20,151 research outputs found
Current Correlations in Quantum Spin Hall Insulators
We consider a four-terminal setup of a two-dimensional topological insulator
(quantum spin Hall insulator) with local tunneling between the upper and lower
edges. The edge modes are modeled as helical Luttinger liquids and the
electron-electron interactions are taken into account exactly. Using
perturbation theory in the tunneling, we derive the cumulant generating
function for the inter-edge current. We show that different possible transport
channels give rise to different signatures in the current noise and current
cross-correlations, which could be exploited in experiments to elucidate the
interplay between electron-electron interactions and the helical nature of the
edge states.Comment: 5 pages, 2 figure
Emission of entangled Kramers pairs from a helical mesoscopic capacitor
The realization of single-electron sources in integer quantum Hall systems
has paved the way for exploring electronic quantum optics experiments in
solid-state devices. In this work, we characterize a single Kramers pair
emitter realized by a driven antidot embedded in a two-dimensional topological
insulator, where spin-momentum locked edge states can be exploited for
generating entanglement. Contrary to previous proposals, the antidot is coupled
to both edges of a quantum spin Hall bar, thus enabling this mesoscopic
capacitor to emit an entangled two-electron state. We study the concurrence
of the emitted state and the efficiency of its
emission as a function of the different spin-preserving and spin-flipping
tunnel couplings of the antidot with the edges. We show that the efficiency
remains very high () even for maximally entangled states
(). We also discuss how the entanglement can be probed by means
of noise measurements and violation of the Clauser-Horne-Shimony-Holt
inequality.Comment: 9 pages, 5 figure
Quantum thermodynamics of the resonant-level model with driven system-bath coupling
We study nonequilibrium thermodynamics in a fermionic resonant level model
with arbitrary coupling strength to a fermionic bath, taking the wide-band
limit. In contrast to previous theories, we consider a system where both the
level energy and the coupling strength depend explicitly on time. We find that,
even in this generalized model, consistent thermodynamic laws can be obtained,
up to the second order in the drive speed, by splitting the coupling energy
symmetrically between system and bath. We define observables for the system
energy, work, heat, and entropy, and calculate them using nonequilibrium
Green's functions. We find that the observables fulfill the laws of
thermodynamics, and connect smoothly to the known equilibrium results.Comment: 9 pages, 5 figure
Structure factor of interacting one-dimensional helical systems
We calculate the dynamical structure factor S(q, {\omega}) of a weakly
interacting helical edge state in the presence of a magnetic field B. The
latter opens a gap of width 2B in the single-particle spectrum, which becomes
strongly nonlinear near the Dirac point. For chemical potentials |{\mu}| > B,
the system then behaves as a nonlinear helical Luttinger liquid, and a
mobile-impurity analysis reveals interaction-dependent power-law singularities
in S(q,{\omega}). For |{\mu}| < B, the low-energy excitations are gapped, and
we determine S(q,{\omega}) by using an analogy to exciton physics.Comment: 5 pages, 3 figure
Electron transport in multiterminal networks of Majorana bound states
We investigate electron transport through multiterminal networks hosting
Majorana bound states (MBS) in the framework of full counting statistics (FCS).
In particular, we apply our general results to T-shaped junctions of two
Majorana nanowires. When the wires are in the topologically nontrivial regime,
three MBS are localized near the outer ends of the wires, while one MBS is
localized near the crossing point, and when the lengths of the wires are finite
adjacent MBS can overlap. We propose a combination of current and
cross-correlation measurements to reveal the predicted coupling of four
Majoranas in a topological T~junction. Interestingly, we show that the
elementary transport processes at the central lead are different compared to
the outer leads, giving rise to characteristic non-local signatures in
electronic transport. We find quantitative agreement between our analytical
model and numerical simulations of a tight-binding model. Using the numerical
simulations, we discuss the effect of weak disorder on the current and the
cross-correlation functions.Comment: 9 pages, 3 figure
Rydberg crystallization detection by statistical means
We investigate an ensemble of atoms which can be excited into a Rydberg
state. Using a disordered quantum Ising model, we perform a numerical
simulation of the experimental procedure and calculate the probability
distribution function to create a certain number of Rydberg atoms ,
as well as their pair correlation function. Using the latter, we identify the
critical interaction strength above which the system undergoes a phase
transition to a Rydberg crystal. We then show that this phase transition can be
detected using alone.Comment: 7 pages, 9 figure
Spin texture of generic helical edge states
We study the spin texture of a generic helical liquid, the edge modes of a
two-dimensional topological insulator with broken axial spin-symmetry. By
considering honeycomb and square lattice realizations of topological
insulators, we show that in all cases the generic behavior of a
momentum-dependent rotation of the spin quantization axis is realized. Here we
establish this mechanism also for disk geometries with continuous rotational
symmetry. Finally, we demonstrate that the rotation of spin-quantization axis
remains intact for arbitrary geometries, i.e. in the absence of any continuous
symmetry. We also calculate the dependence of this rotation on the model and
material parameters. Finally we propose a spectroscopy measurement which should
directly reveal the rotation of the spin-quantization axis of the helical edge
states.Comment: 16 pages, 17 figure
Detection of qubit-oscillator entanglement in nanoelectromechanical systems
Experiments over the past years have demonstrated that it is possible to
bring nanomechanical resonators and superconducting qubits close to the quantum
regime and to measure their properties with an accuracy close to the Heisenberg
uncertainty limit. Therefore, it is just a question of time before we will
routinely see true quantum effects in nanomechanical systems. One of the
hallmarks of quantum mechanics is the existence of entangled states. We propose
a realistic scenario making it possible to detect entanglement of a mechanical
resonator and a qubit in a nanoelectromechanical setup. The detection scheme
involves only standard current and noise measurements of an atomic point
contact coupled to an oscillator and a qubit. This setup could allow for the
first observation of entanglement between a continuous and a discrete quantum
system in the solid state.Comment: 9 pages, 3 figure
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