  Recent results in relativistic quantum information and quantum thermodynamics
have independently shown that in the quantum regime, a system may fail to
thermalise when subject to quantum-controlled application of the same, single
thermalisation channel. For example, an accelerating system with fixed proper
acceleration is known to thermalise to an acceleration-dependent temperature,
known as the Unruh temperature. However, the same system in a superposition of
spatially translated trajectories that share the same proper acceleration fails
to thermalise. Here, we provide an explanation of these results using the
framework of quantum field theory in relativistic noninertial reference frames.
We show how a probe that accelerates in a superposition of spatial translations
interacts with incommensurate sets of field modes. In special cases where the
modes are orthogonal (for example, when the Rindler wedges are translated in a
direction orthogonal to the plane of motion), thermalisation does indeed
result, corroborating the here provided explanation. We then discuss how this
description relates to an information-theoretic approach aimed at studying
quantum aspects of temperature through quantum-controlled thermalisations. The
present work draws a connection between research in quantum information,
relativistic physics, and quantum thermodynamics, in particular showing that
relativistic quantum effects can provide a natural realisation of quantum
thermodynamical scenarios.
