A. S. Pazgalev

Comparison of discharge lamp and laser pumped cesium magnetometers

We have performed a comparison of laser (LsOPM) and lamp (LpOPM) pumped cesium vapor magnetometers. Although the LsOPM operated 50% above its shot-noise limit we found an intrinsic sensitivity of 15 fT/√Hz and 25 fT/√Hz for the LsOPM and the LpOPM, respectively. Two modes of operation, viz. the phase-stabilized and the self-oscillating modes, were investigated and found to yield a similar performance. We have compared the performance of the LsOPM and the LpOPM directly by simultaneous measurements of field fluctuations of a 2-μT magnetic field inside a multilayer magnetic shield and have used one of the magnetometers for an active field stabilization. In the stabilized mode we found a gradient instability of 25 fT within an integration time of 100 s, which represents an upper limit of the long-term stability of the magnetometers. Our research is motivated by the need for an improved control of magnetic fields and gradients in a planned neutron electric dipole experiment.

Test of Lorentz invariance with spin precession of ultracold neutrons

A clock comparison experiment, analyzing the ratio of spin precession frequencies of stored ultracold neutrons and 199Hg atoms, is reported. No daily variation of this ratio could be found, from which is set an upper limit on the Lorentz invariance violating cosmic anisotropy field b perpendicular < 2 x 10(-20) eV (95% C.L.). This is the first limit for the free neutron. This result is also interpreted as a direct limit on the gravitational dipole moment of the neutron |gn| < 0.3 eV/c2 m from a spin-dependent interaction with the Sun. Analyzing the gravitational interaction with the Earth, based on previous data, yields a more stringent limit |gn| < 3 x 10(-4) eV/c2 m.

Towards a new measurement of the neutron electric dipole moment

The effort towards a new measurement of the neutron electric dipole moment (nEDM) at the Paul Scherrer Instituts (PSI) new high intensity source of ultracold neutrons (UCN) is described. The experimental technique relies on Ramseys method of separated oscillatory fields, using UCN in vacuum with the apparatus at ambient temperature. In the first phase, R&D towards the upgrade of the RAL/Sussex/ILL apparatus is being performed at the Institut Laue-Langevin (ILL). In the second phase the apparatus, moved from ILL to PSI, will allow an improvement in experimental sensitivity by a factor of 5. In the third phase, a new spectrometer should gain another order of magnitude in sensitivity. The improvements will be mainly due to (1) much higher UCN intensity, (2) improved magnetometry and magnetic field control, and (3) a double chamber configuration with opposite electric field directions.

Theory of double resonance magnetometers based on atomic alignment

We present a theoretical study of the spectra produced by optical\char21{}radio-frequency double resonance devices, in which resonant linearly polarized light is used in the optical pumping and detection processes. We extend previous work by presenting algebraic results which are valid for atomic states with arbitrary angular momenta, arbitrary rf intensities, and arbitrary geometries. The only restriction made is the assumption of low light intensity. The results are discussed in view of their use in optical magnetometers.

Experimental study of laser-detected magnetic resonance based on atomic alignment

We present an experimental study of the spectra produced by optical-radio-frequency double resonance in which resonant linearly polarized laser light is used in the optical pumping and detection processes. We show that the experimental spectra obtained for cesium are in excellent agreement with a very general theoretical model developed in our group [Weis, Bison, and Pazgalev, Phys. Rev. A 74, 033401 (2006)] and we investigate the limitations of this model. Finally, the results are discussed in view of their use in the study of relaxation processes in aligned alkali-metal vapors.

Testing a Prototype of the Neutron Magnetic Resonance Stabilization System

The design of a multichannel system of stabilization of the magnetic resonance of ultracold neutrons in a multichamber spectrometer developed in the search for the electric dipole moment (EDM) of the neutron is briefly described. The results of tests on a prototype of this system are presented, which show the possibility of ensuring the stability of resonance lines that is equivalent to a magnetic field variation not exceeding ∼30 fT over a 100-s period of EDM measurements.

Fast Three-Component Magnetometer-Variometer Based on a Cesium Sensor

A new fast three-component variometer-magnetometer based on a cesium sensor is developed and tested. The device is intended for measuring the longitudinal component of the geomagnetic field in the range from 20 to 65 μT and two transverse components in the range ±1 μT. The reproducibility of measurements is ±0.15 nT, and the noise-limited sensitivity is 0.01 nT (in terms of the rms deviation) or 0.04˝ for a measurement time of 0.1 s.

Optically Pumped Quantum M X Magnetometers: Digital Measurement of the M X Resonance Frequency in a Rapidly Varying Field

A new way of digitally constructing a phase-locked loop for an optically pumped quantum MX magnetometer is suggested. It provides a high accuracy and speed of magnetic resonance frequency tracking in a rapidly varying field.

Design and performance of an absolute 3He/Cs magnetometer

We report on the design and performance of a highly sensitive combined 3He/Cs magnetometer for the absolute measurement of magnetic fields. The magnetometer relies on the magnetometric detection of the free spin precession of nuclear spin polarized 3He gas by optically pumped cesium magnetometers. We plan to deploy this type of combined magnetometer in an experiment searching for a permanent electric dipole moment of ultracold neutrons at the Paul-Scherrer Institute (Switzerland). A prototype magnetometer was built at the University of Fribourg (Switzerland) and tested at Physikalisch-Technische Bundesanstalt (Berlin, Germany). We demonstrate that the combined magnetometer allows Cramér-Rao-limited field determinations with recording times in the range of, measurements above being limited by the stability of the applied magnetic field. With a recording time we were able to perform an absolute measurement of a magnetic field of ≈ with a standard uncertainty of, corresponding to ΔB/B < 6 ×10−8.Graphical abstract

Optimization of the Q factor of the magnetic M x resonance under optical pump conditions

Optimization of parameters of the Mx resonance, which excited between Zeeman sublevels of a single HFS level of the ground state of an alkali metal in a vacuum cell in a circuit with a single beam for pumping and detection (Mx magnetometer circuit), has been carried out. A simple model taking into account all main factors controlling the resolving power of the Mx resonance (including spin-exchange broadening and absorption in a thick layer of the cell has been constructed. It is shown that the spin-resonance broadening of the resonance line is mainly determined by the requirements imposed on the optical thickness of the cell, which considerably restricts the realization of advantages of ultranarrow (<1 Hz) lines in magnetometry. The experiment confirming the efficiency of the model has been carried out.