Native Conditional $i$SWAP Operation with Superconducting Artificial Atoms

TL;DR

This paper demonstrates a superconducting quantum transistor capable of implementing a native conditional iSWAP operation with high fidelity, advancing quantum information routing and processing.

Contribution

It introduces the smallest quantum transistor with a superconducting processor that performs native conditional iSWAP operations controlled by a coupler, considering higher energy levels for fidelity.

Findings

Achieved 92.36% fidelity for the iSWAP operation

Achieved 95.23% fidelity for the identity operation

Demonstrated effective quantum switching with a superconducting qubit architecture

Abstract

Controlling the flow of quantum information is a fundamental task for quantum computers, which is unfeasible to realize on classical devices. Coherent devices which can process quantum states are thus required to route the quantum states that encode information. In this paper we demonstrate experimentally the smallest quantum transistor with a superconducting quantum processor which is composed of a collector qubit, an emitter qubit, and a coupler (transistor gate). The interaction strength between the collector and emitter qubits is controlled by the frequency and state of the coupler, effectively implementing a quantum switch. Through the coupler-state-dependent Heisenberg (inherent) interaction between the qubits, a single-step (native) conditional $i$SWAP operation can be applied. To this end, we find that it is important to take into consideration higher energy level for achieving a native and high-fidelity transistor operation. By reconstructing the Quantum Process Tomography, we obtain an operation fidelity of $92.36\%$ when the transistor gate is open ($i$SWAP implementation) and $95.23 \%$ in the case of closed gate (identity gate implementation). The architecture has strong potential in quantum information processing applications with superconducting qubits.