arXiv subjects

Carlos A. Meriles

Publications and source records attributed to Carlos A. Meriles.

At least 19 recordsLinked to original sources

arXiv2026

Observation of long-lived spin order in nanoconfined water

Liquids confined to nanometer-scale geometries exhibit behavior that departs markedly from their bulk counterparts, yet studying their dynamics under controlled conditions remains experimentally challenging. Here, we use nitrogen-vacancy (NV) center nuclear magnetic resonance (NMR) spectroscopy to probe water confined in 5.6 nm channels as a function of temperature. The system remains liquid throughout the investigated temperature range and exhibits strongly suppressed diffusivity, enabling direct detection of its 1H NMR spectrum. Occasionally, the proton resonance transforms into a doublet with a splitting of several tens of kilohertz, which we tentatively attribute to hyperfine interactions mediated by long-lived paramagnetic charge complexes, in turn seeded by solvated electrons optically injected during laser illumination. The intermittent appearance of this feature suggests a metastable state comprising a correlated population of charge-hydration complexes extending throughout the confined liquid.

cond-mat.mes-hall↗

arXiv2026

Dynamic locking of an interacting spin system via periodic driving

Periodic driving plays a central role in quantum control, but its application in interacting spin systems is often restricted to near-resonant conditions, where standard averaging techniques remain valid. Here we investigate how detuning from resonance can be used to dynamically spin-lock a dipolar-coupled ensemble. We show that the combination of offset and pulse structure generates an effective Rabi field with sharply structured amplitude and tilt. This behavior - supported by a semi-analytical framework, numerical simulations and experiment - enables new approaches to many-body system control, here exemplified via offset-induced reversible interconversion of Zeeman and dipolar order, and heterospin polarization transfer away from rf-field matching conditions. Further, we leverage artificial-intelligence-assisted sequence design to explore regimes with long control cycles - where average Hamiltonian theory breaks down, but effective locking persists - opening pathways to rich offset-dependent responses. These findings position offset-enabled dynamic locking as a promising tool for quantum sensing, energy transfer, and spin-order manipulation beyond traditional approaches.

quant-ph↗

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↗

arXiv2026

Magnetically tunable telecom emission from Er3+ ions in layered WS2

Erbium ions (Er3+) provide a telecom-band optical transition with strong magnetic-dipole character, making them attractive for quantum communication and spin-photon interfaces. Identifying host environments that combine low decoherence with photonic compatibility, however, remains a central challenge. Here we investigate Er3+ emission in tungsten disulfide (WS2) flakes, a layered host offering low nuclear-spin density and narrow telecom emission. Using time- and polarization-resolved photoluminescence under modest magnetic fields (< 0.2 T), we observe pronounced dimming, lifetime extension, and rotation of the emission dipole when the field has an out-of-plane component, whereas in-plane fields produce little change. Effective model calculations of Er3+ in monolayer WS2 parametrized from density functional theory indicate that these effects arise primarily from Zeeman-induced mixing of near-degenerate crystal-field sublevels, which modifies the magnitude and orientation of the optical transition dipole moments. Comparative measurements in flakes of different thickness and numerical estimates of the local density of optical states further suggest a secondary contribution from dipole coupling to the anisotropic photonic environment of thin WS2 layers. These findings identify layered WS2 as a platform where magnetic fields can tune telecom emission through an interplay of crystal-field physics and anisotropic photonic coupling.

cond-mat.mes-hall↗

arXiv2026

On-chip electrically reconfigurable octave-bandwidth optical amplification from visible to near-infrared

Achieving broadband on-chip optical amplification spanning the visible and near-infrared (NIR) can enable diverse quantum sensing, metrology, and classical communication applications within a single unified device. However, conventional semiconductor and ion-doped amplifiers suffer from limited gain bandwidths set by fixed energy levels, while optical parametric amplifiers (OPAs) operating continuously from the visible to the NIR have remained elusive due to dispersion-limited bandwidth and the high pump powers required in the visible or ultraviolet (UV). Here, we overcome these limitations by introducing an electrically reconfigurable OPA architecture on lithium niobate integrated photonics. By synergistically combining ultra-high effective $χ^{(2)}$ nonlinearity ($\sim$7,000\%/W-cm$^2$), high-order dispersion engineering, and local electro-thermal tuning of quasi-phase matching, our device achieves record gain spectral spanning more than an optical octave, from 770 to 1650 nm. This range covers key transitions of many photonic quantum systems and all telecommunication bands. Moreover, our approach eliminates the need for high-power, wavelength-tunable visible or UV pumps, delivering a peak on-chip gain of 23.67 dB with a single 1060 nm pump at 90 mW average on-chip power. This work opens new avenues for multi-functional, reconfigurable photonics unifying the visible and infrared regimes, with broad implications for quantum sensing and communications.

physics.optics↗

arXiv2026

Erbium Probes of Magnetic Order in a Layered van der Waals Material

There is growing interest in characterizing magnetic order and dynamics in two-dimensional magnets, yet most efforts to date rely on external probes that interrogate the sample from tens of nanometers away and inevitably average over that length scale. Here we use internal, lattice-embedded Er3+ defects in CrSBr as atomic-scale probes, accessing their telecom-band photoluminescence with spectroscopy and temperature-dependent confocal imaging to read out magnetism from within the material. At room temperature we observe narrow, long-lived photoluminescence (PL) lines in the telecom band, characteristic of erbium emitters. Upon cooling to 3 K and reheating, the Er3+ PL intensity and excited-state lifetime display pronounced thermal hysteresis with a minimum near 132 K, at the reported antiferromagnetic (AFM) transition of CrSBr. Remarkably, we observe magnetic signatures persisting over a broader temperature range than expected from bulk benchmarks, suggesting nanoscale magnetic order that locally survives beyond the nominal phase boundary. Further, a moderate in-plane field of 0.3 T shifts the PL minimum by +8 K, which we tentatively associate to field-biased ferromagnetic correlations.

cond-mat.mes-hall↗

arXiv2026

Emission of nitrogen-vacancy centers in diamond shaped by topological photonic waveguide modes

As the ability to integrate single photon emitters into photonic architectures improves, so does the need to characterize and understand their interaction. Here, we use a scanning diamond nanocrystal to investigate the interplay between the emission of room-temperature nitrogen-vacancy (NV) centers and a proximal topological waveguide. In our experiments, NVs serve as local, spectrally broad light sources which we exploit to characterize the waveguide bandwidth as well as the correspondence between light injection site and directionality of wave propagation. Further, we find that near-field coupling to the waveguide influences the spectral shape and ellipticity of the NV photoluminescence, hence allowing us to reveal nanostructured light fields with a spatial resolution defined by the nanoparticle size. Our results expand on the sensing modalities afforded by color centers, and portend novel opportunities in the development of on-chip, quantum optics devices leveraging topological photonics to best manipulate and readout single-photon emitters.

physics.optics↗

arXiv2025

Statistical imaging of NV centers reveals clustered defect formation in diamond

The sharp optical resonances of NV- centers in diamond at cryogenic temperatures offer powerful new capabilities for material characterization, but extracting the most detailed information typically requires careful calibration of individual sensors, limiting scalability. In this work, we use resonant photoluminescence excitation imaging to optically resolve and monitor hundreds of individual NVs across large fields of view, enabling statistical analysis of their spatial distribution with sub-diffraction resolution. This multiplexed, non-destructive approach allows quantum sensors to characterize the material platform they inhabit. Focusing on CVD-grown diamond, we uncover significant deviations from random distributions, including an unexpectedly high occurrence of closely spaced clusters comprising two or more NVs. These findings suggest non-Poissonian formation dynamics and point to spatially correlated defect generation mechanisms. Beyond offering insight into diamond growth and NV center formation, our approach enables the scalable identification of naturally occurring NV clusters - configurations that are promising for entanglement-assisted quantum information protocols and correlated sensing - and establishes a path toward structural and electronic defect analysis in various material hosts at the single-emitter level.

cond-mat.mtrl-sci↗

arXiv2025

Density-functional theory study of the interaction between NV$^{-}$ centers and native defects in diamond

The NV$^{-}$ color center in diamond has been demonstrated as a nanoscale sensor for quantum metrology. However, the properties that make it ideal for measuring, e.g., minute electric and magnetic fields also make it sensitive to imperfections in the diamond host. In this work, we quantify the impact of nearby native defects on the many-body states of NV$^{-}$. We combine previous quantum embedding results of strain and electric-field susceptibilities of NV$^{-}$ with density-functional theory calculations on native defects. The latter are used to parametrize continuum models in order to extrapolate the effects of native defects up to the micrometer scale. We show that under ideal measuring conditions, the optical properties of NV$^{-}$ are measurably affected by the strain caused by single carbon interstitials and vacancies up to 200 nm away; in contrast, the NV$^{-}$ is measurably affected by the electric field of such charged (neutral) native defects within a micron (100 nm). Finally, we show how measuring multiple individual NV$^{-}$ centers in the vicinity of a native defect can be used to determine the nature of the defect and its charge state.

cond-mat.mtrl-sci↗

arXiv2025

Nitrogen-Vacancy Magnetometry of Edge Magnetism in WS2 Flakes

Two-dimensional (2D) magnets are of significant interest both as a platform for exploring novel fundamental physics and for their potential in spintronic and optoelectronic devices. Recent bulk magnetometry studies have indicated a weak ferromagnetic response in WS2, and theoretical predictions suggest edge-localized magnetization in flakes with partial hydrogenation. Here, we use room-temperature wide-field quantum diamond magnetometry to image pristine and Fe-implanted WS2 flakes of varying thicknesses (45-160 nm), exfoliated from bulk crystals and transferred to NV-doped diamond substrates. We observe direct evidence of edge-localized stray magnetic fields, which scale linearly with applied external magnetic field (4.4-220 mT), reaching up to 4.7 uT. The edge signal shows a limited dependence on the flake thickness, consistent with dipolar field decay and sensing geometry. Magnetic simulations using five alternative models favor the presence of edge magnetization aligned along an axis slightly tilted from the normal to the WS2 flake plane, consistent with spin canting in antiferromagnetically coupled edge states. Our findings establish WS2 as a promising platform for edge-controlled 2D spintronics.

cond-mat.mes-hall↗

arXiv2025

Beyond ensemble averaging: Parallelized single-shot readout of hole capture in diamond

Understanding the generation, transport and capture of charge carriers in semiconductors is of fundamental technological importance. However, the ensemble measurement techniques ubiquitous in electronics offer limited insight into the nanoscale environment that is crucial to the operation of modern quantum-electronic devices. Here, we combine widefield optical microscopy with precision spectroscopy to examine the capture of photogenerated holes by negatively charged nitrogen vacancy (NV-) centers in diamond. Simultaneous single-shot charge readout over hundreds of individual NVs allows us to resolve the roles of ionized impurities, reveal the formation of space charges fields, and monitor the thermalization of hot photo-carriers during diffusion. We measure effective NV- hole capture radii in excess of 0.2 um, a value approaching the Onsager limit and made possible here thanks to the near-complete neutralization of coexisting charge traps. These results establish a new platform for resolving charge dynamics beyond ensemble averages, with direct relevance to nanoscale electronics and quantum devices.

cond-mat.mes-hall↗

arXiv2025

Probing interfacial water via color-center-enabled spin magnetometry

Understanding the behavior of confined water at liquid-solid interfaces is central to numerous physical, chemical, and biological processes, yet remains experimentally challenging. Here, we utilize shallow nitrogen-vacancy (NV) centers in diamond to investigate the nanoscale dynamics of interfacial water confined between the diamond surface and an overlying fluorinated oil droplet. Using NV-based nuclear magnetic resonance protocols selectively sensitive to 1H and 19F, we independently track water and oil near the interface under ambient conditions. Comparing opposite sides of a doubly-implanted diamond membrane - one exposed to oil, the other not - we uncover a slow, multi-day process in which the interfacial water layer is gradually depleted. This desorption appears to be driven by sustained interactions with the fluorinated oil and is supported by molecular dynamics simulations and surface-sensitive X-ray spectroscopies. Our findings provide molecular-level insight into long-timescale hydration dynamics and underscore the power of NV-NMR for probing liquid-solid heterointerfaces with chemical specificity.

physics.chem-ph↗

arXiv2025

Erbium-implanted WS2 flakes with room-temperature photon emission at telecom wavelengths

Optically addressable spin impurities in crystals along with device engineering provide an attractive route to realizing quantum technologies in the solid state, but reconciling disparate emitter and host material constraints for a given target application is often challenging. Rare-earth ions in two-dimensional (2D) materials could mitigate this problem given the atomic-like transitions of the emitters and the versatile nature of van der Waals systems. Here we combine ion implantation, confocal microscopy, and ab-initio calculations to examine the photon emission of Er-doped WS2 flakes. Optical spectroscopy reveals narrow, long-lived photo-luminescence lines in the telecom band, which we activate after low-temperature thermal annealing. Spectroscopic and polarization-selective measurements show a uniform response across the ensemble, while the fluorescence brightness remains mostly unchanged with temperature, suggesting non-radiative relaxation channels are inefficient. Our results create opportunities for novel solid state devices coupling 2D-hosted, telecom-band emitters to photonic heterostructures separately optimized for photon manipulation.

cond-mat.mes-hall↗

arXiv2025

High-Efficiency, High-Fidelity Charge Initialization of Shallow Nitrogen Vacancy Centers in Diamond

Nitrogen vacancy (NV) centers in diamond exhibit long spin coherence times, optical initialization, and optical spin readout under ambient conditions, making them excellent quantum sensors. However, the conventional scheme for charge state initialization based on off-resonant green excitation results in significant state preparation errors, typically around 30%. One method for improving charge state initialization fidelity is to use multicolor excitation, which has been demonstrated to achieve a near-unity preparation fidelity for bulk NV centers by using a few milliseconds of near-infrared (5 mW) and green (10 μW) excitation. The translation of such schemes to NV centers near the diamond surface with higher efficiency optical pumping would enable myriad tasks in nanoscale sensing. Here, we demonstrate a protocol for efficient charge initialization of shallow NV centers between 5 nm and 15 nm from the diamond surface. By carefully studying the charge dynamics of shallow NV centers, we identify a region of parameter space that allows for near-unity (95%) charge initialization within 300 μs of near-infrared (1 mW) and green (10 μW) excitation. The time to 90% charge initialization can be as fast as 10 μs for 4 mW of near-infrared and 39 μW of green illumination. This fast, efficient charge initialization protocol will enable nanoscale sensing applications where state preparation errors currently prohibit scaling, such as measuring higher-order multi-point correlators.

cond-mat.mtrl-sci↗

arXiv2024

Slow water in engineered nano-channels revealed by color-center-enabled sensing

Nanoscale confinement of molecules in a fluid can result in enhanced viscosity, local fluidic order, or collective motion. Confinement also affects ion transport and/or the rate and equilibrium concentration in a chemical reaction, all of which makes it the subject of broad interest. Studying these effects, however, is notoriously difficult, mainly due to the lack of experimental methods with the required sensitivity and spatial or time resolution. Here we leverage shallow nitrogen-vacancy (NV) centers in diamond to probe the dynamics of room-temperature water molecules entrapped within ~6-nm-tall channels formed between the diamond crystal and a suspended hexagonal boron nitride (hBN) flake. NV-enabled nuclear magnetic resonance measurements of confined water protons reveal a much reduced H2O self-diffusivity, orders of magnitude lower than in bulk water. We posit the slow dynamics stem from the accumulation of photogenerated carriers at the interface and trapped fluid, a notion we support with the help of molecular dynamics modeling. Our results provide feedback for theories describing interfacial water, and lay out a route for investigating other fluids under confinement.

cond-mat.mes-hall↗

arXiv2024

Quantum embedding study of strain and charge induced Stark effects on the NV$^{-}$ center in diamond

The NV$^{-}$ color center in diamond has been demonstrated as a powerful nanosensor for quantum metrology due to the sensitivity of its optical and spin properties to external electric, magnetic, and strain fields. In view of these applications, we use quantum embedding to derive a many-body description of strain and charge induced Stark effects on the NV$^{-}$ center. We quantify how strain longitudinal to the axis of NV$^{-}$ shifts the excited states in energy, while strain with a component transverse to the NV$^{-}$ axis splits the degeneracies of the $^{3}E$ and $^{1}E$ states. The largest effects are for the optically relevant $^{3}E$ manifold, which splits into $E_{x}$ and $E_{y}$ with transverse strain. From these responses we extract strain susceptibilities for the $E_{x/y}$ states within the quasi-linear regime. Additionally, we study the many-body dipole matrix elements of the NV$^{-}$ and find a permanent dipole 1.64 D at zero strain, which is somewhat smaller than that obtained from recent density functional theory calculations. We also determine the transition dipole between the $E_{x}$ and $E_{y}$ and how it evolves with strain.

cond-mat.mtrl-sci↗

arXiv2024

Quantum Noise Spectroscopy of Criticality in an Atomically Thin Magnet

Dynamic critical fluctuations in magnetic materials encode important information about magnetic ordering in the associated critical exponents. Using nitrogen-vacancy centers in diamond, we implement $T_2$ (spin-decoherence) noise magnetometry to study critical dynamics in a 2D Van der Waals magnet CrSBr. By analyzing NV decoherence on time scales approaching the characteristic correlation time $τ_c$ of critical fluctuations, we extract the critical exponent $ν$ for the correlation length. Our result deviates from the Ising prediction and highlights the role of long-range dipolar interactions in 2D CrSBr. Furthermore, analyzing the divergence of the correlation length suggests the possibility of 2D-XY criticality in CrSBr in a temperature window near $T_C$ where static magnetic domains are absent. Our work provides a first demonstration of $T_2$ noise magnetometry to quantitatively analyze critical scaling behavior in 2D materials.

cond-mat.mes-hall↗

arXiv2024

Photoinduced charge injection from shallow point defects in diamond into water

Thanks to its low or negative surface electron affinity and chemical inertness, diamond is attracting broad attention as a source material of solvated electrons produced by optical excitation of the solid-liquid interface. Unfortunately, its wide bandgap typically imposes the use of wavelengths in the ultra-violet range, hence complicating practical applications. Here we probe the photocurrent response of water surrounded by single-crystal diamond surfaces engineered to host shallow nitrogen-vacancy (NV) centers. We observe clear signatures of diamond-induced photocurrent generation throughout the visible range and for wavelengths reaching up to 594 nm. Experiments as a function of laser power suggest that NV centers and other co-existing defects - likely in the form of surface traps - contribute to carrier injection, though we find that NVs dominate the system response in the limit of high illumination intensities. Given our growing understanding of near-surface NV centers and adjacent point defects, these results open new perspectives in the application of diamond-liquid interfaces to photo-carrier-initiated chemical and spin processes in fluids.

cond-mat.mtrl-sci↗