More Like this

1. Autonomous dynamics of two-dimensional insulating domain with superclimbing edges

   https://doi.org/10.1103/PhysRevResearch.6.033008  

   Kuklov, Anatoly; Prokof'ev, Nikolay; Svistunov, Boris (July 2024, Physical Review Research)

   Superclimbing dynamics is the signature feature of transverse quantum fluids describing wide superfluid one-dimensional interfaces and/or edges with negligible Peierls barrier. Using Lagrangian formalism, we show how the essence of the superclimb phenomenon—dynamic conjugation of the fields of the superfluid phase and geometric shape—clearly manifests itself via characteristic modes of autonomous motion of the insulating domain (“droplet”) with superclimbing edges. In the translation invariant case and in the absence of supercurrent along the edge, the droplet demonstrates ballistic motion with the velocity-dependent shape and zero bulk currents. In an isotropic trapping potential, the droplet features a doubly degenerate sloshing mode. The period of the ground-state evolution of the superfluid phase (dictating the frequency of the AC Josephson effect) is sensitive to the geometry of the droplet. The supercurrent along the edge dramatically changes the droplet dynamics: The motion acquires features resembling that of a two-dimensional charged particle interacting with a perpendicular magnetic field. In a linear external potential (uniform force field), the state with a supercurrent demonstrates a spectacular gyroscopic effect—uniform motion in the perpendicular to the force direction. Published by the American Physical Society2024 

   more » « less
2. Unidirectional Maxwellian spin waves

   https://doi.org/10.1515/nanoph-2019-0092  

   Van Mechelen, Todd; Jacob, Zubin (June 2019, Nanophotonics)

   Abstract In this article, we develop a unified perspective of unidirectional topological edge waves in nonreciprocal media. We focus on the inherent role of photonic spin in nonreciprocal gyroelectric media, i.e. magnetized metals or magnetized insulators. Due to the large body of contradicting literature, we point out at the outset that these Maxwellian spin waves are fundamentally different from well-known topologically trivial surface plasmon polaritons. We first review the concept of a Maxwell Hamiltonian in nonreciprocal media, which immediately reveals that the gyrotropic coefficient behaves as a photon mass in two dimensions. Similar to the Dirac mass, this photonic mass opens bandgaps in the energy dispersion of bulk propagating waves. Within these bulk photonic bandgaps, three distinct classes of Maxwellian edge waves exist – each arising from subtle differences in boundary conditions. On one hand, the edge wave solutions are rigorous photonic analogs of Jackiw-Rebbi electronic edge states. On the other hand, for the exact same system, they can be high frequency photonic counterparts of the integer quantum Hall effect, familiar at zero frequency. Our Hamiltonian approach also predicts the existence of a third distinct class of Maxwellian edge wave exhibiting topological protection. This occurs in an intriguing topological bosonic phase of matter, fundamentally different from any known electronic or photonic medium. The Maxwellian edge state in this unique quantum gyroelectric phase of matter necessarily requires a sign change in gyrotropy arising from nonlocality (spatial dispersion). In a Drude system, this behavior emerges from a spatially dispersive cyclotron frequency that switches sign with momentum. A signature property of these topological electromagnetic edge states is that they are oblivious to the contacting medium, i.e. they occur at the interface of the quantum gyroelectric phase and any medium (even vacuum). This is because the edge state satisfies open boundary conditions – all components of the electromagnetic field vanish at the interface. Furthermore, the Maxwellian spin waves exhibit photonic spin-1 quantization in exact analogy with their supersymmetric spin-1/2 counterparts. The goal of this paper is to discuss these three foundational classes of edge waves in a unified perspective while providing in-depth derivations, taking into account nonlocality and various boundary conditions. Our work sheds light on the important role of photonic spin in condensed matter systems, where this definition of spin is also translatable to topological photonic crystals and metamaterials. 

   more » « less
3. Robust preparation of many-body ground states in Jaynes–Cummings lattices

   https://doi.org/10.1038/s41534-021-00433-y  

   Cai, Kang; Parajuli, Prabin; Long, Guilu; Wong, Chee Wei; Tian, Lin (December 2021, npj Quantum Information)

   Abstract Strongly correlated polaritons in Jaynes–Cummings (JC) lattices can exhibit quantum phase transitions between the Mott-insulating and superfluid phases at integer fillings. The prerequisite to observe such phase transitions is to pump polariton excitations into a JC lattice and prepare them into appropriate ground states. Despite previous efforts, it is still challenging to generate many-body states with high accuracy. Here, we present an approach for the robust preparation of many-body ground states of polaritons in finite-sized JC lattices by optimized nonlinear ramping. We apply a Landau–Zener type of estimation to this finite-sized system and derive the optimal ramping index for selected ramping trajectories, which can greatly improve the fidelity of the prepared states. With numerical simulation, we show that by choosing an appropriate ramping trajectory, the fidelity in this approach can remain close to unity in almost the entire parameter space. This approach can shed light on high-fidelity state preparation in quantum simulators and advance the implementation of quantum simulation with practical devices. 

   more » « less
4. Free at last: Bose metal uncaged

   https://doi.org/10.1126/science.aaz9902  

   Phillips, Philip W. (December 2019, Science)

   Even the particle world is not immune to identity politics. Bosons have been in a bit of an identity crisis, or so it has seemed since 1989 ( 1 ). Quantum mechanics requires bosons made of two paired electrons to either condense into a superfluid with a well-defined phase with zero electrical resistance or localize in an insulating state with infinite resistance. The direct transition from superconducting to insulating states was widely observed in a range of thin films ( 2 – 4 ). The most popular model for explaining these observations ( 5 ) claims that the destruction of superconductivity occurs when the resistance of the thin film exceeds a critical value. For bosons on the brink of localization, electrically insulating behavior is observed if the resistance is greater than the quantum of resistance, R q = h /4 e 2 , otherwise superconductivity persists, where h is Planck's constant and e is the electric charge. On page 1505 of this issue, Yang et al. ( 6 ) offer a counterexample by establishing that a bosonic metallic phase disrupts the superconductor-insulator transition (SIT) in the high-temperature superconductor YBa 2 Cu 3 O 7– x (YBCO). 

   more » « less
5. Terahertz conductivity of monolayer MoS$$_2$$

   https://doi.org/10.1007/s10825-023-02023-x  

   Mitra, S.; Avazpour, L.; Knezevic, I. (March 2023, Journal of Computational Electronics)

   We calculate the electrical conductivity of suspended and supported monolayer MoS2 at terahertz (THz) frequencies by means of EMC–FDTD, a multiphysics simulation tool combining an ensemble Monte Carlo (EMC) solver for electron transport and a finite-difference time-domain (FDTD) solver for full-wave electrodynamics. We investigate the role of carrier and impurity densities, as well as substrate choice (SiO2 or hexagonal boron nitride, hBN), in frequency-dependent electronic transport. Owing to the dominance of surface-optical-phonon scattering, MoS2 on SiO2 has the lowest static conductivity, but also the weakest overall frequency dependence of the conductivity. In fact, at high THz frequencies, the conductivity of MoS2 on SiO2 exceeds that of either suspended or hBN-supported MoS2. We extract the parameters for Drude-model fits to the conductivity versus frequency curves obtained from microscopic simulation, which may aid in the experimental efforts toward MoS2 THz applications. 

   more » « less