Recent advances in muonic x-ray experiments have reinvigorated efforts in measurements of absolute nuclear charge radii. Here, a modern approach is presented, and demonstrated through determination of the charge radii of the two stable chlorine nuclides $^{35}$Cl and $^{37}$Cl. Knowledge of these radii has implications for fundamental studies in nuclear and atomic physics. For this purpose, a state-of-the-art experiment was performed at the $\pi$E1 beamline in the Paul Scherrer Institute (Switzerland), using a large-scale HPGe detector array in order to extract precise energies of the muonic $^{35}$Cl and $^{37}$Cl $np1s$ transitions. The nuclear charge radius extraction relies on modern calculations for QED effects and nuclear polarization with rigorous uncertainty quantification, including effects that were not accounted for in older studies. Additionally, we established a new method for applying the nuclear shape correction directly from energy density functionals, which are amenable to isotopes for which no high-quality electron scattering experiments are available. The resulting charge radii are $3.3335(23) fm$ for $^{35}$Cl and $3.3445(23) fm$ for $^{37}$Cl, thus improving the uncertainty of the available electron scattering values by a factor of seven. The correlation of several observables was evaluated between the different isotopes in order to produce a more precise value of the differential mean square charge radius $\delta \langle r^2 \rangle^{37, 35}=+0.0771(66) fm^{2}$. In this case, improvement of the uncertainty by more than one order of magnitude was achieved compared to the literature value. This precision is sufficient to use this differential as input for isotope shift factor determination.

Topological edge states in systems of two (or more) dimensions offer scattering-free transport, exhibiting robustness to inhomogeneities and disorder. In a different domain, time-modulated systems, such as photonic time crystals (PTCs), offer non-resonant amplification drawing energy from the modulation. Combining these concepts, we explore topological systems that vary periodically in both time and space, manifesting the best of both worlds. We present topological phases and topological edge states in photonic space-time crystals - materials in which the refractive index varies periodically in both space and time, displaying bandgaps in both frequency and momentum. The topological nature of this system leads to topological invariants that govern the phase between refracted and reflected waves generated from both the spatial and the temporal interfaces. The 2D nature of this system leads to propagating edge states, and a unique edge state that grows exponentially in power whilst following the space-time edge.

High-harmonic generation (HHG), the hallmark effect of attosecond science, is a nonperturbative nonlinear process leading to the emission of high harmonic light from gases and solids. In gases, extreme driving laser pulse intensities can deplete the ground state, suppressing harmonic emission during the trailing edge of the pulse. Here, we report pronounced ultrafast depletion dynamics during HHG in a gapless Dirac semimetal -- highly oriented pyrolytic graphite (HOPG). Remarkably, HOPG supports nonperturbative harmonic generation at laser intensities as low as $10^{10}$ W cm$^{-2}$, facilitated by its vanishing bandgap. Using two-color spectroscopy, we reveal the excitation dynamics of Dirac electron-hole pairs as it affects the emission of harmonics during the presence of the driving laser pulse. Notably, valence band depletion near the Dirac points leads to a marked suppression of interband harmonics and induces measurable temporal shifts. These observations are supported by simulations based on semiconductor Bloch equations. Our findings uncover a new regime of strong-field light-matter interaction in gapless solids and establish HHG as a sensitive, all-optical probe of ultrafast carrier dynamics, offering new opportunities for ultrafast optoelectronics in Dirac materials.

Collective spontaneous emission occurs when multiple quantum emitters decay into common radiation modes, resulting in enhanced or suppressed emission. Here, we find the quantum state of light collectively emitted from emitters exhibiting quantum correlations. We unveil under what conditions the quantum correlations are not lost during the emission but are instead transferred to the output light. Under these conditions, the inherent nonlinearity of the emitters can be tailored to create desired photonic states in the form of traveling single-mode pulses, such as Gottesman–Kitaev–Preskill and Schrödinger-cat states, that are useful for error correction in quantum computation. To facilitate such predictions, our work reveals the multimode nature of collective spontaneous emission, capturing the role of the emitters’ positions, losses, interactions, and beyond-Markov dynamics on the emitted quantum state of light. We present manifestations of these effects in different physical systems, with examples of cavity QED, waveguide QED, and atomic arrays with up to a few dozen emitters. Our findings suggest paths for creating and manipulating multiphoton quantum light for bosonic codes in continuous-variable-based quantum computation, communications, and sensing.

Although quasiparticles in flat bands have zero group velocity, they can display an anomalous velocity due to the quantum geometry. We address the thermal and thermoelectric transport in flat bands in the clean limit with a small amount of broadening due to inelastic scattering. We derive general Kubo formulas for flat bands in the dc limit up to linear order in the broadening and extract expressions for the thermal conductivity, the Seebeck and Nernst coefficients. Under the condition of zero particle flow, the Seebeck coefficient for flat Chern bands is topological up to second-order corrections in the broadening. We identify thermal and thermoelectric transport signatures of two generic flat Chern bands and also of the generalized flattened Lieb model, which describes a family of three equally spaced flat Chern bands where the middle one is topologically trivial. Both families of Hamiltonians saturate the lower bound of the trace of the quantum metric, permitting the derivation of general transport results with minimal assumptions. Finally, we address the saturation of the quantum metric lower bound for a generic family of Hamiltonians with an arbitrary number of flat Chern bands corresponding to SU(2) coherent states. We find that only the extremal bands in this class of Hamiltonians saturate the bound, provided that the momentum dependence of their Hamiltonians is described by a meromorphic function.

Enhancing the efficiency and stability of lead halide perovskite devices is crucial to their practical application. Previous treatments with thiocyanate (SCN^–) have demonstrated significant improvements in the photoluminescence quantum yield (PLQY) and stability of CsPbBr₃ nanocrystals (NCs), but the underlying mechanisms remain partially unresolved. Addressing the challenge of low SCN^– solubility in traditional nonpolar solvents, our study introduces a urea-ammonium thiocyanate (UAT)-based ionic liquid surface treatment. This method facilitates a higher SCN^– loading by creating a liquid–liquid interface that is compatible with the organic colloidal suspension, preventing NC degradation, and achieving near-unity PLQY. Utilizing transmission electron microscopy techniques, we present atomic resolution evidence that thiocyanate-treated surfaces are rich in sulfur and display structural dilation of the lattice spacing of 3%. This supports that thiocyanate acts as a pseudohalide and binds to Pb cations on the NC surfaces. As a result, the treated NCs show enhanced stability against ionic substitution while maintaining the perovskite structure intact. Our findings provide conclusive evidence that the primary mechanism of performance enhancement is the passivation of surface traps attributed to bromide vacancies rather than the scavenging of excess lead cation. This surface treatment method slows ion migration, a prominent challenge in photovoltaics, offering a significant advancement in the development of perovskite-based devices.

Cosmic rays and background radioactive decay can deposit significant energy into superconducting quantum circuits on planar chips. This energy converts into pair-breaking phonons that travel across the substrate and generate quasiparticles, leading to correlated energy and phase errors in nearby qubits. To mitigate this, we fabricated two separate dies and placed them adjacently without a galvanic connection between them. This blocks phonon propagation from one die to the other. Using microwave kinetic inductance detectors on both dies, we successfully detected high-energy bursts and conclusively demonstrated the blocking effect. However, we also observed simultaneous events in both dies, likely from a single cosmic particle traversing both dies.

Two-dimensional (2D) semiconductors are promising for photonic applications due to their exceptional optoelectronic properties, including large exciton binding energy, strong spin–orbit coupling, and potential integration with the standard complementary silicon-oxide-semiconductor (CMOS) technology. The dielectric environment can significantly affect the photoluminescence (PL) spectra of transition metal dichalcogenide (TMD) monolayers by modulating excitonic properties such as optical transitions and binding energies. Specifically, substrates with higher dielectric permittivity reduce exciton binding energy and the quasiparticle bandgap. Doping and the charge carrier concentration can further modify the emitted spectra by affecting the PL excitonic content. Increased doping can enhance trion formation and bandgap renormalization phenomena, leading to PL spectral shifts that depend on the semiconductor type. This study systematically investigates the substrate-induced dielectric screening, doping, and trapped charges in CVD-grown n-type 1L-WS₂ and p-type 1L-WSe₂ transferred onto CMOS-relevant SiO₂ and HfO₂ dielectrics. Our results show that p-type 1L-WSe₂ exhibits higher PL intensity and red-shifted trion emission on HfO₂, whereas n-type 1L-WS₂ shows a blue-shifted, lower-intensity PL for a similar dielectric environment. The difference arises from the interplay of the semiconductor type, doping, dielectric screening, and charge carrier concentration. We demonstrate that suspending the monolayers at the nanoscale enhances PL by reducing nonradiative recombination, enabling controlled micro-PL patterning and the formation of localized emission hot spots. Our results provide valuable insights for the development of next-generation CMOS-compatible optoelectronic devices.

Benchmarking quantum computers often deals with the parameters of single qubits or gates and sometimes deals with algorithms run on an entire chip or a noisy simulator of a chip. Here we propose the idea of using protocols to benchmark quantum computers. The advantage of using protocols, especially the seven suggested here, over other benchmarking methods is that there is a clear cutoff (i.e., a threshold) distinguishing quantumness from classicality for each of our protocols. The protocols we suggest enable a comparison among various circuit-based quantum computers, and also between real chips and their noisy simulators. This latter method may then be used to better understand the various types of noise of the real chips. We use some of these protocols to answer an important question: ``How many effective qubits are there in this N-qubit quantum computer/simulator?'', and we then conclude which effective sub-chips can be named ``truly-quantum''.

This paper presents a new continuous-flow electron spin resonance (ESR) microfluidic device designed to perform 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 magnetic field hotspot while minimizing dielectric losses. The effective sample volume is ~0.06 nL, and the device supports standard microfluidic connectors, facilitating continuous 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 with 10 scans while the resonator quality factor was Q ~15–20. This corresponds to a spin sensitivity of ~4.5×10⁸ spins at SNR = 1 with an 80 s averaging time. Pulsed ESR measurements, performed with 0.1 W microwave power and 10 ns π pulses, achieved an SNR of ~33 within just 1 s of averaging, corresponding to a spin sensitivity of ~1.27×10⁸ spins. The Rabi frequency of ~50 MHz implies a microwave conversion efficiency of ~56 G/√W, 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 improvements 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. Its simplicity, compatibility with commercial ESR systems, and promising sensitivity make it well suited for advancing microscale and dynamic ESR spectroscopy.