The ability to control the chirality of physical devices is of great scientific and technological importance, from investigations of topologically protected edge states in condensed matter systems to wavefront engineering, isolation, and unidirection
al communication. When dealing with large networks of oscillators, the control over the chirality of the bulk states becomes significantly more complicated and requires complex apparatus for generating asymmetric coupling or artificial gauge fields. Here we present a new approach for precise control over the chirality of a triangular array of hundreds of symmetrically-coupled lasers, by introducing a weak non-Hermitian complex potential. In the unperturbed network, lasing states with opposite chirality (staggered vortex and staggered anti-vortex) are equally probable. We show that by tuning the complex potential to an exceptional point, a nearly pure chiral lasing state is achieved. While our approach is applicable to any oscillators network, we demonstrate how the inherent non-linearity of the lasers effectively pulls the network to the exceptional point, making the chirality extremely resilient against noises and imperfections.
Dynamical potentials appear in many advanced electronic-structure methods, including self-energies from many-body perturbation theory, dynamical mean-field theory, electronic-transport formulations, and many embedding approaches. Here, we propose a n
ovel treatment for the frequency dependence, introducing an algorithmic inversion method that can be applied to dynamical potentials expanded as sum over poles. This approach allows for an exact solution of Dyson-like equations at all frequencies via a mapping to a matrix diagonalization, and provides simultaneously frequency-dependent (spectral) and frequency-integrated (thermodynamic) properties of the Dyson-inverted propagators. The transformation to a sum over poles is performed introducing $n$-th order generalized Lorentzians as an improved basis set to represent the spectral function of a propagator, and using analytic expressions to recover the sum-over-poles form. Numerical results for the homogeneous electron gas at the $G_0W_0$ level are provided to argue for the accuracy and efficiency of such unified approach.
Inspired by the recent achievements of the strong magnons- and spin textures-photons coupling via dipolar interaction, the coupling between magnons and the local resonances of spin textures through direct exchange interaction is expected but not real
ized yet. In this work, we demonstrated the coherent coupling between propagating magnons and local skyrmion resonances. Besides the Rabbi coupling gap (RCG) in the frequency field dispersion, a magnonic analog of polariton gap, polaragnonic band gap (PBG), is also observed in the frequency-wavenumber dispersion. The realization of coupling requires the gyrotropic skyrmion modes to satisfy not only their quantum number larger than one but also their chirality opposite to that of magnons. The observed PBG and RCG can be controlled to exist within different Brillouin zones (BZs) as well as at BZ boundaries. The coupling strength can approach the strong regime by selecting the wavenumber of propagating magnons. Our findings could provide a pure magnonic platform for investigating quantum optics phenomena in quantum information technology.
Spinful superfluids of ultracold atoms are ideal for investigating the intrinsic properties of spin current and texture because they are realized in an isolated, nondissipative system free from impurities, dislocations, and thermal fluctuations. This
study theoretically reveals the impact of spin current on a magnetic domain wall in spinful superfluids. An exact wall solution is obtained in the ferromagnetic phase of a spin-1 Bose--Einstein condensate with easy-axis anisotropy at zero temperature. The bosonic-quasiparticle mechanics analytically show that the spin current along the wall becomes unstable if the spin-current velocity exceeds the criteria, leading to complicated situations because of the competition between transverse magnons and ripplons. Our direct numerical simulation reveals that this system has a mechanism to generate an eccentric fractional skyrmion, which has a fractional topological charge, but its texture is not similar to that of a meron. This mechanism is in contrast to the generation of conventional skyrmions in easy-axis magnets [S. K. Kim and Y. Tserkovnyak, Phys. Rev. Lett. ${bf 119}$, 047202 (2017)]. The theoretical findings can be examined in the same situation as in a recent experiment on ultracold atoms and indicate unexplored similar phenomena in different physical systems, such as chiral superfluids and superconductors, magnets, spintronics, and particle physics.
Neutron diffraction studies of HoFeO$_3$ single crystal were performed under external magnetic fields. The interplay between the external magnetic field, Dzyaloshinsky-Moria antisymmetric exchange and isotropic exchange interactions between Fe and Ho
sublattice and inside Fe sublattice provides a rich phase diagram. As the result of the balance of exchange interactions inside crystal and external magnetic field we found 8 different magnetic phases, produced or suppressed by the field.
Transition metal carbides have sparked unprecedented enthusiasm as high-performance catalysts in recent years. Still, the catalytic properties of copper (Cu) carbide remain unexplored. By introducing subsurface carbon (C) to Cu(111), displacement rea
ction of proton in carboxyl acid group with single Cu atom is demonstrated at the atomic scale and room temperature. Its occurrence is attributed to the C-doping induced local charge of surface Cu atoms (up to +0.30 e/atom), which accelerates the rate of on-surface deprotonation via reduction of the corresponding energy barrier, thus enabling the instant displacement of a proton with a Cu atom when the molecules land on the surface. Such well-defined and robust Cu$^{delta +}$ surface based on the subsurface C doping offers a novel catalytic platform for on-surface synthesis.
Aluminium based platforms have allowed to reach major milestones for superconducting quantum circuits. For the next generation of devices, materials that are able to maintain low microwave losses while providing new functionalities, such as large kin
etic inductance or compatibility with CMOS platform are sought for. Here we report on a combined direct current (DC) and microwave investigation of titanium nitride lms of dierent thicknesses grown using CMOS compatible methods. For microwave resonators made of TiN lm of thickness $sim$3 nm, we measured large kinetic inductance LK $sim$ 240 pH/sq, high mode impedance of $sim$ 4.2 k$Omega$ while maintaining microwave quality factor $sim$ 10^5 in the single photon limit. We present an in-depth study of the microwave loss mechanisms in these devices that indicates the importance of quasiparticles and provide insights for further improvement.
We establish a relation between entanglement in simple quantum mechanical qubit systems and in wormhole physics as considered in the context of the AdS/CFT correspondence. We show that in both cases, states with the same entanglement structure, indis
tinguishable by any local measurement, nevertheless are characterized by a different Berry phase. This feature is experimentally accessible in coupled qubit systems where states with different Berry phase are related by unitary transformations. In the wormhole case, these transformations are identified with a time evolution of one of the two throats.
Heavy metal-ferromagnet bilayer structures have attracted great research interest for charge-to-spin interconversion. In this work, we have investigated the effect of the permalloy seed layer on the Ta polycrystalline phase and its spin Hall angle. I
nterestingly, for the same deposition rates the crystalline phase of Ta deposited on Py seed layer strongly depends on the thickness of the seed layer. We have observed a phase transition from $alpha$-Ta to ($alpha$+$beta$)-Ta while increasing the Py seed layer thickness. The observed phase transition is attributed to the strain at interface between Py and Ta layers. Ferromagnetic resonance-based spin pumping studies reveal that the spin-mixing conductance in the to ($alpha$+$beta$)-Ta is relatively higher as compared to the to $alpha$-Ta. Spin Hall angles of to $alpha$-Ta and to ($alpha$+$beta$)-Ta are extracted from inverse spin Hall effect (ISHE) measurements. Spin Hall angle of the to ($alpha$+$beta$)-Ta is estimated to be $theta$_SH=-0.15 which is relatively higher than that of to $alpha$-Ta. Our systematic results connecting the phase of the Ta with seed layer and its effect on the efficiency of spin to charge conversion might resolve ambiguities across various literature and open up new functionalities based on the growth process for the emerging spintronic devices.
A Hamiltonian time crystal can emerge when a Noether symmetry is subject to a condition that prevents the energy minimum from being a critical point of the Hamiltonian. A somewhat trivial example is the Schrodinger equation of a harmonic oscillator.
The Noether charge for its particle number coincides with the square norm of the wave function, and the energy eigenvalue is a Lagrange multiplier for the condition that the wave function is properly normalized. A more elaborate example is the Gross-Pitaevskii equation that models vortices in a cold atom Bose-Einstein condensate. In an oblate, essentially two dimensional harmonic trap the energy minimum is a topologically protected timecrystalline vortex that rotates around the trap center. Additional examples are constructed using coarse grained Hamiltonian models of closed molecular chains. When knotted, the topology of a chain can support a time crystal. As a physical example, high precision all-atom molecular dynamics is used to analyze an isolated cyclopropane molecule. The simulation reveals that the molecular D$_{3h}$ symmetry becomes spontaneously broken. When the molecule is observed with sufficiently long stroboscopic time steps it appears to rotate like a simple Hamiltonian time crystal. When the length of the stroboscopic time step is decreased the rotational motion becomes increasingly ratcheting and eventually it resembles the back-and-forth oscillations of Sisyphus dynamics. The stroboscopic rotation is entirely due to atomic level oscillatory shape changes, so that cyclopropane is an example of a molecule that can rotate without angular momentum. Finally, the article is concluded with a personal recollection how Franks and Betsys Stockholm journey started.
