Kerr squeezing in optical waveguides and its use to improve the sensitivity of interferometers

Squeezed light is one of the key resources of photonic quantum technology. Among the various applications of squeezed light states, measurement beyond the standard quantum limit is one of the most prominent. Squeezed light is regularly used in large-scale gravitational wave detectors. Among the various nonlinear interactions that can produce squeezing, the optical Kerr effect is particularly interesting because it can potentially be implemented in a wide variety of materials and arrangements. It does not require phase matching, and one can use optical waveguides to achieve long interaction lengths. The amount of squeezing can reach significant levels due to the tight confinement in the fibres (and thus high intensity). However, the advantages of generating bright squeezed states in third-order nonlinear media are somewhat masked by difficulties in using them for applications such as interferometry, because the uncertainty distribution in phase space for these states is tilted with respect to both phase and amplitude quadrature. In this talk, we review various techniques for generating squeezed light in optical waveguides (and in particular optical fibres), and discuss a novel approach to overcome difficulties in applying Kerr-squeezed light to quantum-enhanced interferometry. One popular approach to work with the Kerr-squeezed tilted states is to create a polarisation-squeezed state by combining two such states in orthogonal polarisations of the same spatial mode. In a polarisation squeezed state the fluctuations of a particular Stokes parameter are smaller than in a coherent state with the same mean polarisation state. In such setups, it is important to use pulsed light and to protect the polarisation modes from cross-Kerr interaction by temporally separating the pulses. This can be done efficiently and in a very stable manner using polarisation-maintaining fibres and/or polarisation-sensitive group delay compensators. We report on a very stable approach to build an all-fiber setup for the generation of Kerr-squeezed light states based on polarisation-maintaining silica fibers [1], and on a demonstration of interferometric sensitivity enhancement beyond the shot noise limit using these states [2]. We also present the first experimental observation of squeezed light generation in chalcogenide fibres. Chalcogenide glass fibres have 3-5 orders of magnitude higher nonlinearity than standard silica fibres. They also exhibit a wide range of mid-IR transparency. This stimulates the study of chalcogenide (and other soft highly nonlinear glasses such as tellurite) as it promotes the development of non-classical light sources in an extended wavelength range that is not readily accessible with current technologies. In the talk we also discuss some aspects of numerical modelling and optimisation [3] of squeezed light generation in nonlinear waveguides made of different materials (silica, soft tellurite and chalcogenide glasses), paying special attention to parasitic effects such as Raman scattering.
[1] N. Kalinin, T. Dirmeier, A. A. Sorokin, E. A. Anashkina, L. L. Sanchez?Soto, J. F. Corney, G. Leuchs, and A. V. Andrianov, "Observation of Robust Polarization Squeezing via the Kerr Nonlinearity in an Optical Fiber," Adv Quantum Tech 6(3), 2200143 (2023).
[2] N. Kalinin, T. Dirmeier, A. A. Sorokin, E. A. Anashkina, L. L. Sanchez-Soto, J. F. Corney, G. Leuchs, and A. V. Andrianov, "Quantum-enhanced interferometer using Kerr squeezing," Nanophotonics 12(14), 2945–2952 (2023).
[3] A. V. Andrianov, N. A. Kalinin, A. A. Sorokin, E. A. Anashkina, L. L. Sanchez-Soto, J. F. Corney, and G. Leuchs, "Optimizing the generation of polarization squeezed light in nonlinear optical fibers driven by femtosecond pulses," Opt. Express 31(1), 765 (2023).