Circuit QED: single-step realization of a multiqubit controlled phase gate with one microwave photonic qubit simultaneously controlling $n-1$ microwave photonic qubits

TL;DR

This paper proposes a simple, single-step method to implement a multiqubit controlled phase gate in circuit QED, where one microwave photonic qubit controls multiple target qubits, with high fidelity and minimal decoherence.

Contribution

It introduces a novel, efficient protocol for realizing multiqubit controlled phase gates using a superconducting flux qutrit coupled to multiple cavities, without classical pulses or measurements.

Findings

High-fidelity gate implementation feasible with current technology

Gate operation time is independent of the number of qubits

No classical pulses or measurements needed during operation

Abstract

We present a novel method to realize a multi-target-qubit controlled phase gate with one microwave photonic qubit simultaneously controlling $n-1$ target microwave photonic qubits. This gate is implemented with $n$ microwave cavities coupled to a superconducting flux qutrit. Each cavity hosts a microwave photonic qubit, whose two logic states are represented by the vacuum state and the single photon state of a single cavity mode, respectively. During the gate operation, the qutrit remains in the ground state and thus decoherence from the qutrit is greatly suppressed. This proposal requires only a single-step operation and thus the gate implementation is quite simple. The gate operation time is independent of the number of the qubits. In addition, this proposal does not need applying classical pulse or any measurement. Numerical simulations demonstrate that high-fidelity realization of a controlled phase gate with one microwave photonic qubit simultaneously controlling two target microwave photonic qubits is feasible with current circuit QED technology. The proposal is quite general and can be applied to implement the proposed gate in a wide range of physical systems, such as multiple microwave or optical cavities coupled to a natural or artificial $\Lambda$-type three-level atom.