Amplification of electroweak left-right asymmetry in atoms by stimulated emission

This work describes quantitatively the amplification of the electroweak left-right asymmetry, a remarkable and attractive feature of the experiment in progress on the 6S _1/2 → 7S _1/2 cesium transition using detection by stimulated emission on the 7S _1/2 → 6P _3/2 transition. The process relies on the optical anisotropy of the atomic medium resulting from the 7S _1/2 alignment created by excitation with linearly polarized light. The crucial parameter (α_⊥?α_∥)/α_∥ involves the amplification coefficients for the probe field oriented in a direction either parallel or perpendicular to the alignment axis. Explicit computations are done by a semiclassical approach (classical for the field, quantum mechanical for the atomic states). The larger the optical anisotropy and the optical density, the stronger the asymmetry amplification; among all hyperfine components of the 7S _1/2 → 6P _3/2 transition, the ΔF=0 ones and more particularly the 4 → 4 offer the largest anisotropy. It is also predicted that saturation of the probe transition by the optical field should provide manifestation of the effect at lower optical densities and notwithstanding at larger fluxes of transmitted photons. Indirect production of 6P _3/2 atoms by the excitation pulse does not reduce the left-right asymmetry, neither its amplification which then appears at lower effective optical densities.     

Search for a parity violation induced by neutral currents in the 6S–7S transition of atomic cesium

Parity violating, time-reversal invariant, weak neutral currents can induce an electric dipole transition moment, E₁^p.v., between atomic states of same parity. We report here on the preliminary results of an experiment designed to measure E₁^p.v. in the 6S–7S transition of atomic cesium, using a polarization effect characteristic of the interference of E₁^p.v. with the electric dipole transition moment E₁^ind. induced by a d.c. electric field. At a 90% confidence level we find the upper limit: |E₁^p.v.| < 2.0 × 10^?9|e|a₀. As a consequence the coupling constant of the electron-nucleon interaction involving the product of an axial electronic neutral current by a vector nucleonic one must be less than 44 G_F.     

Observation of a parity violation in cesium

We have measured a parity violation in the 6S–7S transition of Cs in an electric field. Our result is Im $\text{E}{}_1{}^{\mathrm{<mtext>pv</mtext>}}\text{β}\text{= -1.34 ± 0.22}$$\text{(}\text{rms statistical deviation}\text{) ± ～0.11 (}\text{systematic uncertainty}\text{)}\text{mV}\text{cm;}\text{E}{}_1{}^{\mathrm{<mtext>pv</mtext>}}$ is the parity violating electric dipole amplitude, ß is the vector polarizability. This result is consistent with the Weinberg-Salam prediction.     

Superconductivity in ropes of single-walled carbon nanotubes

We report measurements on ropes of single-walled carbon nanotubes (SWNT) in low-resistance contact to nonsuperconducting (normal) metallic pads, at low voltage and at temperatures down to 70 mK. In one sample, we find a 2 orders of magnitude resistance drop below 0.55 K, which is destroyed by a magnetic field of the order of 1 T, or by a dc current greater than 2.5 microA. These features strongly suggest the existence of superconductivity in ropes of SWNT.     

New observation of a parity violation in cesium

The parity violation induced by weak neutral currents is measured in a ΔF=1 hyperfine component of the 6S–7S transition of the Cs atom. The measured value (statistical rms deviation) ±0.12 (systematic uncertainty) mV/cm, agrees with our previous measurement in a ΔF=0 component, and constitutes an important cross-check. Our result excludes a parity violation induced by a purely axial hadronic neutral current.     

Measuring the Fr weak nuclear charge by observing a linear stark shift with small atomic samples

We study the chirality of ground-state alkali atoms in E and B fields, dressed with a circularly-polarized beam near-detuned ( less, similar1 GHz) from an E-field-assisted forbidden transition such as 7S-8S in Fr. We predict parity violating energy shifts of their sublevels, linear in E and the weak nuclear charge Q_(W). A dressing beam of 10 kW/cm(2) at 506 nm produces a shift of approximately 100 microHz at E=100 V/cm, B greater, similar50 mG which should be observable with approximately 10(4) Fr atoms confined in an optical dipole trap. We discuss optimal conditions, parameter reversals, and a calibration procedure to measure Q_(W)     

Theory of transition probability saturation for photodissociation of Cs2 and photoionization of the 5D 5/2 product atoms

Transition probability saturation has been used as a means of investigation of cesium photoionization via photodissociative states of Cs₂ around 550 nm. We present here a theoretical interpretation of the data obtained with polarized light. It allows for dispersion of the cross-sections due to the multi-level structure of the dissociated molecules and of the 5D _5/2 product atoms. Thehfs in 5D _5/2 is also taken into account. From best data fits we obtain determinations of the averaged cross-sections, free of uncertainty due to Cs or Cs₂ densities. The 5D _5/2 ionization cross-section agrees with theoretical prediction.     

Investigation of antirelaxation coatings for alkali-metal vapor cells using surface science techniques

Many technologies based on cells containing alkali-metal atomic vapor benefit from the use of antirelaxation surface coatings in order to preserve atomic spin polarization. In particular, paraffin has been used for this purpose for several decades and has been demonstrated to allow an atom to experience up to 10?000 collisions with the walls of its container without depolarizing, but the details of its operation remain poorly understood. We apply modern surface and bulk techniques to the study of paraffin coatings in order to characterize the properties that enable the effective preservation of alkali spin polarization. These methods include Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, near-edge x-ray absorption fine structure spectroscopy, and x-ray photoelectron spectroscopy. We also compare the light-induced atomic desorption yields of several different paraffin materials. Experimental results include the determination that crystallinity of the coating material is unnecessary, and the detection of C[Double Bond]C double bonds present within a particular class of effective paraffin coatings. Further study should lead to the development of more robust paraffin antirelaxation coatings, as well as the design and synthesis of new classes of coating materials.     

Cylindrical symmetry discrimination of magnetoelectric optical systematic effects in a pump-probe atomic parity violation experiment

A pump-probe atomic parity violation (APV) experiment performed in a longitudinal electric field , has the advantage of providing a signal which breaks mirror symmetry but preserves cylindrical symmetry of the set-up, i.e. this signal remains invariant when the pump and probe linear polarizations are simultaneously rotated about their common direction of propagation. The excited vapor acts on the probe beam as a linear dichroic amplifier, imprinting a very specific signature on the detected signal. Our differential polarimeter is oriented to yield a null result unless a chirality of some kind is acting on the excited atoms. Ideally, only the APV ( -odd) and the calibration ( -even) signals should participate in such a chiral atomic response, a situation highly favourable to sensitive detection of a tiny effect. In the present work, we give a thorough analysis of possible undesirable defects such as spurious transverse fields or misalignments, which may spoil the ideal configuration and generate a chiral response leading to possible systematics. We study a possible way to get rid of such defects by performing global rotations of the experiment by incremental angular steps , leaving both stray fields and misalignments unaltered. Our analysis shows that at least two defects are necessary for the -odd polarimeter output to be affected; a modulation in the global rotations reveals the transverse nature of the defects. The harmful systematic effects are those which subsist after we average over four configurations obtained by successive rotations of 45 . They require the presence of a stray transverse electric field. By doing auxiliary atomic measurements made in known, applied, magnetic fields which amplify the systematic effect, it is possible to measure the transverse E-field and to minimize it. Transverse magnetic fields must also be carefully compensated following a similar procedure. We discuss the feasibility of reducing the systematic uncertainty below the one percent level. We also propose statistical correlation tests as diagnoses of the aforementioned systematic effects.Received: 19 November 2003, Published online: 19 February 2004PACS: 32.80.Ys Weak-interaction effects in atoms - 32.60. + i Zeeman and Stark effects - 33.55.Fi Other magnetooptical and electrooptical effects - 42.25.Lc Birefringence     

Measurements of flux-dependent screening in aharonov-bohm rings

In order to investigate the effect of electronic phase coherence on screening we have measured the flux-dependent polarizability of isolated mesoscopic rings at 350 MHz. At low temperatures (below 100 mK) both the nondissipative and the dissipative parts of the polarizability exhibit flux oscillations with a period of one-half a flux quantum in a ring. The sign and amplitude of the effect are in good agreement with recent theoretical predictions. The observed positive magnetopolarizability corresponds to an enhancement of screening when time reversal symmetry is broken. The effect of electronic density and temperature are also measured.