Generating "squeezed" superpositions of coherent states using photon addition and subtraction

TL;DR

This paper demonstrates how photon addition and subtraction techniques can generate high-fidelity squeezed superpositions of coherent states with large amplitudes, advancing quantum state engineering for quantum information applications.

Contribution

It introduces a method to produce SSCS with nearly perfect fidelity and large amplitudes using photon subtraction and addition, including analysis of experimental imperfections.

Findings

Photon subtraction yields SSCS with fidelity > 0.999 regardless of photon number.

Increasing the number of subtracted photons increases the SSCS amplitude.

Photon addition after subtraction produces SSCS with higher amplitude but slightly lower fidelity.

Abstract

We study how photon addition and subtraction can be used to generate squeezed superpositions of coherent states in free-traveling fields (SSCSs) with high fidelities and large amplitudes. It is shown that an arbitrary $N$-photon subtraction results in the generation of a SSCS with nearly the perfect fidelity ($F>0.999$) regardless of the number of photons subtracted. In this case, the amplitude of the SSCS increases as the number of the subtracted photons gets larger. For example, two-photon subtraction from a squeezed vacuum state of 6.1dB can generate a SSCS of $\alpha=1.26$, while in the case of the four-photon subtraction a SSCS of a larger amplitude $\alpha=1.65$ is obtained under the same condition. When a photon is subtracted from a squeezed vacuum state and another photon is added subsequently, a SSCS with a lower fidelity ($F\approx 0.96$) yet higher amplitude ($\alpha\approx2$) can be generated. We analyze some experimental imperfections including inefficiency of the detector used for the photon subtraction.