Searcharxiv⌕ Search

arXiv subjects

Antonio Vigilante

Publications and source records attributed to Antonio Vigilante.

14 recordsLinked to original sources
arXiv2021

Spin dynamic response to a time dependent field

The dynamic response of a parametric system constituted by a spin precessing in a time dependent magnetic field is studied by means of a perturbative approach that unveils unexpected features, and is then experimentally validated. The first-order analysis puts in evidence different regimes: beside a tailorable low-pass-filter behaviour, a band-pass response with interesting potential applications emerges. Extending the analysis to the second perturbation order permits to study the response to generically oriented fields and to characterize several non-linear features in the behaviour of such kind of systems.

physics.app-ph↗
arXiv2021

Electromagnetic induction imaging with a scanning radio-frequency atomic magnetometer

We demonstrate electromagnetic induction imaging with an unshielded, portable radio-frequency atomic magnetometer scanning over the target object. This configuration satisfies standard requirements in typical applications, from security screening to medical imaging. The ability to scan the magnetometer over the object relies on the miniaturization of the sensor head and on the active compensation of the ambient magnetic field. Additionally, a procedure is implemented to extract high-quality images from the recorded spatial dependent magnetic resonance. The procedure is shown to be effective in suppressing the detrimental effects of the spatial variation of the magnetic environment.

physics.atom-ph↗
arXiv2021

Studying and applying magnetic dressing with a Bell and Bloom magnetometer

The magnetic dressing phenomenon occurs when spins precessing in a static field (holding field) are subject to an additional, strong, alternating field. It is usually studied when such extra field is homogeneous and oscillates in one direction. We study the dynamics of spins under dressing condition in two unusual configurations. In the first instance, an inhomogeneous dressing field produces space dependent dressing phenomenon, which helps to operate the magnetometer in strongly inhomogeneous static field. In the second instance, beside the usual configuration with static and the strong orthogonal oscillating magnetic fields, we add a secondary oscillating field, which is perpendicular to both. The system shows novel and interesting features that are accurately explained and modelled theoretically. Possible applications of these novel features are briefly discussed.

physics.atom-ph↗
arXiv2021

Validation of a fast and accurate magnetic tracker operating in the environmental field

We characterize the performance of a system based on a magnetoresistor array. This instrument is developed to map the magnetic field, and to track a dipolar magnetic source in the presence of a static homogeneous field. The position and orientation of the magnetic source with respect to the sensor frame is retrieved together with the orientation of the frame with respect to the environmental field. A nonlinear best-fit procedure is used, and its precision, time performance, and reliability are analyzed. This analysis is performed in view of the practical application for which the system is designed that is an eye-tracking diagnostics and rehabilitative tool for medical purposes, which require high speed ($\ge 100$~Sa/s) and sub-millimetric spatial resolution. A throughout investigation on the results makes it possible to list several observations, suggestions, and hints, which will be useful in the design of similar setups.

physics.app-ph↗
arXiv2020

Fast, cheap, and scalable magnetic tracker with an array of magnetoresistors

We present the hardware of a cheap multi-sensor magnetometric setup where a relatively large set of magnetic field components is measured in several positions by calibrated magnetoresistive detectors. The setup is developed with the scope of mapping the (inhomogeneous) field generated by a known magnetic source, which is measured as superimposed to the (homogeneous) geomagnetic field. The final goal is to use the data produced by this hardware to reconstruct position and orientation of the magnetic source with respect to the sensor frame, simultaneously with the orientation of the frame with respect to the environmental field. Possible applications of the setup are shortly discussed, together with a synthetic description of the data elaboration and analysis.

physics.ins-det↗
arXiv2020

Harmonic fine tuning and triaxial spatial anisotropy of dressed atomic spins

The addition of a weak oscillating field modifying strongly dressed spins enhances and enriches the system quantum dynamics. Through low-order harmonic mixing the bichromatic driving generates additional rectified static field acting on the spin system. The secondary field allows for a fine tuning of the atomic response and produces effects not accessible with a single dressing field, such as a spatial triaxial anisotropy of the spin coupling constants and acceleration of the spin dynamics. This tuning-dressed configuration introduces an extra handle for the system full engineering for quantum control applications. Tuning amplitude, harmonic content, spatial orientation and phase relation are control parameters. A theoretical analysis, based on perturbative approach, is experimentally validated by applying a bichromatic radiofrequency field to an optically pumped Cs atomic vapour. We measure the resonance shifts produced by tuning fields up to the third harmonic.

quant-ph↗
arXiv2020

Ferromagnetic contamination of Ultra-Low-Field-NMR sample containers. Quantification of the problem and possible solutions

The presence of a weak remanence in Ultra-Low-Field (ULF) NMR sample containers is investigated on the basis of proton precession. The high-sensitivity magnetometer used for the NMR detection, enables simultaneously the measurement of the static field produced in the sample proximity by ferromagnetic contaminants. The presence of the latter is studied by high resolution chemical analyses of the surface, based on X-ray fluorescence spectroscopy and secondary ions mass spectroscopy. Methodologies to reduce the contamination are explored and characterized. This study is of relevance in any ULF-NMR experiment, as in the ULF regime spurious ferromagnetism becomes easily a dominant cause of artefacts.

physics.ins-det↗
arXiv2020

Fast switching coil system for sample premagnetization in an unshielded ultra-low-field Nuclear Magnetic Resonance experiment

We present a system developed to premagnetize liquid samples in an ultra-low-field Nuclear Magnetic Resonance (NMR) experiment. Liquid samples of a few milliliter are exposed to a magnetic field of about 70~mT, which is abruptely switched off, so to leave a transverse microtesla field where nuclei start precessing. An accurate characterization of the transients and intermediate field level enables a reliable operation of the detection system, which is based on an optical magnetometer.

physics.ins-det↗
arXiv2019

Sub-millimetric ultra-low-field MRI detected in situ by a dressed atomic magnetometer

Magnetic Resonance Imaging (MRI) is universally acknowledged as an excellent tool to extract detailed spatial information with minimally invasive measurements. Efforts toward ultra-low-field (ULF) MRI are made to simplify the scanners and to reduce artefacts and incompatibilities. Optical Atomic Magnetometers (OAMs) are among the sensitive magnetic detectors eligible for ULF operation, however they are not compatible with the strong field gradients used in MRI. We show that a magnetic-dressing technique restores the OAMs operability despite the gradient, and we demonstrate sub-millimetric resolution MRI with a compact experimental setup based on an in situ detection. The proof-of-concept experiment produces unidimensional imaging of remotely magnetized samples with a dual sensor, but the approach is suited to be adapted for 3-D imaging of samples magnetized in loco. An extension to multi-sensor architectures is also possible.

physics.app-ph↗
arXiv2019

Spurious Ferromagnetic Remanence Detected by Hybrid Magnetometer

Nuclear magnetic resonance detection in ultra low field regime enables the measurement of different components of a spurious remanence in the polymeric material constituting the sample container. A differential atomic magnetometer detects simultaneously the static field generated by the container and the time-dependent signal from the precessing nuclei. The nuclear precession responds with frequency shifts and decay rate variations to the container magnetization. Two components of the latter act independently on the atomic sensor and on the nuclear sample. A model of the measured signal allows a detailed interpretation, on the basis of the interaction geometry.

physics.ins-det↗
arXiv2019

Restoring Narrow Linewidth to a Gradient-Broadened Magnetic Resonance by Inhomogeneous Dressing

We study the possibility of counteracting the line-broadening of atomic magnetic resonances due to inhomogeneities of the static magnetic field by means of spatially dependent magnetic dressing, driven by an alternating field that oscillates much faster than the Larmor precession frequency. We demonstrate that an intrinsic resonance linewidth of 25~Hz that has been broadened up to hundreds Hz by a magnetic field gradient, can be recovered by the application of an appropriate inhomogeneous dressing field. The findings of our experiments may have immediate and important implications, because they facilitate the use of atomic magnetometers as robust, high sensitivity detectors in ultra-low-field NMR imaging.

physics.atom-ph↗
arXiv2018

Self-adaptive loop for external disturbance reduction in differential measurement set-up

We present a method developed to actively compensate common-mode magnetic disturbances on a multi-sensor device devoted to differential measurements. The system uses a field-programmable-gated-array card, and operates in conjunction with a high sensitivity magnetometer: compensating the common-mode of magnetic disturbances results in a relevant reduction of the difference-mode noise. The digital nature of the compensation system allows for using a numerical approach aimed at automatically adapting the feedback loop filter response. A common mode disturbance attenuation exceeding 50 dB is achieved, resulting in a final improvement of the differential noise floor by a factor of 10 over the whole spectral interval of interest.

physics.ins-det↗
arXiv2017

Simultaneous Detection of H and D NMR Signals in a micro-Tesla Field

We present NMR spectra of remote-magnetized deuterated water, detected in an unshielded environment by means of a differential atomic magnetometer. The measurements are performed in a $μ$T field, while pulsed techniques are applied -following the sample displacement- in a 100~$μ$T field, to tip both D and H nuclei by controllable amounts. The broadband nature of the detection system enables simultaneous detection of the two signals and accurate evaluation of their decay times. The outcomes of the experiment demonstrate the potential of ultra-low-field NMR spectroscopy in important applications where the correlation between proton and deuteron spin-spin relaxation rates as a function of external parameters contains significant information.

physics.chem-ph↗