Vacuum source-field correlations and advanced waves in quantum optics

TL;DR

This paper reveals that quantum correlations between source and vacuum fields include advanced wave contributions, which, despite not affecting detection amplitudes, influence measurement statistics and could be experimentally observed.

Contribution

It demonstrates the existence of advanced wave-like correlations in quantum optics and their impact on measurement statistics, providing potential experimental evidence for advanced waves.

Findings

Quantum correlations include advanced wave contributions.

Advanced waves influence the dispersion of a charge's momentum.

Potential for experimental detection of advanced waves in quantum vacuum.

Abstract

The solution to the wave equation as a Cauchy problem with prescribed fields at an initial time t=0 is purely retarded. Similarly, in the quantum theory of radiation the specification of Heisenberg picture photon annihilation and creation operators at time t>0 in terms of operators at t=0 automatically yields purely retarded source-fields. However, we show that two-time quantum correlations between the retarded source-fields of a stationary dipole and the quantum vacuum-field possess advanced wave-like contributions. Despite their advanced nature, these correlations are perfectly consistent with Einstein causality. It is shown that while they do not significantly contribute to photo-detection amplitudes in the vacuum state, they do effect the statistics of measurements involving the radiative force experienced by a point charge in the field of the dipole. Specifically, the dispersion in the charge's momentum is found to increase with time. This entails the possibility of obtaining direct experimental evidence for the existence of advanced waves in physical reality, and provides yet another signature of the quantum nature of the vacuum.