In this Letter, we demonstrate initialization and readout of nuclear spins via a negatively charged silicon-vacancy (SiV) electron spin qubit. Under Hartmann-Hahn conditions the electron spin polarization is coherently transferred to the nuclear spin. The readout of the nuclear polarization is observed via the fluorescence of the SiV. We also show that the coherence time of the nuclear spin (6 ms) is limited by the electron spin-lattice relaxation due to the hyperfine coupling to the electron spin. This Letter paves the way toward realization of building blocks of quantum hardware with an efficient spin-photon interface based on the SiV color center coupled to a long lasting nuclear memory.

We present a new solution to the hierarchy problem, where the Higgs boson mass is at its observed electroweak value because such a patch inflates the most in the early Universe. If the Higgs boson mass depends on a field undergoing quantum fluctuations during inflation, then inflation will fill the Universe with the Higgs boson mass that corresponds to the largest vacuum energy. The hierarchy problem is solved if the maximum vacuum energy occurs for the observed Higgs boson mass. We demonstrate this notion with a proof-of-principle model containing an axion, a modulus field and the Higgs boson, and show that inflation can be responsible for the weak scale.

A search for charge-parity ($CP$) violation in Cabibbo-suppressed $D_s^{+}\to K_{\mathrm{S}}^0{\pi }^{+}$, $D^{+}\to K_{\mathrm{S}}^0{K}^{+}$, and $D^{+}\to \varphi {\pi }^{+}$ decays is reported using proton-proton collision data, corresponding to an integrated luminosity of $3.8{\mathrm{fb}}^{-1}$, collected at a center-of-mass energy of 13 TeV with the LHCb detector. High-yield samples of kinematically and topologically similar Cabibbo-favored $D_{(s)}^{+}$ decays are analyzed to subtract nuisance asymmetries due to production and detection effects, including those induced by $CP$ violation in the neutral kaon system. The results are $$\begin{gathered} {\mathcal{A}}_{CP}(D_s^{+}\to K_{\mathrm{S}}^0{\pi }^{+})=(1.3\pm 1.9\pm 0.5)\times {10}^{-3}, \\ {\mathcal{A}}_{CP}(D^{+}\to K_{\mathrm{S}}^0{K}^{+})=(-0.09\pm 0.65\pm 0.48)\times {10}^{-3}, \\ {\mathcal{A}}_{CP}(D^{+}\to \varphi {\pi }^{+})=(0.05\pm 0.42\pm 0.29)\times {10}^{-3}, \end{gathered}$$where the first uncertainties are statistical and the second systematic. They are the most precise measurements of these quantities to date, and are consistent with $CP$ symmetry. A combination with previous LHCb measurements, based on data collected at 7 and 8 TeV, is also reported.

The first observation of the decays $B_{(s)}^0\to J/\psi p\overline{p}$ is reported, using proton-proton collision data corresponding to an integrated luminosity of $5.2{\mathrm{fb}}^{-1}$, collected with the LHCb detector. These decays are suppressed due to limited available phase space, as well as due to Okubo-Zweig-Iizuka or Cabibbo suppression. The measured branching fractions are $\mathcal{B}(B^0\to J/\psi p\overline{p})=[4.51\pm 0.40(\text{stat})\pm 0.44(\text{syst})]\times {10}^{-7}$, $\mathcal{B}(B_s^0\to J/\psi p\overline{p})=[3.58\pm 0.19(\text{stat})\pm 0.39(\text{syst})]\times {10}^{-6}$. For the $B_s^0$ meson, the result is much higher than the expected value of $\mathcal{O}({10}^{-9})$. The small available phase space in these decays also allows for the most precise single measurement of both the $B^0$ mass as $5279.74\pm 0.30(\text{stat})\pm 0.10(\text{syst})\mathrm{MeV}$ and the $B_s^0$ mass as $5366.85\pm 0.19(\text{stat})\pm 0.13(\text{syst})\mathrm{MeV}$.

We show that recently discovered rotational echoes of molecules provide an efficient tool for studying collisional molecular dynamics in high-pressure gases. Our study demonstrates that rotational echoes enable the observation of extremely fast collisional dissipation, at timescales of the order of a few picoseconds, and possibly shorter. The decay of the rotational alignment echoes in ${\mathrm{CO}}_2$ gas and ${\mathrm{CO}}_2\text{−}\mathrm{He}$ mixture up to 50 bar was studied experimentally, delivering collision rates that are in good agreement with the theoretical expectations. The suggested measurement protocol may be used in other high-density media, and potentially in liquids.

We report on the experimental observation of multiorbital polarons in a two-dimensional Fermi gas of ${}^{173}\mathrm{Yb}$ atoms formed by mobile impurities in the metastable ${}^3{P}_0$ orbital and a Fermi sea in the ground-state ${}^1{S}_0$ orbital. We spectroscopically probe the energies of attractive and repulsive polarons close to an orbital Feshbach resonance and characterize their coherence by measuring the quasiparticle residue. For all probed interaction parameters, the repulsive polaron is a long-lived quasiparticle with a decay rate more than 2 orders of magnitude below its energy. We formulate a many-body theory, which accurately treats the interorbital interactions in two dimensions and agrees well with the experimental results. Our work paves the way for the investigation of many-body physics in multiorbital ultracold Fermi gases.

We investigate the dynamics of a spinor Bose-Einstein condensate inside an optical cavity, driven transversely by a laser with a controllable polarization angle. We focus on a two-component Dicke model with complex light-matter couplings, in the presence of photon losses. We calculate the steady-state phase diagram and find dynamical instabilities in the form of limit cycles, heralded by the presence of exceptional points and level attraction. We show that the instabilities are induced by dissipative processes that generate nonreciprocal couplings between the two collective spins. Our predictions can be readily tested in state-of-the-art experiments and open up the study of nonreciprocal many-body dynamics out of equilibrium.

All-dielectric resonant nanophotonics lies at the heart of modern optics and nanotechnology due to the unique possibilities to control scattering of light from high-index dielectric nanoparticles and metasurfaces. One of the important concepts of dielectric Mie-resonant nanophotonics is associated with the Kerker effect that drives the unidirectional scattering of light from nanoantennas and Huygens metasurfaces. Here we suggest and demonstrate experimentally a novel effect manifested in the nearly complete simultaneous suppression of both forward and backward scattered fields. This effect is governed by the Fano resonance of an electric dipole and off-resonant quadrupoles, providing necessary phases and amplitudes of the scattered fields to achieve the transverse scattering. We extend this concept to dielectric metasurfaces that demonstrate zero reflection with transverse scattering and strong field enhancement for resonant light filtering, nonlinear effects, and sensing.

Direct numerical simulations of homogeneous sheared and stably stratified turbulence are considered to probe the asymptotic high dynamic range regime suggested by Gargett et al. J. Fluid Mech. 144, 231 (1984) and Shih et al. J. Fluid Mech. 525, 193 (1999). We consider statistically stationary configurations of the flow that span three decades in dynamic range defined by the separation between the Ozmidov length scale $L_O=\sqrt{\epsilon /N^3}$ and the Kolmogorov length scale $L_K=({\nu }^3/\epsilon {)}^{1/4}$, up to ${\mathrm{Re}}_b\equiv (L_O/L_K{)}^{4/3}=\epsilon /(\nu N^2)\sim O(1000)$, where $\epsilon$ is the mean turbulent kinetic energy dissipation rate, $\nu$ is the kinematic viscosity, and $N$ is the buoyancy frequency. We isolate the effects of ${\mathrm{Re}}_b$, particularly on irreversible mixing, from the effects of other flow parameters of stratified and sheared turbulence. Specifically, we evaluate the influence of dynamic range independent of initial conditions. We present evidence that the flow approaches an asymptotic state for ${\mathrm{Re}}_b⪆300$, characterized both by an asymptotic partitioning between the potential and kinetic energies and by the approach of components of the dissipation rate to their expected values under the assumption of isotropy. As ${\mathrm{Re}}_b$ increases above 100, there is a slight decrease in the turbulent flux coefficient $\mathrm{\Gamma }=\chi /\epsilon$, where $\chi$ is the dissipation rate of buoyancy variance, but, for this flow, there is no evidence of the commonly suggested $\mathrm{\Gamma }\propto {{\mathrm{Re}}_b}^{-1/2}$ dependence when $100\le {\mathrm{Re}}_b\le 1000$.

Nonequilibrium steady state conditions induced by a dc current can alter the physical properties of strongly correlated electron systems. In this regard, it was recently shown that dc current can trigger novel electronic states, such as current-induced diamagnetism, which cannot be realized in equilibrium conditions. However, reversible control of diamagnetism has not been achieved yet. Here, we demonstrate reversible in situ control between a Mott insulating state and a diamagnetic semimetal-like state by a dc current in the Ti-substituted bilayer ruthenate ${\mathrm{Ca}}_3({\mathrm{Ru}}_{1-x}{\mathrm{Ti}}_x{)}_2{\mathrm{O}}_7$ ($x=0.5\%$). By performing simultaneous magnetic and resistive measurements, we map out the temperature vs current-density phase diagram in the nonequilibrium steady state of this material. The present results open up the possibility of creating novel electronic states in a variety of strongly correlated electron systems under dc current.

New materials such as nodal-line semimetals offer a unique setting for novel transport phenomena. Here, we calculate the quantum correction to conductivity in a disordered nodal-line semimetal. The torus-shaped Fermi surface and encircled $\pi$ Berry flux carried by the nodal loop result in a fascinating interplay between the effective dimensionality of electron diffusion and band topology, which depends on the scattering range of the impurity potential relative to the size of the nodal loop. For a short-range impurity potential, backscattering is dominated by the interference paths that do not encircle the nodal loop, yielding a 3D weak localization effect. In contrast, for a long-range impurity potential, the electrons effectively diffuse in various 2D planes and the backscattering is dominated by the interference paths that encircle the nodal loop. The latter leads to weak antilocalization with a 2D scaling law. Our results are consistent with symmetry consideration, where the two regimes correspond to the orthogonal and symplectic classes, respectively. Furthermore, we present weak-field magnetoconductivity calculations at low temperatures for realistic experimental parameters and predict that clear scaling signatures $\propto \sqrt{B}$ and $\propto -\ln B$, respectively. The crossover between the 3D weak localization and 2D weak antilocalization can be probed by tuning the Fermi energy, giving a unique transport signature of the nodal-line semimetal.

Geometrically frustrated interactions may render classical ground states macroscopically degenerate. The connection between classical and quantum liquids and how the degeneracy is affected by quantum fluctuations is, however, not completely understood. We study a simple model of coupled quantum and classical degrees of freedom, the so-called Falicov-Kimball model, on a triangular lattice and away from half-filling. For weak interactions the phase diagram features a charge disordered state down to zero temperature. We provide compelling evidence that this phase is a liquid and show that it is divided by a crossover line that terminates in a quantum critical point. Our results offer a new vantage point to address how quantum liquids can emerge from their classical counterparts.

We demonstrate the experimental feasibility of probing the fully nonperturbative regime of quantum electrodynamics with a 100 GeV-class particle collider. By using tightly compressed and focused electron beams, beamstrahlung radiation losses can be mitigated, allowing the particles to experience extreme electromagnetic fields. Three-dimensional particle-in-cell simulations confirm the viability of this approach. The experimental forefront envisaged has the potential to establish a novel research field and to stimulate the development of a new theoretical methodology for this yet unexplored regime of strong-field quantum electrodynamics.

We prove a trade-off relation between the entanglement cost and classical communication round complexity of a protocol in implementing a class of two-qubit unitary gates by two distant parties, a key subroutine in distributed quantum information processing. The task is analyzed in an information theoretic scenario of asymptotically many input pairs with a small error that is required to vanish sufficiently quickly. The trade-off relation is shown by (i) one ebit of entanglement per pair is necessary for implementing the unitary by any two-round protocol, and (ii) the entanglement cost by a three-round protocol is strictly smaller than one ebit per pair. We also provide an example of bipartite unitary gates for which there is no such trade-off.

The ability to achieve ultrastrong coupling between light and matter promises to bring about new means to control material properties, new concepts for manipulating light at the atomic scale, and new insights into quantum electrodynamics (QED). Thus, there is a need to develop quantitative theories of QED phenomena in complex electronic and photonic systems. In this Letter, we develop a variational theory of general non-relativistic QED systems of coupled light and matter. Essential to our Ansatz is the notion of an effective photonic vacuum whose modes are different than the modes in the absence of light-matter coupling. This variational formulation leads to a set of general equations that can describe the ground state of multielectron systems coupled to many photonic modes in real space. As a first step toward a new ab initio approach to ground and excited state energies in QED, we apply our Ansatz to describe a multilevel emitter coupled to many optical modes, a system with no analytical solution. We find a compact semianalytical formula which describes ground and excited state energies very well in all regimes of coupling parameters allowed by sum rules. Our formulation provides a nonperturbative theory of Lamb shifts and Casimir-Polder forces, as well as suggest new physical concepts such as the Casimir energy of a single atom in a cavity. Our method thus give rise to highly accurate nonperturbative descriptions of many other phenomena in general QED systems.

Topology manifesting in many branches of physics deepens our understanding on state of matters. Topological photonics has recently become a rapidly growing field since artificial photonic structures can be well designed and constructed to support topological states, especially a promising large-scale implementation of these states using photonic chips. Meanwhile, due to the inapplicability of Hall conductance to photons, it is still an elusive problem to directly measure the integer topological invariants and topological phase transitions in photonic system. Here, we present a direct observation of topological winding numbers by using bulk-state photon dynamics on a chip. Furthermore, we for the first time experimentally observe the topological phase transition points via single-photon dynamics. The integrated topological structures, direct measurement in the single-photon regime and strong robustness against disorder add the key elements into the toolbox of “quantum topological photonics” and may enable topologically protected quantum information processing in large scale.