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Journal of the Optical Society of America B

Enhancement of squeezing with cascaded and coherent feedback-controlled degenerate optical parametric amplifiers

Yashuai Han, Zhao Zhang, Zhengxian Zhou, Jun Qu, Jun He, Junmin Wang

Published Sep 2, 2021• 3 citations
Publisher

Abstract

The squeezing level of light on atomic resonance produced by a degenerate optical parametric amplifier (DOPA) is now limited by blue or violet pump-light-induced loss, and it is difficult to improve the squeezing by simply reducing the loss of DOPA. In this study, two promising schemes, namely, the cascaded DOPA (C-DOPA) and the coherent feedback-controlled DOPA (CFC-DOPA), are theoretically discussed. For a ideal case, the CFC-DOPA can realize infinite squeezing output but requires almost infinite accuracy in phase locking. For a practical case with feasible physical parameters of realistic systems, the performance of squeezing enhancement for the C-DOPA and CFC-DOPA is compared. The C-DOPA shows advantages in the megahertz frequency range, while the CFC-DOPA shows advantages in the low-frequency range. At a general analysis frequency of 2 MHz, C-DOPA shows better robustness against the loss of the system. As a price, it requires a smaller instability tolerance for phase locking. With the C-DOPA, the squeezing on Rb atomic resonance can be pushed from − 5 d B to − 7 d B . Our analytical results can provide a valuable reference for designing experimental devices to efficiently produce high-quality squeezed light on atomic resonance, which has potential applications in quantum information processing and quantum metrology.

DOI
10.1364/josab.439467

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The squeezing level of light on atomic resonance produced by a degenerate optical parametric amplifier (DOPA) is now limited by blue or violet pump-light-induced loss, and it is difficult to improve the squeezing by simply reducing the loss of DOPA. In this study, two promising schemes, namely, the cascaded DOPA (C-DOPA) and the coherent feedback-controlled DOPA (CFC-DOPA), are theoretically discussed. For a ideal case, the CFC-DOPA can realize infinite squeezing output but requires almost infinite accuracy in phase locking. For a practical case with feasible physical parameters of realistic systems, the performance of squeezing enhancement for the C-DOPA and CFC-DOPA is compared. The C-DOPA shows advantages in the megahertz frequency range, while the CFC-DOPA shows advantages in the low-frequency range. At a general analysis frequency of 2 MHz, C-DOPA shows better robustness against the loss of the system. As a price, it requires a smaller instability tolerance for phase locking. With the C-DOPA, the squeezing on Rb atomic resonance can be pushed from − 5 d B to − 7 d B . Our analytical results can provide a valuable reference for designing experimental devices to efficiently produce high-quality squeezed light on atomic resonance, which has potential applications in quantum information processing and quantum metrology.
The intensity-difference squeezed state is an important concept in quantum optics, which is not only of great significance for fundamental research in quantum physics, but also an important quantum resource in the fields of quantum communication, quantum computing, and quantum precision measurement. The optical parametric amplifier based on atomic four-wave mixing is one of the most effective means to achieve intensity-difference squeezed light. However, due to the absorption loss of atomic vapor in the light field, the output squeezing still needs improving. By feeding the non-classical optical field from the optical parametric amplifier back to the input port, the quantum characteristics of its output optical field can be enhanced. However, the intensity-difference squeezing enhancement from a phase-insensitive amplifier is experimentally realized based on coherent feedback control. The intensity-difference squeezing enhancement of the phase-sensitive amplifier has not been discussed. In this work, a two-port coherent feedback-controlled phase-sensitive amplifier is analyzed theoretically. The dependence of the intensity-difference squeezing, respectively, on the feedback intensity, the intensity gain of the optical parametric amplifier, and the losses of the system are investigated. For the ideal case in which the losses of the system are ignored, infinite squeezing can be achieved by adjusting the strength and phase of feedback. Considering the actual atomic absorption losses, squeezing enhancement can also be achieved over a wide range of intensity gains within a certain feedback intensity range. In addition, the squeezing enhancement is quite efficient for the medium intensity gain range. The intensity-difference squeezing enhancement strongly depends on the absorption loss of atomic vapor. The smaller the absorption loss, the more significant the squeezing enhancement effect is. Furthermore, the experimental feasibility of this scheme is also considered in detail. Our research can provide useful references for achieving high-quality non classical light fields in experiment, which may find applications in quantum information processing and quantum precise measurement.
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We demonstrate the enhanced quantum noise reduction of the output field from an optical parametric amplifier (OPA) by employing the cascaded optical parametric amplifiers (COPA), in which the output field of one OPA is the input field of the subsequent one. The output field noise formulas of the cascaded degenerate and nondegenerate OPAs (CDOPA and CNOPA) are obtained. The analytical results show that a CDOPA and a CNOPA can generate squeezing beams and entangled beams with a wider bandwidth under a low pump parameter, respectively. The cavity output efficiency and the intracavity loss are the main factors for improving the degrees of squeezing and entanglement. Our work will provide improved schemes for designing COPAs to efficiently produce high-quality squeezed and entangled states, which have potential applications in quantum-information processing.
In the paper, the intensity-difference squeezing enhancement from a two-port feedback optical parametric amplifier (TFPA) is theoretically discussed. The performance of squeezing enhancement with the TFPA is compared with that of a one-port feedback optical parametric amplifier (OFPA) and a phase-sensitive optical amplifier. For the ideal case, the infinite squeezing can be achieved for both TFPA and OFPA by manipulating the strength of the feedback and the phase delay induced by the feedback loops. Furthermore, the TFPA can realize the all-phase squeezing enhancement. For the lossy case, the TFPA shows unique advantages in squeezing enhancement against the other two schemes. Our results provide new ideas on the generation of high-quality intensity-difference squeezed light, which may find potential applications in quantum information and quantum metrology.
The purpose of this article is to present an efficient coherent feedback control technique for squeezing enhancement of degenerate parametric amplifiers (DPAs). The feedback controllers to be designed are in the form of linear quantum stochastic systems which can be described by quantum feedback networks theory recently developed. The problem of squeezing enhancement is formulated as a non-convex constrained nonlinear programming problem, whose solution yields the coherent feedback controllers to be designed. Compared with the previous study, the proposed approach reveals clear advantage when DPAs are lossy, as is always the case in practice. Based on the recently developed quantum network synthesis theory, we show how the designed coherent feedback controllers can be implemented by means of quantum optical devices.
Summary form only given.We describe the generation and detection of broadband squeezed states at 1047 nm in a lithium triborate (LiB/sub 3/O/sub 5/) degenerate optical parametric amplifier (DOPA). The light source used is a laser-diode-pumped additive pulse mode-locked Nd:LiYF/sub 4/ laser, which produces pulses 3 ps in duration at repetition rate of 140 MHz, and the average output power is 1 W. The fundamental light is frequency doubled in an external ring enhancement cavity, and the resulting high peak power of the doubled light means that it is possible to produce significant squeezing even in a single-pass or traveling-wave parametric amplifier.