arXiv subjects

Alexander M. Zaitsev

Publications and source records attributed to Alexander M. Zaitsev.

7 recordsLinked to original sources

arXiv2026

Characterizing the nitrogen-vacancy center singlet transition and its phonon sideband for absorption-based room-temperature magnetometry

Magnetometry with nitrogen-vacancy (NV) centers in diamond has shown great promise in recent years. In particular, absorption-based magnetometry techniques, employing a cavity to enhance the absorption length, can improve the contrast and sensitivity compared to conventional techniques based on reading out the NV$^-$ triplet fluorescence. The absorption techniques rely on magnetic-field-dependent absorption at the NV$^-$ singlet zero phonon line at 1042$\,$nm and its phonon sideband. In a cavity-enhanced spectroscopy approach, we study pump-laser- and microwave-induced cavity signal changes at room temperature over a spectral range of 680-1050$\,$nm. Through normalization, we eliminate the cavity-enhancement effect and provide quasi-single-pass values for the absorption and optically detected magnetic resonance (ODMR) contrast. The highest contrast is found at 1042$\,$nm, but multiple points of high contrast are found at the peaks of the phonon sideband. Additionally, cavity-enhanced ODMR contrasts in the range of 50-80$\,\%$ are presented. We further measure the broadband singlet absorption cross section at room temperature with a novel method through microwave-induced signal changes. This method is insensitive to pump-laser-induced signal changes by other defects and quantifies the room-temperature absorption strength of the singlet transition and its entire phonon sideband. We determine the absorption cross section at 1042$\,$nm to be $σ^{\,\bigstar}_{1042}=(0.89\pm0.14)\cdot 10^{-21}\,\text{m}^2$ or $σ^{\,\blacktriangle}_{1042}=(2.9\pm0.5)\cdot 10^{-21}\,\text{m}^2$. depending on the employed 532$\,$nm NV$^-$ absorption cross section.

quant-ph↗

arXiv2026

Laser-enhanced quantum sensing boosts sensitivity and dynamic range

Magnetometers based on nitrogen-vacancy (NV) centers in diamond have emerged as the most important solid-state quantum sensors. However, ensembles are limited in optical contrast to typically a few percent and high-sensitivity variants usually possess only a few $\mathrm{\upmu}$T dynamic range. Here, we demonstrate a laser threshold magnetometry-based NV system that avoids these limitations. By integrating the NV centers into a laser cavity and showing magnetic-field-dependent shifts of the laser threshold, we observe 100\,\% optical contrast, i.\,e., we are able to entirely switch off the laser system with the NV centers magnetic resonance. At the same time we achieve strong output signals up to 50\,mW. The system exhibits a photon-shot-noise-limited (PSNL) sensitivity of $<$400\,fT/$\sqrt{\textrm{Hz}}$ for all vector components, which we demonstrate to improve super-linearly with contrast. The ratio of the sensing-relevant parameters PSNL sensitivity and dynamic range, that can be traded at the cost of each other, marks an improvement factor of up to 590 over typical fluorescence-based readout and vapor cell sensors while also adding vector magnetometry capabilities. Such performance improvements provide a perspective for a highly sensitive magnetometer, which could be operated outside a magnetically-shielded room. This could bring a new generation of sensors for applications including magnetoencephalography, magnetic navigation, and magnetic anomaly detection.

quant-ph↗

arXiv2025

Two-media laser threshold magnetometry: A magnetic-field-dependent laser threshold

Nitrogen-vacancy (NV) centers in diamond are a promising platform for high-precision magnetometry. In contrast to the use of spontaneous emission in a number of NV-magnetometers, laser threshold magnetometry (LTM) exploits stimulated emission of NV centers by placing an NV-doped diamond inside an optical cavity. The NV laser system is predicted to reach a high magnetic-field-dependent contrast and coherent signal strength, leading to an improved magnetic field sensitivity combined with a high linearity. Here, we consider a two-media setup where the cavity additionally includes a vertical external cavity surface emitting laser. This optically active material compensates cavity losses at \SI{750}{nm} while still allowing for magnetic-field-dependent effects from the NV-diamond. We demonstrate a magnetic-field-dependent laser threshold and investigate the effects of pump laser induced absorption of the diamond. The experimental data is supported by an analytical simulation based on a rate model. Furthermore, we derive a generalized formula to compute the shot-noise-limited magnetic field sensitivity in the regime of high contrast yielding 49.07(33) pT/$\sqrt{\text{Hz}}$ for the present setup. Simulations with an optimized NV-diamond suggest that values down to 4.9 ft/$\sqrt{\text{Hz}}$ are possible.

physics.optics↗

arXiv2024

Discovery of ST2 centers in natural and CVD diamond

The ST2 center is an optically addressable point defect in diamond that facilitates spin initialization and readout. However, while this study presents the discovery of ST2 centers first observed in a natural diamond and provides a reliable technique for artificially creating them, its chemical structure remains unknown. To assess the potential of ST2, we map out its basic optical characteristics, reveal its electronic level structure, and quantify the intrinsic transition rates. Furthermore, we investigate its response to microwaves, static magnetic fields, and the polarization of excitation laser light, revealing twelve inequivalent orientations of the ST2 center. Simultaneous exposure to microwaves and static magnetic fields also reveals an exceptionally wide acceptance angle for sensing strong magnetic fields, unlike the well-established NV center, which is sensitive only within a narrow cone aligned with its symmetry axis. This finding establishes the ST2 center as a highly promising candidate for nanoscale quantum sensing.

physics.optics↗

arXiv2024

High-contrast absorption magnetometry in the visible to near-infrared range with nitrogen-vacancy ensembles

Magnetometry with nitrogen-vacancy (NV) centers has so far been measured via emission of light from NV centers or via absorption at the singlet transition at 1042 nm. Here, we demonstrate a phenomenon of broadband optical absorption by the NV centers starting in the emission wavelength and reaching up to 1000 nm. The measurements are enabled by a high-finesse cavity, which is used for room temperature continuous wave pump-probe experiments. The red to infrared probe beam shows the typical optically detected magnetic resonance (ODMR) signal of the NV spin with contrasts up to 42 %. This broadband optical absorption is not yet reported in terms of NV magnetometry. We argue that the lower level of the absorbing transition could be the energetically lower NV singlet state, based on the increased optical absorption for a resonant microwave field and the spectral behavior. Investigations of the photon-shot-noise-limited sensitivity show improvements with increasing probe wavelength, reaching an optimum of 7.5 pT/$\sqrt{\mathrm{Hz}}$. The results show significantly improved ODMR contrast compared to emission-based magnetometry. This opens a new detection wavelength regime with coherent laser signal detection for high-sensitivity NV magnetometry.

physics.app-ph↗

arXiv2020

High-dynamic-range transmission-mode detection of synchrotron radiation using X-ray excited optical luminescence in diamond

We demonstrate enhancement of X-ray excited optical luminescence in a 100-micron-thick diamond plate by introduction of defect states via electron beam irradiation and subsequent high-temperature annealing. The resulting X-ray transmission-mode scintillator features a linear response to incident photon flux in the range of 7.6$\times$10$^8$ to 1.26$\times10^{12}$ photons/s/mm$^2$ for hard X-rays (15.9 keV) using exposure times from 0.01 to 5 s. These characteristics enable a real-time transmission-mode imaging of X-ray photon flux density without disruption of X-ray instrument operation.

physics.ins-det↗

arXiv2015

Ion Irradiation of Nanocrystalline Graphene on Quartz and Sapphire

The effects of Ga+ ion irradiation and high temperature annealing on behavior of nanocrystalline graphene directly grown on quartz and sapphire are presented. It is shown that nanocrystalline graphene stands fairly high doses of ion irradiation (up to 3e14 cm-2 of 5 to 50 keV Ga+ ions) without degradation in conductance. At higher doses, nanocrystalline graphene rapidly loses its conductance and at doses over 2e15 cm-2 becomes actually insulating. Annealing in vacuum restores conductance of the irradiated nanocrystalline graphene and, if the irradiation has not exceeded a dose of 3e15 cm-2, this restoration can be complete. Ion irradiation at high doses approaching 1e16 cm-2 results in complete ion sputtering of a few layer graphene. Along with the irradiation-induced reduction of conductance and the temperature-induced restoration of conductance, two other effects of the ion irradiation are the enhancement of adhesion of graphene to substrate and the increase in the nucleation capability of substrate for direct deposition of graphene. For 50 keV Ga+ ions, the enhancement of adhesion is observed at irradiation doses over 2e14 cm-2. The promoted graphene nucleation is observed in a broad dose range. It is shown that the above effects can be used for development of methods of patterning of graphene on insulating substrates and a method of imprint lithography of graphene.

cond-mat.mes-hall↗