Thermality, causality, and the quantum-controlled Unruh–deWitt detector

Magdalena Zych,Joshua Foo,Robert B Mann,Sho Onoe

doi:10.1103/physrevresearch.3.043056

Abstract

Particle detector models such as the Unruh-deWitt detector are widely used in relativistic quantum information and field theory to probe the global features of spacetime and quantum fields. These detectors are typically modelled as coupling locally to the field along a classical worldline. In this paper, we utilize a recent framework which enables us to prepare the detector in a quantum-controlled superposition of trajectories, and study its response to the field in finite-temperature Minkowski spacetime and an expanding de Sitter universe. Unlike a detector on a classical path which cannot distinguish these spacetimes, the superposed detector can do so by acquiring nonlocal information about the geometric and causal structure of its environment, demonstrating its capability as a probe of these global properties.

Highlights

In quantum field theory (QFT), the physical nature of phenomena such as particle production and long-range correlations is grounded in an ability to couple local probes to the field, which can subsequently perform measurements of it
Due to the different spacetime geometries under consideration as well as the thermalization processes investigated in this paper, our results show that the quantum-controlled UdW detector model represents an accessible approach for probing the geometric and causal features of spacetime and connects the research in curved spacetime QFT with quantum information [32], quantum control of quantum channels [33,34], and quantum thermodynamics [35,36]
We have shown that by introducing a quantum-controlled superposition of trajectories, a UdW detector gains information about the field and the global structure of spacetime through nonlocal correlation functions that would be otherwise inaccessible to a single detector

Summary

INTRODUCTION

In quantum field theory (QFT), the physical nature of phenomena such as particle production and long-range correlations is grounded in an ability to couple local probes to the field, which can subsequently perform measurements of it. Phenomena exemplifying this include the Unruh and Gibbons-Hawking effects The former predicts that a uniformly accelerated detector in Minkowski spacetime perceives the vacuum state to be thermal at the Unruh temperature: TU. FOO, ONOE, MANN, AND ZYCH of them would yield the same thermal state of the detector, their superposition is sensitive to nonlocal field correlations between the trajectories, which notably depend on the causal relations between them. These correlations can perturb the final detector state away from thermalization. We apply the superposed detector model to the above scenarios: a thermal field state in Minkowski spacetime and the conformally coupled vacuum state in an expanding de Sitter spacetime.

DETECTORS IN SUPERPOSITION

Gaussian switching

Compact switching

DETECTOR TRANSITION RATES

CONCLUSION