We revisit the extraction of the | ⁢ | Cabibbo-Kobayashi-Maskawa (CKM) matrix element from the superallowed transition decay rate of 2 6 ⁢ A l → 2 6 M g , focusing on finite nuclear size effects. The decay rate dependence on the 2 6 ⁢ A l charge radius is found to be four times higher than previously believed, necessitating precise determination. However, for a short-lived isotope of an odd element such as 2 6 ⁢ A l , radius extraction relies on challenging many-body atomic calculations. We performed the needed calculations, finding an excellent agreement with previous ones, which used a different methodology. This sets a new standard for the reliability of isotope shift factor calculations in many-electron systems. The ℱ ⁡ value obtained from our analysis is lower by 2 . 2 than the corresponding value in the previous critical survey, resulting in an increase in | ⁢ | 2 by 0 . 9 . Adopting | ⁢ | from this decay alone reduces the CKM unitarity deficit by one standard deviation, irrespective of the choice of | ⁢ | .

The spectra of the Kohmoto model give rise to a fractal phase diagram, known as the Kohmoto butterfly. The butterfly encapsulates the spectra of all periodic Kohmoto Hamiltonians, whose index invariants are sought after. Topological methods - such as Chern numbers - are ill defined due to the discontinuous potential, and hence fail to provide index invariants. This Letter overcomes that obstacle and provides a complete classification of the Kohmoto model indices. Our approach encodes the Kohmoto butterfly as a spectral tree graph, reflecting the quasiperiodic nature via the periodic spectra. This yields a complete coloring of the phase diagram and a new perspective on other spectral butterflies.

We explore the potential of precision spectroscopy of heavy exotic atoms where electrons are substituted by negative hadrons to detect new force carriers with hadronic couplings. The selected transitions are unaffected by nuclear contact terms, thus enabling highly accurate calculations using bound-state QED, provided that the nuclear polarization is under control. Alternatively, we demonstrate that the dipole polarizability, a fundamental property of nuclei, can be extracted from the spectroscopy of exotic atoms in a novel way by combining two transitions while maintaining high sensitivity to new physics. Based on existing data, we extracted world-leading bounds on mediator masses ranging from 0.1 to 10 MeV for two benchmark models and show that forthcoming experiments could enhance the sensitivity to new physics by 2 orders of magnitude.

Phase singularities are universal features found across diverse wave systems. Their ensembles exhibit distance correlations governing exotic material phases. However, the full correlations in phase-space have remained unexplored and experimentally inaccessible. Here, we directly measure the ultrafast dynamics of optical singularity ensembles, capturing their phase-space correlations. Our observations reveal that phase singularities exhibit acceleration to unbounded velocities before annihilation, indicated by measurements of velocities exceeding the speed of light. These superluminal velocities are paradoxically amplified by the slow group velocity of hyperbolic phonon polaritons in our material platform, hexagonal boron nitride membranes. We demonstrate these phenomena using combined hardware and algorithmic advances in ultrafast electron microscopy, achieving spatial and temporal resolutions each an order of magnitude below the polaritonic wavelength and cycle period. Our findings enable probing topological defect dynamics at previously unattainable timescales, deepening our understanding of phase-singularity universality and suggesting phenomena of ultrafast information flow in polaritonic media.

An optical comb featuring an unusual structure has been recently observed in a fiber-loop laser running at cryogenic temperatures. In the present work, the effect of optical polarization on the operation of the laser is explored. Multi--mode lasing with a relatively high degree of inter--mode coherency is experimentally demonstrated. The setup can be used for applications to spectroscopy, communications, and quantum data storage.

We report a microwave spectroscopy measurement of the muonium $2S_{1/2}-2P_{3/2}$ fine structure transition, yielding a transition frequency of $9871.0 \pm 7.0~\mathrm{MHz}$, in agreement with state-of-the-art QED predictions within one standard deviation. In combination with the recent Lamb shift result, the $2P_{1/2}-2P_{3/2}$ splitting is determined, improving the spectroscopic characterization of the $n=2$ manifold in muonium. These results provide a stringent test of bound-state QED in a purely leptonic system and establish a path toward future searches for Lorentz violation and muon-specific new physics.

Employing non-Hermitian Floquet theory, the strong-field process of high harmonic (HH) generation by a classical continuous-wave field irradiating ground-state atom is discovered to be controllable by placing the irradiated atom inside a single-mode quantum cavity initiated even with a single photon. Judicious cavity coupling of cavity-free photo-induced atomic Floquet states forms polaritonic Floquet states that generate side harmonics around the (standard no-cavity) odd harmonics. The different possible cavity-controlled HH spectra, including also the ones resulting from several cavities in a row, enable attosecond-pulse sequences different from the one produced without a cavity. Moreover, the present study sets the framework and opens the way for further cavity control over the HH generation process as well as over other strong-field processes

Optoelectronic systems based on multiple modes of light can often exceed the performance of their single-mode counterparts. However, multimode nonlinear interactions often introduce considerable amounts of noise, limiting the ultimate performance of these systems. It is therefore crucial to develop ways to simultaneously control complex nonlinear interactions while also gaining control over their noise. Here, we show that noise buildup in nonlinear multimode systems can be strongly suppressed by controlling the input wavefront. We demonstrate this approach in a multimode fiber by using an active wavefront-shaping protocol to focus a region of high intensity - yet low intensity noise - at the output. Our programmable control of both the input and output reduces the beam noise by 12 dB beyond what linear attenuation achieves, reaching levels near the quantum shot-noise limit. We show that this is possible because the optimally shaped wavefront maximally decouples the output intensity fluctuations from the input laser fluctuations. These findings are supported by a new theoretical and simulation framework that efficiently captures spatiotemporal quantum noise dynamics in highly multimode nonlinear systems. Our results highlight the potential of programmable wavefront shaping to enable nonlinear multimode technologies that overcome noise buildup to operate at quantum-noise limits.

We present controlled interplay between the surface second-order and bulk third-order nonlinearities of gold, utilizing wave mixing between surface plasmons on the metal-air interface and free-space photons. By tuning the nonlinear interactions, we demonstrate experimentally that photons emerging from these inherently different mechanisms can interfere, while both their relative amplitude and phase are controlled solely by the pump beam. These results provide a foundation for engineering plasmonic nonlinearities and open new possibilities for quantum photonic applications.

This paper presents a novel continuous-flow electron spin resonance (ESR) microfluidic device designed for both continuous-wave (CW) and pulsed ESR measurements on sub-nanoliter liquid samples. The system integrates a planar surface microresonator (ParPar type) operating at ∼9.4 GHz with a precision-fabricated quartz microfluidic chip, enabling spatial confinement of the sample within the resonator’s microwave magnetic field hotspot while minimizing dielectric losses. The effective sample volume is ∼0.06 nL, and the device supports standard microfluidic connectors, facilitating both continuous and stopped-flow experiments. Using a 1 mM aqueous solution of deuterated Finland trityl (dFT) radical, CW ESR measurements yielded a peak signal-to-noise ratio (SNR) of ∼83 for a 100-point spectrum acquired over 80 s, with a resonator quality factor of Q ∼15–20. This corresponds to a spin sensitivity of ∼1.04 × 10⁹ spins/√Hz/G. Pulsed ESR measurements, performed with 0.1 W microwave power and 10 ns π pulses, achieved an SNR of ∼47 with 1 s of averaging, corresponding to a spin sensitivity of ∼7.8 × 10⁸ spins/√Hz. A Rabi frequency of ∼50 MHz was measured, indicating a microwave conversion efficiency of ∼56 G/√W. Both the pulsed spin sensitivity and Rabi frequency are consistent with simulated values. This device represents a significant step toward ESR-based detection of individual, slowly flowing cells—analogous to flow cytometry but with magnetic resonance contrast. With future enhancements such as higher operating frequencies, cryogenic integration, or optimized resonator geometries, the system is expected to enable practical ESR measurements at the single-cell level.