Recent observation of quantum emitters in monolayers of hexagonal boron nitride (h-BN) has provided a novel platform for optomechanical experiments where the single-photon emitters can couple to the motion of a freely suspended h-BN membrane. Here, we propose a scheme where the electronic degree of freedom (d.o.f.) of an embedded color center is coupled to the motion of the hosting h-BN resonator via dispersive forces. We show that the coupling of membrane vibrations to the electronic d.o.f. of the emitter can reach the strong regime. By suitable driving of a three-level $\mathrm{\Lambda }$-system composed of two spin d.o.f. in the electronic ground state as well as an isolated excited state of the emitter, a multiple electromagnetically induced transparency spectrum becomes available. The experimental feasibility of the efficient vibrational ground-state cooling of the membrane via quantum interference effects in the two-color drive scheme is numerically confirmed. More interestingly, the emission spectrum of the defect exhibits a frequency comb with frequency spacings as small as the fundamental vibrational mode, which finds applications in high-precision spectroscopy.

A new relativistic vortex cutter driven by the Laguerre-Gaussian (LG) mode is carried out for the first time in three-dimensional particle-in-cell simulations. Studies show that the electric fields periodically concentrate and emanate within every laser wavelength for the reflected circularly polarized ${\mathrm{LG}}_p^l$ ($p=0$, $l=1$, ${\sigma }_z=-1$) laser, which works just like a vortex cutter, resulting in a relativistic ultrashort collimated electron cluster with a constant period in space. A single particle model is given and verifies that the cluster formation has a close relation with the parameters of orbital angular momentum ($l$) and spin angular momentum (${\sigma }_z$). Such a relativistic vortex cutter potentially can be applied for the accelerator, generating high-flux particle and coherent radiation sources, and so on.

The propagation of fast electron currents in near solid-density media was investigated via proton probing. Fast currents were generated inside dielectric foams via irradiation with a short ($\sim 0.6\mathrm{ps}$) laser pulse focused at relativistic intensities ($I{\lambda }^2\sim 4\times {10}^{19}\mathrm{W}{\mathrm{cm}}^{-2}\mu {\mathrm{m}}^2$). Proton probing provided a spatially and temporally resolved characterization of the evolution of the electromagnetic fields and of the associated net currents directly inside the target. The progressive growth of beam filamentation was temporally resolved and information on the divergence of the fast electron beam was obtained. Hybrid simulations of electron propagation in dense media indicate that resistive effects provide a major contribution to field generation and explain well the topology, magnitude, and temporal growth of the fields observed in the experiment. Estimations of the growth rates for different types of instabilities pinpoints the resistive instability as the most likely dominant mechanism of beam filamentation.

Despite the importance of porous two-dimensional (2D) molecules and materials in advanced technological applications, the question of how the void space in these systems affects the van der Waals (vdW) scaling landscape has been largely unanswered. Analytical and numerical models presented herein demonstrate that the mere presence of a pore leads to markedly different vdW scaling across nonasymptotic distances, with certain relative pore sizes yielding effective power laws ranging from simple monotonic decay to the formation of minima, extended plateaus, and even maxima. These models are in remarkable agreement with first-principles approaches for the 2D building blocks of covalent organic frameworks (COFs), and reveal that COF macrocycle dimers and periodic bilayers exhibit unique vdW scaling behavior that is quite distinct from their nonporous analogs. These findings extend across a range of distances relevant to the nanoscale, and represent a hitherto unexplored avenue towards governing the self-assembly of complex nanostructures from porous 2D molecules and materials.

Material properties depend sensitively on the atomic arrangements and atomic bonding, but these are notoriously difficult to measure in nanosized atomic clusters due to the small size of the objects and the challenge of obtaining bulk samples of identical clusters. Here, we have combined the recent ability to make gram quantities of identical semiconductor quantum-dot nanoparticles with the ability to measure lattice dynamics on small sample quantities of hydrogenated materials using high energy resolution inelastic x-ray scattering, to measure the size dependence of the phonon density of states in CdSe quantum dots. The fact that we have atomically precise structural models for these nanoparticles allows the calculation of the phonon density of states using density functional theory, providing both experimental and theoretical confirmations of the important role that the inertia of the surface capping species plays on determining the lattice dynamics.

In recent years experiments revealed intriguing hints for new physics (NP) in $B$ decays involving $b\to c\tau \nu$ and $b\to s{\ell }^{+}{\ell }^{-}$ transitions at the $4\sigma$ and $5\sigma$ level, respectively. In addition, there are slight disagreements in $b\to u\tau \nu$ and $b\to d{\mu }^{+}{\mu }^{-}$ observables. While not significant on their own, they point in the same direction. Furthermore, $V_{us}$ extracted from $\tau$ decays shows a slight tension ($\approx 2.5\sigma$) with its value determined from Cabibbo-Kobayashi-Maskawa unitarity, and an analysis of BELLE data found an excess in $B_d\to {\tau }^{+}{\tau }^{-}$. Concerning NP explanations, the vector leptoquark SU(2) singlet is of special interest since it is the only single particle extension of the standard model which can (in principle) address all the anomalies described above. For this purpose, large couplings to $\tau$ leptons are necessary and loop effects, which we calculate herein, become important. Including them in our phenomenological analysis, we find that neither the tension in $V_{us}$ nor the excess in $B_d\to {\tau }^{+}{\tau }^{-}$ can be fully explained without violating bounds from $K\to \pi \nu \overline{\nu }$. However, one can account for $b\to c\tau \nu$ and $b\to u\tau \nu$ data finding intriguing correlations with $B_q\to {\tau }^{+}{\tau }^{-}$ and $K\to \pi \nu \overline{\nu }$. Furthermore, the explanation of $b\to c\tau \nu$ predicts a positive shift in $C_7$ and a negative one in $C_9$, being nicely in agreement with the global fit to $b\to s{\ell }^{+}{\ell }^{-}$ data. Finally, we point out that one can fully account for $b\to c\tau \nu$ and $b\to s{\ell }^{+}{\ell }^{-}$ without violating bounds from $\tau \to \varphi \mu$, $\mathrm{\Upsilon }\to \tau \mu$, or $b\to s\tau \mu$ processes.

The first observation of two structures consistent with resonances in the final states ${\mathrm{\Lambda }}_b^0{\pi }^{-}$ and ${\mathrm{\Lambda }}_b^0{\pi }^{+}$ is reported using samples of $pp$ collision data collected by the LHCb experiment at $\sqrt{s}=7$ and 8 TeV, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$. The ground states ${\mathrm{\Sigma }}_b^{\pm }$ and ${\mathrm{\Sigma }}_b^{*\pm }$ are also confirmed and their masses and widths are precisely measured.

Two-dimensional topological insulators possess conducting edge states at their boundary while being insulating in the bulk. We investigate the edge state emergent at a smooth topological phase boundary of interacting fermions within a full real-space analysis of the time-reversal invariant Hofstadter-Hubbard model. We characterize the localization of the edge state and the topological phase boundary by means of the local compressibility, the spectral density, a generalized local spin Chern marker as well as the Hall response and find good agreement between all these quantities. Computing the edge state spectra at the interface we observe robustness of the edge state against fermionic two-body interactions and conclude that interactions only shift its position. Hence the bulk-boundary correspondence for the interacting system is confirmed. Since experimental probing of edge states remains a challenge in ultracold atom setups, we propose the detection of the local compressibility by measuring correlations with a quantum gas microscope.

We develop energy efficient, continuous microwave schemes to couple electron and nuclear spins, using phase or amplitude modulation to bridge their frequency difference. These controls have promising applications in biological systems, where microwave power should be limited, as well as in situations with high Larmor frequencies due to large magnetic fields and nuclear magnetic moments. These include nanoscale NMR where high magnetic fields achieves enhanced thermal nuclear polarization and larger chemical shifts. Our controls are also suitable for quantum information processors and nuclear polarization schemes.

Dynamical decoupling (DD) is an active and effective method for suppressing decoherence of a quantum system from its environment. In contrast to the nominal biaxial DD, this work presents a uniaxial decoupling protocol that requires a significantly reduced number of pulses and a much lower bias field satisfying the “magic” condition. We show this uniaxial DD protocol works effectively in a number of model systems of practical interest, e.g., a spinor atomic Bose-Einstein condensate in stray magnetic fields (classical noise), or an electron spin coupled to nuclear spins (quantum noise) in a semiconductor quantum dot. It requires only half the number of control pulses and a 10–100 times lower bias field for decoupling as normally employed in the above mentioned illustrative examples, and the overall efficacy is robust against rotation errors of the control pulses. The uniaxial DD protocol we propose shines new light on coherent controls in quantum computing and quantum information processing, quantum metrology, and low field nuclear magnetic resonance.

We characterize a fluxonium qubit consisting of a Josephson junction inductively shunted with a NbTiN nanowire superinductance. We explain the measured energy spectrum by means of a multimode theory accounting for the distributed nature of the superinductance and the effect of the circuit nonlinearity to all orders in the Josephson potential. Using multiphoton Raman spectroscopy, we address multiple fluxonium transitions, observe multilevel Autler-Townes splitting and measure an excited state lifetime of $T_1=20\mu \mathrm{s}$. By measuring $T_1$ at different magnetic flux values, we find a crossover in the lifetime limiting mechanism from capacitive to inductive losses.

We present accurate fits for the remnant properties of generically precessing binary black holes, trained on large banks of numerical-relativity simulations. We use Gaussian process regression to interpolate the remnant mass, spin, and recoil velocity in the seven-dimensional parameter space of precessing black-hole binaries with mass ratios $q\le 2$, and spin magnitudes ${\chi }_1$, ${\chi }_2\le 0.8$. For precessing systems, our errors in estimating the remnant mass, spin magnitude, and kick magnitude are lower than those of existing fitting formulae by at least an order of magnitude (improvement is also reported in the extrapolated region at high mass ratios and spins). In addition, we also model the remnant spin and kick directions. Being trained directly on precessing simulations, our fits are free from ambiguities regarding the initial frequency at which precessing quantities are defined. We also construct a model for remnant properties of aligned-spin systems with mass ratios $q\le 8$, and spin magnitudes ${\chi }_1$, ${\chi }_2\le 0.8$. As a byproduct, we also provide error estimates for all fitted quantities, which can be consistently incorporated into current and future gravitational-wave parameter-estimation analyses. Our model(s) are made publicly available through a fast and easy-to-use Python module called surfinBH.

Precision measurements of the inverse-square law via experiments on short-range gravity provide sensitive tests of Lorentz symmetry. A combined analysis of data from experiments at the Huazhong University of Science and Technology and Indiana University sets simultaneous limits on all 22 coefficients for Lorentz violation correcting the Newton force law as the inverse sixth power of distance. Results are consistent with no effect at the level of ${10}^{-12}{\mathrm{m}}^4$.

We study the backreaction of superhorizon fluctuations of a light quantum scalar field on a classical de Sitter geometry by means of the Wilsonian renormalization group. This allows us to treat the gravitationally amplified fluctuations in a nonperturbative manner and to analytically follow the induced renormalization flow of the spacetime curvature as long wavelength modes are progressively integrated out. Unbounded loop corrections in the deep infrared are eventually screened by nonperturbative effects which stabilize the geometry.

We study the quantum mechanics of three-index Majorana fermions ${\psi }^{abc}$ governed by a quartic Hamiltonian with $\mathrm{O}(N{)}^3$ symmetry. Similarly to the Sachdev-Ye-Kitaev model, this tensor model has a solvable large-$N$ limit dominated by the melonic diagrams. For $N=4$ the total number of states is $2^{32}$, but they naturally break up into distinct sectors according to the charges under the $\mathrm{U}(1)\times \mathrm{U}(1)$ Cartan subgroup of one of the O(4) groups. The biggest sector has vanishing charges and contains over 165 million states. Using a Lanczos algorithm, we determine the spectrum of the low-lying states in this and other sectors. We find that the absolute ground state is nondegenerate. If the $\mathrm{SO}(4{)}^3$ symmetry is gauged, it is known from earlier work that the model has 36 states and a residual discrete symmetry. We study the discrete symmetry group in detail; it gives rise to degeneracies of some of the gauge singlet energies. We find all the gauge singlet energies numerically and use the results to propose exact analytic expressions for them.

A search is performed for dark matter particles produced in association with a top quark pair in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$. The data correspond to an integrated luminosity of $35.9{\mathrm{fb}}^{-1}$ recorded by the CMS detector at the LHC. No significant excess over the standard model expectation is observed. The results are interpreted using simplified models of dark matter production via spin-0 mediators that couple to dark matter particles and to standard model quarks, providing constraints on the coupling strength between the mediator and the quarks. These are the most stringent collider limits to date for scalar mediators, and the most stringent for pseudoscalar mediators at low masses.

Using $e^{+}{e}^{-}$ annihilation data of $2.93{\mathrm{fb}}^{-1}$ collected at center-of-mass energy $\sqrt{s}=3.773\mathrm{GeV}$ with the BESIII detector, we measure the absolute branching fraction of $D^0\to K^{-}{\mu }^{+}{\nu }_{\mu }$ with significantly improved precision: ${\mathcal{B}}_{D^0\to K^{-}{\mu }^{+}{\nu }_{\mu }}=(3.413\pm 0.019_{\text{stat}}\pm 0.035_{\text{syst}})\%$. Combining with our previous measurement of ${\mathcal{B}}_{D^0\to K^{-}{e}^{+}{\nu }_e}$, the ratio of the two branching fractions is determined to be ${\mathcal{B}}_{D^0\to K^{-}{\mu }^{+}{\nu }_{\mu }}/{\mathcal{B}}_{D^0\to K^{-}{e}^{+}{\nu }_e}=0.974\pm 0.007_{\text{stat}}\pm 0.012_{\text{syst}}$, which agrees with the theoretical expectation of lepton flavor universality within the uncertainty. A study of the ratio of the two branching fractions in different four-momentum transfer regions is also performed, and no evidence for lepton flavor universality violation is found with current statistics. Taking inputs from global fit in the standard model and lattice quantum chromodynamics separately, we determine $f_{+}^K(0)=0.7327\pm 0.0039_{\text{stat}}\pm 0.0030_{\text{syst}}$ and $|V_{cs}|=0.955\pm {0.005}_{\text{stat}}\pm {0.004}_{\text{syst}}\pm {0.024}_{\mathrm{LQCD}}$.