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Journal of the Optical Society of America B

Quantum squeezing enhancement with a two-port feedback optical parametric amplifier

Yashuai Han, Juanzhong Qiang

Published Nov 22, 2024• 0 citations
Publisher

Abstract

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.

DOI
10.1364/josab.541149

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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 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.
How to achieve the maximal entanglement, for given finite entanglement resources? In this paper, we propose a two-port feedback optical parametric amplifier (TFPA) consisting of a nondegenerate optical parametric amplifier (NOPA) and two linear beam splitters. The former is an entanglement resource, and the latter serve as feedback controllers that feed the two entangled beams generated from the NOPA back into its input ports. By manipulating the reflectivity of the beam splitters and the phase delays introduced by the feedback paths, an entanglement enhancement can be achieved by the TFPA. Furthermore, we demonstrate that such entanglement enhancement can happen at all phase points for the ideal case, and the maximal entanglement can be infinitely large. For the lossy case, our TFPA also has its unique advantages in the robustness of the losses of the system.
Coherent feedback control has been proved to be an effective approach in entanglement enhancement of the entangled states produced by a nondegenerate optical parametric amplifier (NOPA). However, the present research mainly focuses on a two-port feedback NOPA (TFPA). In this study, a scheme of single-port feedback NOPA (SFPA) is proposed and investigated. For the ideal case, both SFPA and TFPA have the potential to realize an infinite degree of entanglement. For the practical case with feasible physical parameters of realistic systems, the features of entanglement enhancement for two schemes are compared. The effect of entanglement enhancement for SFPA is relatively weaker than that of TFPA, but has a loose phase-locking accuracy requirement. Our results may provide useful references on the control of nonclassical light fields.
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.
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.
High precision interferometers are the building blocks of precision metrology and the ultimate interferometric sensitivity is limited by the quantum noise. Here, we propose and experimentally demonstrate a compact quantum interferometer involving two optical parametric amplifiers and the squeezed states generated within the interferometer are directly used for the phase-sensing quantum state. By both squeezing shot noise and amplifying phase-sensing intensity the sensitivity improvement of 4.86±0.24 dB beyond the standard quantum limit is deterministically realized and a minimum detectable phase smaller than that of all present interferometers under the same phase-sensing intensity is achieved. This interferometric system has significantly potential applications in a variety of measurements for tiny variances of physical quantities.