Method for direct observation of coherent quantum oscillations in a superconducting phase qubit

TL;DR

This paper introduces a novel method for directly observing Rabi oscillations in superconducting phase qubits by detecting supercurrent oscillations with a resonant tank circuit, enabling clearer quantum state monitoring.

Contribution

It proposes a new technique for direct measurement of quantum oscillations in superconducting qubits using resonant circuits, improving upon previous indirect methods.

Findings

Rabi oscillations can be detected with conventional RF circuitry.

The method is effective at both zero and non-zero temperatures.

Estimated dephasing and relaxation times support practical implementation.

Abstract

Time-domain observations of coherent oscillations between quantum states in mesoscopic superconducting systems were so far restricted to restoring the time-dependent probability distribution from the readout statistics. We propose a new method for direct observation of Rabi oscillations in a phase qubit. The external source, typically in GHz range, induces transitions between the qubit levels. The resulting Rabi oscillations of supercurrent in the qubit loop are detected by a high quality resonant tank circuit, inductively coupled to the phase qubit. Detailed calculation for zero and non-zero temperature are made for the case of persistent current qubit. According to the estimates for dephasing and relaxation times, the effect can be detected using conventional rf circuitry, with Rabi frequency in MHz range.