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Physical Review Applied

Generating a bandwidth-tunable squeezed state via phase manipulation of entangled sideband modes

Yimiao Wu, Shaoping Shi, Xuan Liu, Long Tian, Wei Li, Yajun Wang, Yaohui Zheng

Published Apr 8, 2025• 4 citations
Publisher

Abstract

A squeezed state is one of the most vital quantum resources in quantum information processing. The extensive attention has increasingly shifted to not only the squeezed degree but also the squeezed bandwidth in quantum precise measurement. Here, we demonstrate the generation of a bandwidth-tunable squeezed state by exploiting the entangled sideband modes and the postprocessing scheme, with the quantum noise reduction of $8.0\ifmmode\pm\else\textpm\fi{}0.3$ dB across a wide frequency range from 10 Hz to 10 MHz. Moreover, the bandwidth and rotation frequency can be conveniently manipulated in the whole frequency range according to the application requirement. There is no doubt that the demonstration will open up some potential applications about squeezed-state interaction with atoms.

DOI
10.1103/physrevapplied.23.044021

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A squeezed state is one of the most vital quantum resources in quantum information processing. The extensive attention has increasingly shifted to not only the squeezed degree but also the squeezed bandwidth in quantum precise measurement. Here, we demonstrate the generation of a bandwidth-tunable squeezed state by exploiting the entangled sideband modes and the postprocessing scheme, with the quantum noise reduction of 8.0\ifmmode±\else\textpm\fi0.38.0\ifmmode\pm\else\textpm\fi{}0.38.0\ifmmode±\else\textpm\fi0.3 dB across a wide frequency range from 10 Hz to 10 MHz. Moreover, the bandwidth and rotation frequency can be conveniently manipulated in the whole frequency range according to the application requirement. There is no doubt that the demonstration will open up some potential applications about squeezed-state interaction with atoms.
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The strength of the quantum correlations of a continuous-variable entangled state is determined by several relative phases in the preparation, transmission, and detection processes of entangled states. In this paper, we report the first experimental and theoretical demonstrations of the precision of relative phases associated with the strength of quadrature correlations. Based on the interrelations of the relative phases, three precisely phase-locking methodologies are established: ultralow RAM control loops for the lengths and relative phases stabilization of the DOPAs, difference DC locking for the relative phase between the two squeezed beams, and DC-AC joint locking for the relative phases in BHDs. The phase-locking loops ensure the total phase noise to be 9.7±0.32/11.1±0.36 mrad. Finally, all the relative phase deviations are controlled to be in the range of -35 to 35 mrad, which enhances the correlations of the amplitude and phase quadratures to -11.1 and -11.3 dB. The entanglement also exhibits a broadband squeezing bandwidth up to 100 MHz. This paves a valuable resource for experimental realization and applications in quantum information and precision measurement.
Two-mode orthogonal squeezed vacuum states are an important quantum resource for quantum communication, quantum computing, quantum simulation, quantum precision measurement and sensing. It is essential to obtain stable two-mode orthogonal squeezed vacuum states in a low frequency range and compact configurations for practical applications, especially in quantum precision measurement and sensing. Two-mode orthogonal squeezed vacuum states are commonly produced via a subthreshold nondegenerate optical parametric amplifier (NOPA) in a continuous variable system. However, it is a difficult problem that the subthreshold NOPA cavity is phase sensitive manipulated to obtain stable squeezed vacuum states. Previous signal light injecting scheme relies on an injection of a weak light field into the subthreshold NOPA for phase sensitive manipulation. The injected signal light has the same frequency as the generated squeezed vacuum state. Thereby even the weakest injected signal light can introduce large amounts of excessive noise at low frequencies and the squeezing degree of two-mode squeezed vacuum states will be reduced or squeezing cannot be achieved. In this paper, a single sideband frequency shifted light injecting scheme is proposed for phase sensitive manipulation of NOPA. The comparison between the single sideband frequency shifted light injecting scheme and the signal light injecting scheme for realization of phase sensitive manipulation of NOPA is conducted. The effects of the two schemes on the generation of the low-frequency two-mode orthogonal squeezed vacuum state light field are investigated experimentally . The experimental results show that in the signal light injecting scheme for phase sensitive manipulation, the squeezing degree of the two-mode orthogonal squeezed vacuum state continuously decreases until it disappears as the power of injected signal light increases. In the process of phase sensitive manipulation of NOPA by using the single sideband frequency shifted light injecting scheme, the squeezing degree of the two-mode orthogonal squeezed vacuum state does not change with the power of the injected frequency shifted light increasing. Stable phase sensitive manipulation is realized by injecting single sideband frequency shifted light into NOPA. The NOPA is operated in a phase sensitive amplification state for 30 min. Stable low-frequency two-mode orthogonal squeezed vacuum states are obtained. The (4.1 ± 0.1) dB amplitude orthogonal squeezed vacuum states and (4.0 ± 0.2) dB phase orthogonal squeezed vacuum states at a frequency of 200 kHz are generated stably, in a compact NOPA configuration.
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.
Nonclassical states of light are of increasing interest due to their applications in the emerging field of quantum information processing and communication. Squeezed light is such a state of the electromagnetic field in which the quantum noise properties are altered compared with those of coherent light. Squeezed light and squeezed vacuum states are potentially useful for quantum information protocols as well as optical measurements, where sensitivities can be limited by quantum noise. We experimentally study a source of squeezed vacuum resulting from the interaction of near-resonant light with both cold and hot Rb atoms via the nonlinear polarization self-rotation effect (PSR). We investigate the optimal conditions for noise reduction in the resulting squeezed states, reaching quadrature squeezing levels of up to 2.6 dB below shot noise, as well as observing noise reduction for a broad range of detection frequencies, from tens of kHz to several MHz. We use this source of squeezed vacuum at 795 nm to further study the noise properties of these states and how they are affected by resonant atomic interactions. This includes the use of a squeezed light probe to give a quantum enhancement to an optical magnetometer, as well as studying the propagation of squeezed vacuum in an atomic medium under conditions of electromagnetically induced transparency (EIT). We also investigate the propagation of pulses of quantum squeezed light through a dispersive atomic medium, where we examine the possibilities for quantum noise signals traveling at subluminal and superluminal velocities. The interaction of squeezed light with resonant atomic vapors finds various potential applications in both quantum measurements and continuous variable quantum memories.