One-step implementation of a multi-target-qubit controlled phase gate with cat-state qubits in circuit QED

TL;DR

This paper proposes a simple, single-step method to implement a multi-target-qubit controlled phase gate using cat-state qubits in circuit QED, reducing decoherence and avoiding classical pulses or measurements.

Contribution

It introduces a novel, efficient single-step protocol for multi-target-qubit controlled phase gates with cat-state qubits, enhancing fidelity and simplicity in circuit QED systems.

Findings

High-fidelity gate feasible with current technology

Gate operation suppresses decoherence by keeping the qutrit in ground state

No classical pulses or measurements needed during the gate

Abstract

We propose a single-step implementation of a muti-target-qubit controlled phase gate with one cat-state qubit (\textit{cqubit}) simultaneously controlling $n-1$ target \textit{cqubits}. The two logic states of a \textit{cqubit} are represented by two orthogonal cat states of a single cavity mode. In this proposal, the gate is implemented with $n$ microwave cavities coupled to a superconducting transmon qutrit. Because the qutrit remains in the ground state during the gate operation, decoherence caused due to the qutrit's energy relaxation and dephasing is greatly suppressed. The gate implementation is quite simple because only a single-step operation is needed and neither classical pulse nor measurement is required. Numerical simulations demonstrate that high-fidelity realization of a controlled phase gate with one cqubit simultaneously controlling two target cqubits is feasible with present circuit QED technology. This proposal can be extended to a wide range of physical systems to realize the proposed gate, such as multiple microwave or optical cavities coupled to a natural or artificial three-level atom.