmode\pm\else\textpm\fi{}0.02$ dB, which is the highest squeezing reported for a retrieved pulse, was achieved.
Abstract Quantum memories are essential for quantum information processing. Techniques have been developed for quantum memory based on atomic ensembles. The atomic memories through optical resonance usually suffer from the narrow-band limitation. The far off-resonant Raman process is a promising candidate for atomic memories due to broad bandwidths and high speeds. However, to date, the low memory efficiency remains an unsolved bottleneck. Here, we demonstrate a high-performance atomic Raman memory in 87 Rb vapour with the development of an optimal control technique. A memory efficiency of above 82.0% for 6 ns~20 ns optical pulses is achieved. In particular, an unconditional fidelity of up to 98.0%, significantly exceeding the no-cloning limit, is obtained with the tomography reconstruction for a single-photon level coherent input. Our work marks an important advance of atomic memory towards practical applications in quantum information processing.
Abstract The ability to efficiently realize storage and readout of optical squeezed states plays a key roll in continuous-variables quantum information processing. Here we study the quantum memory for squeezed state of propagating light in atoms based on the hybrid photon echo re-phasing. The optical quantum state is recorded in two sublevels of the ground state of an atomic ensemble to realize long-lived quantum memory. Taking into account the noise effect due to atomic decay, our estimation indicates that high fidelities larger than the classical fidelity threshold 81.5% are obtainable even with currently available techniques. Moreover, our result shows that the decay rate of atoms restricts the maximal fidelity. Our work provides some practical guidance for the realization of efficient and faithful photon-echo-based memory for squeezed light.