Quantum sensing with bright Gaussian states of light

  • Alex D M G Belsley

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Precision measurements and sensing are crucial in every scientific and technological field. Quantum metrology, a branch of quantum information science, aims to maximize precision in estimating relevant physical quantities. One notable application of quantum metrology is the use of squeezed states to detect gravitational waves with unparalleled sensitivity, which is a prime example of a phase estimation problem. Although quantum probes can provide higher precision in parameter estimation compared to classical strategies, many quantum states of light have limited practical advantage in real-world sensing scenarios subject to dephasing and loss mechanisms.

In this thesis, we propose new sensing architectures with the aim of achieving meaningful, practical precision improvements. To accomplish this, we focus on bright Gaussian probe states, which can be generated with large photon numbers, and engineer their interaction with the physical object being characterized.

We leverage circular birefringence and dichroism to estimate the concentration of chiral molecules in solution. This is an important metric in a wide range of industrial applications and material science research. Our proposed strategy employs a common-mode interference scheme with bright polarization squeezed states of light and balanced detection. We find it is possible to enhance the precision in estimating the concentration by a factor of four when compared to a classical probe with the same mean photon number.

We then investigate the use of all-pass ring resonators for absorption and refractive-index estimation. Remarkably, we find that, because of the combined effects of interference and resonant enhancement, coherent states are the optimal probe in a ring resonator scheme. Moreover, this strategy is superior to any single-pass method independent of the quantum nature of the probe state.

Finally, we propose a novel gas sensing strategy that employs frequency modulated amplitude squeezed state probes together with homodyne detection. This strategy allows for independent sampling of multiple points within an absorption line profile, facilitating precise determination of the temperature, concentration, and pressure of a given gas. The signal-to-noise ratio scales exponentially with the squeezing level. At currently attainable squeezing levels, we predict a significant improvement over classical absorption estimation strategies with the same input energy.
Date of Award5 Dec 2023
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorJonathan C F Matthews (Supervisor) & Krishna Coimbatore Balram (Supervisor)

Cite this

'