# Quantum phase properties of photon added and subtracted displaced Fock states

## TL;DR

This paper investigates the quantum phase properties of photon added and subtracted displaced Fock states, revealing how quantum state engineering operations influence phase distributions, fluctuations, and their applications in quantum phase estimation.

## Contribution

It provides analytic expressions for phase distributions and shows photon subtraction as a more effective engineering tool than addition.

## Key findings

- Photon subtraction narrows phase distribution more than addition.
- Photon added displaced Fock states are advantageous for quantum phase estimation.
- Photon subtraction reveals antibunching in engineered states.

## Abstract

Quantum phase properties of photon added and subtracted displaced Fock states (and a set of quantum states which can be obtained as the limiting cases of these states) are investigated from a number of perspectives, and it is shown that the quantum phase properties are dependent on the quantum state engineering operations performed. Specifically, the analytic expressions for quantum phase distributions and angular $Q$ distribution as well as measures of quantum phase fluctuation and phase dispersion are obtained. The uniform phase distribution of the initial Fock states is observed to be transformed by the unitary operation (i.e., displacement operator) into non-Gaussian shape, except for the initial vacuum state. It is observed that the phase distribution is symmetric with respect to the phase of the displacement parameter and becomes progressively narrower as its amplitude increases. The non-unitary (photon addition/subtraction) operations make it even narrower in contrast to the Fock parameter, which leads to broadness. The photon subtraction is observed to be a more powerful quantum state engineering tool in comparison to the photon addition. Further, one of the quantum phase fluctuation parameters is found to reveal the existence of antibunching in both the engineered quantum states under consideration. Finally, the relevance of the engineered quantum states in the quantum phase estimation is also discussed, and photon added displaced Fock state is shown to be preferable for the task.