187 research outputs found
Large-Area, Low-Noise, High Speed, Photodiode-Based Fluorescence Detectors with Fast Overdrive Recovery
Two large-area, low noise, high speed fluorescence detectors have been built.
One detector consists of a photodiode with an area of 28 mm x 28 mm and a low
noise transimpedance amplifier. This detector has a input light-equivalent
spectral noise density of less than 3 pW/Hz^1/2, can recover from a large
scattered light pulse within 10 us, and has a bandwidth of at least 900 kHz.
The second detector consists of a 16 mm diameter avalanche photodiode and a
low-noise transimpedance amplifier. This detector has an input light-equivalent
spectral noise density of 0.08 pW/Hz^1/2, also can recover from a large
scattered light pulse within 10 us, and has a bandwidth of 1 MHz.Comment: Submitted to Review of Scientific Instrument
Hyperfine-interaction- and magnetic-field-induced Bose-Einstein-statistics suppressed two-photon transitions
Two-photon transitions between atomic states of total electronic angular
momentum and are forbidden when the photons are of the same
energy. This selection rule is analogous to the Landau-Yang theorem in particle
physics that forbids decays of vector particle into two photons. It arises
because it is impossible to construct a total angular momentum
quantum-mechanical state of two photons that is permutation symmetric, as
required by Bose-Einstein statistics. In atoms with non-zero nuclear spin, the
selection rule can be violated due to hyperfine interactions. Two distinct
mechanisms responsible for the hyperfine-induced two-photon transitions are
identified, and the hyperfine structure of the induced transitions is
evaluated. The selection rule is also relaxed, even for zero-nuclear-spin
atoms, by application of an external magnetic field. Once again, there are two
similar mechanisms at play: Zeeman splitting of the intermediate-state
sublevels, and off-diagonal mixing of states with different total electronic
angular momentum in the final state. The present theoretical treatment is
relevant to the ongoing experimental search for a possible
Bose-Einstein-statistics violation using two-photon transitions in barium,
where the hyperfine-induced transitions have been recently observed, and the
magnetic-field-induced transitions are being considered both as a possible
systematic effect, and as a way to calibrate the measurement
Experimental determination of the 6s^2 ^1S_0 -> 5d6s ^3 D_1 magnetic-dipole transition amplitude in atomic ytterbium
We report on a measurement of the highly forbidden 6s^2 ^1S_0 \to 5d6s ^3
D_1 magnetic-dipole transition in atomic ytterbium using the
Stark-interference technique. This amplitude is important in interpreting a
future parity nonconservation experiment that exploits the same transition. We
find , where the larger uncertainty comes from the previously
measured vector transition polarizability . The amplitude is small
and should not limit the precision of the parity nonconservation experiment.Comment: 4 pages, 5 figures Paper resubmitted with minor corrections and
additions based on comments from referee
Enhancement of the electric dipole moment of the electron in PbO
The a(1) state of PbO can be used to measure the electric dipole moment of
the electron d_e. We discuss a semiempirical model for this state, which yields
an estimate of the effective electric field on the valence electrons in PbO.
Our final result is an upper limit on the measurable energy shift, which is
significantly larger than was anticipated earlier: .Comment: 4 pages, revtex4, no figures, submitted to PR
Cavity QED in a molecular ion trap
We propose an approach for studying quantum information and performing high
resolution spectroscopy of rotational states of trapped molecular ions using an
on-chip superconducting microwave resonator. Molecular ions have several
advantages over neutral molecules. Ions can be loaded into deep (1 eV) RF traps
and are trapped independent of the electric dipole moment of their rotational
transition. Their charge protects them from motional dephasing and prevents
collisional loss, allowing 1 s coherence times when used as a quantum memory,
with detection of single molecules possible in <10 ms. An analysis of the
detection efficiency and coherence properties of the molecules is presented.Comment: 9 pages, 1 figur
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