arXiv subjects

Ekrem Taha Güldeste

Publications and source records attributed to Ekrem Taha Güldeste.

3 recordsLinked to original sources

arXiv2024

Wavelet-based Ramsey magnetometry enhancement of a single NV center in diamond

Nitrogen-vacancy (NV) centers in diamond constitute a solid-state nanosensing paradigm. Specifically for high-precision magnetometry, the so-called Ramsey interferometry is the prevalent choice where the sensing signal is extracted from time-resolved spin-state-dependent photoluminescence (PL) data. Its sensitivity is ultimately limited by the photon shot noise, which cannot be sufficiently removed by averaging or frequency filtering. Here, we propose Ramsey DC magnetometry of a single NV center enhanced by a wavelet-denoising scheme specifically tailored to suppress photon shot noise. It simply operates as a classical post-processing applied on a collected PL time series. Our implementation is based on a method that we named template margin thresholding which enables not only frequency but also time-dependent denoising. We computationally benchmark its DC magnetic field sensing signal-to-noise-ratio improvement over the raw PL data around an order of magnitude.

quant-ph↗

arXiv2022

Wavelet-resolved coherence beats in the Overhauser field of a thermal nuclear spin ensemble

This work introduces the so-called synchrosqueezed wavelet transform, to shed light on the dipolar fluctuations of a thermal ensemble of nuclear spins in a diamond crystal structure, hyperfine-coupled to a central spin. The raw time series of the nuclear spin bath coherent dynamics is acquired through the two-point correlation function computed using the cluster correlation expansion method. The dynamics can be conveniently analyzed according to zero-, single-, and double-quantum transitions derived from the dipolar pairwise spin flips. We show that in the early-time behavior when the coherence is preserved in the spin ensemble, the Overhauser field fluctuations are modulated by dipole-dipole-induced small inhomogeneous detunings of nearly resonant transitions within the bath. The resulting beating extending over relatively longer time intervals is featured on the scalograms where both temporal and spectral behaviors of nuclear spin noise are unveiled simultaneously. Moreover, a second kind of beating that affects faster dynamics is readily discernible, originating from the inhomogeneous spread of the hyperfine coupling of each nucleus with the central spin. Additionally, any quadrupolar nuclei within the bath imprint as beating residing in the zero-quantum channel. The nuclear spin environment can be directionally probed by orienting the hyperfine axis. Thereby, crucial spatial information about the closely separated spin clusters surrounding the central spin are accessible. Thus, a wavelet-based post processing can facilitate the identification of proximal nuclear spins as revealed by their unique beating patterns on the scalograms. Finally, when these features are overwhelmed by either weakly or strongly coupled classical noise sources, we demonstrate the efficacy of thresholding techniques in the wavelet domain in denoising contaminated scalograms.

quant-ph↗

arXiv2018

Loschmidt echo driven by hyperfine and electric-quadrupole interactions in nanoscale nuclear spin baths

The nuclear spin bath (NSB) dynamics and its quantum control are of importance for the storage and processing of quantum information within a semiconductor environment. In the presence of a carrier spin, primarily it is the hyperfine interaction that rules the high frequency NSB characteristics. Here, we first study the overall coherence decay and rephasings in a hyperfine-driven NSB through the temporal and spectral behaviors of the so-called Loschmidt echo (LE). Its dependence on the NSB size, initial polarization, and coupling inhomogeneity are separately investigated, which leads to a simple phenomenological expression that can accommodate all of these attributes. Unlike the prevailing emphasis on spin 1/2, the NSBs with larger spin quantum numbers are equally considered. For this case, additionally the effect of nuclear electric quadrupole interaction is taken into account where its biaxiality term is influential on the decoherence. The insights gained from model systems are then put to use for two generic realistic semiconductor systems, namely, a donor center and a quantum dot that represent small and large nanoscale NSB examples, respectively. The spectrum of LE for large quantum dots can reach the 100~MHz range, whereas, for donor centers, it reduces to a few MHz, making them readily amenable for dynamical decoupling techniques. The effect of quadrupole interaction on LE is seen to be negligible for large quantum dots, while it becomes significant for donor centers, most notably in the form of depolarizing a polarized NSB.

quant-ph↗