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, Mira Diekmann, Robert Berger,
Published: 14 September 2021
Physical Review X, Volume 11; https://doi.org/10.1103/physrevx.11.031056

Abstract:
Molecular matter-wave interferometry enables novel strategies for manipulating the internal mechanical motion of complex molecules. Here, we show how chiral molecules can be prepared in a quantum superposition of two enantiomers by far-field matter-wave diffraction and how the resulting tunneling dynamics can be observed. We determine the impact of rovibrational phase averaging and propose a setup for sensing enantiomer-dependent forces, parity-violating weak interactions, and environment-induced superselection of handedness, as suggested to resolve Hund’s paradox. Using ab initio tunneling calculations, we identify [4]-helicene derivatives as promising candidates to implement the proposal with state-of-the-art techniques. This work opens the door for quantum sensing with chiral molecules.
, R. Srinivas
Published: 14 September 2021
Physical Review A, Volume 104; https://doi.org/10.1103/physreva.104.032609

Abstract:
Using discrete and continuous variable subsystems, hybrid approaches to quantum information could enable more quantum computational power for the same physical resources. Here, we propose a hybrid scheme that can be used to generate the necessary Gaussian and non-Gaussian operations for universal continuous variable quantum computing in trapped ions. This scheme utilizes two linear spin-motion interactions to generate a broad set of nonlinear effective spin-motion interactions including one- and two-mode squeezing, beam splitter, and trisqueezing operations in trapped ion systems. We discuss possible experimental implementations using laser-based and laser-free approaches.
L. Martin-Monier, , P. L. Piveteau, ,
Physical Review Applied, Volume 16; https://doi.org/10.1103/physrevapplied.16.034025

Abstract:
When a liquid film lies on a nonwettable substrate, the configuration is unstable, and the film spontaneously ruptures to form droplets. This phenomenon, known as dewetting, commonly leads to undesirable morphological changes. Nevertheless, recent works, combining spontaneous dewetting triggered by thermal annealing and topographic pattern-directed dewetting, demonstrate the possibility of harnessing dewetting with a degree of precision on par with that of advanced lithographic processes for high-performance nanophotonic applications. Since resonant behavior is highly sensitive to geometrical changes, predicting quantitatively dewetting dynamics is of high interest. Here, we develop a continuum model that predicts the evolution of a thin film on a patterned substrate, from the initial reflow to the nucleation and growth of holes. We provide an operative framework based on macroscopic measurements to model the intermolecular interactions at the origin of the dewetting process, involving length scales that span from sub-nanometer to micrometer. A comparison of experimental and simulated results shows that the model can accurately predict the final distributions, thereby offering predictive tools to tailor the optical response of dewetted nanostructures.
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.064036

Abstract:
We study scalar, fermionic and gauge fields coupled nonminimally to gravity in the Einstein-Cartan formulation. We construct a wide class of models with nondynamical torsion whose gravitational spectra comprise only the massless graviton. Eliminating nonpropagating degrees of freedom, we derive an equivalent theory in the metric formulation of gravity. It features contact interactions of a certain form between, and among, the matter and gauge currents. We also discuss briefly the inclusion of curvature-squared terms.
Chen Lu, Meng-Meng Gao, Ting-Ting Hu,
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.115304

Abstract:
The physical model of nanosecond laser ablation of semi-insulating 4H-SiC irradiated by KrF excimer laser with a wavelength of 248 nm was studied. The etching depth was tested by a stylus surface profiler. The morphology of the ablation pit and the thickness of the damaged layer were observed through scanning electron microscope. The phases at the laser irradiated surface were analyzed by Raman spectroscopy. In situ x-ray photoelectron spectroscopy was used to obtain component distribution of the damaged layer and a reasonable thermophysical model was constructed. The temperature distribution of the substrate after the laser irradiation was calculated according to this model. It was found that the etching depth had a linear relationship with the number of laser pulses and the thickness of the uniform damaged layer was independent of pulse number (>10). The thickness of the ablated layer and the newly generated damaged layer are equivalent for each laser irradiation. The established laser ablation model deepens the understanding of physical process and mechanism of nanosecond laser etching of SiC and provides a theoretical guidance for laser processing of SiC.
, Samudra Roy, Shailendra K. Varshney
Published: 14 September 2021
Physical Review A, Volume 104; https://doi.org/10.1103/physreva.104.033514

Abstract:
Understanding the intracavity field dynamics in passive microresonator systems has already been intriguing. It becomes fascinating when the system is complex, such as a concentric dual microring resonator that exhibits avoided mode crossing (AMC). In this work, we present a systematic study of intracavity oscillatory field dynamics near AMC in a concentric silicon-nitride microring resonator with the help of coupled Lugiato-Lefever equation. We identify two regions where the hybrid modes are strongly coupled and weakly coupled based on their eigenfrequency separation, which originate from mode coupling near AMC. We calculate the overlap integral to identify the cutoff pump wavelength region to observe the existence of the two hybrid modes. In a strongly coupled hybrid mode region, we observe intracavity power oscillation and transfer of energy between the two hybrid modes in a periodic manner. We also evaluate the nonidentical phase variation of these two modes. In a weakly coupled hybrid mode region, power oscillation and energy transfer between modes reduces significantly, whereas their phases vary in almost identical fashion. We validate our numerical findings with the semianalytical variational method, leading to an in-depth understanding of the mode-coupling-induced dynamics. We finally analyze the polarization properties of the field confined in the coupled system. Exploiting the Stokes parameters and Jones vector, we deduce a polarization-evolving state and a polarization-locked state in strongly coupled region and weakly coupled region, respectively.
Yonghee Kim, , ,
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.054012

Abstract:
Chiral effective theory of scalar and vector diquarks is formulated according to the linear sigma model. The main application is to describe the ground and excited states of singly heavy baryons with a charm or bottom quark. Applying the potential quark model between the diquark and the heavy quark (Q=c, b), we construct a heavy-quark–diquark model. The spectra of the positive- and negative-parity states of ΛQ, ΣQ, ΞQ(), and ΩQ are obtained. The masses and interaction parameters of the effective theory are fixed partly from the lattice QCD data and also from fitting low-lying heavy-baryon masses. We find that the negative parity excited states of ΞQ (flavor 3¯) are different from those of ΛQ, because of the inverse hierarchy of the pseudoscalar diquark. On the other hand, ΣQ, ΞQ, and ΩQ (flavor 6) baryons have similar spectra. We compare our results of the heavy-quark–diquark model with experimental data as well as the quark model.
Physical Review Letters, Volume 127; https://doi.org/10.1103/physrevlett.127.123603

Abstract:
The optomechanical character of molecules was discovered by Raman about one century ago. Today, molecules are promising contenders for high-performance quantum optomechanical platforms because their small size and large energy-level separations make them intrinsically robust against thermal agitations. Moreover, the precision and throughput of chemical synthesis can ensure a viable route to quantum technological applications. The challenge, however, is that the coupling of molecular vibrations to environmental phonons limits their coherence to picosecond time scales. Here, we improve the optomechanical quality of a molecule by several orders of magnitude through phononic engineering of its surrounding. By dressing a molecule with long-lived high-frequency phonon modes of its nanoscopic environment, we achieve storage and retrieval of photons at millisecond timescales and allow for the emergence of single-photon strong coupling in optomechanics. Our strategy can be extended to the realization of molecular optomechanical networks.
Physical Review Letters, Volume 127; https://doi.org/10.1103/physrevlett.127.122301

Abstract:
We explore the out-of-equilibrium dynamics of the quark-gluon plasma at zero and finite net-baryon density based on an effective kinetic theory of quantum chromodynamics (QCD). By investigating the isotropization of the longitudinal pressure, we determine the relevant time and temperature scales for the onset of viscous hydrodynamics and quantify the dependence on the chemical composition of the quark-gluon plasma. By extrapolating our results to realistic coupling strength, we discuss phenomenological consequences regarding the role of the preequilibrium phase at different collision energies.
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.066015

Abstract:
We derive an explicit expression for the transition amplitude from black to white hole horizon at the end of Hawking evaporation using covariant loop quantum gravity.
Physical Review Research, Volume 3; https://doi.org/10.1103/physrevresearch.3.033246

Abstract:
In colloidal systems, Brownian motion emerges from the massive separation of time and length scales associated with characteristic dynamics of the solute and solvent constituents. This separation of scales produces several temporal regimes in the colloidal dynamics when combined with the effects of the interaction between the particles, confinement conditions, and state variables, such as density and temperature. Some examples are the short- and long-time regimes in two- and three-dimensional open systems and the diffusive and subdiffusive regimes observed in the single-file (SF) dynamics along a straight line. In this paper, we address the way in which a confining geometry induces new time scales. We report on the dynamics of interacting colloidal particles moving along a circle by combining a heuristic theoretical analysis of the involved scales, Brownian dynamics computer simulations, and video-microscopy experiments with paramagnetic colloids confined to lithographic circular channels subjected to an external magnetic field. The systems display four temporal regimes in the following order: one-dimensional free diffusion, SF subdiffusion, free-cluster rotational diffusion, and the expected saturation due to the confinement. We also report analytical expressions for the mean-square angular displacement and crossover times obtained from scaling arguments, which accurately reproduce both experiments and simulations. Our generic approach can be used to predict the long-time dynamics of many other confined physical systems.
, I. Yusipov, T. Laptyeva, S. Denisov, D. Chruściński,
Published: 14 September 2021
Physical Review E, Volume 104; https://doi.org/10.1103/physreve.104.034118

Abstract:
Continuous-time Markovian evolution appears to be manifestly different in classical and quantum worlds. We consider ensembles of random generators of N-dimensional Markovian evolution, quantum and classical ones, and evaluate their universal spectral properties. We then show how the two types of generators can be related by superdecoherence. In analogy with the mechanism of decoherence, which transforms a quantum state into a classical one, superdecoherence can be used to transform a Lindblad operator (generator of quantum evolution) into a Kolmogorov operator (generator of classical evolution). We inspect spectra of random Lindblad operators undergoing superdecoherence and demonstrate that, in the limit of complete superdecoherence, the resulting operators exhibit spectral density typical to random Kolmogorov operators. By gradually increasing strength of superdecoherence, we observe a sharp quantum-to-classical transition. Furthermore, we define an inverse procedure of supercoherification that is a generalization of the scheme used to construct a quantum state out of a classical one. Finally, we study microscopic correlation between neighboring eigenvalues through the complex spacing ratios and observe the horseshoe distribution, emblematic of the Ginibre universality class, for both types of random generators. Remarkably, it survives both superdecoherence and supercoherification.
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.054013

Abstract:
We outline a strategy of how to search for QCD instantons of invariant mass 20–60 GeV in diffractive events in low-luminosity runs at the LHC. We show that, by imposing appropriate selection criteria on the final states, one can select the kinematic regime where the instanton signal exceeds the background by a factor of at least 8. In spite of the relatively strong cuts that we impose on the total transverse energy and the number of charged tracks, iET,i>15GeV and Nch>20 measured within the 0<η<2 interval and excluding events with high-pT particles, the expected cross section is sufficiently large to study the instanton production in events with large rapidity gaps at low luminosities, thus avoiding problems with pileup. The paper also includes an updated computation of instanton cross sections and other parameters relevant for ongoing studies.
Zheng Liu, , Yafei Ren, Qian Niu,
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.l121403

Abstract:
We identify a valley-polarized Chern insulator in a van der Waals heterostructure, monolayer Pt2HgSe3/monolayer CrI3, for potential applications with interplay between electric, magnetic, optical, and mechanical effects. The interlayer proximity magnetic coupling nearly closes the band gap of monolayer Pt2HgSe3, and the strong intralayer spin-orbit coupling further lifts the valley degeneracy by over 100 meV, leading to positive and negative band gaps at opposite valleys. In the valley with negative gap, the interfacial Rashba spin-orbit coupling opens a topological band gap of 17.8 meV, which is enlarged to 30.8 meV by adding a hexagonal boron nitride (h-BN) layer. We find large orbital magnetization in the Pt2HgSe3 layer that is much larger than spin, which can induce a measurable optical Kerr effect. The valley polarization and Chern number are coupled to the magnetic order of the nearest-neighbor CrI3 layer, which is switchable by electric, magnetic, and mechanical means in experiments. The presence of h-BN protects the topological phase, allowing the construction of superlattices with valley, spin, and layer degrees of freedom.
, Xun-Wang Yan, Zhong-Yi Lu, Tao Xiang
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.l100504

Abstract:
The discovery of high-temperature superconductivity in hydrogen-rich compounds has fueled the enthusiasm for finding materials with more promising superconducting properties among hydrides. However, the ultrahigh pressure needed to synthesize and maintain high-temperature hydrogen-rich superconductors hinders the experimental investigation of these materials. For practical applications, it is also highly desired to find more hydrogen-rich materials that superconduct at high temperatures but under relatively lower pressures. Based on first-principles density functional theory, we calculate the electronic and phonon band structures for a ternary borohydride formed by intercalating BH4 tetrahedrons into a fcc potassium lattice, KB2H8. Remarkably, we find that this material is dynamically stable and one of its sp3-hybridized σ-bonding bands is metallized (i.e., partially filled) above a moderate high pressure. This metallized σ-bonding band couples strongly with phonons, giving rise to a strong superconducting pairing potential. By solving the anisotropic Eliashberg equations, we predict that the superconducting transition temperature of this compound is 134–146 K around 12 GPa.
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.054014

Abstract:
We discuss transverse momentum dependent (TMD) gluon distributions within high energy factorization at next-to-leading order in the strong coupling within the framework of Lipatov’s high energy effective action. We provide a detailed discussion of both rapidity divergences related to the TMD definition and its soft factor on the one hand, and rapidity divergences due to high energy factorization on the other hand, and discuss common features and differences between Collins-Soper (CS) and Balitsky-Fadin-Kuarev-Lipatov (BFKL) evolution. While we confirm earlier results which state that the unpolarized and linearly polarized gluon TMD agree in the BFKL limit at leading order, we find that both distributions differ, once next-to-leading order corrections are being included. Unlike previous results, our framework allows us to recover the complete anomalous dimension associated with the Collins-Soper-Sterman (CSS) evolution of the TMD distribution, including also single-logarithmic terms in the CSS evolution. As an additional result, we provide a definition of kT factorization, i.e., matching of off shell coefficients to collinear factorization at next-to-leading order within high energy factorization and the effective action framework. We furthermore establish a link between the QCD operator definition of the TMD gluon distribution and a previously derived off shell TMD gluon-to-gluon splitting function, which is within the present framework obtained as the real one-loop correction.
, , Mikihiko Oogane, Hiroshi Imamura, Yasuo Ando, Masashi Sahashi
Physical Review Materials, Volume 5; https://doi.org/10.1103/physrevmaterials.5.094406

Abstract:
Cr2O3 is the archetypal magnetoelectric (ME) material, which has a linear coupling between electric and magnetic polarizations. Quadratic ME effects are forbidden for the magnetic point group of Cr2O3, due to space-time inversion symmetry. In Cr2O3 films grown by sputtering, we find a signature of a quadratic ME effect that is not found in bulk single crystals. We use Raman spectroscopy and magnetization measurements to deduce the removal of space-time symmetry and corroborate the emergence of the quadratic ME effect. We propose that metastable site-selective trace dopants remove the space, time, and space-time inversion symmetries from the original magnetic point group of bulk Cr2O3. We include the quadratic ME effect in a model describing the switching process during ME field cooling and estimate the effective quadratic susceptibility value. The quadratic magnetoelectric effect in a uniaxial antiferromagnet is promising for multifunctional antiferromagnetic and magnetoelectric devices that can incorporate optical, strain-induced, and multiferroic effects.
Mahdi Afshar,
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.094418

Abstract:
A new mechanism for the topological Hall effect (THE) was recently proposed for the spiral magnet YMn6Sn6, which requires transverse conical spiral magnetism, induced by external magnetic field, combined with thermally excited helical spiral magnons. In principle, this mechanism should be applicable to other itinerant spiral magnets as well. In this paper, we show that another magnetic compound, Fe3Ga4, in which THE was observed experimentally before, in one of its phases satisfies this condition, and the proposed theory of thermal-fluctuation-driven THE is quantitatively consistent with the experiment. This finding suggests that this mechanism is indeed rather universal, and the effect may have been observed in other compounds before but overlooked.
, Q. L. He
Physical Review Materials, Volume 5; https://doi.org/10.1103/physrevmaterials.5.090301

Abstract:
In this progress report, we examine recent efforts towards the introduction of magnetic order into topologically nontrivial systems through magnetic proximity effects, with a particular emphasis on the methods of characterizing magnetization induced at the interface. We focus on the challenges associated with comparing magneto-transport measurements with magnetic scattering and spectroscopy techniques, considering the limitations and potential artifacts associated with topological insulator heterostructures. Taking the (Bi,Sb)2(Se,Te)3 family of three-dimensional topological insulators as an example, we discuss the results associated with a wide range of magnetically ordered reservoirs and highlight the wide discrepancies in reported magnetic proximity effect strengths detected using different characterization techniques. Finally, we discuss the outlook of magnetic proximity effects in topological insulator heterostructures as a route towards a higher-temperature quantum anomalous Hall effect.
S. Clymton,
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.056015

Abstract:
We have developed a covariant isobar model to phenomenologically explain the four possible isospin channels of KΣ photoproduction. To obtain a consistent reaction amplitude, which is free from the lower-spin background problem, we used the consistent electromagnetic and hadronic interactions described in our previous report. We used all available experimental data, including the recent MAMI A2 2018 data obtained for the K0Σ+ and K0Σ0 isospin channels. By fitting the calculated observables to these data we extract the resonance properties, including their Breit-Wigner and pole parameters. Comparison of the extracted parameters with those listed by the Particle Data Group yields a nice agreement. An extensive comparison of the calculated observables with experimental data is also presented. By using the model we investigated the effects of three different form factors used in the hadronic vertex of each diagram. A brief discussion on the form factors is given.
, , P. Steffens, K. Kaneko, A. Rosuel, , J. Flouquet, D. Aoki, G. Lapertot, S. Raymond
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.l100409

Abstract:
Inelastic-neutron-scattering measurements were performed on a single crystal of the heavy-fermion paramagnet UTe2 above its superconducting temperature. We confirm the presence of antiferromagnetic fluctuations with the incommensurate wave-vector k1=(0,0.57,0). A quasielastic signal is found, whose momentum-transfer dependence is compatible with fluctuations of magnetic moments μa with a sine-wave modulation of wave-vector k1 and in-phase moments on the nearest U atoms. Low dimensionality of the magnetic fluctuations, consequence of the ladder structure, is indicated by weak correlations along the direction c. These fluctuations saturate below the temperature T1*15K, in possible relation with anomalies observed in thermodynamic, electrical-transport, and nuclear-magnetic-resonance measurements. The absence or weakness of ferromagnetic fluctuations in our data collected at temperatures down to 2.1 K and energy transfers from 0.6 to 7.5 meV is emphasized. These results constitute constraints for models of magnetically mediated superconductivity in UTe2.
Leon Hostetler, , Ryo Sakai, Judah Unmuth-Yockey, Alexei Bazavov, Yannick Meurice
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.054505

Abstract:
Motivated by recent attempts to quantum simulate lattice models with continuous Abelian symmetries using discrete approximations, we define an extended-O(2) model by adding a γcos(qφ) term to the ordinary O(2) model with angular values restricted to a 2π interval. In the γ limit, the model becomes an extended q-state clock model that reduces to the ordinary q-state clock model when q is an integer and otherwise is a continuation of the clock model for noninteger q. By shifting the 2π integration interval, the number of angles selected can change discontinuously and two cases need to be considered. What we call case 1 has one more angle than what we call case 2. We investigate this class of clock models in two space-time dimensions using Monte Carlo and tensor renormalization group methods. Both the specific heat and the magnetic susceptibility show a double-peak structure for fractional q. In case 1, the small-β peak is associated with a crossover, and the large-β peak is associated with an Ising critical point, while both peaks are crossovers in case 2. When q is close to an integer by an amount Δq and the system is close to the small-β Berezinskii-Kosterlitz-Thouless transition, the system has a magnetic susceptibility that scales as 1/(Δq)11/δ with δ estimates consistent with the magnetic critical exponent δ=15. The crossover peak and the Ising critical point move to Berezinskii-Kosterlitz-Thouless transition points with the same power-law scaling. A phase diagram for this model in the (β,q) plane is sketched. These results are possibly relevant for configurable Rydberg-atom arrays where the interpolations among phases with discrete symmetries can be achieved by varying continuously the distances among atoms and the detuning frequency.
Giovanni Pecci, Piero Naldesi, Luigi Amico, Anna Minguzzi
Physical Review Research, Volume 3; https://doi.org/10.1103/physrevresearch.3.l032064

Abstract:
We study the persistent currents of an attractive Fermi gas confined in a tightly confining ring trap and subjected to an artificial gauge field all through the BCS-BEC crossover. At weak attractions, on the Bardeen-Cooper-Schrieffer (BCS) side, fermions display a parity effect in the persistent currents, i.e., their response to the gauge field is paramagnetic or diamagnetic depending on the number of pairs on the ring. At resonance and on the Bose-Einstein condensate (BEC) side of the crossover we find a doubling of the periodicity of the ground-state energy as a function of the artificial gauge field and disappearance of the parity effect, indicating that persistent currents can be used to infer the formation of tightly bound bosonic pairs. Our predictions can be accessed in ultracold atom experiments through noise interferograms.
K. H. Spicer, C. T. Plowman, , , , Sh. U. Alladustov
Published: 14 September 2021
Physical Review A, Volume 104; https://doi.org/10.1103/physreva.104.032818

Abstract:
In a series of papers we present a comprehensive investigation of the four-body proton-helium differential scattering problem using the two-center wave-packet convergent close-coupling approach in the intermediate energy region where coupling between various channels is important. The approach uses correlated two-electron wave functions for the helium target. For comparison, a recently developed method that reduces the target to an effective single-electron system is also used. In this paper we present calculations of angular differential cross sections for elastic-scattering, target excitation, and electron-capture processes. The results of the two-electron and effective single-electron methods exhibit a good level of agreement. They also agree well with available experimental data. It is concluded that both versions of the wave-packet convergent close-coupling approach are capable of providing a realistic differential picture of all interdependent and interconnected binary processes taking place in proton-helium collisions at intermediate energies.
Ziqi Wang, Linfeng Jiang, Yihong Du, ,
Physical Review Fluids, Volume 6; https://doi.org/10.1103/physrevfluids.6.l091501

Abstract:
The extent and the morphology of ice forming in a differentially heated cavity filled with water are studied by means of experiments and numerical simulations. We show that the main mechanism responsible for the ice shaping is the existence of a cold upward convective current in the system. Such a current is ascribed to the peculiar equation of state of water, i.e., the nonmonotonous dependence of density with temperature. The precise form of the ice front depends on several factors, first, the temperature difference across the cell which drives the convection, and second, the wall inclination with respect to the vertical, both of which are explored here. We propose a boundary-layer model and a buoyancy-intensity model which account for the main features of the ice morphology.
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.055017

Abstract:
We revisit the possibilities of accommodating the experimental indications of the lepton flavor universality violation in b-hadron decays in the minimal scenarios in which the Standard Model is extended by the presence of a single O(1TeV) leptoquark state. To do so we combine the most recent low energy flavor physics constraints, including RK(*)exp and RD(*)exp, and combine them with the bounds on the leptoquark masses and their couplings to quarks and leptons as inferred from the direct searches at the LHC and the studies of the large pT tails of the pp differential cross section. We find that none of the scalar leptoquarks of mLQ1÷2TeV can accommodate the B-anomalies alone. Only the vector leptoquark, known as U1, can provide a viable solution which, in the minimal setup, provides an interesting prediction, i.e., a lower bound to the lepton flavor violating bsμ±τ decay modes, such as B(BKμτ)0.7×107.
, Eugene F. Dumitrescu,
Physical Review Research, Volume 3; https://doi.org/10.1103/physrevresearch.3.033248

Abstract:
We present a method to identify distinct tunneling modes in a tunable superconducting tunnel junction composed of a superconducting tip and a sample in a scanning tunneling microscope. Combining the relative decay constant of tunneling current extracted from IVz spectroscopy with its statistical analysis over the atomic disorders in the sample surface, we identified the crossover of dominant tunneling modes between single charge tunneling, Andreev reflection (AR), and Josephson tunneling with respect to the bias voltage at a measurement temperature nearly half of the critical temperature. The method enables one to determine the specific tunneling regime independently of the spectral shapes and to reveal intrinsic modulation of AR and Josephson current by disorder that will be crucial for superconducting quantum information processing.
, Xiao Chen, , Matthew P. A. Fisher
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.104305

Abstract:
We establish the emergence of a conformal field theory (CFT) in a (1+1)-dimensional hybrid quantum circuit right at the measurement-driven entanglement transition by revealing space-time conformal covariance of entanglement entropies and mutual information for various subregions at different circuit depths. While the evolution takes place in real time, the spacetime manifold of the circuit appears to host a Euclidean field theory with imaginary time. Throughout the paper we investigate Clifford circuits with several different boundary conditions by injecting physical qubits at the spatial and/or temporal boundaries, all giving consistent characterizations of the underlying “Clifford CFT.” We emphasize (super)universal results that are consequences solely of the conformal invariance and do not depend crucially on the precise nature of the CFT. Among these are the infinite entangling speed as a consequence of measurement-induced quantum nonlocality and the critical purification dynamics of a mixed initial state.
F. Giusti, A. Montanaro, , , , F. Glerean, G. Jarc, H. Eisaki, M. Greven, A. Damascelli, et al.
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.125121

Abstract:
Superconductivity in the cuprates is characterized by an anisotropic electronic gap of d-wave symmetry. The aim of this work is to understand how this anisotropy affects the nonequilibrium electronic response of high-Tc superconductors. Here we use a polarization selective time domain experiment to address the dynamics of electronic excitation of different symmetry in optimally doped Bi2Sr2Y0.08Ca0.92Cu2O8+δ and measure the nodal and antinodal nonequilibrium response resulting from photoexcitations with ultrashort pulses with photon energy comparable to the superconducting gap. The response to long wavelength photoexcitation with pump polarization along the Cu-Cu axis of the sample is discussed with the support of an effective d-wave BCS model which suggests that such transient response could be ascribed to an increase of pair coherence in the antinodal region.
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.063525

Abstract:
Axion-CMB scenario” is an interesting possibility to explain the temperature anisotropy of the cosmic microwave background (CMB) by primordial fluctuations of the QCD axion [S. Iso, K. Kawana, and K. Shimada, Phys. Rev. D 102, 103513 (2020)]. In this scenario, fluctuations of radiations are generated by an energy exchange between axions and radiations, which results in the correlation between the primordial axion fluctuations and the CMB anisotropies. Consequently, the cosmological observations stringently constrain a model of the axion and the early history of the universe. In particular, we need a large energy fraction ΩA of the axion at the QCD phase transition, but it must become tiny at the present universe to suppress the isocurvature power spectrum. One of natural cosmological scenarios to realize such a situation is the thermal inflation which can sufficiently dilute the axion abundance. Thermal inflation occurs in various models. In this paper, we focus on a classically conformal (CC) BL model with a QCD axion. In this model, the early universe undergoes a long supercooling era of the BL and electroweak symmetries, and thermal inflation naturally occurs. Thus it can be a good candidate for the axion-CMB scenario. But the axion abundance at the QCD transition is shown to be insufficient in the original CC BL model. To overcome the situation, we extend the model by introducing N scalar fields S (either massive or massless) and consider a novel cosmological history such that the O(N) and the BL sectors evolve almost separately in the early universe. We find that all the necessary conditions for the axion-CMB scenario can be satisfied in some parameter regions for massless S fields, typically N1019 and the mass of BL gauge boson around 5–10 TeV.
Alpna Ojha, , Unnati Gupta, Pushpendra P. Singh, Abhishek Yadav, Devendra P. Singh, Mohd Shuaib, B. P. Singh, R. Prasad
Published: 14 September 2021
Physical Review C, Volume 104; https://doi.org/10.1103/physrevc.104.034615

Abstract:
Incomplete fusion processes and estimation of strength of incomplete fusion in heavy ion induced nuclear reactions have been explored for several combinations of projectile-target nuclei. Dynamics of these reactions is explained using an optical model. Parameters of the optical model affect the shape and depth of nuclear potential and hence influence the theoretical predictions. For heavy ion induced reactions, the optical model potential parameters are not unique and different sets of these parameters may be used for different ranges of mass number A and incident energy E. To explore the effect of optical model potential parameters, a comparative study of available experimental data for excitation functions of four systems, O16+Ta181, C12+Ho165, N14+Dy163, and O16+Ge74, with corresponding theoretically predicted excitation functions, made by PACE4 using different sets of optical model potential parameters, has been done. It has been observed that a single set of optical model potential parameters is not adequate for all the systems. The variations in these parameters change the theoretical cross-section predictions for various channels considerably, which in turn, change the correspondingly estimated fraction of incomplete fusion (FICF). The effect of deformation of target nuclei on fractional incomplete fusion has also been investigated for the above mentioned systems. FICF has been plotted as a function of deformation parameter (β2) of the target nuclei and it is found to increase as the deformation parameter of the corresponding target nuclei increases on either side of the intrinsic spherical symmetry.
Kohei Shiota, Akito Inui, Yuta Hosaka, Ryoga Amano, Yoshichika Ōnuki, Masato Hedo, Takao Nakama, , Jun-Ichiro Ohe, Jun-Ichiro Kishine, et al.
Physical Review Letters, Volume 127; https://doi.org/10.1103/physrevlett.127.126602

Abstract:
A spin-polarized state is examined under charge current at room temperature without magnetic fields in chiral disilicide crystals NbSi2 and TaSi2. We found that a long-range spin transport occurs over ten micrometers in these inorganic crystals. A distribution of crystalline grains of different handedness is obtained via location-sensitive electrical transport measurements. The sum rule holds in the conversion coefficient in the current-voltage characteristics. A diamagnetic nature of the crystals supports that the spin polarization is not due to localized electron spins but due to itinerant electron spins. A large difference in the strength of antisymmetric spin-orbit interaction associated with 4d electrons in Nb and 5d ones in Ta is oppositely correlated with that of the spin polarization. A robust protection of the spin polarization occurs over long distances in chiral crystals.
, Pulak K. Ghosh, Fabio Marchesoni
Physical Review Research, Volume 3; https://doi.org/10.1103/physrevresearch.3.l032065

Abstract:
We numerically investigated the diffusion of a heavy active Brownian particle in a linear periodic array of steady planar counter-rotating convection rolls at high Péclet numbers. We show that, under certain conditions, the particle rises to the surface even if it is denser than the suspension fluid, and floats there for exceedingly long times. Such an apparently counterintuitive phenomenon of “enhanced buoyancy” is a combined effect of gravity, advection, and shear torque.
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.055021

Abstract:
We consider, in general terms, the possible parameter space of thermal dark matter candidates. We assume that the dark matter particle is fundamental and was in thermal equilibrium in a hidden sector with a temperature T, which may differ from that of the Standard Model temperature, T. The candidates lie in a region in the T/T vs. mdm plane, which is bounded by both model-independent theoretical considerations and observational constraints. The former consists of limits from dark matter candidates that decoupled when relativistic (the relativistic floor) and from those that decoupled when nonrelativistic with the largest annihilation cross section allowed by unitarity (the unitarity wall), while the latter concerns big bang nucleosynthesis (Neff ceiling) and free streaming. We present three simplified dark matter scenarios, demonstrating concretely how each fits into the domain.
O. Diatlyk
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.065011

Abstract:
We extend the classic results of the paper [P. C. W. Davies, S. A. Fulling, and W. G. Unruh, Phys. Rev. D 13, 2720 (1976).] “Energy-momentum tensor near an evaporating black hole” by considering a massive scalar field in a two dimensions in the presence of a thin shell collapse. We show that outside the shell the WKB approximation is valid for any value of r if mrg1, where m is the mass of the field, and rg is the Schwarzschild radius. Thus, we use semiclassical modes to calculate the flux in the vicinity of the shell, and at spatial infinity, r+ at the final stage of the collapse, t+ with the use of the covariant point-splitting regularization. We get that near the shell and at the spatial infinity the radiation is thermal with Hawking temperature. We obtain the negative flux Tvv in the vicinity of the shell, which is similar to the classic result in the massless case.
Vinitha Balachandran, , Giulio Casati, Dario Poletti
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.104306

Abstract:
The relaxation of out-of-time-ordered correlators (OTOCs) has been studied as a means to characterize the scrambling properties of a quantum system. We show that the presence of local conserved quantities typically results in, at the fastest, an algebraic relaxation of the OTOC provided (i) the dynamics is local and (ii) the system follows the eigenstate thermalization hypothesis. Our result relies on the algebraic scaling of the infinite-time value of OTOCs with system size, which is typical in thermalizing systems with local conserved quantities, and on the existence of finite speed of propagation of correlations for finite-range-interaction systems. We show that time independence of the Hamiltonian is not necessary as the above conditions (i) and (ii) can occur in time-dependent systems, both periodic or aperiodic. We also remark that our result can be extended to systems with power-law interactions.
Jakob Hinney, Adarsh S. Prasad, , , Arno Rauschenbeutel, , Jürgen Volz,
Physical Review Letters, Volume 127; https://doi.org/10.1103/physrevlett.127.123602

Abstract:
We observe that a weak guided light field transmitted through an ensemble of atoms coupled to an optical nanofiber exhibits quadrature squeezing. From the measured squeezing spectrum we gain direct access to the phase and amplitude of the energy-time entangled part of the two-photon wave function which arises from the strongly correlated transport of photons through the ensemble. For small atomic ensembles we observe a spectrum close to the line shape of the atomic transition, while sidebands are observed for sufficiently large ensembles, in agreement with our theoretical predictions. Furthermore, we vary the detuning of the probe light with respect to the atomic resonance and infer the phase of the entangled two-photon wave function. From the amplitude and the phase of the spectrum, we reconstruct the real and imaginary part of the time-domain wave function. Our characterization of the entangled two-photon component constitutes a diagnostic tool for quantum optics devices.
, Mohd. Shuaib, Ishfaq Majeed, Manoj Kumar Sharma, , Abhishek Yadav, Devendra P. Singh, Pushpendra P. Singh, Unnati Gupta, Rudra N. Sahoo, et al.
Published: 14 September 2021
Physical Review C, Volume 104; https://doi.org/10.1103/physrevc.104.034616

Abstract:
In order to study incomplete fusion (ICF) reaction dynamics, the present work manifests the role of a non-α-cluster N14 projectile on Ta181 target at energies 4–7 MeV/nucleon using the offline γ-ray spectroscopy. The excitation functions for 15 reaction residues populated in N14+Ta181 system have been measured and analyzed within the framework of statistical model code PACE4. The experimentally measured excitation functions of evaporation residues populated via xn/pxn channels are found to be well reproduced by the predictions of code PACE4, which confirms their production solely via complete fusion process. However, an enhancement in the measured excitation function as compared to PACE4 calculations, particularly in tail portion of Hg192 residue (3n channel) has been observed indicating the presence of precompound emission. A significant contribution from precursor decay in pxn channels has also been observed. An enhancement in the measured excitation functions for α-emitting channels as compared to the PACE4 predictions has been observed and attributed to the incomplete fusion process. Further, the contribution from incomplete fusion process in the N14+Ta181 system has also been deduced in terms of strength function (FICF). The results have been discussed in terms of the parameters which influence the dynamics of ICF process. The FICF is found to depend strongly on projectile energies, the product of projectile and target charges, and αQ value of the projectile.
, L. E. Marcucci, R. Schiavilla, M. Viviani
Published: 14 September 2021
Physical Review C, Volume 104; https://doi.org/10.1103/physrevc.104.035501

Abstract:
We report on a study of the Gamow-Teller matrix element contributing to He6β decay with similarity renormalization group (SRG) versions of momentum- and configuration-space two-nucleon interactions. These interactions are derived from two different formulations of chiral effective field theory (χEFT)—without and with the explicit inclusion of Δ isobars. We consider evolution parameters ΛSRG in the range between 1.2 and 2.0 fm1 and, for the Δ-less case, also the unevolved (bare) interaction. The axial current contains one- and two-body terms, consistently derived at tree level (no loops) in the two distinct χEFT formulations we have adopted here. The He6 and Li6 ground-state wave functions are obtained from hyperspherical-harmonics (HH) solutions of the nuclear many-body problem. In A=6 systems, the HH method is limited at present to treat only two-body interactions and non-SRG evolved currents. Our results exhibit a significant dependence on ΛSRG of the contributions associated with two-body currents, suggesting that a consistent SRG-evolution of these is needed in order to obtain reliable estimates. We also show that the contributions from one-pion-exchange currents depend strongly on the model (chiral) interactions and on the momentum- or configuration-space cutoffs used to regularize them. These results might prove helpful in clarifying the origin of the sign difference recently found in no-core-shell-model and quantum Monte Carlo calculations of the He6 Gamow-Teller matrix element.
Shiyi Wang, Yueheng Lan
Published: 14 September 2021
Physical Review E, Volume 104; https://doi.org/10.1103/physreve.104.034211

Abstract:
With the development of probing and computing technology, the study of complex systems has become a necessity in various science and engineering problems, which may be treated efficiently with Koopman operator theory based on observed time series. In the current paper, combined with a singular value decomposition (SVD) of the constructed Hankel matrix, Koopman analysis is applied to a system of coupled oscillators. The spectral properties of the operator and the Koopman modes of a typical orbit reveal interesting invariant structures with periodic, quasiperiodic, or chaotic motion. By checking the amplitude of the principal modes along a straight line in the phase space, cusps of different sizes on the magnitude profiles are identified whenever a qualitative change of dynamics takes place. There seems to be no obstacle to extend the current analysis to high-dimensional nonlinear systems with intricate orbit structures.
Constantia Alexandrou, Martha Constantinou, Kyriakos Hadjiyiannakou, Karl Jansen, Floriano Manigrasso
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.054503

Abstract:
We present results on the quark unpolarized, helicity and transversity parton distributions functions of the nucleon. We use the quasiparton distribution approach within the lattice QCD framework and perform the computation using an ensemble of twisted mass fermions with the strange and charm quark masses tuned to approximately their physical values and light quark masses giving pion mass of 260 MeV. We use hierarchical probing to evaluate the disconnected quark loops. We discuss identification of ground state dominance, the Fourier transform procedure and convergence with the momentum boost. We find nonzero results for the disconnected isoscalar and strange quark distributions. The determination of the quark parton distribution and in particular the strange quark contributions that are poorly known provide valuable input to the structure of the nucleon.
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.056013

Abstract:
The renormalized contribution of fermions to the curvature masses of vector and axial-vector mesons is derived with two different methods at leading order in the loop expansion applied to the (2+1)-flavor constituent quark-meson model. The corresponding contribution to the curvature masses of the scalar and pseudoscalar mesons, already known in the literature, is rederived in a transparent way. The temperature dependence of the curvature mass of various (axial-)vector modes obtained by decomposing the curvature mass tensor is investigated along with the (axial-)vector–(pseudo)scalar mixing. All fermionic corrections are expressed as simple integrals that involve at finite temperature only the Fermi-Dirac distribution function modified by the Polyakov-loop degrees of freedom. The renormalization of the (axial-)vector curvature mass allows us to lift a redundancy in the original Lagrangian of the globally symmetric extended linear sigma model, in which terms already generated by the covariant derivative were reincluded with different coupling constants.
, Tomotaro Namba, , Kenji Ohmori
Published: 14 September 2021
Physical Review A, Volume 104; https://doi.org/10.1103/physreva.104.033107

Abstract:
We use nonlinear optimal control simulation to systematically examine how to suppress wave-packet spreading with strong nonresonant near-infrared (NIR) laser pulses through a case study of a vibrational wave packet in the B state of I2. As the degree of spreading of the vibrational wave packet is controllable by adjusting the pump pulse shape, the vibrational wave packet may be regarded as a prototype system to study spreading suppression by using nonresonant laser pulses. We quantitatively define spreading suppression in terms of the probability of finding the wave packet in the analytically defined, initially excited state at every vibrational period. From optimal control simulation and simulation by using model Gaussian pulse trains that mimic optimal pulses, we conclude that a simple periodic NIR pulse train without highly tuned temporal widths, amplitudes, or irradiation timings can almost perfectly stop the wave-packet spreading over a long control period, provided that the degree of spreading is not too large.
W. Pfäffle, D. Antonov, J. Wrachtrup,
Published: 14 September 2021
Physical Review B, Volume 104; https://doi.org/10.1103/physrevb.104.104105

Abstract:
We present a computational approach, based on density functional theory and screened configuration interaction, able to accurately treat highly correlated electron spins localized around semiconductor defects, typically occurring in the context of qubit implementations. The method is computationally not more demanding than a usual density functional theory calculation, which makes it suitable for the calculation of isolated defects, or defect complexes, typically requiring large simulation cells. We illustrate the approach by applying it to the three different charge states of the nitrogen vacancy defect in diamond and obtain very good agreement with experiment.
V. I. Denisov, B. D. Garmaev, I. P. Denisova
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.055018

Abstract:
The electromagnetic source of arions, as well as axions, is a scalar product of the magnetic field induction and the electric field intensity. For electromagnetic waves, this product can be nonzero only in the near zone. Pulsars and magnetars are natural sources of this type. Based on these considerations, we calculate the generation of arions by coherent electromagnetic field of rotating magnetic dipole of pulsars and magnetars. It is shown that the radiation of arion waves occurs at the frequency of magnetic dipole rotation. This radiation has a maximum when the angle between the rotation axis and the magnetic dipole moment of the neutron star is π/4 and it is completely absent, when the magnetic dipole moment is perpendicular or parallel to this axis. A formula for the angular distribution of arion radiation is constructed; and on its basis, it is shown that the radiation is maximal in the plane which is perpendicular to the axis of rotation.
Published: 14 September 2021
Abstract:
Optimal control theory is a powerful mathematical tool, which has known a rapid development since the 1950s, mainly for engineering applications. More recently, it has become a widely used method to improve process performance in quantum technologies by means of highly efficient control of quantum dynamics. This tutorial aims at providing an introduction to key concepts of optimal control theory that is accessible to physicists and engineers working in quantum control or in related fields. The different mathematical results are introduced intuitively, before being rigorously stated. This tutorial describes modern aspects of optimal control theory, with a particular focus on the Pontryagin maximum principle, which is the main tool for determining open-loop control laws without experimental feedback. The different steps to solve an optimal control problem are discussed, before moving on to more advanced topics such as the existence of optimal solutions or the definition of the different types of extremals, namely normal, abnormal, and singular. The tutorial covers various quantum control issues and describes their mathematical formulation suitable for optimal control. The connection between the Pontryagin maximum principle and gradient-based optimization algorithms used for high-dimensional quantum systems is described. The optimal solution of different low-dimensional quantum systems is presented in detail, illustrating how the mathematical tools are applied in a practical way.
Published: 14 September 2021
Physical Review D, Volume 104; https://doi.org/10.1103/physrevd.104.056016

Abstract:
In a previous paper we proposed a new method based on resummations for studying radiation reaction of an electron in a plane-wave electromagnetic field. In this paper we use this method to study the electron momentum expectation value for a circularly polarized monochromatic field with a0=1, for which standard locally constant-field methods cannot be used. We also find that radiation reaction has a significant effect on the induced polarization, as compared to the results without radiation reaction, i.e., the Sokolov-Ternov formula for a constant field, or the zero result for a circularly monochromatic field. We also study the Abraham-Lorentz-Dirac equation using Borel-Padé resummations.
, , Jonathan Schillings, Amandine Capogna
Physical Review Fluids, Volume 6; https://doi.org/10.1103/physrevfluids.6.094605

Abstract:
This investigation concerns the response of wall turbulences in a channel flow to uniform streamwise and spanwise magnetic fields through direct numerical simulations. More than 20 flow cases with different Stuart numbers were considered. It is found that the spanwise magnetic field leads to flow relaminarization at Stuart numbers significantly smaller than the streamwise magnetic field. The explanation of this phenomenon is not straightforward, and a deep analysis of the fine turbulence structure is needed for a clear understanding. This is achieved in a first step by considering Reynolds shear stress transport equations. It is shown that there are source and destruction terms directly related to the magnetic field. The destruction term overcomes the source terms under the spanwise magnetic field, leading to significant drag reduction once the Stuart number exceeds a critical value. The source term is not negligible and retards the relaminarization under the streamwise magnetic field. Subsequently, the conditional averages of the fluctuating velocity field and the electric current educed from the near wall coherent quasistreamwise vortices are discussed in detail. The electric current field is decomposed into an electromotive and conductive part. Their conditional averages are analyzed separately, in order to shed light on the topological differences. It is further shown that the quasistreamwise vortex paradigm allows an easy way to analyze the results leading to pertinent interpretations.
Zhichao Guo, Fan Jia, Lintao Li, Yinfeng Ma, , Xiaoling Cui,
Physical Review Research, Volume 3; https://doi.org/10.1103/physrevresearch.3.033247

Abstract:
The beyond-mean-field Lee-Huang-Yang (LHY) correction is ubiquitous in dilute ultracold quantum gases. However, its effects are often elusive due to the typically much larger influence of the mean-field (MF) energy. In this work, we study an ultracold mixture of Na23 and Rb87 with tunable attractive interspecies interactions. The LHY effects manifest in the formation of self-bound quantum liquid droplets and the expansion dynamics of the gas-phase sample. A liquid-to-gas-phase diagram is obtained by measuring the critical atom numbers below which the self-bound behavior disappears. In stark contrast to trapped gas-phase condensates, the gas-phase mixture formed following the liquid-to-gas-phase transition shows an anomalous expansion featuring a larger release energy for increasing MF attractions.
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