2,773 research outputs found
Quantum back-action of optical observations on Bose condensates
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. We find that
phase-contrast imaging is not a quantum nondemolition measurement of the atomic
density. Instead, the condensate gets gradually depleted at a 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.Comment: 11 pages RevTex, 2 ps figures, revised. European Physical Journal D
(in press
Reply to the ``Comment on `quantum backaction of optical observations on Bose-Einstein condensates' ''
In our paper we estimated the quantum backaction of dispersive imaging with
off-resonant light on Bose-Einstein condensates. We have calculated the rates
of the two processes involved, phase diffusion and depletion of the condensate.
We compare here the depletion rate obtained within our model limitations to the
Rayleigh scattering rate, both having the same physical origin: dispersive
interaction of light with matter. We show that residual absorption sets indeed
the limit of dispersive imaging.Comment: 1 page (Reply to comment
Theory of elementary excitations in unstable Bose-Einstein condensates
Like classical fluids, quantum gases may suffer from hydrodynamic instabilities. Our paper develops a quantum version of the classical stability analysis in fluids, the Bogoliubov theory of elementary excitations in unstable Bose-Einstein condensates. In unstable condensates the excitation modes have complex frequencies. We derive the normalization conditions for unstable modes such that they can serve in a mode decomposition of the noncondensed component. Furthermore, we develop approximative techniques to determine the spectrum and the mode functions. Finally, we apply our theory to sonic horizons - sonic black and white holes. For sonic white holes the spectrum of unstable modes turns out to be intrinsically discrete, whereas black holes may be stable
Partial Transmutation of Singularities in Optical Instruments
Some interesting optical instruments such as the Eaton lens and the Invisible
Sphere require singularities of the refractive index for their implementation.
We show how to transmute those singularities into harmless topological defects
in anisotropic media without the need for anomalous material properties
Quantum levitation by left-handed metamaterials
Left-handed metamaterials make perfect lenses that image classical
electromagnetic fields with significantly higher resolution than the
diffraction limit. Here we consider the quantum physics of such devices. We
show that the Casimir force of two conducting plates may turn from attraction
to repulsion if a perfect lens is sandwiched between them. For optical
left-handed metamaterials this repulsive force of the quantum vacuum may
levitate ultra-thin mirrors
Fermat's principle of least time in the presence of uniformly moving boundaries and media
The refraction of a light ray by a homogeneous, isotropic and non-dispersive
transparent material half-space in uniform rectilinear motion is investigated
theoretically. The approach is an amalgamation of the original Fermat's
principle and the fact that an isotropic optical medium at rest becomes
optically anisotropic in a frame where the medium is moving at a constant
velocity. Two cases of motion are considered: a) the material half-space is
moving parallel to the interface; b) the material half-space is moving
perpendicular to the interface. In each case, a detailed analysis of the
obtained refraction formula is provided, and in the latter case, an intriguing
backward refraction of light is noticed and thoroughly discussed. The results
confirm the validity of Fermat's principle when the optical media and the
boundaries between them are moving at relativistic speeds.Comment: 11 pages, 6 figures, RevTeX 4, comments welcome; V2: revised, Fig. 7
added; V3: several typos corrected, accepted for publication in European
Journal of Physics (online at: http://stacks.iop.org/EJP/28/933
Ultrahigh sensitivity of slow-light gyroscope
Slow light generated by Electromagnetically Induced Transparency is extremely
susceptible with respect to Doppler detuning. Consequently, slow-light
gyroscopes should have ultrahigh sensitivity
Operational Theory of Homodyne Detection
We discuss a balanced homodyne detection scheme with imperfect detectors in
the framework of the operational approach to quantum measurement. We show that
a realistic homodyne measurement is described by a family of operational
observables that depends on the experimental setup, rather than a single field
quadrature operator. We find an explicit form of this family, which fully
characterizes the experimental device and is independent of a specific state of
the measured system. We also derive operational homodyne observables for the
setup with a random phase, which has been recently applied in an ultrafast
measurement of the photon statistics of a pulsed diode laser. The operational
formulation directly gives the relation between the detected noise and the
intrinsic quantum fluctuations of the measured field. We demonstrate this on
two examples: the operational uncertainty relation for the field quadratures,
and the homodyne detection of suppressed fluctuations in photon statistics.Comment: 7 pages, REVTe
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