[ww520]

So is the idea of a "time crystal is supposed to have periodic structure at the lowest energy state" out of the window?

If an external periodic pulse is required to drive the crystal to change its structure periodically, the time aspect is coming from the external pulse. The crystal itself doesn't have an intrinsic structural periodicity. The periodicity comes from the external pulsing. Is it still qualified to be called a "time crystal"?

The 2X slower reversing rate does show it has a time magnifying aspect, which can be huge.

[jdrov]

See my response here, about the way in which the response frequency depends on both the nature of the drive and the nature of the internal interactions in the system:

https://news.ycombinator.com/item?id=16999031

The idea of a ground state time crystal was shown to be impossible, which led to the proposals for a non-equilibrium time crystal, connecting the idea (serendipitously) to the research that was already taking place in non-equilibrium systems by condensed matter physicists.

While we do think that each of the 4 existing experiments on discrete time crystals are showing the same effect, we're not yet sure how these observed "signatures of DTC order" will be eventually interpreted relative to the original idea of the time crystal (hence our conservatively named papers/descriptions). Sean's lab used subtleties of complex pulse systems to enable high-resolution MRI imaging in solids like bone (!), and we're pretty sure (not certain) that there's a connection between some of the effects related to those pulse sequences, and what we're now observing in these "DTC signatures"... that's what got us looking at these non-equilibrium ideas originally, and we're pursuing the possible connection.

[ww520]

Thanks for the detail explanation. Good work in expanding our knowledge of new material.