1,312 research outputs found
Assembling Single RbCs Molecules with Optical Tweezers
Optical tweezer arrays are useful tools for manipulating single atoms and molecules.
An exciting avenue for research with optical tweezers is using the interactions between polar molecules for quantum computation or quantum simulation.
Molecules can be assembled in an optical tweezer array starting from pairs of atoms.
The atoms must be initialised in the relative motional ground state of a common trap.
This work outlines the design of a Raman sideband cooling protocol which is implemented to prepare an 87-Rubidium atom in the motional ground state of an 817 nm tweezer, and a 133-Caesium atom in the motional ground state of a 938 nm tweezer.
The protocol circumvents strong heating and dephasing associated with the trap by operating at lower trap depths and cooling from outside the Lamb-Dicke regime.
By analysing several sources of heating, we design and implement a merging sequence that transfers the Rb atom and the Cs atom to a common trap with minimal motional excitation.
Subsequently, we perform a detailed characterisation of AC Stark shifts caused by the tweezer light, and identify several situations in which the confinement of the atom pair influences their interactions.
Then, we demonstrate the preparation of a molecular bound state after an adiabatic ramp across a magnetic Feshbach resonance.
Measurements of molecular loss rates provide evidence that the atoms are in fact associated during the merging sequence, before the magnetic field ramp.
By preparing a weakly-bound molecule in an optical tweezer, we carry out important steps towards assembling an array of ultracold RbCs molecules in their rovibrational ground states
Modern optical astronomy: technology and impact of interferometry
The present `state of the art' and the path to future progress in high
spatial resolution imaging interferometry is reviewed. The review begins with a
treatment of the fundamentals of stellar optical interferometry, the origin,
properties, optical effects of turbulence in the Earth's atmosphere, the
passive methods that are applied on a single telescope to overcome atmospheric
image degradation such as speckle interferometry, and various other techniques.
These topics include differential speckle interferometry, speckle spectroscopy
and polarimetry, phase diversity, wavefront shearing interferometry,
phase-closure methods, dark speckle imaging, as well as the limitations imposed
by the detectors on the performance of speckle imaging. A brief account is
given of the technological innovation of adaptive-optics (AO) to compensate
such atmospheric effects on the image in real time. A major advancement
involves the transition from single-aperture to the dilute-aperture
interferometry using multiple telescopes. Therefore, the review deals with
recent developments involving ground-based, and space-based optical arrays.
Emphasis is placed on the problems specific to delay-lines, beam recombination,
polarization, dispersion, fringe-tracking, bootstrapping, coherencing and
cophasing, and recovery of the visibility functions. The role of AO in
enhancing visibilities is also discussed. The applications of interferometry,
such as imaging, astrometry, and nulling are described. The mathematical
intricacies of the various `post-detection' image-processing techniques are
examined critically. The review concludes with a discussion of the
astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics,
2002, to appear in April issu
Towards real-time reconstruction of velocity fluctuations in turbulent channel flow
We develop a framework for efficient streaming reconstructions of turbulent
velocity fluctuations from limited sensor measurements with the goal of
enabling real-time applications. The reconstruction process is simplified by
computing linear estimators using flow statistics from an initial training
period and evaluating their performance during a subsequent testing period with
data obtained from direct numerical simulation. We address cases where (i) no,
(ii) limited, and (iii) full-field training data are available using estimators
based on (i) resolvent modes, (ii) resolvent-based estimation, and (iii)
spectral proper orthogonal decomposition modes. During training, we introduce
blockwise inversion to accurately and efficiently compute the resolvent
operator in an interpretable manner. During testing, we enable efficient
streaming reconstructions by using a temporal sliding discrete Fourier
transform to recursively update Fourier coefficients using incoming
measurements. We use this framework to reconstruct with minimal time delay the
turbulent velocity fluctuations in a minimal channel at from sparse planar measurements. We evaluate reconstruction accuracy in
the context of the extent of data required and thereby identify potential use
cases for each estimator. The reconstructions capture large portions of the
dynamics from relatively few measurement planes when the linear estimators are
computed with sufficient fidelity. We also evaluate the efficiency of our
reconstructions and show that the present framework has the potential to help
enable real-time reconstructions of turbulent velocity fluctuations in an
analogous experimental setting.Comment: 36 pages, 22 figures, accepted by Physical Review Fluid
SETI science working group report
This report covers the initial activities and deliberations of a continuing working group asked to assist the SETI Program Office at NASA. Seven chapters present the group's consensus on objectives, strategies, and plans for instrumental R&D and for a microwave search for extraterrestrial in intelligence (SETI) projected for the end of this decade. Thirteen appendixes reflect the views of their individual authors. Included are discussions of the 8-million-channel spectrum analyzer architecture and the proof-of-concept device under development; signal detection, recognition, and identification on-line in the presence of noise and radio interference; the 1-10 GHz sky survey and the 1-3 GHz targeted search envisaged; and the mutual interests of SETI and radio astronomy. The report ends with a selective, annotated SETI reading list of pro and contra SETI publications
Microwaves in Quantum Computing
Quantum information processing systems rely on a broad range of microwave
technologies and have spurred development of microwave devices and methods in
new operating regimes. Here we review the use of microwave signals and systems
in quantum computing, with specific reference to three leading quantum
computing platforms: trapped atomic ion qubits, spin qubits in semiconductors,
and superconducting qubits. We highlight some key results and progress in
quantum computing achieved through the use of microwave systems, and discuss
how quantum computing applications have pushed the frontiers of microwave
technology in some areas. We also describe open microwave engineering
challenges for the construction of large-scale, fault-tolerant quantum
computers.Comment: Invited review article, to appear in IEEE Journal of Microwaves. 29
pages, 13 figures, to H
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