Measuring the amplitude and the absolute phase of a monochromatic microwave field at a specific point of space and time has many potential applications, including precise qubit rotations and wavelength quantum teleportation. Here we show how such a measurement can indeed be made using resonant atomic probes, via detection of incoherent fluorescence induced by a laser beam. This measurement is possible due to self-interference effects between the positive and negative frequency components of the field. In effect, the small cluster of atoms here act as a highly localized pick-up coil, and the fluorescence channel acts as a transmission line.
@article{arxiv.quant-ph/0410219,
title = {In-Situ absolute phase detection of a microwave field via incoherent fluorescence},
author = {George C. Cardoso and Prabhakar Pradhan and Jacob Morzinski and M. S. Shahriar},
journal= {arXiv preprint arXiv:quant-ph/0410219},
year = {2007}
}