2,315 research outputs found
Ultra-cold mechanical resonators coupled to atoms in an optical lattice
We propose an experiment utilizing an array of cooled micro-cantilevers
coupled to a sample of ultra-cold atoms trapped near a micro-fabricated
surface. The cantilevers allow individual lattice site addressing for atomic
state control and readout, and potentially may be useful in optical lattice
quantum computation schemes. Assuming resonators can be cooled to their
vibrational ground state, the implementation of a two-qubit controlled-NOT gate
with atomic internal states and the motional states of the resonator is
described. We also consider a protocol for entangling two or more cantilevers
on the atom chip with different resonance frequencies, using the trapped atoms
as an intermediary. Although similar experiments could be carried out with
magnetic microchip traps, the optical confinement scheme we consider may
exhibit reduced near-field magnetic noise and decoherence. Prospects for using
this novel system for tests of quantum mechanics at macroscopic scales or
quantum information processing are discussed.Comment: 5 pages, 3 figure
Generation of amplitude-squeezed light from a room-temperature Fabry-Perot semiconductor laser
Amplitude-squeezed light with intensity fluctuations 29% below the standard quantum limit (SQL) is produced from a pump-suppressed room-temperature semiconductor laser, corresponding to 41% below the SQL after correction for detection efficiency. Excess noise, which degrades the observed squeezing, appears to be associated with the presence of weak longitudinal side modes
Linewidth reduction and frequency stabilization of a semiconductor laser with a combination of FM sideband locking and optical feedback
We describe a novel method for semiconductor laser noise reduction that uses a combination of optical and electronic feedback. A Doppler-free Faraday resonance in Cs vapor provided both optical feedback and discrimination for an electronic feedback scheme incorporating FM sideband spectroscopy. The introduction of electronic feedback further reduced the low-frequency fluctuation noise power by more than 2 orders of magnitude, resulting in a linewidth of 1.4 kHz
3D Photometric Cosmic Shear
Here we present a number of improvements to weak lensing 3D power spectrum
analysis, 3D cosmic shear, that uses the shape and redshift information of
every galaxy to constrain cosmological parameters. We show how photometric
redshift probability distributions for individual galaxies can be directly
included in this statistic with no averaging. We also include the Limber
approximation, considerably simplifying full 3D cosmic shear analysis, and we
investigate its range of applicability. Finally we show the relationship
between weak lensing tomography and the 3D cosmic shear field itself; the steps
connecting them being the Limber approximation, a harmonic-space transform and
a discretisation in wavenumber. Each method has its advantages: 3D cosmic shear
analysis allows straightforward inclusion of all relevant modes, thus ensuring
minimum error bars, and direct control of the range of physical wavenumbers
probed, to avoid the uncertain highly nonlinear regime. On the other hand,
tomography is more convenient for checking systematics through direct
investigation of the redshift dependence of the signal. Finally, for
tomography, we suggest that the angular modes probed should be
redshift-dependent, to recover some of the 3D advantages.Comment: Accepted to MNRAS. 15 pages, 7 figure
3D Weak Gravitational Lensing of the CMB and Galaxies
In this paper we present a power spectrum formalism that combines the full
three-dimensional information from the galaxy ellipticity field, with
information from the cosmic microwave background (CMB). We include in this
approach galaxy cosmic shear and galaxy intrinsic alignments, CMB deflection,
CMB temperature and CMB polarisation data; including the inter-datum power
spectra between all quantities. We apply this to forecasting cosmological
parameter errors for CMB and imaging surveys for Euclid-like, Planck, ACTPoL,
and CoRE-like experiments. We show that the additional covariance between the
CMB and ellipticity measurements can improve dark energy equation of state
measurements by 15%, and the combination of cosmic shear and the CMB, from
Euclid-like and CoRE-like experiments, could in principle measure the sum of
neutrino masses with an error of 0.003 eV.Comment: Accepted to MNRA
Self-quenching of the semiconductor laser linewidth below the Schawlow-Townes limit by using optical feedback
We demonstrate theoretically and experimentally self-quenching of the fundamental semiconductor laser frequency fluctuations to a level that is orders of magnitude below the Schawlow-Townes limit for a solitary laser. It is shown that the main operative mechanism is the combined action of a frequency-dependent internal loss and amplitude-to-phase coupling. The internal frequency-dependent loss is introduced by means of spectrally narrow external optical feedback, which provides a strong frequency-dependent dispersion. Linewidth reduction by a factor of 2 X 10^3 is demonstrated by using a narrow Doppler-free Faraday resonance in Cs vapor
Amplitude noise reduction in semiconductor lasers with weak, dispersive optical feedback
We present the theory and measurements of the amplitude noise spectrum from a semiconductor laser with weak optical feedback (Pfb/Pout ~10^-6) from an external cavity containing an element of dispersive loss. The laser noise is found to be reduced over most of the low-frequency spectrum, although an increase in the noise is observed at frequencies corresponding to multiples of the external-cavity free spectral range. The low-frequency noise reduction closely follows theoretical predictions, and a reduction of as much as 7 dB is measured at an injection current of 1.5 times the threshold current. The potential of this method for contributing to the production of amplitude-squeezed light is discussed
Measuring dark energy properties with 3D cosmic shear
We present parameter estimation forecasts for present and future 3D cosmic
shear surveys. We demonstrate that, in conjunction with results from cosmic
microwave background (CMB) experiments, the properties of dark energy can be
estimated with very high precision with large-scale, fully 3D weak lensing
surveys. In particular, a 5-band, 10,000 square degree ground-based survey to a
median redshift of zm=0.7 could achieve 1- marginal statistical errors,
in combination with the constraints expected from the CMB Planck Surveyor, of
w0=0.108 and wa=0.099 where we parameterize w by
w(a)=w0+wa(1-a) where a is the scale factor. Such a survey is achievable with a
wide-field camera on a 4 metre class telescope. The error on the value of w at
an intermediate pivot redshift of z=0.368 is constrained to
w(z=0.368)=0.0175. We compare and combine the 3D weak lensing
constraints with the cosmological and dark energy parameters measured from
planned Baryon Acoustic Oscillation (BAO) and supernova Type Ia experiments,
and find that 3D weak lensing significantly improves the marginalized errors. A
combination of 3D weak lensing, CMB and BAO experiments could achieve
w0=0.037 and wa=0.099. Fully 3D weak shear analysis avoids the
loss of information inherent in tomographic binning, and we show that the
sensitivity to systematic errors is much less. In conjunction with the fact
that the physics of lensing is very soundly based, this analysis demonstrates
that deep, wide-angle 3D weak lensing surveys are extremely promising for
measuring dark energy properties.Comment: 18 pages, 16 figures. Accepted to MNRAS. Figures now in grayscale.
Further discussions on non-Gaussianity and photometric redshift errors. Some
references adde
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