ObjectiveA phase-insensitive amplifier (PIA) based on atomic four-wave mixing is one of the ideal schemes for experimentally producing intensity-difference squeezed light. Improving its quantum properties is of great significance for the application of this non-classical light in the fields of quantum information and quantum precision measurement. By using a beam splitter as a feedback controller, the conjugated light from a PIA is partially fed back to the vacuum port, which can enhance the squeezing characteristics of its output intensity-difference squeezed light. This paper systematically investigates the dependence of the squeezing enhancement effect, induced by coherent feedback, on the physical parameters of the phase-insensitive amplifier. Our results indicate that in the ideal case of ignoring losses, infinite squeezing enhancement can be achieved by adjusting the reflectivity of the feedback controller. Under the parameter conditions of the actual experimental system, the PIA with coherent feedback can still realize significant squeezing enhancement. The research results can lay a theoretical foundation for the manipulation of the non-classical light field based on coherent feedback.MethodsThis paper focuses on the PIA based on the four-wave mixing process of ⁸⁵Rb atoms. The conjugated light from a PIA is partially fed back to the vacuum port. Based on the input-output relationship of the PIA and a beam splitter, the noise formula of the output intensity-difference squeezed light is finally obtained. Based on this, the dependence of the squeezing characteristics on physical system parameters is explored.Results and DiscussionsBased on the noise formula, the dependence of intensity-difference squeezing form the PIA on feedback intensity, intensity gain, the absorption loss of the atomic vapor, and the optical loss of the feedback loop is numerically simulated and presented in the paper. The paper delves into the impact of feedback on controlling the non-classical properties of the output light field from the PIA, both in the ideal case of no loss and considering actual experimental parameters.ConclusionsIn an idealized scenario. the results indicate that infinite intensity-difference squeezing enhancement can be achieved by adjusting the feedback strength. For situations considering actual experimental parameters, significant squeezing enhancement can be achieved within a certain parameter range. It can be found that the squeezing enhancement effect is more pronounced at medium and low intensity gains, while the squeezing enhancement effect gradually weakens at high intensity gains. Our research results can provide a theoretical basis for the coherent feedback control of non-classical light fields, laying the foundation for their applications in quantum communication and quantum precision measurement fields.