Speaker
Description
The extremely pure liquid helium-3 at millikelvin temperatures, with its cosmological analogues, is an ideal test bed to study the early-Universe phase transitions in laboratory. In helium-3 both the first and second order phase transitions are accessible, with the mechanism of the phase transition between its topological superfluid A and B phases having been a fundamental problem in the condensed matter physics, evading explanation despite decades of both experimental and theoretical work. Whereas the models for an intrinsic first-order phase-transition - homogeneous nucleation via thermal fluctuations or quantum tunnelling - predict a timescale for such a phase transition to take place far longer than the age of the Universe under relevant experimental conditions, in laboratory they are routinely observed to take place within seconds to hours, often facilitated by the sample container construction. Here we show that confining helium-3 inside five nanofabricated well-isolated atomically smooth phase-transition chambers protects against any obvious spurious sources of phase nucleation. Only remaining external trigger is ionising radiation, effect of which is also suppressed by the tiny volumes of the chambers. We extensively study this over a wide temperature and pressure range and discover a rich non-monotonic dependence of the lifetime of the supercooled metastable A phase on both temperature and pressure. Our SQUID-amplified nuclear magnetic resonance experiments are supported by high-performance computer simulations to understand the nonequilibrium superfluid dynamics, revealing the vital role played by the Kibble-Zurek mechanism. In the future, this strengthened understanding of the radiation-triggered phase transitions will give the elusive intrinsic mechanisms a chance to become detectable.