All-optical noise spectroscopy of a solid-state spin

Noise spectroscopy elucidates the fundamental noise sources in spin systems, which is essential for developing spin qubits with long coherence times for quantum information processing, communication, and sensing. But noise spectroscopy typically relies on microwave coherent spin control to extract the noise spectrum, which becomes infeasible when there are high-frequency noise components stronger than the available microwave power. Here, we demonstrate an alternative all-optical approach to performing noise spectroscopy. Our approach utilises coherent Raman rotations of the spin state with controlled timing and phase to implement Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences. Analysing the spin dynamics under these sequences enables us to extract the noise spectrum of a dense ensemble of nuclear spins interacting with a single spin in a quantum dot, which has thus far only been modelled theoretically. By providing large spectral bandwidths of over 100 MHz, our Raman-based approach could serve as an important tool to study spin dynamics and decoherence mechanisms for a broad range of solid-state spin qubits.

Spin noise gradient echoes

Nuclear spin noise spectroscopy in the absence of radio frequency pulses was studied under the influence of pulsed field gradients (PFGs) on pure and mixed liquids. Under conditions where the radiation-damping-induced line broadening is smaller than the gradient-dependent inhomogeneous broadening, echo responses can be observed in difference spectra between experiments employing pulsed field gradient pairs of the same and opposite signs. These observed spin noise gradient echoes (SNGEs) were analyzed through a simple model to describe the effects of transient phenomena. Experiments performed on high-resolution nuclear magnetic resonance (NMR) probes demonstrate how refocused spin noise behaves and how it can be exploited to determine sample properties. In bulk liquids and their mixtures, transverse relaxation times and translational diffusion constants can be determined from SNGE spectra recorded following tailored sequences of magnetic field gradient pulses.

FNS-parameterization of human magnetoencephalograms for the diagnosis of photosensitive epilepsy

This work presents the results of parameterization of magnetoencephalogram signals from healthy subjects and a patient with photosensitive epilepsy. Diagnostic criteria were established during the extraction of resonant and high-frequency (chaotic) components of the initial time signals. It is shown that an increase in the intensity of the chaotic components of the studied signals in the high-frequency region leads to a violation of cross-correlation relationships and a decrease in the level of manifestation of frequency-phase synchronization. The discovered signs of photosensitive epilepsy will contribute to the development of new methods for the diagnosis and medical control of this disease based on Flicker-Noise Spectroscopy.

Chemical Current Source Express Diagnostics Using Noise Spectroscopy on the Example of Lithium-Thionyl Chloride Battery

Lithium-thionyl chloride battery voltage is practically not changing during the discharge process and drops sharply being completely discharged. In this regard, the problem of non-destructive quality control of the chemical current sources (first of all, the discharge degree) before installation thereof in the equipment becomes of particular importance. Microcalorimetric studies make it possible to rather correctly determine the current source internal self-discharge rate, predict the LCCS shelf life and its performance term. However, the heat release absolute value in current sources with sufficient storability, i.e., with low self-discharge, is very small; therefore, it is necessary to use sensitive, stationary and large-sized equipment. This makes such diagnostics impossible when operating in the stand-alone conditions. The impedance spectroscopy method could be proposed to solve this problem. However, satisfactory results are only obtained in the 0--70 % residual capacitance range. Determination of residual capacitance in the 70--100 % range appears to be rather difficult due to the absence of noticeable alteration in the informative parameter within the limits of its absolute deviation from the mean value. In this regard, it looks advisable to use noise spectroscopy as a physically independent method in diagnosing the state of chemical current sources to expand the residual capacitance diagnostics range to the 70--100 % domain, as well as to increase reliability of the chemical current source diagnostic estimate in the range of 50--70 %. Results of the electrochemical noise measurement analysis confirm promising application of the noise spectroscopy method in estimating current state of the primary chemical current sources in their low discharge domains

The Elucidation of the Molecular Mechanism of the Extrusion Process

Extrusion is a popular method for producing homogenous population of unilamellar liposomes. The technique relies on forcing a lipid suspension through cylindrical pores in a polycarbonate membrane. The quantification of the extrusion and/or recalibration processes make possible the acquisition of experimental data, which can be correlated with the mechanical properties of the lipid bilayer. In this work, the force needed for the extrusion process was correlated with the mechanical properties of a lipid bilayer derived from other experiments. Measurements were performed using a home-made dedicated device capable of maintaining a stable volumetric flux of a liposome suspension through well-defined pores and to continuously measure the extrusion force. Based on the obtained results, the correlation between the lipid bilayer bending rigidity and extrusion force was derived. Specifically, it was found that the bending rigidity of liposomes formed from well-defined lipid mixtures agrees with data obtained by others using flicker-noise spectroscopy or micromanipulation. The other issue addressed in the presented studies was the identification of molecular mechanisms leading to the formation of unilamellar vesicles in the extrusion process. Finally, it was demonstrated that during the extrusion, lipids are not exchanged between vesicles, i.e., vesicles can divide but no membrane fusion or lipid exchange between bilayers was detected.

Spin-Noise Gradient Echoes

Nuclear spin-noise spectroscopy in absence of radio frequency pulses was studied under the influence of pulsed field gradients (PFGs) on pure and mixed liquids. Under conditions, where the radiation-damping induced line broadening is smaller than the gradient dependent inhomogeneous broadening, echo responses can be observed in difference spectra between experiments employing pulsed field gradient pairs of same and opposite signs. These observed “spin-noise gradient echoes” (SNGEs) were analyzed through a simple model to describe the effects of transient phenomena. Experiments performed on high resolution NMR probes demonstrate how “refocused spin noise” behaves and how it can be exploited to determine sample properties. In bulk liquids and their mixtures transverse relaxation times as well as translational diffusion constants can be determined from SNGE spectra recorded following tailored sequences of magnetic field gradient pulses.