894 research outputs found
Atomic-state diagnostics and optimization in cold-atom experiments
We report on the creation, observation and optimization of superposition
states of cold atoms. In our experiments, rubidium atoms are prepared in a
magneto-optical trap and later, after switching off the trapping fields,
Faraday rotation of a weak probe beam is used to characterize atomic states
prepared by application of appropriate light pulses and external magnetic
fields. We discuss the signatures of polarization and alignment of atomic spin
states and identify main factors responsible for deterioration of the atomic
number and their coherence and present means for their optimization, like
relaxation in the dark with the strobe probing. These results may be used for
controlled preparation of cold atom samples and in situ magnetometry of static
and transient fieldsComment: 15 pages and 9 figures (including supplementary information
Tailoring quantum superpositions with linearly polarized amplitude-modulated light
Amplitude-modulated nonlinear magneto-optical rotation is a powerful
technique that offers a possibility of controllable generation of given quantum
states. In this paper, we demonstrate creation and detection of specific
ground-state magnetic-sublevel superpositions in Rb. By appropriate
tuning of the modulation frequency and magnetic-field induction the efficiency
of a given coherence generation is controlled. The processes are analyzed
versus different experimental parameters.SComment: Submitted to Phys. Rev.
Circularly polarized microwaves for magnetic resonance study in the GHz range: application to nitrogen-vacancy in diamonds
The ability to create time-dependent magnetic fields of controlled
polarization is essential for many experiments with magnetic resonance. We
describe a microstrip circuit that allows us to generate strong magnetic field
at microwave frequencies with arbitrary adjusted polarization. The circuit
performance is demonstrated by applying it to an optically detected magnetic
resonance and Rabi nutation experiments in nitrogen-vacancy color centers in
diamond. Thanks to high efficiency of the proposed microstrip circuit and
degree of circular polarization of 85% it is possible to address the specific
spin states of a diamond sample using a low power microwave generator.Comment: 4 pages, 7 figures, nitrogen-vacancy, microwave circular
polarization, spin-state addressin
Analysis and calibration of absorptive images of Bose-Einstein condensate at non-zero temperatures
We describe the method allowing quantitative interpretation of absorptive
images of mixtures of BEC and thermal atoms which reduces possible systematic
errors associated with evaluation of the contribution of each fraction. By
using known temperature dependence of the BEC fraction, the analysis allows
precise calibration of the fitting results. The developed method is verified in
two different measurements and compares well with theoretical calculations and
with measurements performed by another group.Comment: 17 pages, 8 figure
Coherent population oscillations with nitrogen-vacancy color centers in diamond
We present results of our research on two-field (two-frequency) microwave
spectroscopy in nitrogen-vacancy (NV-) color centers in a diamond. Both fields
are tuned to transitions between the spin sublevels of the NV- ensemble in the
3A2 ground state (one field has a fixed frequency while the second one is
scanned). Particular attention is focused on the case where two microwaves
fields drive the same transition between two NV- ground state sublevels (ms=0
-> ms=+1). In this case, the observed spectra exhibit a complex narrow
structure composed of three Lorentzian resonances positioned at the pump-field
frequency. The resonance widths and amplitudes depend on the lifetimes of the
levels involved in the transition. We attribute the spectra to coherent
population oscillations induced by the two nearly degenerate microwave fields,
which we have also observed in real time. The observations agree well with a
theoretical model and can be useful for investigation of the NV relaxation
mechanisms.Comment: 17 page
How do you know if you ran through a wall?
Stable topological defects of light (pseudo)scalar fields can contribute to
the Universe's dark energy and dark matter. Currently the combination of
gravitational and cosmological constraints provides the best limits on such a
possibility. We take an example of domain walls generated by an axion-like
field with a coupling to the spins of standard-model particles, and show that
if the galactic environment contains a network of such walls, terrestrial
experiments aimed at detection of wall-crossing events are realistic. In
particular, a geographically separated but time-synchronized network of
sensitive atomic magnetometers can detect a wall crossing and probe a range of
model parameters currently unconstrained by astrophysical observations and
gravitational experiments.Comment: 5 pages, 2 figure; to appear in the PR
Microwave saturation spectroscopy of nitrogen-vacancy ensembles in diamond
Negatively-charged nitrogen-vacancy (NV) centers in diamond have
generated much recent interest for their use in sensing. The sensitivity
improves when the NV ground-state microwave transitions are narrow, but these
transitions suffer from inhomogeneous broadening, especially in high-density NV
ensembles. To better understand and remove the sources of broadening, we
demonstrate room-temperature spectral "hole burning" of the NV ground-state
transitions. We find that hole burning removes the broadening caused by
magnetic fields from C nuclei and demonstrate that it can be used for
magnetic-field-insensitive thermometry.Comment: Main text: 5 pages, 4 figures. Supplement: 6 pages, 3 figure
- …