Quantum state truncation using an optical parametric amplifier and a beamsplitter

TL;DR

This paper proposes a quantum state truncation scheme using an optical parametric amplifier and beamsplitter that relies on Gaussian states, enabling generation of nonclassical states with practical components and analyzing their properties and efficiencies.

Contribution

It introduces a novel quantum scissors method combining a nondegenerate optical parametric amplifier with a beamsplitter, requiring only Gaussian states, unlike previous linear-optics-based schemes.

Findings

Generated states exhibit sub-Poissonian statistics and squeezing.

The protocol's efficiency depends on detector quantum efficiency and dark counts.

Different photodetector configurations produce various truncated states.

Abstract

We present a scheme of quantum state truncation in the Fock basis (quantum scissors), based on the combined action of a nondegenerate optical parametric amplifier and a beamsplitter. Differently from previously proposed linear-optics-based quantum scissors devices, which depend on reliable Fock states sources, our scheme requires only readily available Gaussian states, such as coherent states inputs (vacuum state included). A truncated state is generated after performing photodetections in the global state. We find that, depending on which output ports each of the two photodetectors is positioned, different types of truncated states may be produced: i) states having a maximum Fock number of $N$, or ii) states having a minimum Fock number $N$. In order to illustrate our method, we discuss an example having as input states a coherent state in the beamsplitter and vacuum states in the amplifier, and show that the resulting truncated states display nonclassical properties, such as sub-Poissonian statistics and squeezing. We quantify the nonclassicality degree of the generated states using the Wigner-Yanase skew information measure. For complementarity, we discuss the efficiency of the protocol, e.g., generation probability as well as the effects of imperfections such as the detector's quantum efficiency and dark counts rate.