Room-temperature single-electron transistors are realized within individual metallic single-wall carbon nanotube molecules. The devices feature a short (down to approximately 20 nanometers) section that is created by inducing local barriers into the tube with an atomic force microscope. Coulomb charging observed at room temperature, addition energy of 120 millielectron volts, which substantially exceeds thermal energy. At low temperatures, we resolve quantum levels corresponding small...

We investigate quantum Brownian motion in adiabatically rocked ratchet systems. Above a crossover temperature ${T}_{c}$ tunneling events are rare, yet they already substantially enhance the classical particle current. Below ${T}_{c}$, prevails and predictions grossly underestimate transport. Upon approaching $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ current exhibits induced reversal, tends to finite limit.

We study the dissipative dynamics of a two-level system (TLS) exposed to strong ac driving. By combining Floquet theory with Van Vleck perturbation in TLS tunneling matrix element, we diagonalize time-dependent Hamiltonian and provide corrections renormalized Rabi frequency TLS, which are valid for both biased unbiased go beyond known high-frequency rotating-wave results. In order mimic environmental influences on couple weakly thermal bath solve analytically corresponding...

Various theoretical methods address transport effects in quantum dots beyond single-electron tunneling while accounting for the strong interactions such systems. In this paper we report a detailed comparison between three prominent approaches to transport: fourth-order Bloch-Redfield master equation (BR), real-time diagrammatic technique (RT), and scattering rate approach based on T-matrix (TM). Central BR RT is generalized reduced density matrix. We demonstrate exact equivalence of these...

We analyze the nanocaloritronic performance of an interacting quantum dot that is subject to applied bias and temperature gradient. It now well known that, in absence phonon contribution, a weakly coupled non-interacting can operate at thermoelectric efficiencies approaching Carnot limit. However, it has also been recently pointed out such peak only be achieved when operated reversible limit, with vanishing current hence power output. In this paper, we point three fundamental results...

We study quantum stochastic resonance (QSR) in the periodically driven biased spin-boson system. The amplitude and phase of nonlinear response function vs temperature are studied incoherent coherent tunneling regimes, encompassing adiabatic nonadiabatic driving, weak strong Ohmic coupling $\ensuremath{\alpha}$. For $\ensuremath{\alpha}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$ we present exact QSR results. As a general feature, principal maximum appears when static asymmetry...

We have measured a quantum ratchet effect for vortices moving in quasi-one-dimensional Josephson junction array. In this solid-state device the shape of vortex potential energy, and consequently band structure, can be accurately designed. This structure determines presence or absence effect. particular, asymmetric structures possessing only one below barrier do not exhibit current rectification at low temperatures bias currents. The nature transport is also revealed universal/nonuniversal...

Interference effects strongly affect the transport characteristics of a benzene single-electron transistor, and for this reason we call it interference transistor (I-SET). We focus on degeneracies between many-body states isolated benzene. show that particular current blocking selective conductance suppression occurring in I-SET are due to orbitally degenerate states. Further study impact reduced symmetry anchor groups or potential drop over molecule. identify quasidegeneracy involved...

We examine a two-level system coupled to quantum oscillator, typically representing experiments in cavity and circuit electrodynamics. show how such can be treated analytically the ultrastrong coupling limit, where ratio $g/\ensuremath{\Omega}$ between strength oscillator frequency approaches unity goes beyond. In this regime Jaynes-Cummings model is known fail because counter-rotating terms have taken into account. By using Van Vleck perturbation theory higher orders qubit tunneling matrix...

We present a comprehensive, analytical treatment of the finite Kitaev chain for arbitrary chemical potential and length. By means an exact diagonalization in real space, we derive momentum quantization conditions formulas resulting energy spectrum eigenstate wave functions, encompassing boundary bulk states. In accordance with analysis based on winding number topological invariant, as expected from bulk-edge correspondence, states are nature. They can have zero, exponentially small or even...

In the regime of weak bath coupling and low temperature we demonstrate numerically for spin-boson dynamics equivalence between two widely used but seemingly different roads approximation, namely path integral approach Bloch-Redfield theory. The excellent agreement these methods is corroborated by a novel efficient analytical high-frequency approach: it well approximates decay quantum coherence via series damped coherent oscillations. Moreover, suitably tuned control field can selectively...

We study the quantum dynamics of a periodically driven biased two-state system which additionally is subject to either Ohmic or frequency-dependent damping. Within noninteracting-blip approximation for stochastic forces, solution given in terms series defined by recursion relations. Avoiding rotating wave and Markovian approximation, we deduce closed form important cases high- low-frequency driving. For driving, governed rate equation with time-dependent adiabatic equilibrium state. In...

The interplay between Coulomb interaction and orbital symmetry produces specific transport characteristics in molecular single electron transistors (SETs) that can be considered as the fingerprints of contacted molecule. Specifically we predict, for a benzene SET, selective conductance suppression appearance negative differential when changing contacts from para to meta configuration. Both effects originate destructive interference involving states with degeneracy.

The magnetoconductance of an open carbon nanotube (CNT)-quantum wire was measured in pulsed magnetic fields. At low temperatures, we find a peculiar split peak close to the charge-neutrality point. Our analysis data reveals that this splitting is intimately connected spin-orbit interaction and tube chirality. Band-structure calculations suggest current regions highly spin polarized, which calls for application future CNT-based spintronic devices.

This paper reports on the experimental and theoretical investigation of nonequilibrium Kondo effect in carbon nanotube quantum dots. At low temperature absence magnetic field, authors observe two symmetric satellite features either side zero bias peak due to splitting single-particle states by spin-orbit coupling valley mixing. Further results are discussed based underlying symmetries energy spectrum.

Abstract Quantum two-level systems interacting with the surroundings are ubiquitous in nature. The interaction suppresses quantum coherence and forces system towards a steady state. Such dissipative processes captured by paradigmatic spin-boson model, describing two-state particle, “spin”, an environment formed harmonic oscillators. A fundamental question to date is what extent intense coherent driving impacts strongly system. Here we investigate experimentally theoretically superconducting...

Abstract Illumination of atoms by resonant lasers can pump electrons into a coherent superposition hyperfine levels which no longer absorb the light. Such is known as dark state, because fluorescent light emission then suppressed. Here we report an all-electric analogue this destructive interference effect in carbon nanotube quantum dot. The states are valley (angular momentum) decoupled from either drain or source leads. Their emergence visible asymmetric current−voltage characteristics,...

We present exact analytical results for the differential conductance of a finite Kitaev chain in an N-S-N configuration, where topological superconductor is contacted on both sides with normal leads. Our are obtained Keldysh nonequilibrium Green's function technique, using full spectrum without resorting to minimal models. A closed formula linear given, and procedure obtain transport mediated by higher excitations described. The attains maximum value ${e}^{2}/h$ only zero-energy states....

Topological insulator (TI) nanowires in proximity to conventional superconductors have been proposed as a tunable platform realize topological superconductivity and Majorana zero modes. The tuning is done using an axial magnetic flux $\ensuremath{\phi}$ which allows transforming the system from trivial at $\ensuremath{\phi}=0$ topologically nontrivial when half quantum ${\ensuremath{\phi}}_{0}/2$ threads cross-section of wire. Here, we explore expected transition TI-wire-based Josephson...

Abstract Heat transport in a qubit-oscillator junction described by the quantum Rabi model is investigated. Upon variation of temperature, bias on qubit and coupling strength, rich variety effects identified. For weak to bosonic heat baths, essentially controlled $g$ which defines Kondo-like temperature $T_K(g)$. At temperatures much lower than $T_K$ , coherent transfer via virtual processes yields $T^3$ behavior linear conductance as function $T$, modulated prefactor determined junc- tion...

The dynamics of the driven dissipative two-state system is formulated in terms an exact nonconvolutive master equation. kernel expressed as power series intersite coupling, which lowest order corresponds to familiar noninteracting-blip approximation. We use this formalism calculate systematically all orders coupling for weak damping, and we solve affiliated equation high-frequency driving analytic form. Our approach finds straightforward generalization any multistate tight-binding system.

Abstract The nature of superconductivity in monolayer transition metal dichalcogenides is still under debate. It has already been argued that repulsive Coulomb interactions, combined with the disjoint Fermi surfaces around K , ʹ valleys and at Γ point, can lead to superconducting instabilities <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mtext>NbSe</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math> . Here, we demonstrate two-bands arises...