Quantum backaction of optical observations on Bose-Einstein condensates
Physics Department, Royal Institute of Technology (KTH), Lindstedtsvägen 24, 10044
2 Department of Nonlinear and Quantum Optics, Institute for Solid State Physics and Optics, P.O. Box 49, 1525 Budapest, Hungary
3 Abteilung für Quantenphysik, Universität Ulm, 89069 Ulm, Germany
Published online: 15 October 1999
Impressive pictures of moving Bose-Einstein condensates have been taken using phase-contrast imaging [ M.R. Andrews et al., Science 273, 84 (1996)] . We calculate the quantum backaction of this measurement technique, assuming the absence of residual absorption. We find that the condensate gets gradually depleted at a universal rate that is proportional to the light intensity and to the inverse cube of the optical wave length. The fewer atoms are condensed the higher is the required intensity to see a picture, and, consequently, the higher is the induced backaction. To describe the quantum physics of phase-contrast imaging we put forward a new approach to quantum-optical propagation. We develop an effective field theory of paraxial optics in a fully quantized atomic medium.
PACS: 03.75.Fi – Phase coherent atomic ensembles; quantum condensation phenomena / 03.65.Bz – Foundations, theory of measurement, miscellaneous theories (including Aharonov-Bohm effect, Bell inequalities, Berry's phase) / 42.50.Dv – Nonclassical field states; squeezed, antibunched, and sub-Poissonian states; operational definitions of the phase of the field; phase measurements
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999