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

Elastic Rod Model of a Supercoiled DNA Molecule

We study the elastic behaviour of a supercoiled DNA molecule. The simplest model is that of a rod like chain, involving two elastic constants, the bending and the twist rigidities. We show that this model is singular and needs a small distance cut-off, which is a natural length scale giving the limit of validity of the model, of the order of the double helix pitch. The rod like chain in presence of the cutoff is able to reproduce quantitatively the experimentally observed effects of supercoiling on the elongation-force characteristics, in the small supercoiling regime. An exact solution of the model, using both transfer matrix techniques and its mapping to a quantum mechanics problem, allows to extract, from the experimental data,the value of the twist rigidity. We also analyse the variation of the torque and the writhe to twist ratio versus supercoiling, showing analytically the existence of a rather sharp crossover regime which can be related to the excitation of plectonemic-like structures. Finally we study the extension fluctuations of a stretched and supercoiled DNA molecule, both at fixed torque and at fixed supercoiling angle, and we compare the theoretical predictions to some preliminary experimental data.Comment: 29 pages Revtex 5 figure

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 $^{87}$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 $^{87}$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

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

Electric field-controlled rippling of graphene

International audienceMetal-graphene interfaces generated by electrode deposition induce barriers or potential modulations influencing the electronic transport properties of graphene based devices. However, their impact on the local mechanical properties of graphene is much less studied. Here we show that graphene near a metallic interface can exhibit a set of ripples self-organized into domains whose topographic roughness is controlled by the tip bias of a scanning tunneling microscope. The reconstruction from topographic images of graphene bending energy maps sheds light on the local electro-mechanical response of graphene under STM imaging and unveils the role of the stress induced by the vicinity of the graphene-metal interface in the formation and the manipulation of these ripples. Since microscopic rippling is one of the important factors that limit charge carrier mobility in graphene, the control of rippling with a gate voltage may have important consequences in the conductance of graphene devices where transverse electric fields are created by contactless suspended gate electrodes. This opens up also the possibility to dynamically control the local morphology of graphene nanomembranes

Atomic interferometer measurements of Berry and Aharonov-Anandan phases for isolated spins S > 1/2 nonlinearly coupled to external fields

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La résonance dans la diffusion méson π— méson π et le moment magnétique anormal du méson μ

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