319,562 research outputs found
Macroscopic tunneling of a membrane in an optomechanical double-well potential
The macroscopic tunneling of an optomechanical membrane is considered. A
cavity mode which couples quadratically to the membranes position can create
highly tunable adiabatic double-well potentials, which together with the high
Q-factors of such membranes render the observation of macroscopic tunneling
possible. A suitable, pulsed measurement scheme using a linearly coupled mode
of the cavity for the verification of the effect is studied.Comment: 5 pages, 5 figure
Rydberg state mediated quantum gates and entanglement of pairs of neutral atoms
Experiments performed within the last year have demonstrated Rydberg state
mediated quantum gates and deterministic entanglement between pairs of trapped
neutral atoms. These experiments validate ten year old proposals for Rydberg
mediated quantum logic, but are only the beginning of ongoing efforts to
improve the fidelity of the results obtained and scale the experiments to
larger numbers of qubits. We present here a summary of the results to date,
along with a critical evaluation of the prospects for higher fidelity Rydberg
gates.Comment: submitted to ICAP 2010 proceeding
Multiwavelength Observations of the BL Lacertae Object PKS 2155-304 with XMM-Newton
The optical-UV and X-ray instruments on-board XMM-Ndewton provide an
excellent opportunity to perform simultaneous observations of violently
variable objects over a broad wavelength range. The UV and X-ray bright BL Lac
object PKS 2155-304 has been repeatedly observed with XMM-Ndewton about twice
per year. In this paper, we present a detailed analysis of the simultaneous
multiwavelength variability of the source from optical to X-rays, based on the
currently available XMM-Ndewton observations. These observations probed the
intra-day multiwavelength variability at optical-UV and X-ray wavelengths of
the source. The UV variability amplitude is substantially smaller than the
X-ray one, and the hardness ratios of the UV to X-rays correlates with the
X-ray fluxes: the brighter the source, the flatter the UV-X-ray spectra. On
2000 May 30-31 the UV and X-ray light curves were weakly correlated, while the
UV variations followed the X-ray ones with no detectable lags on 2000 November
19-21. On 2001 November 30 the source exhibited a major X-ray flare that was
not detected in the optical. The intra-day UV and X-ray variability presented
here is not similar to the inter-day UV and X-ray variability obtained from the
previous coordinated extensive multiwavelength campaigns on the source,
indicating that different ``modes'' of variability might be operating in PKS
2155-304 on different timescales or from epoch to epoch.Comment: Accepted by Ap
Thermodynamic properties of a dipolar Fermi gas
Based on the semi-classical theory, we investigate the thermodynamic
properties of a dipolar Fermi gas. Through a self-consistent procedure, we
numerically obtain the phase space distribution function at finite temperature.
We show that the deformations in both momentum and real space becomes smaller
and smaller as one increases the temperature. For homogeneous case, we also
calculate pressure, entropy, and heat capacity. In particular, at low
temperature limit and in weak interaction regime, we obtain an analytic
expression for the entropy, which agrees qualitatively with our numerical
result. The stability of a trapped gas at finite temperature is also explored
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