arXiv subjects

Morgan Hedges

Publications and source records attributed to Morgan Hedges.

8 recordsLinked to original sources

arXiv2026

Spin-Dependent Charge-State Conversion in NV Ensembles Mediated by Electron Tunneling

The nitrogen-vacancy (NV) center in diamond enables optical initialization and readout of its electronic spin, forming the basis of a wide range of quantum sensing and metrology applications. A central challenge in such measurements is the coexistence of two charge states, NV- and NV0: While detection protocols rely on the spin-dependent properties of NV-, fluorescence from NV0 does not carry useful contrast and is typically removed as background, reducing the available signal. Here, we show that the origin of NV0 emission depends strongly on the excitation wavelength in nitrogen-containing diamond. Using ensembles of NV centers with varying nitrogen concentrations, we compare excitation at the NV0 zero-phonon line (ZPL) at 575 nm with the commonly used 532 nm. We find that excitation at 575 nm generates NV0 predominantly through spin-selective tunneling from the excited state of NV- to nearby nitrogen donors, such that the NV0 emission follows the spin polarization of NV-. As a result, the NV0 fluorescence contributes to the measurable spin contrast, allowing the full fluorescence signal to be used for detection. This result opens opportunities for improved sensitivity in NV-based sensing applications.

cond-mat.mes-hall↗

arXiv2024

Pulsed Dual-axis Alkali-metal-noble-gas Comagnetometer

Alkali-metal-noble-gas comagnetometers are precision probes well-suited for tests of fundamental physics and inertial rotation sensing, combining high sensitivity of the spin-exchange-relaxation free (SERF) magnetometers with inherent suppression of magnetic field noise. Past versions of the device utilizing continuous-wave optical pumping are sensitive to a single axis perpendicular to the plane spanned by the orthogonal pump and probe laser beams. These devices are susceptible to light shifts in the alkali atoms, and to power and beam pointing fluctuations of both the probe and pump lasers, the latter of which is a dominant source of $1/f$ noise. In this work, we model and implement an approach to alkali-metal-noble-gas comagnetometers using pulsed optical pumping. After each pump laser pulse, an off-resonance probe beam measures the precession of noble-gas-spins-coupled alkali spins via optical rotation in the dark, thus eliminating effects from pump laser light shift and power fluctuations. Performing non-linear fitting on the sinusoidal transient signal with a proper phase enables separate and simultaneous measurement of signals along two orthogonal axes in the plane perpendicular to the pump beam. Effects from beam pointing fluctuations of the probe beam in the pump-probe plane is fundamentally eliminated, and signal response to pump beam pointing fluctuations is suppressed by compensation from noble-gas nuclear spins.

physics.atom-ph↗

arXiv2024

Dual axis atomic magnetometer and gyroscope enabled by nuclear spin perturbation

Alkali-noble-gas comagnetometers have become an essential tool for tests of fundamental physics and offer a compact platform for precision gyroscopy. They are, however, limited by technical noise at low frequencies, commonly due to their limited suppression of magnetic noise. Here we investigate a new method for co-magnetometry between a single noble gas and alkali species. While similar to well-known devices using self-compensation, our scheme introduces magnetic pulses that controllably perturb the noble gas and pulsed optical pumping to polarise the alkali atoms. These applied pulses allow our scheme to measure, rather than just suppress, the effect of magnetic noise thereby offering reduced cross-talk. We show numerically that our scheme retrieves four signals (rotations and magnetic fields on two transverse axes) with similar sensitivity to a single axis device. We also present a proof-of-principle experiment based on a 87Rb-129Xe cell. Our data shows a low magnetic-rotation cross-talk of $0.2 \pm 0.1\mu$Hz$/$pT, which is already on par with the most sensitive devices relying on self-compensation.

quant-ph↗

arXiv2024

Progress towards efficient 4-level photon echo memories

Quantum memories could benefit many devices in quantum information processing. For a quantum to be useful in real-world applications, the quantum memory must have a high recall efficiency. Here we demonstrate an efficient (up to 80%) spin-storage quantum memory in Er:YSO, using the 4-level rephased amplified spontaneous emission protocol. We show non-classical correlations between the ASE and RASE fields produced by the quantum memory. Also, we demonstrate the storage of 70 temporal modes, with a write time of 150 us, and a storage time of 25 us. Finally, a clear pathway is presented to improve the efficiency, storage time, and mode capacity. Such a device would have applications in quantum networking and measurement-based quantum computing.

quant-ph↗

arXiv2021

Initialisation protocol for efficient quantum memories using resolved hyperfine structure

We describe a quantum memory spectral preparation strategy that maximises memory efficiency and bandwidth in materials such as 167 Er3+:Y2SiO5 in a high field regime, where the hyperfine structure is resolved. We demonstrate the method in 167 Er3+:Y2SiO5 by preparing spectrally isolated 18 dB-absorbing features on a < 1 dB background. Using these features we create an atomic frequency comb and show quantum storage of 200 ns pulses with 22% efficiency, limited by the background absorption which arises from laser instability. We describe the experimental improvements needed to reach the material limits: O(1) s spin state storage, O(100) MHz bandwidth, and > 90% efficiency.

quant-ph↗

arXiv2021

Search for topological defect dark matter with a global network of optical magnetometers

Ultralight bosons such as axion-like particles are viable candidates for dark matter. They can form stable, macroscopic field configurations in the form of topological defects that could concentrate the dark matter density into many distinct, compact spatial regions that are small compared to the galaxy but much larger than the Earth. Here, we report the results of a search for transient signals from axion-like particle domain walls with the Global Network of Optical Magnetometers for Exotic physics searches (GNOME). We search the data, consisting of correlated measurements from optical atomic magnetometers located in laboratories all over the world, for patterns of signals propagating through the network consistent with domain walls. The analysis of data from a continuous month-long operation of the GNOME finds no statistically significant signals, thus placing experimental constraints on such dark matter scenarios.

astro-ph.CO↗

arXiv2018

NV- - N+ pair centre in 1b diamond

The study establishes that the degree of optically induced spin polarization that can be achieved for NV$^- $in 1b diamond is limited by the concentration of single substitutional nitrogen, N$^0$ . The polarization of the individual NV centres in the diamond is dependent on the separation of the NV$^-$ and the nitrogen donor. When the NV$^-$ - N$^+$ pair separation is large the properties of the pair will be as for single sites and a high degree of spin polarization attainable. When the separation decreases the emission is reduced, the lifetime shortened and the spin polarization downgraded. The deterioration occurs as a consequence of electron tunneling in the excited state from NV$^-$ to N$^+$ and results in an optical cycle that includes NV$^0$. The tunneling process is linear in optical excitation and more prevalent the closer the N$^+$ is to the NV$^-$ centre. However, the separation between the NV$^-$ and its donor N$^+$ can be effected by light through the excitation of NV$^-$ and/or ionization of N$^0$. The optical excitation that creates the spin polarization can also modify the sample properties and during excitation creates charge dynamics. The consequence is that the magnitude of spin polarization, the spin relaxation and coherence times T$_1$ and T$_2$ have a dependence on the nitrogen concentration and on the excitation wavelength. The adjacent N$^+$ gives an electric field that Stark shifts the NV$^-$ transitions and for an ensemble results in line broadening. It is observation of changes of these Stark induced effects that allow the variation in NV$^-$ - N$^+$ separation to be monitored. Spectroscopic measurements including that of the varying line widths are central to the study. They are made at low temperatures and include extensive measurements of the NV$^-$ optical transition at 637 nm, the infrared transition at 1042 nm and ODMR at 2.87 GHz.

cond-mat.mtrl-sci↗

arXiv2005

Scaling of earthquake waiting times and the Olami-Feder-Christensen model

Waiting-time statistics are generated from the Olami-Feder-Christensen model and shown to mimic some aspects of real seismicity. Preliminary analysis of the model data implies a recently proposed universal scaling law for the distribution in seismicity may be due to a mixing between aftershocks and uncorrelated event pairs, thus having limited application. Earthquake catalog data is also presented to support the argument.

physics.geo-ph↗