Advances in quantum metrology: Continuous variables in phase space

TL;DR

This paper introduces quantum metrology using continuous variables in phase space, emphasizing Wigner functions, quantum limits, and the effects of photon addition/subtraction on quantum states of light.

Contribution

It provides a comprehensive guide on applying phase space methods and quantum Fisher information to optimize quantum metrology, including effects of photon manipulation.

Findings

Photon addition/subtraction affects quantum state properties.

Phase measurement is more restrictive than SNR in quantum limits.

Photon addition/subtraction can improve SNR at the cost of measurement time.

Abstract

This dissertation serves as a general introduction to Wigner functions, phase space, and quantum metrology but also strives to be useful as a how-to guide for those who wish to delve into the realm of using continuous variables, to describe quantum states of light and optical interferometry. We discuss the advantages of Wigner functions and their use to describe many quantum states of light. Throughout our metrology discussions, we will also discuss various quantum limits and use quantum Fisher information to show optimal bounds. When applicable, we also discuss the use of quantum Gaussian information and how it relates to our Wigner function treatment. The remainder of our discussion focuses on investigating the effects of photon addition and subtraction to various states of light and analyze the nondeterministic nature of this process. We use examples of $m$ photon additions to a coherent state as well as discuss the properties of an $m$ photon subtracted thermal state. We also provide an argument that this process must always be a nondeterministic one, or the ability to violate quantum limits becomes apparent. We show that using phase measurement as one's metric is much more restrictive, which limits the usefulness of photon addition and subtraction. When we consider SNR however, we show improved SNR statistics, at the cost of increased measurement time. In this case of SNR, we also quantify the efficiency of the photon addition and subtraction process.