Quantum Optics Group
Norman Bridge Laboratory of Physics
California Institute of Technology
In recent years there has been tremendous progress in the ability to generate experimentally states of the electromagnetic field with manifestly quantum or nonclassical characteristics. Squeezed states of light are nonclassical states for
which the fluctuations in one of two quadrature phase amplitudes of the electromagnetic field drop below the level of fluctuations associated with the vacuum state of the field. Squeezed states therefore provide a field which is in some sense quieter than the vacuum state and hence can be employed to improve measurement precision beyond the standard quantum limits.
Research at Caltech explores new avenues for generating squeezed and other nonclassical states of light and for applying these fields to problems in quantum measurement. One example is an experimental realization of the Einstein-Podolsky-Rosen paradox for a system of continuous variables. Other experiments have included investigations of the quantum limits to amplification and of quantum nondemolition detection. Generally this work relies on the techniques of nonlinear optics (e.g., parametric down conversion for which one parent photon is annihilated
and two daughter photons created) to provide the requisite couplings between modes of the field.
For certain quadrature-phase angles, squeezed vacuum (green) is
quieter than ordinary vacuum (red). For the trace shown, the 6dB of
squeezing is "four times as dark as ordinary darkness"
Cavity QED with squeezed vacuum
The excitation of an atom by squeezed or other nonclassical radiation
should give rise to fundamentally new radiative processes. For example,
since radiative decay widths and level shifts of atoms are associated with
the statistical properties of the vacuum ("vacuum fluctuations"), then an
atom in a squeezed vacuum should not have a single relaxation rate, but
rather two rates associated with the enhanced and diminished fluctuations
of a squeezed state relative to the vacuum state. In an experiment
conducted by our group, this phase
sensitivity due to the squeezed vacuum was in fact observed. Squeezed
vacuum
states, created with an optical parametric oscillator, were coupled to the
atom with high efficiency. This efficient atom-vacuum coupling, essential
to the experiment, was achieved through the techniques of cavity QED: by
coupling the atom strongly to the fundamental mode of a high-finesse
optical cavity, a "one-dimensional atom" was created.
Spectroscopy with non-classical light
In addition to the cavity QED squeezed vacuum experiment, recent work in
spectroscopy with squeezed light includes the study of two-photon
excitation with squeezed light, and demonstration of saturation
spectroscopy with squeezed light.
The squeezing lab. Blue illumination is from 426nm laser light,
which is then down-converted to give squeezing at 852nm.
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