7,194 research outputs found
Magnetic field-induced spectroscopy of forbidden optical transitions with application to lattice-based optical atomic clocks
We develop a method of spectroscopy that uses a weak static magnetic field to
enable direct optical excitation of forbidden electric-dipole transitions that
are otherwise prohibitively weak. The power of this scheme is demonstrated
using the important application of optical atomic clocks based on neutral atoms
confined to an optical lattice. The simple experimental implementation of this
method -- a single clock laser combined with a DC magnetic field-- relaxes
stringent requirements in current lattice-based clocks (e.g., magnetic field
shielding and light polarization), and could therefore expedite the realization
of the extraordinary performance level predicted for these clocks. We estimate
that a clock using alkaline earth-like atoms such as Yb could achieve a
fractional frequency uncertainty of well below 10^-17 for the metrologically
preferred even isotopes
Optical Lattice Induced Light Shifts in an Yb Atomic Clock
We present an experimental study of the lattice induced light shifts on the
1S_0-3P_0 optical clock transition (v_clock~518 THz) in neutral ytterbium. The
``magic'' frequency, v_magic, for the 174Yb isotope was determined to be 394
799 475(35)MHz, which leads to a first order light shift uncertainty of 0.38 Hz
on the 518 THz clock transition. Also investigated were the hyperpolarizability
shifts due to the nearby 6s6p 3P_0 - 6s8p 3P_0, 6s8p 3P_2, and 6s5f 3F_2
two-photon resonances at 759.708 nm, 754.23 nm, and 764.95 nm respectively. By
tuning the lattice frequency over the two-photon resonances and measuring the
corresponding clock transition shifts, the hyperpolarizability shift was
estimated to be 170(33) mHz for a linear polarized, 50 uK deep, lattice at the
magic wavelength. In addition, we have confirmed that a circularly polarized
lattice eliminates the J=0 - J=0 two-photon resonance. These results indicate
that the differential polarizability and hyperpolarizability frequency shift
uncertainties in a Yb lattice clock could be held to well below 10^-17.Comment: Accepted to PR
Direct excitation of the forbidden clock transition in neutral 174Yb atoms confined to an optical lattice
We report direct single-laser excitation of the strictly forbidden
(6s^2)^1S_0 -(6s6p)^3P_0 clock transition in the even 174Yb isotope confined to
a 1D optical lattice. A small (~1.2 mT) static magnetic field was used to
induce a nonzero electric dipole transition probability between the clock
states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FHWM) with high
contrast were observed, demonstrating a record neutral-atom resonance quality
factor of 2.6x10^13. The previously unknown ac Stark shift-canceling (magic)
wavelength was determined to be 759.35+/-0.02 nm. This method for using the
metrologically superior even isotope can be easily implemented in current Yb
and Sr lattice clocks, and can create new clock possibilities in other alkaline
earth-like atoms such as Mg and Ca.Comment: Submitted to Physics Review Letter
Sonoluminescence as Quantum Vaccum Radiation
We argue that the available experimental data is not compatible with models
of sonoluminescence which invoke dynamical properties of the interface without
regard to the compositional properties of the trapped gas inside the bubble.Comment: 2 pages,Revtex,No figures,Submitted to PRL(comments
The Schrodinger particle in an oscillating spherical cavity
We study a Schrodinger particle in an infinite spherical well with an
oscillating wall. Parametric resonances emerge when the oscillation frequency
is equal to the energy difference between two eigenstates of the static cavity.
Whereas an analytic calculation based on a two-level system approximation
reproduces the numerical results at low driving amplitudes, epsilon, we observe
a drastic change of behaviour when epsilon > 0.1, when new resonance states
appear bearing no apparent relation to the eigenstates of the static system.Comment: 9 pages, 6 figures, corrected typo
Emergence of hexatic and long-range herringbone order in two-dimensional smectic liquid crystals : A Monte Carlo study
Using a high resolution Monte Carlo simulation technique based on
multi-histogram method and cluster-algorithm, we have investigated critical
properties of a coupled XY model, consists of a six-fold symmetric hexatic and
a three-fold symmetric herringbone field, in two dimensions. The simulation
results demonstrate a series of novel continues transitions, in which both
long-range hexatic and herringbone orderings are established simultaneously. It
is found that the specific-heat anomaly exponents for some regions in coupling
constants space are in excellent agreement with the experimentally measured
exponents extracted from heat-capacity data near the smecticA-hexaticB
transition of two-layer free standing film
Quantum anisotropic Heisenberg chains with superlattice structure: a DMRG study
Using the density matrix renormalization group technique, we study spin
superlattices composed of a repeated pattern of two spin-1/2 XXZ chains with
different anisotropy parameters. The magnetization curve can exhibit two
plateaus, a non trivial plateau with the magnetization value given by the
relative sizes of the sub-chains and another trivial plateau with zero
magnetization. We find good agreement of the value and the width of the
plateaus with the analytical results obtained previously. In the gapless
regions away from the plateaus, we compare the finite-size spin gap with the
predictions based on bosonization and find reasonable agreement. These results
confirm the validity of the Tomonaga-Luttinger liquid superlattice description
of these systems.Comment: 6 pages, 6 figure
Quasiperiodic spin-orbit motion and spin tunes in storage rings
We present an in-depth analysis of the concept of spin precession frequency
for integrable orbital motion in storage rings. Spin motion on the periodic
closed orbit of a storage ring can be analyzed in terms of the Floquet theorem
for equations of motion with periodic parameters and a spin precession
frequency emerges in a Floquet exponent as an additional frequency of the
system. To define a spin precession frequency on nonperiodic synchro-betatron
orbits we exploit the important concept of quasiperiodicity. This allows a
generalization of the Floquet theorem so that a spin precession frequency can
be defined in this case too. This frequency appears in a Floquet-like exponent
as an additional frequency in the system in analogy with the case of motion on
the closed orbit. These circumstances lead naturally to the definition of the
uniform precession rate and a definition of spin tune. A spin tune is a uniform
precession rate obtained when certain conditions are fulfilled. Having defined
spin tune we define spin-orbit resonance on synchro--betatron orbits and
examine its consequences. We give conditions for the existence of uniform
precession rates and spin tunes (e.g. where small divisors are controlled by
applying a Diophantine condition) and illustrate the various aspects of our
description with several examples. The formalism also suggests the use of
spectral analysis to ``measure'' spin tune during computer simulations of spin
motion on synchro-betatron orbits.Comment: 62 pages, 1 figure. A slight extension of the published versio
Universal transport in 2D granular superconductors
The transport properties of quench condensed granular superconductors are
presented and analyzed. These systems exhibit transitions from insulating to
superconducting behavior as a function of inter-grain spacing.
Superconductivity is characterized by broad transitions in which the resistance
drops exponentially with reducing temperature. The slope of the log R versus T
curves turns out to be universaly dependent on the normal state film resistance
for all measured granular systems. It does not depend on the material, critical
temperature, geometry, or experimental set-up. We discuss possible physical
scenarios to explain these findings.Comment: 4 pages, 3 figure
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