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Application of optical squeezing to microresonator based optical sensors

Dariya Salykina, Daniil Shakhbaziants, Igor Bilenko, Farid Khalili

TL;DR

Quantum-noise limits constrain the sensitivity of microresonator-based optical sensors due to shot noise. The paper develops a Kerr nonlinearity-based model with an intracavity parametric drive and analyzes squeezed input light, establishing a linear input-output description that includes loss-related noise. It shows that exploiting squeezing—both at the input and inside the cavity—reduces measurement noise below the shot-noise limit across a broad frequency band, with the ultimate limit set by optical losses and the achievable squeezing degree; intracavity squeezing further mitigates loss effects. The results have practical implications for high-sensitivity sensing, including biosensing and quantum nondemolition measurements of optical power, under realistic loss and squeezing conditions.

Abstract

High-Q optical microresonators combine low losses and high optical energy concentration in a small effective mode volume, making them an attractive platform for optical sensors. While light is confined in the microresonator by total internal reflection, a portion of the optical field, known as the evanescent field, extends outside. This makes the mode's resonant frequency sensitive to changes in the surrounding environment. In this work, we explore the quantum sensitivity limits of this type of sensors. We demonstrate that by preparing the probe light in a squeezed quantum state, it is possible to surpass the shot-noise limit. The resulting sensitivity is constrained only by optical losses and the available degree of squeezing. The influence of the losses can be reduced using additional squeezing of the light inside the microresonator.

Application of optical squeezing to microresonator based optical sensors

TL;DR

Quantum-noise limits constrain the sensitivity of microresonator-based optical sensors due to shot noise. The paper develops a Kerr nonlinearity-based model with an intracavity parametric drive and analyzes squeezed input light, establishing a linear input-output description that includes loss-related noise. It shows that exploiting squeezing—both at the input and inside the cavity—reduces measurement noise below the shot-noise limit across a broad frequency band, with the ultimate limit set by optical losses and the achievable squeezing degree; intracavity squeezing further mitigates loss effects. The results have practical implications for high-sensitivity sensing, including biosensing and quantum nondemolition measurements of optical power, under realistic loss and squeezing conditions.

Abstract

High-Q optical microresonators combine low losses and high optical energy concentration in a small effective mode volume, making them an attractive platform for optical sensors. While light is confined in the microresonator by total internal reflection, a portion of the optical field, known as the evanescent field, extends outside. This makes the mode's resonant frequency sensitive to changes in the surrounding environment. In this work, we explore the quantum sensitivity limits of this type of sensors. We demonstrate that by preparing the probe light in a squeezed quantum state, it is possible to surpass the shot-noise limit. The resulting sensitivity is constrained only by optical losses and the available degree of squeezing. The influence of the losses can be reduced using additional squeezing of the light inside the microresonator.

Paper Structure

This paper contains 4 sections, 36 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Quantum noise
  3. Spectral densities
  4. Discussion

Figures (2)

  • Figure 1: Schematic illustration of optical sensor based on microresonator. NL OMR -- nonlinear optical microresonator, HD -- homodyne detector (the corresponding reference beam is not shown for simplicity), $|{\rm sqz}\rangle$ -- squeezed coherent state of the input mode $\hat{a}$, $\eta$ is the quantum efficiency of the output path, including the photodetection quantum efficiency. The additional "pump" provides the intracavity parametric excitation.
  • Figure 2: Plots of spectral densities \ref{['S0']}, \ref{['S1']}, \ref{['S']}, and \ref{['S_SNL']} for $\kappa'=10\kappa"$, $\eta=0.7$, and $e^{2r}=30$ (15 dB of squeezing).