Implementation of traveling odd Schr$\"o$dinger cat states in circuit-QED

TL;DR

This paper presents a practical method to generate traveling odd Schrödinger cat states and entangled coherent states in circuit-QED using squeezed vacuum states, photon subtraction, and heralded detection, advancing microwave quantum information processing.

Contribution

It introduces a feasible scheme combining Josephson amplifiers, beam-splitters, and photon detectors to produce high-fidelity traveling cat states in circuit-QED.

Findings

High fidelity of generated cat states with optimized squeezing parameters

Probabilistic creation of entangled coherent states for quantum information

Potential applications in error-correctable microwave qudits

Abstract

We propose a realistic scheme of generating a traveling odd Schr$\"o$dinger cat state and a generalized entangled coherent state in circuit quantum electrodynamics (circuit-QED). A squeezed vacuum state is used as initial resource of nonclassical states, which can be created through a Josephson traveling-wave parametric amplifier, and travels through a transmission line. Because a single-photon subtraction from the squeezed vacuum gives with very high fidelity an odd Schr$\"o$dinger cat state, we consider a specific circuit-QED setup consisting of the Josephson amplifier creating the traveling resource in a line, a beam-splitter coupling two transmission lines, and a single photon detector located at the end of the other line. When a single microwave photon is detected by measuring the excited state of a superconducting qubit in the detector, a heralded cat state is generated with high fidelity in the opposite line. For example, we show that the high fidelity of the outcome with the ideal cat state can be achieved with appropriate squeezing parameters theoretically. As its extended setup, we suggest that generalized entangled coherent states can be also built probabilistically and useful for microwave quantum information processing for error-correctable qudits in circuit-QED.