Quantum state measurements using ac susceptibility and muon techniques

Prof. Sean Giblin (Cardiff University)

In this talk I will explore the quantum phases that occur in magnetic systems as probed by ac susceptibility and the muon technique, two novel techniques for this kind of investigation.
i) I will introduce the isolated susceptibility, which may be defined as a (non-thermodynamic) average over the canonical ensemble, but while it has often been discussed in the literature, it has not been clearly measured. In this presentation we demonstrate an unambiguous measurement of the isolated magnetic susceptibility at avoided nuclear-electronic level crossings in a dilute spin ice system, containing well-separated holmium ions. We show that the isolated suscpetibility quantifies the superposition of quasi-classical spin states at these points, and is a direct measure of state concurrence and state population. We also demonstrate other materials showing direct evidence of isolated magnetic suscpetibiltiy and discuss implications of these observations.
ii) Additional In a variety of fluorine containing systems, the muon spin relaxation (μSR) signal from entangled fluorine-muon-fluorine (F–μ–F) spins has been observed and successfully modelled in terms of magnetic dipole-dipole interactions between the muon (spin) and two fluorine (nuclear) magnetic moments. In principle, it should be possible to manipulate the F–μ–F eigenstates and their populations through electromagnetic excitation. Here, we report μSR measurements of the F–μ–F states in single crystal LiY0.95Ho0.05F4 excited in situ with a continuous radio-frequency electromagnetic field, tuned to the highest energy transition of the F–μ–F eigenstates. Clear differences in the μSR signal are observed on application of the excitation field. To model the experimental data, a magnetic dipole-dipole interaction Hamiltonian was constructed for a μF2Li2Ho cluster whose geometry was determined by calculations of the muon stopping site, to which we add a term representing the interaction of the cluster with the applied excitation field. This work opens new avenues for exploring the manipulation of quantum states within the unique μSR experimental environment.

Link de transmissão do google meet: https://meet.google.com/psp-bpqf-kku