We introduce a general and systematic theoretical framework for operational dynamic modeling (ODM) by combining a kinematic description of a model with the evolution of the dynamical average values. The kinematics includes the algebra of the observables and their defined averages. The evolution of the average values is drawn in the form of Ehrenfest-like theorems. We show that ODM is capable of encompassing wide-ranging dynamics from classical non-relativistic mechanics to quantum field theory. The generality of ODM should provide a basis for formulating novel theories.

Determining the optimal implementation of a quantum gate is critical for designing a quantum computer. We consider the crucial task of efficiently decomposing a general single-qubit quantum gate into a sequence of fault-tolerant quantum operations. For a given single-qubit circuit, we construct an optimal gate sequence consisting of fault-tolerant Hadamard ($H$) and $\pi /8$ rotations ($T$). Our scheme is based on a novel canonical form for single-qubit quantum circuits and the corresponding rules for exactly reducing a general single-qubit circuit to our canonical form. The result is optimal in the number of $T$ gates. We demonstrate that a precomputed epsilon net of canonical circuits in combination with our scheme lowers the depth of approximation circuits by up to 3 orders of magnitude compared to previously reported results.

We investigate the efficiency of systems of molecular motors operating at maximum power. We consider two models of kinesin motors on a microtubule: for both the simplified and the detailed model, we find that the many-body exclusion effect enhances the efficiency at maximum power of the many-motor system, with respect to the single motor case. Remarkably, we find that this effect occurs in a limited region of the system parameters, compatible with the biologically relevant range.

Recent observations of the solar wind have pointed out the existence of a cascade of magnetic energy from the scale of the proton Larmor radius ${\rho }_p$ down to the electron Larmor radius ${\rho }_e$ scale. In this Letter we study the spatial properties of magnetic field fluctuations in the solar wind and find that at small scales the magnetic field does not resemble a sea of homogeneous fluctuations, but rather a two-dimensional plane containing thin current sheets and discontinuities with spatial sizes ranging from $l\gtrsim {\rho }_p$ down to ${\rho }_e$ and below. These isolated structures may be manifestations of intermittency that localize sites of turbulent dissipation. Studying the relationship between turbulent dissipation, reconnection, and intermittency is crucial for understanding the dynamics of laboratory and astrophysical plasmas.

We propose a new integral formula for all tree-level scattering amplitudes of $\mathcal{N}=6$ supersymmetric Chern-Simons theory. It resembles the Roiban-Spradlin-Volovich-Witten formula for $\mathcal{N}=4$ supersymmetric Yang-Mills theory based on a twistor string theory formulation. Our formula implies that the ($2k$)-point tree-level amplitude is closely related to degree ($k-1$) curves in ${\mathbb{C}\mathbb{P}}^{k-1}$.

Using a pump-dump-probe technique and Fourier-transform spectroscopy, we study the internuclear separation $R$ dependence and relative strength of the ionization rates of the $\pi$ and $\sigma$ electrons of ${\mathrm{I}}_2$, whose valence orbitals are ${\sigma }_g^2{\pi }_u^4{\pi }_g^4{\sigma }_u^0$. We find that ionization of the highest occupied molecular orbital (HOMO)-2 (${\sigma }_g$) has a strong dependence on $R$ while the HOMO and HOMO-1 do not. Surprisingly, the ionization rate of the HOMO-2 exceeds the combined ionization rate of the less bound orbitals and this branching ratio increases with $R$. Since our technique produces target molecules that are highly aligned with the laser polarization, the $\sigma$ orbitals will be preferentially ionized and undergo enhanced ionization at larger $R$ compared to the $\pi$ orbitals. Nevertheless, it is highly unusual that an inner orbital provides the dominant strong field ionization pathway in a small molecule.

We report on the results of a search for the electron electric dipole moment $d_e$ using paramagnetic ferroelectric ${\mathrm{Eu}}_{0.5}{\mathrm{Ba}}_{0.5}{\mathrm{TiO}}_3$. The electric polarization creates an effective electric field that makes it energetically favorable for the spins of the seven unpaired $4f$ electrons of the ${\mathrm{Eu}}^{2+}$ to orient along the polarization, provided that $d_e\ne 0$. This interaction gives rise to sample magnetization, correlated with its electric polarization, and is therefore equivalent to a linear magnetoelectric effect. A SQUID magnetometer is used to search for the resulting magnetization. We obtain $d_e=(-1.07\pm {3.06}_{\mathrm{stat}}\pm {1.74}_{\mathrm{syst}})\times {10}^{-25}e\mathrm{cm}$, implying an upper limit of $|d_e|<6.05\times {10}^{-25}e\mathrm{cm}$ (90% confidence).

We explore photon coincidence counting statistics in the ultrastrong coupling regime, where the atom-cavity coupling rate becomes comparable to the cavity resonance frequency. In this regime, usual normal order correlation functions fail to describe the output photon statistics. By expressing the electric-field operator in the cavity-emitter dressed basis, we are able to propose correlation functions that are valid for arbitrary degrees of light-matter interaction. Our results show that the standard photon blockade scenario is significantly modified for ultrastrong coupling. We observe parametric processes even for two-level emitters and temporal oscillations of intensity correlation functions at a frequency given by the ultrastrong photon emitter coupling. These effects can be traced back to the presence of two-photon cascade decays induced by counterrotating interaction terms.

Using a vertical undulator, picometer vertical electron beam emittances have been observed at the Australian Synchrotron storage ring. An APPLE-II type undulator was phased to produce a horizontal magnetic field, which creates a synchrotron radiation field that is very sensitive to the vertical electron beam emittance. The measured ratios of undulator spectral peak heights are evaluated by fitting to simulations of the apparatus. With this apparatus immediately available at most existing electron and positron storage rings, we find this to be an appropriate and novel vertical emittance diagnostic.

It is observed that the magnitude of the toroidal rotation speed is reduced by the central electron cyclotron resonance heating (ECRH) regardless of the direction of the toroidal rotation. The magnetohydrodynamics activities generally appear with the rotation change due to ECRH. It is shown that the internal kink mode is induced by the central ECRH and breaks the toroidal symmetry. When the magnetohydrodynamics activities are present, the toroidal plasma viscosity is not negligible. The observed effects of ECRH on the toroidal plasma rotation are explained by the neoclassical toroidal viscosity in this Letter. It is found that the neoclassical toroidal viscosity torque caused by the internal kink mode damps the toroidal rotation.

In this Letter, we show through numerical simulations and analytical results that overlapping multiple ($N$) laser beams in plasmas can lead to strong stochastic ion heating from many ($\propto N^2$) electrostatic perturbations driven by beat waves between pairs of laser beams. For conditions typical of inertial-confinement-fusion experiment conditions, hundreds of such beat waves are driven in ${\mathrm{mm}}^3$-scale plasmas, leading to ion heating rates of several $\mathrm{keV}/\mathrm{ns}$. This mechanism saturates cross-beam energy transfer, with a reduction of linear gains by a factor $\sim 4–5$ and can strongly modify the overall hydrodynamics evolution of such laser-plasma systems.

Recently, numerical evidence for a dynamical first-order phase transition in trajectory space [L. O. Hedges et al., Science 323, 1309 (2009)] has been found. In a model glass former in which clusters of 11 particles form upon cooling, we find that the transition has both dynamical and structural character. It occurs between an active phase with a high fraction of mobile and low fraction of cluster particles, and an inactive phase with few mobile but many cluster particles. The transition can be driven both dynamically and structurally with a chemical potential, showing that local order forms a mechanism for dynamical arrest.

When processing Fe-Pd ferromagnetic shape memory thin films, selection of the desired phases and their transformation temperatures constitutes one of the largest challenges from an application point of view. In the present contribution we demonstrate that irradiation with 1.8 MeV ${\mathrm{Kr}}^{+}$ ions is the method of choice to achieve this goal: Single crystalline ${\mathrm{Fe}}_7{\mathrm{Pd}}_3$ thin films that are grown with molecular beam epitaxy on MgO (001) substrates and subsequently irradiated with ions reveal a phase transformation along the whole phase transformation path ranging from fcc austenite to bcc martensite. While for ${10}^{14}\mathrm{ions}/{\mathrm{cm}}^2$ a fcc-fct phase transformation is observed, increasing the fluence to $5\times {10}^{14}\mathrm{ions}/{\mathrm{cm}}^2$ and $5\times {10}^{15}\mathrm{ions}/{\mathrm{cm}}^2$ leads to a phase transformation to the bcc phase. Pole figure measurements reveal an orientation relationship for the fcc-bcc phase transformation according to Nishiyama and Wassermann.

We experimentally investigate the role of size effects and boundary scattering on the thermal conductivity of silicon-germanium alloys. The thermal conductivities of a series of epitaxially grown ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ thin films with varying thicknesses and compositions were measured with time-domain thermoreflectance. The resulting conductivities are found to be 3 to 5 times less than bulk values and vary strongly with film thickness. By examining these measured thermal conductivities in the context of a previously established model, it is shown that long wavelength phonons, known to be the dominant heat carriers in alloy films, are strongly scattered by the film boundaries, thereby inducing the observed reductions in heat transport. These results are then generalized to silicon-germanium systems of various thicknesses and compositions; we find that the thermal conductivities of ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ superlattices are ultimately limited by finite size effects and sample size rather than periodicity or alloying. This demonstrates the strong influence of sample size in alloyed nanosystems. Therefore, if a comparison is to be made between the thermal conductivities of superlattices and alloys, the total sample thicknesses of each must be considered.

We theoretically investigate the interplay between the fermionic mobile impurity atoms and a Larkin-Ovchinnikov (LO) superfluid in a two dimensional optical lattice. We find that the impurity atoms get localized and can form pairs when the interaction between the impurity atoms and the LO superfluid is strong enough. These features are due to the phenomena of self-localization whose underlying mechanism is revealed by an effective model. The impurity atoms with finite concentrations can drive the transition from a two-dimensional, checkerboardlike LO state to a quasi-one-dimensional, stripelike one. Experimental preparations to observe these features are also discussed.

Extensive scanning tunneling microscopy and spectroscopy experiments complemented by first-principles and parametrized tight binding calculations provide a clear answer to the existence, origin, and robustness of van Hove singularities (vHs) in twisted graphene layers. Our results are conclusive: vHs due to interlayer coupling are ubiquitously present in a broad range (from 1° to 10°) of rotation angles in our graphene on $6H$-SiC(000-1) samples. From the variation of the energy separation of the vHs with the rotation angle we are able to recover the Fermi velocity of a graphene monolayer as well as the strength of the interlayer interaction. The robustness of the vHs is assessed both by experiments, which show that they survive in the presence of a third graphene layer, and by calculations, which test the role of the periodic modulation and absolute value of the interlayer distance. Finally, we clarify the role of the layer topographic corrugation and of electronic effects in the apparent moiré contrast measured on the STM images.

We describe investigations of the largely unexplored field of mesoscopic type-I superconductors. Micromagnetometry and 3D Ginzburg-Landau simulations of our single crystal $\beta$-tin samples in this regime reveal size- and temperature-dependent supercritical fields whose behavior is radically different from the bulk critical field $H_c^B$. We find that complete suppression of the intermediate state in medium-size samples can result in a surprising reduction of the critical field significantly below $H_c^B$. We also reveal an evolution of the superconducting-to-normal phase transition from the expected irreversible first order at low temperatures through the previously unobserved reversible first-order to a second-order transition close to $T_c$, where the critical field can be many times larger than $H_c^B$. Finally, we have identified striking correlations between the mesoscopic $H_{c3}$ for nucleation of surface superconductivity and the thermodynamic $H_c$ near $T_c$. All these observations are entirely unexpected in the conventional type-I picture.

We use symmetry analysis and first-principles calculations to show that the linear magnetoelectric effect can originate from the response of orbital magnetic moments to the polar distortions induced by an applied electric field. Using ${\mathrm{LiFePO}}_4$ as a model compound we show that spin-orbit coupling partially lifts the quenching of the $3d$ orbitals and causes small orbital magnetic moments (${\mu }_{(L)}\approx 0.3{\mu }_B$) parallel to the spins of the ${\mathrm{Fe}}^{2+}$ ions. An applied electric field $\mathbf{E}$ modifies the size of these orbital magnetic moments inducing a net magnetization linear in $\mathbf{E}$.

Rupture, bond breaking, or extraction from a deep and narrow potential well requires considerable force while producing minimal displacement. In thermally fluctuating systems, there is not a single force required to achieve rupture, but a spectrum, as thermal forces can both augment and inhibit the bond breaking. We demonstrate measurement and interpretation of the distribution of rupture forces between pairs of colloidal particles bonded via the van der Waals attraction. The otherwise irreversible bond is broken by pulling the particles apart with optical tweezers. We show that an ensemble of the particle trajectories before, during and after the rupture event may be used to produce a high fidelity description of the distribution of rupture forces. This analysis is equally suitable for describing rupture forces in molecular and biomolecular contexts with a number of measurement techniques.

Dissociative adsorption of molecular oxygen on the Al(111) surface exhibits mechanistic complexity that remains surprisingly poorly understood in terms of the underlying physics. Experiments clearly indicate substantial energy barriers and a mysteriously large number of adsorbed single oxygen atoms instead of pairs. Conventional first principles quantum mechanics (density functional theory) predicts no energy barrier at all; instead, spin selection rules have been invoked to explain the barrier. In this Letter, we show that correct barriers arise naturally when embedded correlated electron wave functions are used to capture the physics of the interaction of ${\mathrm{O}}_2$ with the metal surface. The barrier originates from an abrupt charge transfer (from metal to oxygen), which is properly treated within correlated wave function theory but not within conventional density functional theory. Our potential energy surfaces also identify oxygen atom abstraction as the dominant reaction pathway at low incident energies, consistent with measurements, and show that charge transfer occurs in a stepwise fashion.