Coherent Quantum Dynamics of a Superconducting Flux Qubit

TLDR

The superposition of the two states carrying opposite macroscopic persistent currents is manipulated by resonant microwave pulses. Coherent oscillations between the two persistent‑current states of a three‑junction flux qubit were observed with high fidelity, yielding hundreds of oscillations under strong driving, a 900‑ns relaxation time, a 20‑ns dephasing time, and promising prospects for solid‑state quantum computing.

Abstract

We have observed coherent time evolution between two quantum states of a superconducting flux qubit comprising three Josephson junctions in a loop. The superposition of the two states carrying opposite macroscopic persistent currents is manipulated by resonant microwave pulses. Readout by means of switching-event measurement with an attached superconducting quantum interference device revealed quantum-state oscillations with high fidelity. Under strong microwave driving, it was possible to induce hundreds of coherent oscillations. Pulsed operations on this first sample yielded a relaxation time of 900 nanoseconds and a free-induction dephasing time of 20 nanoseconds. These results are promising for future solid-state quantum computing.