Observation of time quasicrystal and its transition to superfluid time crystal

TL;DR

This paper reports the experimental creation of a quantum time quasicrystal in superfluid helium-3, demonstrating spontaneous symmetry breaking and a transition to a time crystal with long-lived coherent precession.

Contribution

It provides the first experimental realization of a quantum time quasicrystal and its transition to a time crystal, highlighting magnon Bose-Einstein condensation and spin superfluidity.

Findings

Observation of incommensurate coherent spin precession under periodic drive.

Transition from a time quasicrystal to a long-lived time crystal after drive is turned off.

Manifestation of spin superfluidity in the magnon condensate.

Abstract

We report experimental realization of a quantum time quasicrystal, and its transformation to a quantum time crystal. We study Bose-Einstein condensation of magnons, associated with coherent spin precession, created in a flexible trap in superfluid $^3$He-B. Under a periodic drive with an oscillating magnetic field, the coherent spin precession is stabilized at a frequency smaller than that of the drive, demonstrating spontaneous breaking of discrete time translation symmetry. The induced precession frequency is incommensurate with the drive, and hence the obtained state is a time quasicrystal. When the drive is turned off, the self-sustained coherent precession lives a macroscopically-long time, now representing a time crystal with broken symmetry with respect to continuous time translations. Additionally, the magnon condensate manifests spin superfluidity, justifying calling the obtained state a time supersolid or a time super-crystal.