It is theoretically known that the quantum interference of a long sequence of Landau-Zener transitions can result in Rabi oscillations. Because of its stringent requirements, however, this phenomenon has never been experimentally observed in the time domain. Using a nitrogen-vacancy (NV) center spin in isotopically purified diamond, we observed the Rabi oscillations resulting from more than 100 Landau-Zener processes. Our results demonstrate favorable quantum controllability of NV centers, which could find applications in quantum metrology and quantum information processing.

We explore the fractal nature of particle showers using Monte Carlo simulation. We define the fractal dimension of showers measured in a high granularity calorimeter designed for a future lepton collider. The shower fractal dimension reveals detailed information of the spatial configuration of the shower. It is found to be characteristic of the type of interaction and highly sensitive to the nature of the incident particle. Using the shower fractal dimension, we demonstrate a particle identification algorithm that can efficiently separate electromagnetic showers, hadronic showers, and nonshowering tracks. We also find a logarithmic dependence of the shower fractal dimension on the particle energy.

We present results from the first next-to-leading-order (NLO) numerical analysis of forward hadron production in $pA$ and $dA$ collisions in the small-$x$ saturation formalism. Using parton distributions and fragmentation functions at NLO, as well as the dipole amplitude from the solution to the Balitsky-Kovchegov equation with running coupling, together with the NLO corrections to the hard coefficients, we obtain a good description of the available RHIC data in $d\mathrm{Au}$ collisions. In the large $p_{\perp }$ region beyond the saturation scale, we find that the NLO correction becomes dominant and negative, which indicates that other physics beyond NLO becomes important and should also be taken into account. Furthermore, we make predictions for forward hadron production in $p\mathrm{Pb}$ collisions at the LHC. This analysis not only incorporates the important NLO corrections for all partonic channels, but also reduces the renormalization scale dependence and helps to significantly reduce the theoretical uncertainties. It therefore provides a precise test of saturation physics beyond the leading logarithmic approximation.

We perform a triple coincidence study on differential momentum distributions of strong-field double ionization of Ar atoms in linearly polarized fields (795 nm, 45 fs, $7\times {10}^{13}\mathrm{W}/{\mathrm{cm}}^2$). Using a three-dimensional two-electron atomic-ensemble semiclassical model including the tunneling effect for both electrons, we retrieve differential momentum distributions and achieve a good agreement with the measurement. Ionization dynamics of the correlated electrons for the side-by-side and back-to-back emission is analyzed separately. According to the semiclassical model, we find that the doubly excited states are largely populated after the laser-assisted recollision and large amounts of double ionization dominantly takes place through sequential ionization of doubly excited states at such a low laser intensity. Compared with the Coulomb-free and Coulomb-corrected sequential tunneling models, we verify that electrons can obtain an energy as large as $\sim 6.5Up$ through Coulomb scattering in the combined laser and doubly charged ionic fields.

In this Letter we study a system consisting of two nearly degenerate mechanical modes that couple to a single mode of an optical cavity. We show that this coupling leads to nearly complete (99.5%) hybridization of the two mechanical modes into a bright mode that experiences strong optomechanical interactions and a dark mode that experiences almost no optomechanical interactions. We use this hybridization to transfer energy between the mechanical modes with 40% efficiency.

We analyze the tumbling of small nonspherical, axisymmetric particles in random and turbulent flows. We compute the orientational dynamics in terms of a perturbation expansion in the Kubo number, and obtain the tumbling rate in terms of Lagrangian correlation functions. These capture preferential sampling of the fluid gradients, which in turn can give rise to differences in the tumbling rates of disks and rods. We show that this is a weak effect in Gaussian random flows. But in turbulent flows persistent regions of high vorticity cause disks to tumble much faster than rods, as observed in direct numerical simulations [, Phys. Rev. Lett. 109, 134501 (2012)]. For larger particles (at finite Stokes numbers), rotational and translational inertia affects the tumbling rate and the angle at which particles collide, due to the formation of rotational caustics.

We study the competition between domain coarsening in a symmetric binary mixture below critical temperature and turbulent fluctuations. We find that the coarsening process is arrested in the presence of turbulence. The physics of the process shares remarkable similarities with the behavior of diluted turbulent emulsions and the arrest length scale can be estimated with an argument similar to the one proposed by Kolmogorov and Hinze for the maximal stability diameter of droplets in turbulence. Although, in the absence of flow, the microscopic diffusion constant is negative, turbulence does effectively arrest the inverse cascade of concentration fluctuations by making the low wavelength diffusion constant positive for scales above the Hinze length.

Motivated by experimental progress in the growth of heavy transition metal oxides, we theoretically study a class of lattice models of interacting fermions with strong spin-orbit coupling. Focusing on interactions of intermediate strength, we derive a low-energy effective field theory for a fully gapped, topologically ordered, fractionalized state with an eightfold ground-state degeneracy. This state is a fermionic symmetry-enriched topological phase with particle-number conservation and time-reversal symmetry. The topological terms in the effective field theory describe a quantized magnetoelectric response and nontrivial mutual braiding statistics of dynamical extended vortex loops with emergent fermions in the bulk. We explicitly compute the expected mutual statistics in a specific model on the pyrochlore lattice within a slave-particle mean-field theory. We argue that our model also provides a possible condensed-matter realization of oblique confinement.

We report the discovery of surface states in the perovskite superconductor $[{\mathrm{Tl}}_4]{\mathrm{TlTe}}_3$ (${\mathrm{Tl}}_5{\mathrm{Te}}_3$) and its nonsuperconducting tin-doped derivative $[{\mathrm{Tl}}_4]({\mathrm{Tl}}_{0.4}{\mathrm{Sn}}_{0.6}){\mathrm{Te}}_3$ as observed by angle-resolved photoemission spectroscopy. Density functional theory calculations predict that the surface states are protected by a $Z_2$ topology of the bulk band structure. Specific heat and magnetization measurements show that ${\mathrm{Tl}}_5{\mathrm{Te}}_3$ has a superconducting volume fraction in excess of 95%. Thus ${\mathrm{Tl}}_5{\mathrm{Te}}_3$ is an ideal material in which to study the interplay of bulk band topology and superconductivity.

Arguments were recently advanced that hole-doped ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$ exhibits the $s+is$ state at certain doping. Spontaneous breaking of time-reversal symmetry in the $s+is$ state dictates that it possess domain wall excitations. Here, we discuss what are the experimentally detectable signatures of domain walls in the $s+is$ state. We find that in this state the domain walls can have a dipolelike magnetic signature (in contrast to the uniform magnetic signature of domain walls $p+ip$ superconductors). We propose experiments where quench-induced domain walls can be stabilized by geometric barriers and observed via their magnetic signature or their influence on the magnetization process, thereby providing an experimental tool to confirm the $s+is$ state.

Magnetoelectric coupling in multiferroic heterostructures can produce large lateral modulations of magnetic anisotropy enabling the imprinting of ferroelectric domains into ferromagnetic films. Exchange and magnetostatic interactions within ferromagnetic films oppose the formation of such domains. Using micromagnetic simulations and a one-dimensional model, we demonstrate that competing energies lead to the breakdown of domain pattern transfer below a critical domain size. Moreover, rotation of the magnetic field results in abrupt transitions between two scaling regimes with different magnetic anisotropy. The theoretical predictions are confirmed by experiments on $\mathrm{CoFeB}/{\mathrm{BaTiO}}_3$heterostructures.

At low temperatures, ${\mathrm{Tb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ enters a spin liquid state, despite expectations of magnetic order and/or a structural distortion. Using neutron scattering, we have discovered that in this spin liquid state an excited crystal field level is coupled to a transverse acoustic phonon, forming a hybrid excitation. Magnetic and phononlike branches with identical dispersion relations can be identified, and the hybridization vanishes in the paramagnetic state. We suggest that ${\mathrm{Tb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ is aptly named a “magnetoelastic spin liquid” and that the hybridization of the excitations suppresses both magnetic ordering and the structural distortion. The spin liquid phase of ${\mathrm{Tb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ can now be regarded as a Coulomb phase with propagating bosonic spin excitations.

Magnetoelectric coupling is studied using the electric field between the tip of a spin-polarized scanning tunneling microscope and a nanomagnet. Our experiments show that a negative (positive) electric field stabilizes (destabilizes) in-plane magnetization against thermal agitation, whereas it destabilizes (stabilizes) out-of-plane magnetization. We conclude that the electric field $E$ induces a uniaxial anisotropy that favors in-plane magnetization for $E<0$ and out-of-plane magnetization for $E>0$. Our experiments demonstrate magnetic manipulation on the atomic scale without exploiting spin or charge currents.

We present a numerical study of a lattice model of a liquid characterized by a low-symmetry favored local structure. We find that the freezing point is depressed far enough to reveal an exotic liquid-liquid transition characterized by the appearance of an extended chirality, prior to freezing. The ordered liquid can be readily supercooled to zero temperature, as the combination of critical slowing down and competing crystal polymorphs results in a dramatically slow crystallization process. These results provide an explicit scenario by which the ordering of a liquid can proceed via an intermediate liquid-liquid transition, a scenario that may prove helpful in the analysis of low temperature liquids interacting by more realistic interactions.

Highly efficient solar energy utilization is very desirable in photocatalytic water splitting. However, until now, the infrared part of the solar spectrum, which constitutes almost half of the solar energy, has not been used, resulting in significant loss in the efficiency of solar energy utilization. Here, we propose a new mechanism for water splitting in which near-infrared light can be used to produce hydrogen. This ability is a result of the unique electronic structure of the photocatalyst, in which the valence band and conduction band are distributed on two opposite surfaces with a large electrostatic potential difference produced by the intrinsic dipole of the photocatalyst. This surface potential difference, acting as an auxiliary booster for photoexcited electrons, can effectively reduce the photocatalyst’s band gap required for water splitting in the infrared region. Our electronic structure and optical property calculations on a surface-functionalized hexagonal boron-nitride bilayer confirm the existence of such photocatalysts and verify the reaction mechanism.

Teleportation and storage of continuous variable states of light and atoms are essential building blocks for the realization of large-scale quantum networks. Rigorous validation of these implementations require identifying, and surpassing, benchmarks set by the most effective strategies attainable without the use of quantum resources. Such benchmarks have been established for special families of input states, like coherent states and particular subclasses of squeezed states. Here we solve the longstanding problem of defining quantum benchmarks for general pure Gaussian single-mode states with arbitrary phase, displacement, and squeezing, randomly sampled according to a realistic prior distribution. As a special case, we show that the fidelity benchmark for teleporting squeezed states with totally random phase and squeezing degree is $1/2$, equal to the corresponding one for coherent states. We discuss the use of entangled resources to beat the benchmarks in experiments.

A hybrid spin-oscillator system in parametric interaction is experimentally emulated using a single nitrogen vacancy (NV) spin qubit immersed in a radio frequency (rf) field and probed with a quasiresonant microwave (MW) field. We report on the MW-mediated locking of the NV spin dynamics onto the rf field, appearing when the MW-driven Rabi precession frequency approaches the rf frequency and for sufficiently large rf amplitudes. These signatures are analogous to a phononic Mollow triplet in the MW rotating frame for the parametric interaction and promise to have impact in spin-dependent force detection strategies.

In the Einstein-Maxwell-Chern-Simons theory the extremal Reissner-Nordström solution is no longer the single extremal solution with vanishing angular momentum, when the Chern-Simons coupling constant reaches a critical value. Instead a whole sequence of rotating extremal $J=0$ solutions arises, labeled by the node number of the magnetic U(1) potential. Associated with the same near horizon solution, the mass of these radially excited extremal solutions converges to the mass of the extremal Reissner-Nordström solution. On the other hand, not all near horizon solutions are also realized as global solutions.

Multifield models of inflation with nonminimal couplings are in excellent agreement with the recent results from Planck. Across a broad range of couplings and initial conditions, such models evolve along an effectively single-field attractor solution and predict values of the primordial spectral index and its running, the tensor-to-scalar ratio, and non-Gaussianities squarely in the observationally most-favored region. Such models can also amplify isocurvature perturbations, which could account for the low power recently observed in the cosmic microwave background power spectrum at low multipoles. Future measurements of primordial isocurvature perturbations could distinguish between the currently viable possibilities.

We introduce a novel nonminimal coupling between gravity and the inflaton sector. Remarkably, for large values of this coupling all models asymptote to a universal attractor. This behavior is independent of the original scalar potential and generalizes the attractor in the ${\phi }^4$ theory with nonminimal coupling to gravity. The attractor is located in the “sweet spot” of parameter values that are preferred by Planck’s recent results.