189 research outputs found
Atomic Gases at Negative Kinetic Temperature
We show that thermalization of the motion of atoms at negative temperature is
possible in an optical lattice, for conditions that are feasible in current
experiments. We present a method for reversibly inverting the temperature of a
trapped gas. Moreover, a negative-temperature ensemble can be cooled, reducing
abs(T), by evaporation of the lowest-energy particles. This enables the
attainment of the Bose-Einstein condensation phase transition at negative
temperature.Comment: 4 pages 5 figures; v4: Typo corrections. Accepted Phys. Rev. Let
Superpixel-based spatial amplitude and phase modulation using a digital micromirror device
We present a superpixel method for full spatial phase and amplitude control
of a light beam using a digital micromirror device (DMD) combined with a
spatial filter. We combine square regions of nearby micromirrors into
superpixels by low pass filtering in a Fourier plane of the DMD. At each
superpixel we are able to independently modulate the phase and the amplitude of
light, while retaining a high resolution and the very high speed of a DMD. The
method achieves a measured fidelity for a target field with fully
independent phase and amplitude at a resolution of pixels per
diffraction limited spot. For the LG orbital angular momentum mode the
calculated fidelity is , using DMD pixels. The
superpixel method reduces the errors when compared to the state of the art Lee
holography method for these test fields by and , with a comparable
light efficiency of around . Our control software is publicly available.Comment: 9 pages, 6 figure
Spatial quantum correlations in multiple scattered light
We predict a new spatial quantum correlation in light propagating through a
multiple scattering random medium. The correlation depends on the quantum state
of the light illuminating the medium, is infinite range, and dominates over
classical mesoscopic intensity correlations. The spatial quantum correlation is
revealed in the quantum fluctuations of the total transmission or reflection
through the sample and should be readily observable experimentally.Comment: Reference adde
Pathlengths of open channels in multiple scattering media
We report optical measurements of the spectral width of open transmission
channels in a three-dimensional diffusive medium. The light transmission
through a sample is enhanced by efficiently coupling to open transmission
channels using repeated digital optical phase conjugation. The spectral
properties are investigated by enhancing the transmission, fixing the incident
wavefront and scanning the wavelength of the laser. We measure the transmitted
field to extract the field correlation function and the enhancement of the
total transmission. We find that optimizing the total transmission leads to a
significant increase in the frequency width of the field correlation function.
Additionally we find that the enhanced transmission persists over an even
larger frequency bandwidth. This result shows open channels in the diffusive
regime are spectrally much wider than previous measurements in the localized
regime suggest
Design of a 3D photonic band gap cavity in a diamond-like inverse woodpile photonic crystal
We theoretically investigate the design of cavities in a three-dimensional
(3D) inverse woodpile photonic crystal. This class of cubic diamond-like
crystals has a very broad photonic band gap and consists of two perpendicular
arrays of pores with a rectangular structure. The point defect that acts as a
cavity is centred on the intersection of two intersecting perpendicular pores
with a radius that differs from the ones in the bulk of the crystal. We have
performed supercell bandstructure calculations with up to
unit cells. We find that up to five isolated and dispersionless bands appear
within the 3D photonic band gap. For each isolated band, the electric-field
energy is localized in a volume centred on the point defect, hence the point
defect acts as a 3D photonic band gap cavity. The mode volume of the cavities
resonances is as small as 0.8 (resonance wavelength cubed),
indicating a strong confinement of the light. By varying the radius of the
defect pores we found that only donor-like resonances appear for smaller defect
radius, whereas no acceptor-like resonances appear for greater defect radius.
From a 3D plot of the distribution of the electric-field energy density we
conclude that peaks of energy found in sharp edges situated at the point
defect, similar to how electrons collect at such features. This is different
from what is observed for cavities in non-inverted woodpile structures. Since
inverse woodpile crystals can be fabricated from silicon by CMOS-compatible
means, we project that single cavities and even cavity arrays can be realized,
for wavelength ranges compatible with telecommunication windows in the near
infrared.Comment: 11 figure
Scattering Lens Resolves sub-100 nm Structures with Visible Light
The smallest structures that conventional lenses are able to optically
resolve are of the order of 200 nm. We introduce a new type of lens that
exploits multiple scattering of light to generate a scanning nano-sized optical
focus. With an experimental realization of this lens in gallium phosphide we
have succeeded to image gold nanoparticles at 97 nm optical resolution. Our
work is the first lens that provides a resolution in the nanometer regime at
visible wavelengths.Comment: 4 pages, 3 figure
Analysis of Photoassociation Spectra for Giant Helium Dimers
We perform a theoretical analysis to interpret the spectra of purely
long-range helium dimers produced by photoassociation (PA) in an ultra-cold gas
of metastable helium atoms. The experimental spectrum obtained with the PA
laser tuned closed to the atomic line has been
reported in a previous Letter. Here, we first focus on the corrections to be
applied to the measured resonance frequencies in order to infer the molecular
binding energies. We then present a calculation of the vibrational spectra for
the purely long-range molecular states, using adiabatic potentials obtained
from perturbation theory. With retardation effects taken into account, the
agreement between experimental and theoretical determinations of the spectrum
for the purely long-range potential well is very good. The results
yield a determination of the lifetime of the atomic state
Imaging trapped quantum gases by off-axis holography
We present a dispersive imaging method for trapped quantum gases based on
digital off-axis holography. Both phase delay and intensity of the probe field
are determined from the same image. Due to the heterodyne gain inherent to the
holographic method it is possible to retrieve the phase delay induced by the
atoms at probe beam doses two orders of magnitude lower than phase-contrast
imaging methods. Using the full field of the probe beam we numerically correct
for image defocusing.Comment: 4 pages, 5 figure
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