Boiling Quantum Vacuum: Thermal Subsystems from Ground-State Entanglement

TL;DR

This paper demonstrates that vacuum entanglement in certain quantum systems can produce thermal states in lower-dimensional subsystems, with potential experimental observation in cold atom simulators.

Contribution

It identifies a class of accessible quantum systems where vacuum entanglement leads to thermal density matrices in subsystems, linking quantum field theory and quantum simulation.

Findings

Reduced density matrices of subsystems have a thermal form.

Vacuum entanglement can make a gapped system appear as a hot gapless system.

Proposes experiments in cold atom quantum simulators.

Abstract

In certain special circumstances, such as in the vicinity of a black hole or in a uniformly accelerating frame, vacuum fluctuations appear to give rise to a finite-temperature environment. This effect, currently without experimental confirmation, can be interpreted as a manifestation of quantum entanglement after tracing out vacuum modes in an unobserved region. In this work, we identify a class of experimentally accessible quantum systems where thermal density matrices emerge from vacuum entanglement. We show that reduced density matrices of lower-dimensional subsystems embedded in $D$-dimensional gapped Dirac fermion vacuum, either on a lattice or continuum, have a thermal form with respect to a lower-dimensional Dirac Hamiltonian. Strikingly, we show that vacuum entanglement can even conspire to make a subsystem of a gapped system at zero temperature appear as a hot gapless system. We propose concrete experiments in cold atom quantum simulators to observe the vacuum entanglement induced thermal states.