2,430 research outputs found
Optical Maser Emission from Trivalent Praseodymium in Calcium Tungstate
Coherent emission at 1.047 µ from trivalent praseodymium in calcium tungstate was observed. This emission coincides with strong infrared fluorescence at the same wavelength and was found to be stimulated mostly by absorption of blue light by the 3P0, 3P1, and 3P2 bands. The emission corresponds to a 1G4-->3H4 transition with the terminal level 377 cm^–1 from the ground state. The oscillation threshold was the same at 4.2°, 20°, and 78°K. No stimulated emission was observed at room temperature. The lifetime of the metastable state 1G4 is 50×10^–3 sec. A new technique used to measure the lifetime is described
Spin induced multipole moments for the gravitational wave flux from binary inspirals to third Post-Newtonian order
Using effective field theory techniques we calculate the source multipole
moments needed to obtain the spin contributions to the power radiated in
gravitational waves from inspiralling compact binaries to third Post-Newtonian
order (3PN). The multipoles depend linearly and quadratically on the spins and
include both spin(1)spin(2) and spin(1)spin(1) components. The results in this
paper provide the last missing ingredient required to determine the phase
evolution to 3PN including all spin effects which we will report in a separate
paper.Comment: 35 pages, 7 figures. Published versio
Randomized benchmarking of atomic qubits in an optical lattice
We perform randomized benchmarking on neutral atomic quantum bits (qubits)
confined in an optical lattice. Single qubit gates are implemented using
microwaves, resulting in a measured error per randomized computational gate of
1.4(1) x 10^-4 that is dominated by the system T2 relaxation time. The results
demonstrate the robustness of the system, and its viability for more advanced
quantum information protocols.Comment: 11 pages, 4 figure
The tail effect in gravitational radiation-reaction: time non-locality and renormalization group evolution
We use the effective field theory (EFT) framework to calculate the tail
effect in gravitational radiation reaction, which enters at 4PN order in the
dynamics of a binary system. The computation entails a subtle interplay between
the near (or potential) and far (or radiation) zones. In particular, we find
that the tail contribution to the effective action is non-local in time, and
features both a dissipative and a `conservative' term. The latter includes a
logarithmic ultraviolet (UV) divergence, which we show cancels against an
infrared (IR) singularity found in the (conservative) near zone. The origin of
this behavior in the long-distance EFT is due to the point-particle limit
-shrinking the binary to a point- which transforms a would-be infrared
singularity into an ultraviolet divergence. This is a common occurrence in an
EFT approach, which furthermore allows us to use renormalization group (RG)
techniques to resum the resulting logarithmic contributions. We then derive the
RG evolution for the binding potential and total mass/energy, and find
agreement with the results obtained imposing the conservation of the (pseudo)
stress-energy tensor in the radiation theory. While the calculation of the
leading tail contribution to the effective action involves only one diagram,
five are needed for the one-point function. This suggests logarithmic
corrections may be easier to incorporate in this fashion. We conclude with a
few remarks on the nature of these IR/UV singularities, the (lack of)
ambiguities recently discussed in the literature, and the completeness of the
analytic Post-Newtonian framework.Comment: 24 pages. 3 figures. v2: Extended discussion on the nature of IR/UV
singularities. Published versio
Recoverable One-dimensional Encoding of Three-dimensional Protein Structures
Protein one-dimensional (1D) structures such as secondary structure and
contact number provide intuitive pictures to understand how the native
three-dimensional (3D) structure of a protein is encoded in the amino acid
sequence. However, it has not been clear whether a given set of 1D structures
contains sufficient information for recovering the underlying 3D structure.
Here we show that the 3D structure of a protein can be recovered from a set of
three types of 1D structures, namely, secondary structure, contact number and
residue-wise contact order which is introduced here for the first time. Using
simulated annealing molecular dynamics simulations, the structures satisfying
the given native 1D structural restraints were sought for 16 proteins of
various structural classes and of sizes ranging from 56 to 146 residues. By
selecting the structures best satisfying the restraints, all the proteins
showed a coordinate RMS deviation of less than 4\AA{} from the native
structure, and for most of them, the deviation was even less than 2\AA{}. The
present result opens a new possibility to protein structure prediction and our
understanding of the sequence-structure relationship.Comment: Corrected title. No Change In Content
Conditional probabilities with Dirac observables and the problem of time in quantum gravity
We combine the "evolving constants" approach to the construction of
observables in canonical quantum gravity with the Page--Wootters formulation of
quantum mechanics with a relational time for generally covariant systems. This
overcomes the objections levied by Kucha\v{r} against the latter formalism. The
construction is formulated entirely in terms of Dirac observables, avoiding in
all cases the physical observation of quantities that do not belong in the
physical Hilbert space. We work out explicitly the example of the parameterized
particle, including the calculation of the propagator. The resulting theory
also predicts a fundamental mechanism of decoherence.Comment: 4 pages, no figures, RevTe
Differential Light Shift Cancellation in a Magnetic-Field-Insensitive Transition of Rb
We demonstrate near-complete cancellation of the differential light shift of
a two-photon magnetic-field-insensitive microwave hyperfine (clock) transition
in Rb atoms trapped in an optical lattice. Up to of the
differential light shift is canceled while maintaining magnetic-field
insensitivity. This technique should have applications in quantum information
and frequency metrology.Comment: 5 pages, 4 figure
A lattice of double wells for manipulating pairs of cold atoms
We describe the design and implementation of a 2D optical lattice of double
wells suitable for isolating and manipulating an array of individual pairs of
atoms in an optical lattice. Atoms in the square lattice can be placed in a
double well with any of their four nearest neighbors. The properties of the
double well (the barrier height and relative energy offset of the paired sites)
can be dynamically controlled. The topology of the lattice is phase stable
against phase noise imparted by vibrational noise on mirrors. We demonstrate
the dynamic control of the lattice by showing the coherent splitting of atoms
from single wells into double wells and observing the resulting double-slit
atom diffraction pattern. This lattice can be used to test controlled neutral
atom motion among lattice sites and should allow for testing controlled
two-qubit gates.Comment: 9 pages, 11 figures Accepted for publication in Physical Review
Strongly inhibited transport of a 1D Bose gas in a lattice
We report the observation of strongly damped dipole oscillations of a quantum
degenerate 1D atomic Bose gas in a combined harmonic and optical lattice
potential. Damping is significant for very shallow axial lattices (0.25 photon
recoil energies), and increases dramatically with increasing lattice depth,
such that the gas becomes nearly immobile for times an order of magnitude
longer than the single-particle tunneling time. Surprisingly, we see no
broadening of the atomic quasimomentum distribution after damped motion. Recent
theoretical work suggests that quantum fluctuations can strongly damp dipole
oscillations of 1D atomic Bose gas, providing a possible explanation for our
observations.Comment: 5 pages, 4 figure
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