arXiv subjects

Raphael Kircher

Publications and source records attributed to Raphael Kircher.

5 recordsLinked to original sources

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

Chemically-polarized material for nuclear and particle physics

Spin-polarized solid targets have underpinned many recent key advances in nuclear and particle physics, yet traditional methods to produce them face significant limitations due to the high cost and demanding cryogenic and magnetic field requirements. These factors constrain experimental geometries and present challenges in intense radiation environments where depolarization and materials damage can occur. We present the first results assessing the capabilities of the chemical hyperpolarization (ChHP) method Signal Amplification By Reversible Exchange (SABRE) to act as the polarization method to produce targets or active detector media. We show by using in-beam measurements that there is no depolarizing effect observed with the SABRE-polarized material in the A2 photon beam at the Mainzer Mikrotron (MAMI), as well as showing the resilience of such media to radioactive doses of up to \SI{3}{\kilo\gray}. We also illustrate the capabilities for using SABRE-polarized material as a scintillation or Cherenkov detector.

physics.ins-det↗

arXiv2025

Zero- to low-field J-spectroscopy with a diamond magnetometer

We report measurements of zero- to ultra-low-field nuclear magnetic resonance (ZULF NMR) signals at frequencies of a few hertz with a diamond-based magnetic sensor. The sensing diamond is a truncated pyramid with 0.18 mm height and a 0.5 mm x 0.5mm base. The minimum stand-off distance is < 1 mm, and the sensor sensitivity is 13 pT/(Hz)^(1/2) at frequencies f above 5 Hz with 1/f-like behavior at lower frequencies. NMR signals were generated via signal amplification by reversible exchange (SABRE) parahydrogen-based hyperpolarization resulting in zero-field signals at 1.7 Hz and 3.4 Hz corresponding to the expected hetero-nuclear J-coupling pattern of acetonitrile. This work demonstrates a magnet-free platform for detecting chemically specific NMR signals at ultra-low frequencies paving the way for portable noninvasive diagnostics in microscopic sample volumes for biomedicine, industrial sensing through metal enclosures, and field-deployable quantum analytical devices.

physics.app-ph↗

arXiv2025

Hyperpolarized Molecular Nuclear Spins Achieve Magnetic Amplification

The use of nuclear spins as physical sensing systems is disadvantaged by their low signal responsivity, particularly when compared to sensing techniques based on electron spins. This primarily results from the small nuclear gyromagnetic ratio and the difficulties in achieving high spin polarization. Here we develop a new approach to investigating the response of hyperpolarized molecular nuclear spins to magnetic fields and demonstrate orders-of-magnitude enhanced magnetic responsivity over state-of-the-art proton and Overhauser magnetometers. Using hyperpolarized molecules with proton spins, we report the realization of magnetic amplification in linear and nonlinear types. We further extend this amplification to hyperpolarized scalar-coupled multi-spin molecules and observe substantial magnetic amplification exceeding 10%. Moreover, we observe an anomalous amplification with dispersive frequency dependence that originates from magnetic interference effects. Our work highlights the potential of hyperpolarized molecular nuclear spins for use in a new class of quantum sensors, with promising applications in both applied and fundamental physics, including highly accurate absolute magnetometry and the exploration of axion-nucleon exotic interactions.

quant-ph↗

arXiv2025

Quantum Magnetic J-Oscillators

We introduce quantum J-oscillators that exploit intrinsic nuclear spin-spin (scalar J) couplings in molecules to produce phase-coherent oscillations. Operated in zero magnetic field and driven by a digital feedback, they operate from sub-hertz to a few tens of hertz frequencies. In a proof-of-principle experiment on [15N]-acetonitrile, the oscillator produced a 337 uHz linewidth over 3000 s, more than two orders narrower than in conventional zero-field NMR. This may facilitate precision measurements of J-coupling constants and allows distinguishing mixtures of molecules whose zero-field NMR spectra would otherwise be hard to separate. In addition, the combination of strongly coupled spin systems and programmable feedback turns the J-oscillator into a compact tabletop (and, eventually, chip-scale) platform for exploring nonlinear spin dynamics, including chaos, dynamical phase transitions, and perhaps time-crystal behavior. By uniting high-resolution spectroscopy and controllable quantum dynamics in a single, magnet-free setup, J-oscillators open new opportunities for applications where ultraprecise frequency references or molecular fingerprints are required.

quant-ph↗