326 research outputs found
Near-Horizon Extremal Geometries: Coadjoint Orbits and Quantization
The NHEG algebra is an extension of Virasoro introduced in
[arXiv:1503.07861]; it describes the symplectic symmetries of
-dimensional Near Horizon Extremal Geometries with isometry. In this work we construct the NHEG group and classify the
(coadjoint) orbits of its action on phase space. As we show, the group consists
of maps from an -torus to the Virasoro group, so its orbits are bundles of
standard Virasoro coadjoint orbits over . We also describe the unitary
representations that are expected to follow from the quantization of these
orbits, and display their characters. Along the way we show that the NHEG
algebra can be built from u(1) currents using a twisted Sugawara construction.Comment: 22 pages, one figure. v2: Title expanded, various minor
clarifications added. Published in JHE
Mesoscopic atomic entanglement for precision measurements beyond the standard quantum limit
Squeezing of quantum fluctuations by means of entanglement is a well
recognized goal in the field of quantum information science and precision
measurements. In particular, squeezing the fluctuations via entanglement
between two-level atoms can improve the precision of sensing, clocks,
metrology, and spectroscopy. Here, we demonstrate 3.4 dB of metrologically
relevant squeezing and entanglement for ~ 10^5 cold cesium atoms via a quantum
nondemolition (QND) measurement on the atom clock levels. We show that there is
an optimal degree of decoherence induced by the quantum measurement which
maximizes the generated entanglement. A two-color QND scheme used in this paper
is shown to have a number of advantages for entanglement generation as compared
to a single color QND measurement.Comment: 6 pages+suppl, PNAS forma
Entanglement between more than two hundred macroscopic atomic ensembles in a solid
We create a multi-partite entangled state by storing a single photon in a
crystal that contains many large atomic ensembles with distinct resonance
frequencies. The photon is re-emitted at a well-defined time due to an
interference effect analogous to multi-slit diffraction. We derive a lower
bound for the number of entangled ensembles based on the contrast of the
interference and the single-photon character of the input, and we
experimentally demonstrate entanglement between over two hundred ensembles,
each containing a billion atoms. In addition, we illustrate the fact that each
individual ensemble contains further entanglement. Our results are the first
demonstration of entanglement between many macroscopic systems in a solid and
open the door to creating even more complex entangled states.Comment: 10 pages, 8 figures; see also parallel submission by Frowis et a
Squeezing of Atomic Quantum Projection Noise
We provide a framework for understanding recent experiments on squeezing of a
collective atomic pseudo-spin, induced by a homodyne measurement on
off-resonant probe light interrogating the atoms. The detection of light
decimates the atomic state distribution and we discuss the conditions under
which the resulting reduced quantum fluctuations are metrologically relevant.
In particular, we consider a dual probe scheme which benefits from a
cancelation of classical common mode noise sources such that quantum
fluctuations from light and atoms are the main contributions to the detected
signal.Comment: Submitted to Journal of Modern Optic
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