Motional Averaging in a Superconducting Qubit

TL;DR

This paper demonstrates motional averaging in a superconducting transmon qubit by modulating its flux bias with pseudo-random noise, revealing quantum coherence and spectral line merging, advancing quantum simulation capabilities.

Contribution

It introduces the first experimental realization of motional averaging in a superconducting qubit using controlled flux modulation, linking condensed matter phenomena with quantum circuits.

Findings

Spectral lines merge into a narrow motional-averaged line at high modulation speeds.

Quantum coherence is maintained during flux modulation, with altered transition frequencies.

Complex sideband patterns emerge under sinusoidal modulation.

Abstract

Superconducting circuits with Josephson junctions are promising candidates for developing future quantum technologies. Of particular interest is to use these circuits to study effects that typically occur in complex condensed-matter systems. Here, we employ a superconducting quantum bit (qubit),a transmon, to carry out an analog simulation of motional averaging, a phenomenon initially observed in nuclear magnetic resonance (NMR) spectroscopy. To realize this effect, the flux bias of the transmon is modulated by a controllable pseudo-random telegraph noise, resulting in stochastic jumping of the energy separation between two discrete values. When the jumping is faster than a dynamical threshold set by the frequency displacement of the levels, the two separated spectral lines merge into a single narrow-width, motional-averaged line. With sinusoidal modulation a complex pattern of additional sidebands is observed. We demonstrate experimentally that the modulated system remains quantum coherent, with modified transition frequencies, Rabi couplings, and dephasing rates. These results represent the first steps towards more advanced quantum simulations using artificial atoms.