Observation of critical spin dressing

It has long been proposed that spin dressing could be employed to realize a highly effective helium-3 nuclear precession co-magnetometer for a neutron electric dipole moment (nEDM) search. The proposal is to apply an intense, continuous, and far off-resonant oscillating magnetic field, called a dressing field, in such a way that the apparent Larmor precession frequencies of the helium-3 and the neutron are modified. Under appropriateconditions a desirable situation known as critical spin dressing (CSD) is anticipated: the neutron and the helium-3 nucleus (or more generally, any two spin species) are expected to behave as if they had the same gyromagnetic ratio and hence should precess at the same rate in a static magnetic field. Spin dressing has been studied in the context of the neutron, helium-3, and a variety of other systems. Critical spin dressing, however, has not previously been demonstrated. In this thesis I report the first experimental demonstration of pulsed CSD in which simultaneous spin dressing of 1H and 19F nuclei is achieved and studied. I also demonstrate that CSD can be performed using variety of different dressing field waveforms, a consideration that until now has received little or no attention. Examples of parameters studied include the role of phase and amplitude modulation on spin dressing. Of particular note is a significant improvement in reproducibility achieved by alternating the phase of successive cycles of the dressing field waveform by pi radians. Such innovations may prove useful in an eventual nEDM search where demands on precession stability are anticipated to be extreme. To enable my study of CSD I developed a simple and robust apparatus. The central innovation was the first use of Magneto-Impedance (MI) sensors to detect weak magnetic fields associated with the precession of nuclear magnetic moments. The thesis thus begins with summaries of experiments to characterise and validate the use of MI sensors for ultra-low field (ULF) nuclear magnetic resonance. I then describe a refined version of the ULF NMR apparatus, and the manner in which it is used to investigate CSD

Improved search for neutron to mirror-neutron oscillations in the presence of mirror magnetic fields with a dedicated spparatus at the PSI UCN source

While the international nEDM collaboration at the Paul Scherrer Institut (PSI) took data in 2017 that covered a considerable fraction of the parameter space of claimed potential signals of hypothetical neutron (n) to mirror-neutron (n′) transitions, it could not test all claimed signal regions at various mirror magnetic fields. Therefore, a new study of n−n′ oscillations using stored ultracold neutrons (UCNs) is underway at PSI, considerably expanding the reach in parameter space of mirror magnetic fields (B′) and oscillation time constants (τnn′). The new apparatus is designed to test for the anomalous loss of stored ultracold neutrons as a function of an applied magnetic field. The experiment is distinguished from its predecessors by its very large storage vessel (1.47 m3), enhancing its statistical sensitivity. In a test experiment in 2020 we have demonstrated the capabilities of our apparatus. However, the full analysis of our recent data is still pending. Based on already demonstrated performance, we will reach sensitivity to oscillation times τnn′/√ cos(β) well above a hundred seconds, with β being the angle between B′ and the applied magnetic field B. The scan of B will allow the finding or the comprehensive exclusion of potential signals reported in the analysis of previous experiments and suggested to be consistent with neutron to mirror-neutron oscillations.ISSN:2073-899