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Physical Review Letters

Interference-Induced Quantum Squeezing Enhancement in a Two-beam Phase-Sensitive Amplifier

Shengshuai Liu, Yanbo Lou, Jietai Jing

Published Sep 9, 2019• 91 citations
Publisher

Abstract

We experimentally demonstrate a method for realizing quantum squeezing enhancement which is induced by the interference in a two-beam phase-sensitive amplifier (PSA) based on a four-wave mixing process. Compared to the normal phase-insensitive amplifier with an intensity-difference squeezing (IDS) of 8.97±0.24 dB or 8.76±0.26 dB, the IDS of our two-beam PSA is enhanced to 10.13±0.21 dB under the same experimental situation. Furthermore, we study how various parameters influence the quantum squeezing enhancement of the PSA. These results clearly show that the physical mechanism inducing the IDS enhancement of the two-beam PSA is its intrinsic interference nature. Our results may find potential applications in improving the fidelity of quantum information processing and the precision of quantum metrology.

DOI
10.1103/physrevlett.123.113602

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We experimentally demonstrate a method for realizing quantum squeezing enhancement which is induced by the interference in a two-beam phase-sensitive amplifier (PSA) based on a four-wave mixing process. Compared to the normal phase-insensitive amplifier with an intensity-difference squeezing (IDS) of 8.97±0.24 dB or 8.76±0.26 dB, the IDS of our two-beam PSA is enhanced to 10.13±0.21 dB under the same experimental situation. Furthermore, we study how various parameters influence the quantum squeezing enhancement of the PSA. These results clearly show that the physical mechanism inducing the IDS enhancement of the two-beam PSA is its intrinsic interference nature. Our results may find potential applications in improving the fidelity of quantum information processing and the precision of quantum metrology.
We experimentally realize the enhancement of six-beam quantum squeezing by utilizing a six-beam phase-sensitive amplifier (PSA) based on cascaded four-wave mixing processes. Compared to the intensity-difference squeezing (IDS) of about 5.03 or 5.09 dB generated by a six-beam phase-insensitive amplifier (PIA), the six-beam IDS generated by the six-beam PSA is enhanced to about 6.64 dB. The intrinsic interference of six-beam PSA induces this enhancement. In addition, we investigate the dependence of IDS generated by the six-beam PSA and PIAs on the powers of two pump beams. The results show that the IDS of six-beam PSA is always better than that of six-beam PIAs. Our scheme may find potential applications in high-precision multi-parameter quantum metrology.
Phase-sensitive amplifiers (PSAs) have been widely studied in fiber amplifiers, with remarkable recent advances. They have also been implemented in an SU(1,1) interferometer. In this paper, we study an experimental scheme for the implementation of a two-mode PSA based on a four-wave mixing process in rubidium vapor. With the process seeded by coherent probe and conjugate beams, quantum correlation including intensity difference/sum squeezing and quadrature entanglement between the output probe and conjugate fields are theoretically analyzed. Compared to previous related research, several new and interesting results are reported here. The maximal degree of intensity difference squeezing can be enhanced by nearly 3 dB compared to a phase-insensitive amplifier with the same gain. It is also possible to generate intensity sum squeezing between the probe and conjugate fields by choosing the specific phase of the input beams. Moreover, quadrature entanglement between the probe and conjugate beams, which can be manipulated by the phase of the input beams, is predicted. Our scheme may find a variety of applications in quantum metrology and quantum information processing owing to its ability of quantum squeezing and entanglement manipulation.
Quantum squeezed states, exhibiting noise reduction below the shot-noise limit, are important resources in quantum optics. The degree of quantum squeezing directly influences the performance of physical systems, making the achievement of higher squeezing levels essential. Here, by utilizing the phase-sensitive cascaded four-wave mixing (PSCFWM) processes, we experimentally demonstrate the enhancement of three-beam quantum squeezing. The intensity-difference squeezing among the three output beams from PSCFWM processes is about 8.2 dB, which is enhanced by about 1.3 dB compared with that generated by phase-insensitive cascaded four-wave mixing processes. Our scheme provides an effective way for enhancing multi-beam quantum squeezing and holds promise for applications in multimode quantum correlated imaging and multiparameter quantum precision measurement.
We give the general expressions of intensity-difference squeezing (IDS) generated from two types of optical parametric amplifiers [i.e. phase-sensitive amplifier (PSA) and phase-insensitive amplifier (PIA)] based on the four-wave mixing process, which clearly shows the IDS transition between the ultra-low average input photon number regime and the ultra-high average input photon number regime. We find that both the IDS of the PSA and the IDS of the PIA get enhanced with the decrease of the average input photon number especially in the ultra-low average input photon number regime. This result is substantially different from the result in the ultra-high average input photon number regime where the IDS does not vary with the average input photon number. Moreover, under the same intensity gain, we find that the optimal IDS of the PSA is better than the IDS of the PIA in the ultra-low average input photon number regime. Our theoretical work predicts the presence of strong quantum correlation in the ultra-low average input photon number regime, which may have potential applications for probing photon-sensitive biological samples.
Abstract Quantum squeezing, which makes measurement sensitivity beyond classical limit by reducing system noise, is an essential non-classical resource for quantum metrology. It is of great importance to enhance quantum squeezing since the squeezing degree directly determines the extent to which measurement sensitivity beats the classical limit. Recently, a two-mode phase-sensitive amplifier has been utilized to enhance the quantum squeezing of phase-insensitive amplifier. However, such enhancement has an intrinsic limit of 3 dB. Here we show that such limit of 3 dB can be overcome by utilizing multi-beam interference. Specifically, a quantum squeezing enhancement of about 3.67 dB is observed by direct measurement. Moreover, we find that the amount of quantum squeezing enhancement increases as the number of multi-beam interference increases, which clearly shows that beating the quantum squeezing enhancement limit of 3 dB is induced by multi-beam interference. Our results here provide an efficient way to enhance the quantum squeezing.
Multipartite quantum correlation is important for both fundamental science and quantum information processing. Its enhancement is critical to improve the performance of physical systems. Therefore, it is of great practical significance to study the enhancement of multipartite quantum correlation. Here, we theoretically investigate a scheme for enhancing quadripartite quantum correlation by utilizing a phase-sensitive cascaded four-wave mixing (CFWM) process. We find that the intensity-difference squeezing (IDS) among the four output beams generated by the phase-insensitive CFWM process can be largely enhanced by introducing the phase-sensitive CFWM process. We also find that our phase-sensitive CFWM process can be used to generate intensity-sum squeezing (ISS), which cannot be generated by the phase-insensitive CFWM process. Moreover, we find that the maximum squeezing value of ISS is equal to that of IDS when the intensity gains of the three four-wave mixing processes are equal in the phase-sensitive cascaded scheme. In the end, we discuss the effects of the losses and the phase fluctuations on the squeezing values of our phase-sensitive CFWM process and the corresponding phase-insensitive CFWM process with the same intensity gains. It can be seen that the squeezing enhancement of our phase-sensitive CFWM process holds also in presence of the losses and the phase fluctuations. Our results pave the way for experimental implementation and may find applications in quantum metrology and quantum communication.