Floquet engineering of long-range p-wave superconductivity

 

Floquet engineering of long-range p-wave superconductivity
M. Benito, A. Gómez-León, V. M. Bastidas, T. Brandes and G. Platero
Pys. Rev. B 90, 205127 (2014)

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Floquet Majorana fermions appear as steady states at the boundary of time-periodic topological phases of matter. In this work, we theoretically study the main features of these exotic topological phases in the periodically driven one-dimensional Kitaev model. By controlling the ac fields, we can predict topological phase transitions that should give rise to signatures of Majorana states in experiments. Moreover, the knowledge of the time dependence of these Majorana states allows one to manipulate them. Our work contains a complete analysis of the monochromatic driving in different frequency regimes.

 

Capacitively coupled nano conductors

 

Capacitively coupled nano conductors
R. Hussein and S. Kohler.
arXiv:1503.00534 Annalen der Physik, March 3, 2015

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We investigate electron transport in two quantum circuits with mutual Coulomb interaction. The first circuit is a double quantum dot connected to two electron reservoirs, while the second one is a quantum point contact in the weak tunneling limit. The coupling is such that an electron in the first circuit enhances the barrier of the point contact and, thus, reduces its conductivity. While such setups are frequently used as charge monitors, we focus on two different aspects. First, we derive transport coefficients which have recently been employed for testing generalized equilibrium conditions known as exchange fluctuation relations. These formally exact relations allows us to test the consistency of our master equation approach. Second, a biased point contact entails noise on the DQD and induces non-equilibrium phenomena such as a ratchet current.

 

Photon assisted long-range tunneling

 

Photon assisted long-range tunneling
F. Gallego-Marcos, R. Sánchez and G. Platero.
J. Appl. Phys. 117, 112808 (2015)

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We analyze long-range transport through an ac driven triple quantum dot with a single electron. Resonant transitions between separated and detuned dots are mediated by the exchange of n photons with the time-dependent field. An effective model is proposed in terms of second order (cotunneling) processes which dominate the long-range transport between the edge quantum dots. The ac field renormalizes the inter dot hopping, modifying the level hybridization. It results in a non-trivial behavior of the current with the frequency and amplitude of the external ac field.

 

 

 

Chiral thermoelectrics with quantum Hall edge states

Chiral thermoelectrics with quantum Hall edge states
R. Sánchez, Björn Sothmann and Andrew N. Jordan.
Phys. Rev. Lett. 114, 146801 (2015)

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The thermoelectric properties of a three-terminal quantum Hall conductor are investigated. We identify a contribution to the thermoelectric response that relies on the chirality of the carrier motion rather than on spatial asymmetries. The Onsager matrix becomes maximally asymmetric with configurations where either the Seebeck or the Peltier coefficients are zero while the other one remains finite. Reversing the magnetic field direction exchanges these effects, which originate from the chiral nature of the quantum Hall edge states. The possibility to generate spin-polarized currents in quantum spin Hall samples is discussed.

 

Floquet Majorana fermions in superconducting quantum dots

Floquet Majorana fermions in superconducting quantum dots
M. Benito and G. Platero.
Physica E 74, 608–613 (2015)

dotsmajoranaWe consider different configurations of ac driven quantum dots coupled to superconductor leads where Majorana fermions can exist as collective quasiparticles. The main goal is to tune the existence, localization and properties of these zero energy quasiparticles by means of periodically driven external gates. In particular, we analyze the relevance of the system and driving symmetry. We predict the existence of different sweet spots with Floquet Majorana fermions in configurations where they are not present in the undriven system.

Degenerate parametric oscillation in quantum membrane optomechanics

Degenerate parametric oscillation in quantum membrane optomechanics
M. Benito, C. Sánchez-Muñoz and C. Navarrete-Benlloch.
Phys. Rev. A 93, 023846 (2016)

dompoIn this work we show that modern optomechanical setups are mature enough to implement one of the most elusive models in the field of open system dynamics: degenerate parametric oscillation. Introduced in the eighties and motivated by its alleged implementability in nonlinear optical resonators, it rapidly became a paradigm for the study of dissipative phase transitions whose corresponding spontaneously broken symmetry is discrete. However, it was found that the intrinsic multimode nature of optical cavities makes it impossible to experimentally study the model all the way through its phase transition. In contrast, here we show that this long-awaited model can be implemented in the motion of a mechanical object dispersively coupled to the light contained in a cavity, when the latter is properly driven with multichromatic laser light. We focus on membranes as the mechanical element, showing that the main signatures of the degenerate parametric oscillation model can be studied in state-of-the-art setups, thus opening the possibility of analyzing spontaneous symmetry breaking and enhanced metrology in one of the cleanest dissipative phase transitions. In addition, the ideas put forward in this work would allow for the dissipative preparation of squeezed mechanical states.

Long-range doublon transfer in a dimer chain induced by topology and ac fields

 

Long-range doublon transfer in a dimer chain induced by topology and ac fields
M. Bello, C. Creffield and G. Platero.
Sci. Rep. 6, 22562 (2016)

Figure_1In this work we study how to induce long-range transfer of interacting particles between the two ends of a dimer chain, by coupling states that are localized just on the chain’s end-points. This has the appealing feature that the transfer occurs only between the end-points – the particle does not pass through the intermediate sites – making the transfer less susceptible to decoherence. Gate potentials and ac fields allow us to induce the the presence of topological or Shockley-like edge states. We can control the quality and speed of the transfer by tuning the different parameters of the model.

Coupled Landau-Zener-Stückelberg quantum dot interferometers

 

Coupled Landau-Zener-Stückelberg quantum dot interferometers
F. Gallego-marcos, R. Sánchez and G. Platero.
Phys. Rev. B 93, 075424 (2016)

mediumWe investigate the interplay between long-range and direct photon-assisted transport in a triple quantum dot chain where local ac voltages are applied to the outer dots. We propose the phase difference between the two ac voltages as an external parameter, which can be easily tuned to manipulate the current characteristics. For gate voltages in phase opposition we find quantum destructive interferences analogous to the interferences in closed-loop undriven triple dots. As the voltages oscillate in phase, interferences between multiple paths give rise to dark states. Those totally cancel the current, and could be experimentally resolved.

Edge-state Blockade of Transport in Quantum Dot Arrays

 

Edge-state Blockade of Transport in Quantum Dot Arrays
M. Benito, M. Niklas, G. Platero and S. Kohler.
Phys. Rev. B 93, 115432 (2016)

figure1We propose a transport blockade mechanism in quantum dot arrays and conducting molecules based on an interplay of Coulomb repulsion and the formation of edge states. As a model we employ a dimer chain that exhibits a topological phase transition. The connection to a strongly biased electron source and drain enables transport. We show that the related emergence of edge states is manifest in the shot noise properties as it is accompanied by a crossover from bunched electron transport to a Poissonian process. For both regions we develop a scenario that can be captured by a rate equation. The resulting analytical expressions for the Fano factor agree well with the numerical solution of a full quantum master equation.

Topological instabilities in ac-driven bosonic systems

 

Topological instabilities in ac-driven bosonic systems
G. Engelhardt, M. Benito, G. Platero and T. Brandes.
Phys. Rev. Lett. 117, 045302 (2016)

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Under nonequilibrium conditions, bosonic modes can become dynamically unstable with an exponentially growing occupation. On the other hand, topological band structures give rise to symmetry protected midgap states. In this Letter, we investigate the interplay of instability and topology. Thereby, we establish a general relation between topology and instability under ac driving. We apply our findings to create dynamical instabilities which are strongly localized at the boundaries of a finite-size system. As these localized instabilities are protected by symmetry, they can be considered as topological instabilities.