Quantum trajectories of superconducting qubits

TL;DR

This review covers recent experimental advances in tracking the real-time evolution of superconducting qubits during measurement, highlighting quantum trajectory reconstruction, state verification, and applications in quantum error correction.

Contribution

It provides a comprehensive overview of experimental techniques for monitoring quantum trajectories in superconducting qubits, including novel methods for state reconstruction and analysis.

Findings

Successful reconstruction of individual quantum trajectories.

Verification of quantum state tracking via tomography.

Discussion of applications in measurement-based quantum error correction.

Abstract

In this review, we discuss recent experiments that investigate how the quantum sate of a superconducting qubit evolves during measurement. We provide a pedagogical overview of the measurement process, when the qubit is dispersively coupled to a microwave frequency cavity, and the qubit state is encoded in the phase of a microwave tone that probes the cavity. A continuous measurement record is used to reconstruct the individual quantum trajectories of the qubit state, and quantum state tomography is performed to verify that the state has been tracked accurately. Furthermore, we discuss ensembles of trajectories, time-symmetric evolution, two-qubit trajectories, and potential applications in measurement-based quantum error correction.