Quantum feedback control of a superconducting qubit: Persistent Rabi oscillations

TL;DR

This paper demonstrates continuous quantum feedback control of a superconducting qubit, stabilizing Rabi oscillations indefinitely by actively using measurement records to counteract decoherence.

Contribution

It introduces a method to use high-fidelity measurements for real-time feedback to sustain quantum coherence in superconducting qubits.

Findings

Persistent Rabi oscillations achieved through feedback control.

High-fidelity measurement enables continuous state tracking.

Potential for continuous quantum error correction.

Abstract

The act of measurement bridges the quantum and classical worlds by projecting a superposition of possible states into a single, albeit probabilistic, outcome. The time-scale of this "instantaneous" process can be stretched using weak measurements so that it takes the form of a gradual random walk towards a final state. Remarkably, the interim measurement record is sufficient to continuously track and steer the quantum state using feedback. We monitor the dynamics of a resonantly driven quantum two-level system -- a superconducting quantum bit --using a near-noiseless parametric amplifier. The high-fidelity measurement output is used to actively stabilize the phase of Rabi oscillations, enabling them to persist indefinitely. This new functionality shows promise for fighting decoherence and defines a path for continuous quantum error correction.