Quantum interference device for controlled two-qubit operations

TL;DR

This paper demonstrates a four-qubit quantum gate using superconducting qubits, exploiting quantum interference for controlled two-qubit operations, and discusses its potential for scalable quantum computing.

Contribution

It introduces a novel four-qubit gate architecture that enables multiple controlled two-qubit operations via quantum interference, advancing scalable quantum computing.

Findings

Implemented four different controlled two-qubit gates.

Utilized superconducting qubits in a diamond-shaped architecture.

Showed potential for connecting multiple devices in a lattice for scalable quantum computing.

Abstract

Universal quantum computing relies on high-fidelity entangling operations. Here we demonstrate that four coupled qubits can operate as a quantum gate, where two qubits control the operation on two target qubits (a four-qubit gate). This configuration can implement four different controlled two-qubit gates: two different entangling swap and phase operations, a phase operation distinguishing states of different parity, and the identity operation (idle quantum gate), where the choice of gate is set by the state of the control qubits. The device exploits quantum interference to control the operation on the target qubits by coupling them to each other via the control qubits. By connecting several four-qubit devices in a two-dimensional lattice, one can achieve a highly connected quantum computer. We consider an implementation of the four-qubit gate with superconducting qubits, using capacitively coupled qubits arranged in a diamond-shaped architecture.