A pump-probe atomic parity violation (APV) experiment performed in a longitudinal electric field, provides a signal breaking mirror symmetry while preserving the cylindrical symmetry of the set-up. 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 the excited atoms are endowed with a chirality of some kind. Ideally, only the APV (E-odd) and the calibration (E-even) signals contribute to a chiral atomic response, a situation highly favourable to the detection of a tiny effect. In the present work we give a thorough analysis of possible unwanted defects like stray transverse fields or misalignments which would spoil the ideal set-up and lead to chiral systematics. A possible way to suppress such effects is to perform global rotations of the experiment by incremental steps of 45 degrees, leaving both stray fields and misalignments unaltered. The conspiration of at least two defects is necessary to affect the E-odd polarimeter signal. The transverse nature of the defects manifests itself by an azimuthal cosine square modulation. The harmful systematics are those which survive the averaging over four successive configurations. They require the presence of a stray transverse electric field, which can be determined and eventually minimized by auxiliary measurements of the systematic effects, amplified by applying a known external magnetic field. Transverse stray magnetic fields must be compensated by a similar procedure. We also propose statistical correlation tests as diagnoses of the aforementioned systematic effects.
A pump-probe atomic parity violation (APV) experiment performed in a longitudinal electric field, provides a signal breaking mirror symmetry while preserving the cylindrical symmetry of the set-up. 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 the excited atoms are endowed with a chirality of some kind. Ideally, only the APV (E-odd) and the calibration (E-even) signals contribute to a chiral atomic response, a situation highly favourable to the detection of a tiny effect. In the present work we give a thorough analysis of possible unwanted defects like stray transverse fields or misalignments which would spoil the ideal set-up and lead to chiral systematics. A possible way to suppress such effects is to perform global rotations of the experiment by incremental steps of 45 degrees, leaving both stray fields and misalignments unaltered. The conspiration of at least two defects is necessary to affect the E-odd polarimeter signal. The transverse nature of the defects manifests itself by an azimuthal cosine square modulation. The harmful systematics are those which survive the averaging over four successive configurations. They require the presence of a stray transverse electric field, which can be determined and eventually minimized by auxiliary measurements of the systematic effects, amplified by applying a known external magnetic field. Transverse stray magnetic fields must be compensated by a similar procedure. We also propose statistical correlation tests as diagnoses of the aforementioned systematic effects.
We detect atomic parity violation (APV) by using stimulated emission, in the form of a chiral optical gain of a cesium vapor on the 7S-6P3/2 probe transition, consecutive to linearly polarized 6S-7S excitation. The method relies on a pump-probe scheme in which the excited 7S state is populated, in zero magnetic field, by an intense, pulsed excitation beam, with a linear polarization [epsilon]ex and a wave vector [k] parallel to the applied electric field [E]. The atoms are then probed by a second, collinear pulsed laser beam, tuned to resonance with the 7S - 6P3/2 transition. The probe beam is amplified by stimulated emission and its linear polarization [epsilon]pr undergoes a small change of direction, due to the presence of the pseudoscaler PV term in the gain. This dichroism, with axes at +/-45° from the ([epsilon]ex,[E]) plane of symmetry of the experiment, is smaller than the parity-conserving, Stark linear dichroism by the ratio of the Stark to the PV 6S-7S transition amplitudes [beta]E/ E1pv, approximately 10^6. As a result the gain axes are tilted by an angle [theta]pv = E1pv/[beta]E, approximately 1µradian.This is the relevant APV quantity, measured by balanced-mode, two channel polarimetry, with dedicated real-time calibration. This detection method has been validated by a measurement of expected sign and magnitude with a 9% accuracy [ref. 1], now improved by more than a factor of two, thanks essentially to a dichroic polarization-tilt magnifier [ref. 2]. Rotational symmetry around the common pump-probe beam axis is used to reduce systematic effects [ref. 3], among which the parity-conserving Jones dichroism due to transverse E and B fields. This latter kind of magneto-optical effects has already been observed in especially chosen liquids thanks to the application of intense (>10T) magnetic fields. Here, symmetry discrimination, applied to the strongly forbidden 6S-7S transition, allows its detection with applied magnetic fields 10^5 to 10^7 times weaker, in a dilute vapor, where the mechanisms involved are clearly understood [ref. 3]. Besides, we discuss a novel kind of magneto-optical effects manifesting parity violation, as possible observables for APV measurements to the 0.1% precision level on the 6S-7S Cs transition. They consist in observing a parity violating circular dichroism in the presence of transverse electric and magnetic fields [ref. 4]. The advantage, as compared to the longitudinal E field configuration, is that the interaction length can be made much longer without increasing the applied potentials. Thanks to the much larger optical density of the excited vapor, stimulated emission gives rise to considerable amplification of the polarimetric signal during the propagation of the probe beam. Even moderate transverse electric fields would allow to reach the triggered superradiance regime, for further enhancing the PV asymmetry. Finally we suggest a means of rotating the transverse direction of the fields so as to restore the cylindrical symmetry and to suppress systematic effects, as in the longitudinal E field configuration. [1] J. Guéna et al.: Phys. Rev. Lett. 90, 143001, (2003) [2] D. Chauvat et al.: Opt. Commun. 138, 249 (1997) [3] M.-A. Bouchiat, J. Guéna, M. Lintz: Eur Phys J D28, 331 (2004) [4] J. Guéna, M. Lintz & M.-A. Bouchiat: arXiv:physics/0403141 & JOSA B, to be published
Amplification by stimulated emission of radiation provides an interesting means for increasing the sensitivity of atomic-parity-violation (APV) measurements in a pump-probe configuration well adapted to the 6S-7S Cs transition. It takes advantage of the large number of atoms excited along the path of the pump beam. In the longitudinal electric field configuration currently exploited in our ongoing APV measurement, this number is limited only by the total voltage sustainable by the Cs vapor. To overcome this limit we consider, both theoretically and experimentally, the possibility of performing the measurements in a transverse electric field configuration requiring a much lower voltage. We discuss the necessarily different nature of the observable and the magnetoelectric optical effects that come into play. These 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% in a quantum-noise-limited measurement can be expected, limited only by the necessity of operating below the threshold of spontaneous superradiant emission of the excited medium. Were we to approach this limit, however, we could greatly amplify the asymmetry using triggered superradiance.
High-precision Mz/Mx atomic magnetometers have “dead zones”, where the magnetic-field information will be lost because the light–atom interaction vanishes at specific field angles. To suppress dead zones, we propose a scheme with polarization-gradient optical pumping field by using counter-propagating lin⊥lin beams. We found through experiments that the lin⊥lin scheme eliminates dead zones in the transverse plane of the probe beam propagation (minimum ∼40% normalized signal) but leaves two noncanonical magic-angle-like directions (≈30 ∘ and 150 ∘ ) in the longitudinal plane, which is distinct from the standard tensor magic angle (≈54 ∘ and 126 ∘ ). These observations are quantitatively explained using a multipole-based model formulated in terms of an effective, spatially averaged density matrix, which is the first time that the spatial average density matrix has been used for energy state analysis in atomic magnetometers. Under the probing of a linearly polarized light, the measured signal is determined by the field-angle-dependent projection of the atomic longitudinal alignment moment ( m 2,0 ) onto the B 0 -defined quantization axis. Compared with other dead-zone elimination schemes, our scheme avoids polarization modulation and multi-cell architectures, showing potential for improving the spatial response range of compact atomic magnetometry.
The interaction between cylindrical vector beams and atoms under a weak magnetic field induces spatially dependent electromagnetically induced transparency (EIT). Based on this coherence effect, we investigated the relationship between the magnitude and orientation of the transverse magnetic field (TMF) and the spatial intensity distribution of cylindrical vector beams passing through a thermal atom ensemble, which is intuitively manifested in polarization selection absorption. The radially polarized beam exhibits a spatial axisymmetric polarization structure. When a TMF is applied, transparent regions in the transmitted beam strongly correlate with the beam’s polarization distribution. Variations in the TMF magnitude alter the absorption of specific polarization components by the atomic system, thereby affecting the local transmittance. This enables the TMF magnitude to be inferred from the single transmittance of the intensity pattern. The alignment of the TMF orientation is reflected in the rotation of the petal-shaped transmission patterns aligned with the mirror axis. Theoretical solutions using optical Bloch equations reveal this specific spatially dependent EIT is closely related to the transverse relaxation rate between the ground state energy levels. Experimental data align perfectly with the theoretical results, suggesting potential applications in light field manipulation and magnetic field measurement.
We have detected, by using stimulated emission, an atomic parity violation (APV) in the form of a chiral optical gain of a cesium vapor on the 7S-6P(3/2) transition, consecutive to linearly polarized 6S-7S excitation. We demonstrate the validity of this detection method of APV, by presenting a 9% accurate measurement of expected sign and magnitude. We stress several advantages of this new approach which fully exploits the cylindrical symmetry of the setup. Future measurements at the percent level will provide an important cross-check of an existing more precise result obtained by a different method.
Ultrasensitive atomic comagnetometers (ACMs) are invaluable tools for both inertial measurement and fundamental physics research. However, the misalignment between the pump light and the main magnetic field affects the polarization characteristics of nuclear spins of the noble gas atoms, making it a significant source of noise. In this article, an atomic magnetometer response model with the optical-magnetic misalignment error is established, and the mechanism of the influence of optical-magnetic misalignment on nuclear spin polarization is analyzed. An in situ evaluation method and a suppression method of optical-magnetic misalignment error are proposed, and their effectiveness is verified through experiments with varying pump light incidence directions. The experimental results indicate that after optical-magnetic alignment using the proposed method, the spin polarization of the coupled atomic ensemble is enhanced by 20.7%, and the longitudinal relaxation rate of the nuclear spin is reduced by 6.9%. Additionally, the amplitude-frequency response (AFR) of the x-axis magnetic field is reduced by 33.2% at 1 Hz and by 53.1% at frequencies below 0.002 Hz. This indicates an improvement in the transverse magnetic field error suppression capability of the ACMs.