Latest Papers in Condensed Matter Physics

Mesoscale And Nanoscale Physics

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Control of the magnon-photon level attraction in a planar cavity (1901.07633v2)

Y. Yang, J. W. Rao, Y. S. Gui, B. M. Yao, W. Lu, C. -M. Hu

2019-01-22

A resistive coupling circuit is used to model the recently discovered dissipative coupling in a hybridized cavity photon-magnon system. With this model as a basis we have designed a planar cavity in which a controllable transition between level attraction and level repulsion can be achieved. This behaviour can be quantitatively understood using an LCR circuit model with a complex coupling strength. Our work therefore develops and verifies a circuit method to model level repulsion and level attraction and confirms the universality of dissipative coupling in the cavity photon-magnon system. The realization of both coherent and dissipative couplings in a planar cavity may provide new avenues for the design and adaptation of dissipatively coupled systems for practical applications in information processing.

Majorana bound states in magnetic skyrmions imposed onto a superconductor (1904.04177v1)

Stefan Rex, Igor V. Gornyi, Alexander D. Mirlin

2019-04-08

We consider a superconducting film exchange-coupled to a close-by chiral magnetic layer and study how magnetic skyrmions can induce the formation of Majorana bound states (MBS) in the superconductor. Inspired by a proposal by Yang et al. [Phys. Rev. B 93, 224505 (2016)], which suggested MBS in skyrmions of even winding number, we explore whether such skyrmions could result from a merger of ordinary skyrmions. We conclude that the formation of higher-winding skyrmions is not realistic in chiral magnets. Subsequently, we present a possibility to obtain MBS from realistic skyrmions of winding number one, if a skyrmion-vortex pair is formed instead of a bare skyrmion. Specifically, we show that MBS are supported in a pair of a circular skyrmion and a vortex which both have a winding number of one. We back up our analytical prediction with results from numerical diagonalization and obtain the spatial profile of the MBS. In light of recent experimental progress on the manipulation of skyrmions, such systems are promising candidates to achieve direct spatial control of MBS.

Topological superconductivity with deformable magnetic skyrmions (1904.03005v2)

Maxime Garnier, Andrej Mesaros, Pascal Simon

2019-04-05

Magnetic skyrmions are nanoscale spin configurations that can be efficiently created and manipulated. They hold great promises for next-generation spintronics applications. In parallel to these developments, the interplay of magnetism, superconductivity and spin-orbit coupling has proved to be a versatile platform for engineering topological superconductivity predicted to host non-abelian excitations, Majorana zero modes. We show that topological superconductivity can be induced by proximitizing magnetic skyrmions and conventional superconductors, without need for additional ingredients. Apart from a previously reported Majorana zero mode in the core of the skyrmion, we find a more universal chiral band of Majorana modes on the edge of the skyrmion. We show that the chiral Majorana band is effectively flat in the physically relevant regime of parameters, leading to interesting robustness and scaling properties. In particular, the number of Majorana modes in the (nearly-)flat band scales with the perimeter length of a deformed skyrmion configuration, while being robust to local disorder.

Speedup of adiabatic multiqubit state-transfer by ultrastrong coupling of matter and radiation (1904.04141v1)

M. Stramacchia, A. Ridolfo, G. Benenti, E. Paladino, F. M. D. Pellegrino, G. D. Maccarrone, G. Falci

2019-04-08

Ultrastrongly coupled quantum hardware may increase the speed of quantum state processing in distributed architectures, allowing to approach fault-tolerant threshold. We show that circuit QED architectures in the ultrastrong coupling regime, which has been recently demonstrated with superconductors, may show substantial speedup for a class of adiabatic protocols resilient to the main source of errors, namely the interplay of dynamical Casimir effect and cavity losses.

Localized surfaces of three dimensional topological insulators (1901.05464v2)

Yang-Zhi Chou, Rahul M. Nandkishore, Leo Radzihovsky

2019-01-16

We study the surface of a three-dimensional spin chiral topological insulator (class CII), demonstrating the possibility of its localization. This arises through an interplay of interaction and statistically-symmetric disorder, that confines the gapless fermionic degrees of freedom to a network of one-dimensional helical domain-walls that can be localized. We identify two distinct regimes of this gapless insulating phase, a clogged' regime wherein the network localization is induced by its junctions between otherwise metallic helical domain-walls, and afully localized' regime of localized domain-walls. The experimental signatures of these regimes are also discussed.

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