What is new research on a phenomenon called "false vacuum collapse" and what does it shed light on?
Mean field energy and bubble formation. The cloud is initially prepared in FV with all atoms in |↑⟩ (A). Although the single spin mode |↓⟩ is lower in energy in the center of the cloud (E↓E↑), the opposite is true in the low-density tails. The interface (domain wall) between ferromagnetic regions with opposite magnetism has positive (kinetic) energy, which is added to the minimum double energy resulting from ferromagnetic interaction. Macroscopic tunneling can occur resonantly in the bubble mode (B), which has a |↓⟩ bubble in the center. The increase in core energy compensates for the cost of domain-wall energy. Crossing the barrier can be caused by quantum fluctuations at zero temperature (full arrow) or by thermal fluctuations at finite temperature (empty arrow). After the tunneling process, the bubble size increases in the presence of dissipation to reach the true vacuum (TV) state (C), without returning to (A). Credit: Nature Physics (2024). DOI: 10.1038/s41567-023-02345-4
An experiment carried out in Italy with theoretical support from the University of Newcastle provided the first experimental evidence of vacuum decay.
In quantum field theory, when a not-so-stable state becomes a true stable state, it is called a "pseudovacuum collapse." This happens through the creation of small local bubbles. While existing theoretical work can predict how often this bubble formation occurs, there is not much empirical evidence.
The Pitaevskii Center for Supercold Atoms Laboratory for the Bose-Einstein Condensation in Trento reports for the first time observations of phenomena related to the stability of our universe. The results are the result of a collaboration between the University of Newcastle, the National Institute of Optics CNR, the Department of Physics at the University of Trento and TIFFA-INFEN and are published in Nature Physics.
The results are supported by theoretical simulations and numerical models, confirming the origin of the quantum field decay and its thermal activation, and opening the way to simulate out-of-equilibrium quantum field phenomena in atomic systems.
This experiment uses a supercooled gas at a temperature less than one microkelvin from absolute zero. At this temperature, the bubbles appear as the vacuum collapses, and Newcastle University's Professor Ian Moss and Dr Tom Billam were able to conclusively show that the bubbles are the result of heat-activated vacuum collapse.
Ian Moss, Professor of Theoretical Cosmology at Newcastle University's School of Mathematics, Statistics and Physics, said: "Vacuum collapse is thought to play a central role in the creation of space, time and matter in the Big Bang, but so far it has not. In particle physics, the decay of the Higgs boson vacuum changes the laws of physics and creates what has been described as the 'ultimate ecological catastrophe'."
Dr Tom Bilam, Senior Lecturer in Applied/Quantum Mathematics, added: "Using the power of ultracold atom experiments to simulate analogues of quantum physics in other systems – in this case the early universe itself – is a very exciting area of research. the moment."
This research opens new avenues in understanding the early universe as well as ferromagnetic quantum phase transitions.
This groundbreaking experiment is only the first step in the discovery of vacuum decay. The ultimate goal is to find vacuum decay at absolute zero temperature, where the process is driven solely by quantum vacuum fluctuations. An experiment in Cambridge, supported by Newcastle as part of the national QSimFP collaboration, is doing just that.
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