Browsing by Author "Simon, Pascal"
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- Disorder-induced exceptional points and nodal lines in Dirac superconductors
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-04-29) Zyuzin, Alexander A.; Simon, PascalWe consider the effect of disorder on the spectrum of quasiparticles in the point-node and nodal-line superconductors. Due to the anisotropic dispersion of quasiparticles disorder scattering may render the Hamiltonian describing these excitations non-Hermitian. Depending on the dimensionality of the system, we show that the nodes in the spectrum are replaced by Fermi arcs or Fermi areas bounded by exceptional points or exceptional lines, respectively. These features are illustrated by first considering a model of a proximity-induced superconductor in an anisotropic two-dimensional (2D) Dirac semimetal, where a Fermi arc in the gap bounded by exceptional points can be realized. We next show that the interplay between disorder and supercurrents can give rise to a 2D Fermi surface bounded by exceptional lines in three-dimensional (3D) nodal superconductors. - Propagation of light through an amplifying honeycomb photonic lattice
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-10-07) Islam, Sk Firoz; Simon, Pascal; Zyuzin, Alexander A.We consider light propagation through a ballistic amplifying photonic honeycomb lattice below the lasing threshold. Two sublattices of the system are formed by waveguides with different complex dielectric permittivities, which results in the non-Hermitian Dirac equation for electromagnetic fields. We reveal that there exists a critical length of the amplifying region for which the photonic lattice exhibits an amplifier-to-generator transition. The transmission and reflection probabilities at the normal angle of incidence are strongly enhanced at a critical length of the system. We also comment on the sensitivity of amplification to the direction of incident light and the thickness of the amplifying region. - Topological state engineering by potential impurities on chiral superconductors
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016-08-11) Kaladzhyan, Vardan; Röntynen, Joel; Simon, Pascal; Ojanen, TeemuIn this work we consider the influence of potential impurities deposited on top of two-dimensional chiral superconductors. As discovered recently, magnetic impurity lattices on an s-wave superconductor may give rise to a rich topological phase diagram. We show that a similar mechanism takes place in chiral superconductors decorated by nonmagnetic impurities, thus avoiding the delicate issue of magnetic ordering of adatoms. We illustrate the method by presenting the theory of potential impurity lattices embedded on chiral p-wave superconductors. While a prerequisite for the topological state engineering is a chiral superconductor, the proposed procedure results in vistas of nontrivial descendant phases with different Chern numbers. - Yu-Shiba-Rusinov Qubit
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-12-07) Mishra, Archana; Simon, Pascal; Hyart, Timo; Trif, MirceaMagnetic impurities in s-wave superconductors lead to spin-polarized Yu-Shiba-Rusinov (YSR) in-gap states. Chains of magnetic impurities offer one of the most viable routes for the realization of Majorana bound states, which hold promise for topological quantum computing. However, this ambitious goal looks distant, since no quantum coherent degrees of freedom have yet been identified in these systems. To fill this gap, we propose an effective two-level system, a YSR qubit, stemming from two nearby impurities. Using a time-dependent wave-function approach, we derive an effective Hamiltonian describing the YSR-qubit evolution as a function of the distance between the impurity spins, their relative orientations, and their dynamics. We show that the YSR qubit can be controlled and read out using state-of-the-art experimental techniques for manipulation of the spins. Finally, we address the effect of spin noise on the coherence properties of the YSR qubit and show robust behavior for a wide range of experimentally relevant parameters. Looking forward, the YSR qubit could facilitate the implementation of a universal set of quantum gates in hybrid systems where they are coupled to topological Majorana qubits.