Coupling qubits in circuit-QED cavities connected by a bridge qubit

TL;DR

This paper proposes a tunable qubit coupling scheme in circuit-QED using a bridge qubit, enabling scalable quantum circuits with adjustable interaction strength and potential for generating entangled states.

Contribution

It introduces a novel active coupling method with a bridge qubit, allowing on/off switching and strength tuning, advancing scalable quantum computing architectures.

Findings

Exact two-qubit coupling expression derived

System can produce W states as eigenstates

Decay rates suggest experimental viability

Abstract

We analyze a coupling scheme for qubits in different cavities of circuit-QED architecture. In contrast to the usual scheme where the cavities are coupled by an interface capacitance we employ a bridge qubit connecting cavities to mediate two-qubit coupling. This active coupling scheme makes it possible to switch on/off and adjust the strength of qubit-qubit coupling, which is essential for scalability of quantum circuit. By transforming the Hamiltonian we obtain an exact expression of two-qubit coupling in the rotating-wave approximation. For the general case of $n$ qubits the Hamiltonian can produce the W state as an eigenstate of the system. We calculate the decay rate of the coupled qubit-resonator system to find that it is viable in real experiments.