arXiv subjects

Dmitry Budker

Publications and source records attributed to Dmitry Budker.

At least 19 recordsLinked to original sources

arXiv2026

Solid-state nuclear magnetic resonance search for axion-like dark matter with broadband SQUID magnetometry

We report the results of an experimental search for ultralight axion-like dark matter in the mass ranges 19.5--20.5 and 21.5--22 neV. The Cosmic Axion Spin Precession Experiment-electric probes the axion-nuclear electric dipole moment coupling. We perform solid-state nuclear magnetic resonance on $^{207}$Pb spin ensembles which reside in a polarized ferroelectric crystal. The background axion-like dark matter field induces an oscillating torque on the $^{207}$Pb spins via the electric dipole moment coupling $g_{d}$. The experiment is calibrated with pulsed magnetic resonance measurements covering two frequency bands (4.6--5.0 and 5.2--5.3 MHz) that correspond to the axion Compton frequencies associated with the identified axion mass ranges. By sweeping the leading magnetic field applied to the sample, we are able to detect the $^{207}$Pb nuclear magnetic resonance in these frequency ranges using a superconducting quantum interference device, inductively coupled to the sample with a broadband circuit. We establish the upper bounds $|g_{d}| < 4\times 10^{-4}$ GeV$^{-2}$ with 95% confidence in these frequency bands. Our results demonstrate the detection and small-tip angle calibration of low-field $^{207}$Pb nuclear magnetic resonance, allowing for sensitivity to axion-like dark matter in the nanoelectron-volt axion mass range.

hep-ex↗

arXiv2026

The QTF-Backbone: Proposal for a Nationwide Optical Fibre Backbone in Germany for Quantum Technology and Time and Frequency Metrology

The recent breakthroughs in the distribution of quantum information and high-precision time and frequency (T&F) signals over long-haul optical fibre networks have transformative potential for physically secure communications, resilience of timing infrastructure (such as that supporting Global Navigation Satellite Systems (GNSS)) and fundamental physics. To date, these capabilities remain confined to isolated testbeds, with quantum and T&F signals accessible, for example in Germany, to only a few institutions. In this white paper we propose the QTF Backbone: a dedicated national fibre-optic infrastructure in Germany for the networked distribution of Quantum and T&F signals using dark fibres and specialised hardware. The QTF Backbone is planned as a four-phase deployment over ten years to ensure scalable, sustainable access for research institutions and industry. The concept builds on successful demonstrations of time and frequency distribution at high Technology Readiness Levels (TRLs) across Europe, including PTB-MPQ links in Germany, REFIMEVE in France, and the Italian LIFT network. The QTF Backbone will enable transformative Research and Development (R&D), support a nationwide QTF ecosystem, and ensure the transition from innovation to deployment. As a national and European hub, it will position Germany and Europe at the forefront of quantum networking, as well as T&F transfer.

physics.ins-det↗

arXiv2026

Superfluid He-4 as Dark Matter Detectors

Superfluid helium-4 is an attractive medium for high-sensitivity detection of dark matter (DM) candidates (as well as other particles). There are several collaborations that have built and tested superfluid helium detectors, particularly focusing on the sub-GeV DM mass range. In this paper we discuss a novel idea for detecting Axion (Anti)Quark Nuggets (AQN) by using parasitically the superfluid helium-4 LHC cooling system as a unique large-scale earth bound DM detector. In the case of the AQN, we address the question of propagation in the metal parts surrounding the helium. An AQN induces significant heating around the propagation track that damages the enclosure.

hep-ph↗

arXiv2026

Wavelength-Resolved Photoinduced Spin Polarization in a Broad Optical Range for a Porphyrin-Quinone System

Photochemically induced dynamic nuclear polarization (photo-CIDNP) in liquid-state donor-acceptor systems is typically studied at a limited number of excitation wavelengths, leaving its spectral dependence incompletely characterized. Understanding the wavelength dependence of photo-CIDNP is important both for elucidating the underlying spin-chemical mechanisms and for optimizing hyperpolarization strategies in chemically and biologically relevant molecular systems. Here, we investigate wavelength-resolved photo-CIDNP in a tetraphenylporphyrin-1,4-benzoquinone donor-acceptor system over the 350-800 nm spectral range. Photon-flux-normalized CIDNP amplitudes were measured using both a tunable laser system and a broadband xenon lamp equipped with interchangeable 10 nm interference filters. The CIDNP response exhibits a non-monotonic dependence on excitation wavelength. Pronounced hyperpolarization is observed near 350 nm and in the 500-550 nm region, whereas excitation within the strongly absorbing 400-450 nm range results in a substantially reduced CIDNP response. Comparison with the UV-Vis absorption spectrum demonstrates that photo-CIDNP efficiency is not governed solely by optical absorption and reflects wavelength-dependent photophysical processes. After normalization to the excitation photon flux, lamp- and laser-based measurements yield consistent CIDNP results, validating broadband filtered excitation as a reliable and experimentally accessible approach for wavelength-resolved photo-CIDNP studies. These results establish excitation wavelength as an independent control parameter for liquid-state photo-CIDNP and provide a framework for systematic investigations of wavelength-dependent spin hyperpolarization.

physics.chem-ph↗

arXiv2026

Is Lindblad for me?

The Lindblad master equation is a foundational tool for modeling the dynamics of open quantum systems. As its use has extended far beyond its original domain, the boundaries of its validity have grown opaque. In particular, the rise of new research areas including open quantum many-body systems, non-equilibrium condensed matter, and the possibility to test its limits in driven-open quantum simulators, call for a critical revision of its regimes of applicability. In this pedagogical review, we re-examine the folklore surrounding its three standard approximations (Born, Markov, and Rotating Wave Approximation), as we build our narrative by employing a series of examples and case studies accessible to any reader with a solid background on the fundamentals of quantum mechanics. As a synthesis of our work, we offer a checklist that contrasts common lore with refined expectations, offering a practical guideline for assessing the breakdown of the Lindblad framework in the problem at hand.

quant-ph↗

arXiv2026

High-Frequency Gravitational Wave Constraints from Precision Spectroscopy

Gravitational waves affect the propagation of electromagnetic waves in laser cavities, modulating the frequency of emitted photons. We use this effect to search for high-frequency gravitational waves between 100 kHz and 100 MHz using optical precision spectroscopy. Our limits constrain much of this frequency range for the first time. We discuss future improvements of the technique, which we expect to enhance the sensitivity by eight orders of magnitude, and to extend the frequency coverage up to at least 1 GHz.

gr-qc↗

arXiv2026

Search for a solar-bound axion halo using the Global Network of Optical Magnetometers for Exotic physics searches

We report on a search for a gravitationally bound solar axion halo using data from the Global Network of Optical Magnetometers for Exotic physics searches (GNOME), a worldwide array of magnetically shielded atomic magnetometers with sensitivity to exotic spin couplings. Motivated by recent theoretical work suggesting that self-interacting ultralight axions can be captured by the Sun's gravitational field and thermalize into the ground state, we develop a signal model for the pseudo-magnetic fields generated by axion-proton gradient couplings in such a halo. The analysis focuses on the fifth GNOME Science Run (69 days, 12 stations), employing a cross-correlation pipeline with time-shifted daily modulation templates to search for the global, direction-dependent, monochromatic signal expected from a solar axion halo. No statistically significant candidate signals are observed. We set 95% confidence-level upper limits on the amplitude of the axion-induced pseudo-magnetic field over the frequency range $\approx 0.05-20$ Hz, translating to constraints on the linear and quadratic axion-proton couplings for halo densities predicted by gravitational capture models and for the maximum overdensities allowed by planetary ephemerides. In the quadratic coupling case, our limits surpass existing astrophysical bounds by over two orders of magnitude across much of the accessible parameter space.

physics.atom-ph↗

arXiv2026

A Levitated-Magnet Vector Force Sensor for Spin-Dependent Exotic Interactions

We present a magnetically levitated ferromagnetic vector force sensor that enables selective searches for spin-dependent exotic interactions mediated by beyond-Standard-Model bosons. A defining feature of spin-dependent exotic interactions is that they can generate forces with distinct directional signatures set by the relative spin configuration of the interacting bodies. We show that our sensor resolves these signatures by mapping forces along different axes onto distinct translational modes with different resonance frequencies, thereby separating interaction channels within the same coupling class. As a representative example, we study parity-violating axial-vector--vector interactions mediated by a spin-1 $Z'$ boson between a sensing and a driving levitated ferromagnet. Using a matched-filter likelihood analysis, we show that a setup based on an already demonstrated experiment can probe the pure electron--electron coupling $g_A^e g_V^e$ in the previously inaccessible force range $λ\lesssim 1\,\mathrm{cm}$, corresponding to mediator masses $M_{Z'} \gtrsim 10^{-5}\,\mathrm{eV}/c^2$. Our results establish levitated ferromagnets as a promising platform for millimeter-scale searches for spin-dependent fifth forces and for resolving the multiple effective potentials associated with a given coupling class.

hep-ph↗

arXiv2026

Generation of continuous-wave laser light at 148.4 nm using cavity-enhanced second harmonic generation in $BaMgF_4$

We experimentally investigate the potential of $BaMgF_4$ crystals to create a continuous-wave (CW) solid state laser at the vacuum ultraviolet (VUV) wavelength of 148.4 nm via cavity-enhanced second harmonic generation. This investigation is motivated by the development of a nuclear optical clock based on a transition between the ground and isomeric state in the $^{229}Th$ nucleus. For this purpose, a $BaMgF_4$ crystal was grown, optically polished and periodically poled. The crystal was inserted into a power-enhancement cavity, resonant at the fundamental wavelength of 296.8 nm and the generated laser light at 148.4 nm was characterized. Within this proof-of-concept investigation, a VUV output power of typically ($16\pm1$) pW is obtained. This marks the first time that this type of crystal is used to generate VUV laser light. The experimental findings are compared to theoretical expectations and provide a clear path for future improvements.

physics.optics↗

arXiv2026

Ferromagnetic broadband sensing of axionlike dark matter

Levitated particles have demonstrated ultrahigh sensitivity to magnetic fields and accelerations owing to their extremely low dissipation. Such systems have strong potential for fundamental physics research, particularly for the detection of axions and axionlike particles, well-motivated dark matter candidates spanning a broad mass range. In this context, both high sensitivity and large bandwidth are essential. Here, we demonstrate a levitated magnet magnetometer based on an engineered double-resonance mode, achieving an effective linewidth at its optimal sensitivity that is approximately three orders of magnitude broader than those of previous approaches. Together with a hard-magnet array that enhances the axion-induced signal and soft-ferromagnetic shielding that suppresses environmental magnetic noise, this system constitutes a hybrid ferromagnetic platform for axionlike dark matter searches. We search for axionlike dark matter through its photon coupling $g_{aγ}$ over the $40$-$3000\,\mathrm{Hz}$ frequency range and establish new direct limits in this frequency band. The best sensitivity is achieved near the upper resonance around $276\,\mathrm{Hz}$, where the magnetometer reaches a magnetic-field resolution of $0.7\,\mathrm{fT}$, corresponding to a limit of $g_{aγ}\sim10^{-7}\,\mathrm{GeV}^{-1}$. At this frequency, this result improves upon previous direct limits by more than four orders of magnitude. The demonstrated high-bandwidth levitated sensor may also enable a broad range of applications, including biological sensing and precision measurements.

hep-ex↗

arXiv2026

Microwave-free vector magnetometry and crystal orientation determination with Nitrogen-Vacancy centers using Bayesian inference

Nitrogen-vacancy (NV) centers in diamond provide a solid-state platform for quantum sensing. While optically detected magnetic resonance techniques offer high sensitivity, their reliance on microwaves introduces heating and stray electromagnetic fields that can perturb nearby samples. Optical approaches based on cross-relaxation between differently oriented NV centers remove this constraint but have so far required stringent alignment of the external field with crystallographic axes, restricting their practicality. Here we introduce a general framework for microwave-free vector magnetometry at near-zero field that leverages Bayesian inference to extract both the magnetic field vector and the NV orientation directly from photoluminescence maps. An analytical model of cross-relaxation resonances enables efficient inference under arbitrary field and orientation configurations, while naturally incorporating the discrete degeneracies of the NV symmetry. We experimentally demonstrate robust orientation determination and vector-field reconstruction, establishing a general route toward compact and alignment-free NV magnetometers for practical sensing applications.

quant-ph↗

arXiv2026

A tunable feedback-controlled magnetic trap for a magnet in free fall

Ferromagnets in free space are predicted to exhibit pure Larmor precession at near-zero magnetic fields and provide exceptional sensitivity for magnetometry and gyroscopy. Notably, pure Larmor precession has not been observed in a macroscopic ferromagnetic particle, despite its fundamental importance and potential for probing relativistic effects and dark-matter interactions. Realizing such dynamics requires true free fall to eliminate clamping losses and trap-induced systematics. A central challenge is designing a tunable trap that is weak enough to permit near-free evolution yet robust enough to withstand the disturbances of launch and release. Here, we propose and demonstrate a novel master proportional-integral-differential magnetic trap (MPIDMT) combining a PID-controlled coil system with a master control coil system. Implemented in the third-generation drop tower - Einstein-Elevator, during the microgravity phase the system stably levitates a ferromagnetic particle against shock accelerations up to 1.5 g and resolves its motion in both a low-field (0.4 g) configuration and in pure free fall. These results represent a key step toward free-fall ferromagnetic magnetometry, the long-sought direct observation of macroscopic Larmor precession, and future space-based experiments.

physics.atom-ph↗

arXiv2026

Optically detected nuclear magnetic resonance of carbon-13 in bulk diamond

Precision measurements based on optically detected nuclear magnetic resonance offer exquisite sensitivity to absolute shifts in spin transition frequencies, with potential applications in fundamental physics experiments and inertial sensing. We investigate 13C nuclear spins in diamond as a candidate system for solid-state implementations, which hold the promise for high-fidelity readout of large numbers of coherent nuclear spins in millitesla or lower magnetic fields. We demonstrate a technique that allows for both optical polarization and readout of large ensembles of ~10^{16} polarized nuclear spins. Our method takes advantage of state-selective Landau-Zener transitions under microwave frequency sweeping, which bidirectionally transfer spin polarization between Nitrogen-Vacancy (NV) electron spins and remote 13C nuclear spins. Using natural isotopic abundance diamonds with nitrogen densities of ~0.5-10 ppm, we perform optically-detected 13C Ramsey spectroscopy and realize a nuclear-spin-dependent fluorescence contrast exceeding 0.5% peak-to-peak. We observe nuclear spin dephasing times T2*~2 ms that only modestly improve with homonuclear dipolar decoupling, indicating that they are limited by the longitudinal spin relaxation of nearby NV electron spins. We study the magnetic field dependence of the optical readout and find comparable contrast and dephasing times for magnetic fields in the range 8-20 mT. Our method can be interpreted as a type of repetitive readout, where each NV center optically reads out the spin state of ~100 nuclei before nuclear spins depolarize.

quant-ph↗

arXiv2026

Continuous coherent spin-frequency metrology in storage rings via resonant beam-driven detection

Precision measurements in storage rings are increasingly limited by the ability to monitor collective spin dynamics coherently over long time scales. Existing polarimetry techniques rely on destructive scattering processes that preclude continuous, non-intercepting tracking of spin evolution and constrain both statistical sensitivity and systematic control. Here we introduce a non-destructive, phase-coherent polarimetry method in which the stored beam polarization is treated as a continuous dynamical observable rather than a quantity inferred from scattering events. Spin-dependent electromagnetic fields generated by a polarized relativistic beam establish a symmetry-selected differential signal on pickup electrodes. This signal is transduced into a narrowband phase modulation of a high-Q resonator interrogated with a coherent probe, while dominant charge-induced backgrounds are rejected through geometric symmetry, helicity reversal, and synchronous demodulation. Controlled spin precession (spin-wheel operation) provides a stable phase reference enabling phase-coherent detection of slow spin evolution. Combined with optimized lattice symmetry and beam cooling, this approach can substantially extend the usable spin coherence time, with values approaching 10^5 s appearing realistic within existing accelerator technology. The resulting readout supports optimal slope-based estimation with T^{-3/2} statistical scaling while eliminating the efficiency penalties inherent to scattering-based polarimetry. For storage-ring EDM experiments, this combination enables sensitivity approaching the level expected within the Standard Model. More broadly, the method establishes a general phase-coherent architecture for collective spin measurements in storage rings, adapting resonant sensing concepts from axion dark-matter searches to charged-particle precision experiments.

hep-ex↗

arXiv2026

Control of relaxation properties of a macroscopic nuclear spin ensemble

Macroscopic spin ensembles in solids are powerful platforms for quantum sensing and precision metrology. A key challenge is controlling the nuclear spin population relaxation time $T_1$, which can become prohibitively long at cryogenic temperatures due to phonon freeze-out. We demonstrate optical control of the $T_1$ relaxation time of the $^{207}$Pb nuclear spin ensemble in lead-containing ferroelectric crystals PbTiO$_3$ (PT) and (PbMg$_{1/3}$Nb$_{2/3}$O$_3$)$_{2/3}$-(PbTiO$_3$)$_{1/3}$ (PMN-PT). Using X-band electron paramagnetic resonance (EPR) spectroscopy at 10 K, we characterize light-induced paramagnetic centers created by 405 nm laser illumination. In PT, we observe paramagnetic Pb$^{3+}$ centers and their hyperfine interaction with nearby nuclear spins. In PMN-PT, we identify two populations: isotropic Pb$^{3+}$ centers and anisotropic Ti$^{3+}$ centers occupying $d$-orbitals, with spin number densities of $(2.5 \pm 1.0) \times 10^{17}$ cm$^{-3}$ and $(4.1 \pm 1.7) \times 10^{17}$ cm$^{-3}$, respectively. Power-dependent EPR measurements enable extraction of spin relaxation times. We investigate the ionization and recombination dynamics of these transient paramagnetic centers. Using saturation-recovery nuclear magnetic resonance, we demonstrate that laser illumination reduces the $^{207}$Pb nuclear $T_1$ by approximately a factor of two, from $(17 \pm 2)$ s to $(7 \pm 1)$ s at 4.6 MHz, and from $(1550 \pm 40)$ s to $(850 \pm 70)$ s at 40 MHz. We develop a model relating the nuclear relaxation rate to the density of photoinduced paramagnetic centers. This optical control of nuclear spin relaxation provides a pathway toward accelerated thermal polarization and dynamic nuclear polarization in solid-state NMR-based precision measurements, including searches for axion-like dark matter.

cond-mat.other↗

arXiv2026

Floquet engineering of spin-spin interactions in a hybrid atomic system

We demonstrate dynamical control of the effective spin-spin interaction, dominated by Fermi-contact interaction, in a hybrid spin system via parametric modulation. We show that, in an alkali-noble-gas comagnetometer, periodic modulation of the direction of the electron spin polarization with respect to the nuclear polarization leads to a Floquet-induced renormalization of the spin-exchange coupling, governed by a zeroth-order Bessel function. This effect enables continuous tuning and suppression of the effective interaction strength without altering the intrinsic properties of the system. We develop a theoretical model that supports the experimental measurements. The results establish a general mechanism for controlling interaction strengths in hybrid atomic systems and provide new opportunities for precision measurements and quantum memories.

physics.atom-ph↗

arXiv2026

Magnetic Microscopy of Skyrmions in Magnetic Thin Films with Chiral Overlayers

Topologically nontrivial magnetic textures such as skyrmions offer promising opportunities for spintronic applications. In recent years, it has been shown that the magnetic properties of layered materials can be affected by depositing chiral molecules on the surface, while the influence of chiral overlayers on skyrmion properties such as their stability and interactions remains largely unexplored. To address this challenge, we employ wide-field nitrogen-vacancy (NV) magnetometry to directly image skyrmions in chiral-molecule-functionalized magnetic thin films, enabling quantitative mapping of magnetic stray fields over extended areas under ambient conditions. Using pixel-resolved optically detected magnetic resonance (ODMR) combined with controlled magnetic fields, we reproducibly nucleate and probe skyrmion states in CoFeB ferromagnetic samples, enabling quantitative investigation of their properties. We find evidence for enantioselective and magnetic-field-polarity-dependent modifications of skyrmion diameter, spacing, and shape, pointing to a possibility of molecular control of topological spin textures via magneto-chiral coupling.

cond-mat.mtrl-sci↗

arXiv2026

100 years of spin: fundamental physics, dark matter, exotic interactions, and all that

For a century, spin has been an indispensable probe of the fundamental laws of nature. A reflection on the role of spin in shaping modern physics is presented, from the early days of quantum mechanics to the latest precision tests of the Standard Model. The significance of magnetic and electric dipole moments in testing CP and CPT symmetries is surveyed, along with the ongoing searches for exotic spin-dependent interactions that may reveal the nature of dark matter and its connection to spacetime geometry. Through these vignettes, it is shown that spin continues to provide a fresh perspective on the most profound questions in physics today.

quant-ph↗