arXiv subjects

L. M. Rushton

Publications and source records attributed to L. M. Rushton.

5 recordsLinked to original sources

arXiv2026

Delay-engineered dynamical phases in a programmable non-Markovian spin oscillator

Non-Markovian dynamics offer a new route towards engineering non-equilibrium matter, where memory and feedback act as programmable resources for controlling order in time. Here we report the realization of a non-Markovian spin oscillator in a hot vapour $^{129}$Xe-Cs co-magnetometer with programmable feedback delay and gain. By tuning these parameters, we observe a hierarchy of dynamical phases, including time-crystalline response, nonlinear bifurcations, and frequency-comb formation. The measured spectra and phase boundaries are captured by linear stability analysis of delayed Bloch equations, revealing these phenomena as different manifestations of the same memory-induced instability structure. These results establish time-delayed feedback as a powerful strategy for controlling non-equilibrium phases, enabling quantum sensing, frequency referencing, and synchronization within a single spin-based platform.

physics.atom-ph↗

arXiv2024

Performance of a radio-frequency two-photon atomic magnetometer in different magnetic induction measurement geometries

Measurements monitoring the inductive coupling between oscillating radio-frequency magnetic fields and objects of interest create versatile platforms for non-destructive testing. The benefits of ultra low frequency measurements, i.e., below 3 kHz, are sometimes outweighed by the fundamental and technical difficulties related to operating pick-up coils or other field sensors in this frequency range. Inductive measurements with the detection based on a two-photon interaction in rf atomic magnetometers address some of these issues, as the sensor gains an uplift in its operational frequency. The developments reported here integrate the fundamental and applied aspects of the two-photon process in magnetic induction measurements. In this paper, all spectral components of the two-photon process are identified, which result from the non-linear interactions between the rf fields and atoms. A method for the retrieval of the two-photon phase information, which is critical for inductive measurements, is also demonstrated. Furthermore, a self-compensation configuration is introduced, whereby high contrast measurements of defects can be obtained due to the sensor's insensitivity to the primary field, including using simplified instrumentation for this configuration by producing two rf fields with a single rf coil.

physics.app-ph↗

arXiv2024

Polarisation of radio-frequency magnetic fields in magnetic induction measurements with an atomic magnetometer

We explore properties of the radio-frequency atomic magnetometer, specifically its sensitivity to the polarisation of an oscillating magnetic field. This aspect can be particularly relevant to configurations where the sensor monitors fields created by more than one source. The discussion, illustrated by theoretical and experimental studies, is done in the context of the signals produced by electrically conductive and magnetically permeable plates in magnetic induction tomography measurements. We show that different components of the secondary magnetic fields create the object response depending on the properties of the material, with the polarisation of the rf field varying across the object's surface. We argue that the ability of the sensor to simultaneously detect different field components enables the optimisation of measurement strategies for different object compositions.

physics.app-ph↗

arXiv2023

Alignment-based optically pumped magnetometer using a buffer gas cell

Alignment-based optically pumped magnetometers (OPMs) are capable of measuring oscillating magnetic fields with high sensitivity in the fT/sqrt(Hz) range. Until now, alignment-based magnetometers have only used paraffin-coated vapour cells to extend the spin relaxation lifetimes of the alkali vapour. The drawback of these cells is that they are hand-blown and are therefore time-intensive, and somewhat unreliable, to produce. Buffer gas cells, on the other hand, can be manufactured on a mass scale using microfabrication techniques. We present the first demonstration of an alignment-based magnetometer using a buffer gas vapour cell containing caesium (Cs) alkali vapour and nitrogen (N2) buffer gas. The OPM is operated at 55 degrees C and we achieve a 325 fT/sqrt(Hz) sensitivity to 10 kHz oscillating magnetic fields with an 800 Hz bandwidth. The alignment-based magnetometer uses a single laser beam for optical pumping and probing and could potentially allow for more rapid commercialisation of radio-frequency OPMs, due to the robustness of the one-beam geometry and the potential for mass-scale microfabrication of buffer gas cells.

physics.app-ph↗

arXiv2022

Unshielded portable optically pumped magnetometer for the remote detection of conductive objects using eddy current measurements

Electrically conductive objects can be detected using the principle of electromagnetic induction where a primary oscillating magnetic field induces eddy currents in the object, which in turn produce a secondary magnetic field that can be measured with a magnetometer. We have developed a portable radio-frequency optically pumped magnetometer (RF OPM) working in unshielded conditions with sub-pT/sqrt(Hz) magnetic field sensitivity when used for the detection of small oscillating magnetic fields, setting a new benchmark for the sensitivity of a portable RF OPM in unshielded conditions. Using this OPM, we have detected the induced magnetic field from aluminium disks with diameters as small as 1.5 cm and with the disks being ~25 cm from both the excitation coil and the magnetometer. When used for eddy current detection, our magnetometer achieves a sensitivity of a 2-6 pT/sqrt(Hz). We have also detected a moving aluminium disk using our RF OPM and analysed the magnetometer signals which depend on the position of the disk, illustrating the potential of high sensitivity RF OPMs for remote sensing applications.

physics.app-ph↗