25 research outputs found
An Atomic Linear Stark Shift Violating P But Not T Arising From the Electroweak Nuclear Anapole Moment
We propose a direct method of detection of the nuclear anapole moment. It is
based on the existence of a linear Stark shift for alkali atoms in their ground
state perturbed by a quadrupolar interaction potential and a magnetic field.
This shift is proportional to the T-even pseudoscalar built from the
quadrupolar potential symmetry axis, the directions of the applied electric and
magnetic fields.It involves on the one hand the anisotropy of the hyperfine
interaction induced by the quadrupolar interaction and, on the other,the static
electric dipole moment arising from electroweak interactions inside the
nucleus. The case of ground state cesium atoms trapped in a uniaxial (hcp)
phase of solid helium-4 is examined. From an explicit evaluation of both the
hyperfine structure anisotropy and the static P-odd T-even dipole deduced from
recent empirical data about the cesium nuclear anapole moment, we predict the
Stark shift. It is three times the experimental upper bound to be set on the
T-odd Stark shift of free cesium atoms in order to improve the present limit on
the electron EDM.Comment: 31 pages, 3 PostScript figure
Atomic Parity Violation. Early days, present results, prospects
This is a personal recollection of the time when the search for APV was
beginning. In spite of today's remarkable results, summarized here, there are
still important goals to be achieved. I indicate a possible way to tackle the
remaining experimental challenges, by adapting methods now of frequent use in
precision metrology.Comment: 7 pages, 4 figures, submitted to Il Nuovo Cimento C (PAVI 2011
conference proceedings
Atomic interferometer measurements of Berry's and Aharonov-Anandan's phases for isolated spins S > 1/2 non-linearly coupled to external fields
The aim of the present paper is to propose experiments for observing the
significant features of Berry's phases for S>1, generated by spin-Hamiltonians
endowed with two couplings, a magnetic dipole and an electric quadrupole one
with external B and E fields, as theoretically studied in our previous work.
The fields are assumed orthogonal, this mild restriction leading to geometric
and algebraic simplifications. Alkali atoms appear as good candidates for
interferometric measurements but there are challenges to be overcome. The only
practical way to generate a suitable E-field is to use the ac Stark effect
which induces an instability of the dressed atom. Besides atom loss, this might
invalidate Berry's phase derivation but this latter problem can be solved by an
appropriate detuning. The former puts an upper limit to the cycle duration,
which is bounded below by the adiabatic condition. By relying upon our previous
analysis of the non-adiabatic corrections, we have been able to reach a
compromise for the Rb hf level F=2, m=0 state, which is our candidate
for an interferometric measurement of the exotic Berry's phase generated by a
rotation of the E-field around the fixed B-field. By a numerical simulation we
have shown that the non-adiabatic corrections can be kept below the 0.1% level.
As an alternative candidate, we discuss the chromium ground state J=S=3, where
the instability problem is easily solved. We make a proposal to extend the
measurement of Aharonov-Anandan's phase beyond S=1/2 to the Rb hf level
F=m=1, by constructing, with the help of light-shifts, a Hamiltonian able to
perform a parallel transport along a closed circuit upon the density matrix
space, without any adiabatic constraint. In Appendix A, Berry's phase
difference for S=3/2 and 1/2, m=1/2 states is used to perform an entanglement
of 3 Qbits.Comment: 23 pages, 6 figures, modifications in the introduction, two
paragraphs adde
Proposal for high-precision Atomic Parity Violation measurements using amplification of the asymmetry by stimulated emission in a transverse E and B field pump-probe experiment
Amplification by stimulated emission of radiation provides an intriguing
means for increasing the sensitivity of Atomic Parity Violation (APV)
measurements in a pump-probe configuration well adapted to the 6S-7S cesium
transition. It takes advantage of the large number of atoms excited along the
path of the pump beam. In the longitudinal E-field configuration currently
exploited in an ongoing APV measurement, this number is limited only by the
total voltage sustainable by the Cs vapor. In order to overcome this limit, we
consider, both theoretically and experimentally, the possibility of performing
the measurements in a transverse E-field configuration requiring a much lower
voltage. We discuss the necessarily different nature of the observable and the
magnetoelectric optical effects entering into play. They condition
modifications of the experimental configuration with, in particular, the
application of a transverse magnetic field. We suggest the possibility of
rotating the transverse direction of the fields so as to suppress systematic
effects. With a long interaction length, a precision reaching 0.1 percent in a
quantum noise limited measurement can be expected, now limited only by the
necessity of operating below the threshold of spontaneous superradiant emission
of the excited medium. If we approached this limit, however, we could greatly
amplify the asymmetry using triggered superradiance.Comment: Articl
A linear Stark shift in dressed atoms as a signal to measure a nuclear anapole moment with a cold atom fountain or interferometer
We demonstrate theoretically the existence of a linear dc Stark shift of the
individual substates of an alkali atom in its ground state, dressed by a
circularly polarized laser field. It arises from the electroweak nuclear
anapole moment violating P but not T. It is characterized by the pseudoscalar
equal to the mixed product formed with the photon angular momentum and static
electric and magnetic fields. We derive the relevant left-right asymmetry with
its complete signature in a field configuration selected for a precision
measurement with cold atom beams. The 3,3 to 4,3 Cs hyperfine-transition
frequency shift amounts to 7 Hz for a laser power of about 1 kW at 877 nm,
E=100 kV/cm and B larger than 0.5 G.Comment: Article, 4 pages, 2 figure
Linear Stark Shifts to Measure the Fr Weak Nuclear Charge with Small Atom Samples
We study the chirality of ground-state alkali atoms in E and B fields,
dressed with a circularly-polarized laser beam close-detuned from an
E-field-assisted forbidden transition, such as 7S-8S in Fr. We predict a parity
violating energy shift of their sublevels, linear in E, and the weak nuclear
charge Q_W^2\sim100 \mu\gtrsim\sim 10^4Q_W$.Comment: 4 pages, 1 tabl
Geometric Phases generated by the non-trivial spatial topology of static vector fields coupled to a neutral spin-endowed particle. Application to 171Yb atoms trapped in a 2D optical lattice
We have constructed the geometric phases emerging from the non-trivial
topology of a space-dependent magnetic field, interacting with the spin
magnetic moment of a neutral particle. Our basic tool is the local unitary
transformation which recasts the magnetic spin interaction under a diagonal
form. Rewriting the kinetic term in the "rotated" frame requires the
introduction of non-Abelian covariant derivatives, involving the gradients of
the Euler angles which define the orientation of the local field. Within the
rotated frame, we have built a perturbation scheme,assuming that the
longitudinal non-Abelian field component dominates the transverse ones, to be
evaluated to second-order. The geometry embedded in the longitudinal gauge
vector field and its curl, the geometric magnetic field, is described by the
associated Aharonov-Bohm phase. As an illustration, we study the physics of
cold 171Yb atoms dressed by two sets of circularly polarized beams, forming
square or triangular 2D optical lattices. The geometric field is computed
explicitly from the Euler angles. The magnitude of 2nd-order corrections due to
transverse fields can be reduced to the percent level by a choice of light
intensity which keeps the dressed atom loss rate below 5 s^{-1}. An auxiliary
optical lattice confines the atoms within 2D domains where the geometric field
is pointing upward.Comment: 12 pages, 4 figures. Comments and one figure added about the effect
of the additional scalar potential (sec. V.B). To be published in J. Phys.
A:Math. Theo
Staphylococcus aureus infective endocarditis versus bacteremia strains: Subtle genetic differences at stake
AbstractInfective endocarditis (IE)(1) is a severe condition complicating 10–25% of Staphylococcus aureus bacteremia. Although host-related IE risk factors have been identified, the involvement of bacterial features in IE complication is still unclear. We characterized strictly defined IE and bacteremia isolates and searched for discriminant features. S. aureus isolates causing community-acquired, definite native-valve IE (n=72) and bacteremia (n=54) were collected prospectively as part of a French multicenter cohort. Phenotypic traits previously reported or hypothesized to be involved in staphylococcal IE pathogenesis were tested. In parallel, the genotypic profiles of all isolates, obtained by microarray, were analyzed by discriminant analysis of principal components (DAPC)(2). No significant difference was observed between IE and bacteremia strains, regarding either phenotypic or genotypic univariate analyses. However, the multivariate statistical tool DAPC, applied on microarray data, segregated IE and bacteremia isolates: IE isolates were correctly reassigned as such in 80.6% of the cases (C-statistic 0.83, P<0.001). The performance of this model was confirmed with an independent French collection IE and bacteremia isolates (78.8% reassignment, C-statistic 0.65, P<0.01). Finally, a simple linear discriminant function based on a subset of 8 genetic markers retained valuable performance both in study collection (86.1%, P<0.001) and in the independent validation collection (81.8%, P<0.01). We here show that community-acquired IE and bacteremia S. aureus isolates are genetically distinct based on subtle combinations of genetic markers. This finding provides the proof of concept that bacterial characteristics may contribute to the occurrence of IE in patients with S. aureus bacteremia