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Optics Express

Precise control of squeezing angle to generate 11 dB entangled state

Wenhui Zhang, Nanjing Jiao, Ruixin Li, Long Tian, Yajun Wang, Yaohui Zheng

Published Jul 6, 2021• 21 citations

Abstract

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.

DOI: 10.1364/oe.428501

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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 $8.0\ifmmode\pm\else\textpm\fi{}0.3$ 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.

We demonstrate experimentally quantum frequency up-conversion of a continuous variable entangled optical field via sum-frequency-generation process. The two-color entangled state initially entangled at 806 and 1518 nm with an amplitude quadrature difference squeezing of 3.2 dB and phase quadrature sum squeezing of 3.1 dB is converted to a new entangled state at 530 and 1518 nm with the amplitude quadrature difference squeezing of 1.7 dB and phase quadrature sum squeezing of 1.8 dB. Our implementation enables the observation of entanglement between two light fields spanning approximately 1.5 octaves in optical frequency. The presented scheme is robust to the excess amplitude and phase noises of the pump field, making it a practical building block for quantum information processing and communication networks.

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Bright two-color continuous variable (CV) entangled optical beams at 0.8 and 1.5 μm are generated by utilizing a phase-insensitive optical parametric amplifier with only 1.5 μm signal field injected. Without locking the relative phase between the signal and pump fields, the amplitude quadrature difference squeezing of 3.30 dB and phase quadrature sum squeezing of 3.35 dB are observed, which satisfy the entanglement criterion. The demonstrated scheme here eliminates the necessity of precise phase control between the signal and pump fields and enables robust generation of two-color CV entangled states.