Engineering Schr\"odinger cat states with a photonic even-parity detector

TL;DR

This paper proposes a method to engineer Schr"odinger cat states using even-parity photon detection, enabling the creation of large, high-fidelity quantum superpositions with potential applications in quantum information processing.

Contribution

The authors introduce a novel scheme utilizing even-parity detection to generate and scale Schr"odinger cat states with high fidelity, advancing quantum state engineering techniques.

Findings

Successfully prepared superpositions of coherent states with opposite amplitudes.

Achieved near-perfect fidelity in generating cat states of arbitrary size.

Demonstrated iterative application for creating complex multi-component cat states.

Abstract

When two equal photon-number states are combined on a balanced beam splitter, both output ports of the beam splitter contain only even numbers of photons. Consider the time-reversal of this interference phenomenon: the probability that a pair of photon-number-resolving detectors at the output ports of a beam splitter both detect the same number of photons depends on the overlap between the input state of the beam splitter and a state containing only even photon numbers. Here, we propose using this even-parity detection to engineer quantum states containing only even photon-number terms. As an example, we demonstrate the ability to prepare superpositions of two coherent states with opposite amplitudes, i.e. two-component Schr\"odinger cat states. Our scheme can prepare cat states of arbitrary size with nearly perfect fidelity. Moreover, we investigate engineering more complex even-parity states such as four-component cat states by iteratively applying our even-parity detector.