Latest Research Papers In Condensed Matter Physics | (Cond-Mat.Mes-Hall) 2019-07-08
Mesoscale And Nanoscale Physics
Magnetoquasistatic Resonances of Small Dielectric Objects (1907.02950v1)
Carlo Forestiere, Giovanni Miano, Mariano Pascale, Guglielmo Rubinacci, Antonello Tamburrino, Roberto Tricarico, Salvatore Ventre
2019-07-05
A small dielectric object with positive permittivity may resonate when the free-space wavelength is large in comparison with the object dimensions if the permittivity is sufficiently high. We show that these resonances are all magnetoquasistatic in nature being associated to values of permittivities and frequencies for which source-free quasistatic magnetic fields exist. They are connected to the eigenvalues of the magnetostatic operator expressing the magnetic vector potential in the Coulomb gauge as a function of the current density. These eigenvalues are independent of the size, frequency, and material permittivity. We present the general physical properties of magnetostatic resonances in dielectrics. Our findings improve the understanding of resonances in high-index dielectric objects, and provide a powerful tool that greatly simplifies the analysis and design of high index resonators.
Rashba cavity QED: a route towards the superradiant quantum phase transition (1907.02938v1)
Pierre Nataf, Thierry Champel, Gianni Blatter, Denis M. Basko
2019-07-05
We develop a theory of cavity quantum electrodynamics for a 2D electron gas in the presence of Rashba spin-orbit coupling and perpendicular static magnetic field, coupled to spatially nonuniform multimode quantum cavity photon fields. We demonstrate that the lowest polaritonic frequency of the full Hamiltonian can vanish for realistic parameters, achieving the Dicke superradiant quantum phase transition. This singular behaviour originates from soft spin-flip transitions possessing a non-vanishing dipole moment at non-zero wave vectors and can be viewed as a magnetostatic instability.
Quantum dynamics of quasicharge in an ultrahigh-impedance superconducting circuit (1907.02937v1)
Ivan V. Pechenezhskiy, Raymond A. Mencia, Long B. Nguyen, Yen-Hsiang Lin, Vladimir E. Manucharyan
2019-07-05
Josephson effect is usually taken for granted because quantum fluctuations of the superconducting phase-difference are stabilized by the low-impedance embedding circuit. To realize the opposite regime, we shunt a weak Josephson junction with a nearly ideal kinetic inductance, whose microwave impedance largely exceeds the resistance quantum, reaching above 160 kOhm. Such an extraordinary value is achieved with an optimally designed Josephson junction chain released off the substrate to minimize the stray capacitance. The low-energy spectrum of the resulting free-standing superconducting loop spectacularly loses magnetic flux sensitivity, explained by replacing the junction with a 2e-periodic in charge capacitance. This long-predicted quantum non-linearity dramatically expands the superconducting electronics toolbox with applications to metrology and quantum information
A topological Josephson junction platform for creating, manipulating, and braiding Majorana bound states (1907.02935v1)
Suraj S. Hegde, Yuxuan Wang, Erik Huemiller, Guang Yue, D. J. Van Harlingen, Smitha Vishveshwara
2019-07-05
As part of the intense effort towards identifying platforms in which Majorana bound states can be realized and manipulated to perform qubit operations, we propose a topological Josephson junction architecture that achieves these capabilities and which can be experimentally implemented. The platform uses conventional superconducting electrodes deposited on a topological insulator film to form networks of proximity-coupled lateral Josephson junctions. Magnetic fields threading the network of junction barriers create Josephson vortices that host Majorana bound states localized in the junction where the local phase difference is an odd multiple of
, i.e. attached to the cores of the Josephson vortices. This enables us to manipulate the Majorana states by moving the Josephson vortices, achieving functionality exclusive to these systems in contrast to others, such as those composed of topological superconductor nanowires. We describe protocols for: 1) braiding localized Majorana states by exchange, 2) controlling the separation and hence the coupling of adjacent localized Majorana states to effect non-Abelian rotations via hybridization of the Majorana modes, and 3) reading out changes in the non-local parity correlations induced by such operations. These schemes make use of the application of current pulses and local magnetic field pulses to control the location of vortices, and measurements of the Josephson current-phase relation to reveal the presence of the Majorana bound states. We describe the architecture and schemes in the context of experiments currently underway.
Exact Quantum Dynamics in Structured Environments (1907.02932v1)
Dominic Gribben, Aidan Strathearn, Jake Iles-Smith, Dainius Kilda, Ahsan Nazir, Brendon W. Lovett, Peter Kirton
2019-07-05
The dynamics of a wide range of technologically important quantum systems are dominated by their interaction with just a few environmental modes. Such highly structured environments give rise to long-lived bath correlations that induce complex dynamics which are very difficult to simulate. These difficulties are further aggravated when spatial correlations between different parts of the system are important. By modeling the dynamics of a pair of two-level quantum systems in a common, structured, environment we show that a recently developed numerical approach, the time-evolving matrix product operator, is capable of accurate simulation under exactly these conditions. We find that tuning the separation to match the wavelength of the dominant environmental modes can drastically modify the system dynamics. To further explore this behavior, we show that the full dynamics of the bath can be calculated directly from those of the system, thus allowing us to develop intuition for the complex system dynamics observed.
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