Nanosecond quantum state detection in a current biased dc SQUID

Abstract

This article presents our procedure to measure the quantum state of a dc SQUID within a few nanoseconds, using an adiabatic dc flux pulse. Detection of the ground state is governed by standard macroscopic quantum theory (MQT), with a small correction due to residual noise in the bias current. In the two level limit, where the SQUID constitutes a phase qubit, an observed contrast of 0.54 indicates a significant loss in contrast compared to the MQT prediction. It is attributed to spurious depolarization (loss of excited state occupancy) during the leading edge of the adiabatic flux measurement pulse. We give a simple phenomenological relaxation model which is able to predict the observed contrast of multilevel Rabi oscillations for various microwave amplitudes.

10 pages, 8 figures

References in corpus (3)

• Approaching Unit Visibility for Control of a Superconducting Qubit with Dispersive Readout
• State tomography of capacitively shunted phase qubits with high fidelity
• Decoherence processes in a current biased dc SQUID

Cited by in corpus (4)

• Strong tunable coupling between a superconducting charge and phase qubit
• Rabi-like oscillations of an anharmonic oscillator: classical versus quantum interpretation
• Quantum dynamics in a camel-back potential of a dc SQUID
• Measuring the distribution of current fluctuations through a Josephson junction with very short current pulses