Enhancement of the shot noise of a quantum dot–Luttinger lead system

We investigate the joint effects of the intralead electron interaction and Coulombic dot–lead interaction on the shot noise of a quantum dot coupled to Luttinger liquid leads. A formula of the shot noise is derived by applying the nonequilibrium Green function technique. The shot noise is enhanced by the dot–lead interaction. For a weak or moderately strong interaction the differential shot noise demonstrates resonant-like behavior as a function of bias and gate voltages. In the limit of strong interaction resonant behavior disappears and the differential shot noise and Fano factor scale as a power law in bias voltage. Under some parameters, the differential shot noise may become negative around resonant peaks, and the physical reason is analyzed.     

Noise correlations in a Coulomb-blockaded quantum dot

We report measurements of current noise auto- and cross correlation in a tunable quantum dot with two or three leads. As the Coulomb blockade is lifted at finite source-drain bias, the autocorrelation evolves from super- to sub-Poissonian in the two-lead case, and the cross correlation evolves from positive to negative in the three-lead case, consistent with transport through multiple levels. Cross correlations in the three-lead dot are found to be proportional to the noise in excess of the Poissonian value in the limit of weak output tunneling.     

Spin-flip shot noise in a quantum dot coupled to carbon nanotube terminals responded by a rotating magnetic field

We have investigated the spectral density of shot noise of the system with a quantum dot (QD) coupled to two single-wall carbon nanotube terminals, where a rotating magnetic field is applied to the QD. The carbon nanotube (CN) terminals act as quantum wires which open quantum channels for electrons to transport through. The shot noise and differential shot noise exhibit novel behaviors originated from the quantum nature of CNs. The shot noise is sensitively dependent on the rotating magnetic field, and the differential shot noise exhibits asymmetric behavior versus source-drain bias and gate voltage. The Fano factor of the system exhibits the deviation of shot noise from the Schottky formula. The super-Poissonian and sub-Poissonian shot noise can be achieved in different regime of source-drain bias.     

Dynamic spin-polarized shot noise in a quantum dot coupled to ferromagnetic terminals under the perturbation of ac fields

We have investigated the shot noise in the mesoscopic system composed of a quantum dot (QD) coupled to ferromagnetic terminals under the perturbation of ac fields. The shot noise has been derived using the nonequilibrium Green's function (NGF) technique to describe the spin polarization effect along with photon absorption and emission processes in the Coulomb blockade regime. We have examined the influence of spin polarization on the shot noise under the perturbation of ac fields in the nonadiabatic regime. The Coulomb blockade effect results in the modification of shot noise compared with the noninteracting case. The spin orientation contributes a spin valve effect for controlling electron tunnelling through this QD, and different resonant forms appear around the Coulomb blockade channel. The photon-assisted spin-splitting and spin-polarization effect contributes a photon-assisted spin valve to adjust the electron tunnelling current and shot noise. The spin-polarization effect varies the value of the Fano factor. However, it does not change the noise type from sub-Poissonian to super-Poissonian.     

AC shot noise through a vibrating quantum dot

In this paper we investigate the joint effects of the electron-phonon interaction and an external alternating (ac) gate voltage on the spectral density of shot noise through a vibrating quantum dot system, by applying the Lang-Firsov canonical transformation and the Keldysh nonequilibrium Green's function (NGF) technique. We find that the effects of the electron-phonon and electron-photon interaction on the differential shot noise are different. The main resonant peak of the differential shot noise is decreased only when a time-dependent gate voltage is imposed on quantum dot. With the ac field amplitude increasing, the main resonant peak of the differential shot noise decreases. The Fano factor of the system, which exhibits the deviation of shot noise from the Schottky formula, is also studied. Super-Poissonian shot noise appears due to the photon absorption (emission) processes in the low bias voltage region.     

Shot noise of the spin inelastic tunneling through a quantum dot with single molecule-magnet

We have studied the quantum fluctuations of inelastic spin-electron scattering in quantum dot with an embedded biaxial single molecule-magnet and particularly investigated the zero-frequency shot noise and Fano factor in different magnetic fields. It is found that the shot noise and Fano factor exhibit a stepwise behaviour as bias increases in the presence of interaction between the electron and molecule-magnet for a weak magnetic field. As magnetic field becomes strong, a dip is displayed in the shot-noise-bias curve due to the suppression of inelastic shot noise caused by the quantum tunneling of magnetisation. Because of the spontaneous inelastic tunneling at zero bias, a small shot noise occurs, which results in the case of Fano factor F >> 1. Moreover, our results show that the sweeping speed can also influence the shot noise and Fano factor obviously.     

Dynamical control of electron states in double quantum dot

Controllable electron dynamics in a double quantum dot has been investigated theoretically in the presence of strong sinusoidal electric field and monotonically varied bias voltage, applied to the structure. It is shown that the possibility to create controllable electron states strongly depends on the relation between Rabi frequency and typical reciprocal time of bias change. As follows from theoretical analysis, when time of bias change is the biggest temporal parameter of the problem, electron density can be fully relocated from one quantum dot to another under the action of both resonant sinusoidal field and slowly varied voltage. When the period of Rabi oscillations is much greater than the time of bias change, electron tunneling between two neighboring quantum dots becomes suppressed. In this case electron density stays in the quantum dot that was initially occupied.     

Photon-assisted Shot noise of the double quantum dot interferometer in weak Kondo regime

The shot noise of a parallel double quantum dot (DQD) system under the perturbation of microwave fields is investigated in the weak Kondo regime. Peak-valley structures exhibit in the differential conductance and shot noise, and side resonant peaks emerge around the Kondo peak due to the absorption and emission of photons. The shot noise is sensitively dependent on the adjusting approach through changing the gate voltages. Large resonant Fano factor accompanying photon-induced side peaks appear by simultaneously varying the two gate voltages. The photon suppression and enhancement of shot noise have been evaluated corresponding to the coherent and incoherent current correlation. The destructive interference causes the suppression of shot noise by changing the Aharonov–Bohm phase.     

Shot noise in a quantum dot coupled to non-magnetic leads: effects of Coulomb interaction

We study electron transport through a quantum dot, connected to non-magnetic leads, in a magnetic field. A super-Poissonian electron noise due to the effects of both interacting localized states and dynamic channel blockade is found when the Coulomb blockade is partially lifted. This is sharp contrast to the sub-Poissonian shot noise found in the previous studies for a large bias voltage, where the Coulomb blockade is completely lifted. Moreover, we show that the super-Poissonian shot noise can be suppressed by applying an electron spin resonance (ESR) driving field. For a sufficiently strong ESR driving field strength, the super-Poissonian shot noise will change to be sub-Poissonian.     

The shot noise of the quantum dot weakly coupled to Luttinger liquid

We study the nonequilibrium transport through a single-level quantum dot weakly coupled to Luttinger liquid leads. A general shot noise expression is derived by using nonequilibrium Green function technique. We find that the differential shot noise and differential conductance demonstrate resonant-like behavior as a function of the bias voltage and the quantum dot's energy level for a weak or moderately strong interaction. In the limit of strong electron-electron interaction, the resonant behavior disappears and shows bias-voltage-dependent power law scalings. And the Fano factor also scales as a power law in high bias voltage region. In addition, the Fano factor is enhanced with the electron-electron interaction increased. It implies that the Fano factor can be controlled by tuning the electron-electron interaction in the leads.     

On Dirichlet-to-Neumann Maps, Nonlocal Interactions, and Some Applications to Fredholm Determinants

We consider Dirichlet-to-Neumann maps associated with (not necessarily self-adjoint) Schrödinger operators describing nonlocal interactions in ${L^2(\Omega; d^n x)}$ , where ${\Omega \subset \mathbb{R}^n}$ , ${n\in\mathbb{N}}$ , ${n\geq 2}$ , are open sets with a compact, nonempty boundary ${\partial\Omega}$ satisfying certain regularity conditions. As an application we describe a reduction of a certain ratio of Fredholm perturbation determinants associated with operators in ${L^2(\Omega; d^{n} x)}$ to Fredholm perturbation determinants associated with operators in ${L^2(\partial\Omega; d^{n-1} \sigma)}$ , ${n\in\mathbb{N}}$ , ${n\geq 2}$ . This leads to an extension of a variant of a celebrated formula due to Jost and Pais, which reduces the Fredholm perturbation determinant associated with a Schrödinger operator on the half-line ${(0,\infty)}$ , in the case of local interactions, to a simple Wronski determinant of appropriate distributional solutions of the underlying Schrödinger equation.     

Effects of time delay on transport processes in an active Brownian particle

The transport properties of an active Brownian particle with a time-delayed feedback and an external bias are investigated theoretically. By virtue of the perturbation theory for small delay, analytical expressions for the mean velocity and effective diffusion coefficient are derived. There exists a critical absolute value of the bias, below and above which the delay, respectively, enhances and weakens the diffusion, for a fixed noise intensity. The effects of delay observed above are more pronounced for weaker noise. These results are further verified via direct numerical simulations.     

Coherence destruction of tunneling in a quantum-dot molecule with bias

This paper studies the constraint conditions for coherence destruction in tunneling by using perturbation theory and numerical simulation for an AC-field with bias and Coulomb interaction between electrons in a quantum dot molecule. Such conditions can be described by using the roots of a Bessel function Jn(x), where n is determined by both the bias and the Coulomb interactions, and x is the ratio of the amplitude to the frequency of the AC-field. Under such conditions, a coherent suppression of tunneling occurs between localized electronic states, which results from the dynamical localization phenomenon. All the conditions are verified with numerical simulations.     

The shot noise of a strongly correlated quantum dot coupled to the Luttinger liquid leads

We study the shot noise of a strongly correlated quantum dot weakly coupled to Luttinger liquid leads in the Kondo regime by means of the extended equation of motion method. A general zero-frequency shot noise formula with good convergence is derived. The shot noise exhibits a non-monotonic dependence on voltage for weak intralead interaction. There is a peak around the Kondo temperature at low voltage when the interaction is very weak, and its height decreases rapidly with the intralead interaction increasing. When the interaction is moderately strong the peak disappears and the shot noise scales as a power law in bias voltage, indicating that the intralead electron interaction suppresses the shot noise. It is possible that the measurements of the shot noise spectrum can extract the information of the intralead interaction.     

Signatures of a noise-induced quantum phase transition in a mesoscopic metal ring

We study a mesoscopic ring with an inline quantum dot threaded by an Aharonov-Bohm flux. Zero-point fluctuations of the electromagnetic environment capacitively coupled to the ring, with omega(s) spectral density, can suppress tunneling through the dot, resulting in a quantum phase transition from an unpolarized to a polarized phase. We show that robust signatures of such a transition can be found in the response of the persistent current in the ring to the external flux as well as to the bias between the dot and the arm. Particular attention is paid to the experimentally relevant cases of Ohmic (s = 1) and sub-Ohmic (s = 1/2) noise.     

Nonequilibrium perturbation theory in Liouville-Fock space for inelastic electron transport

We use a superoperator representation of the quantum kinetic equation to develop nonequilibrium perturbation theory for an inelastic electron current through a quantum dot. We derive a Lindblad-type kinetic equation for an embedded quantum dot (i.e. a quantum dot connected to Lindblad dissipators through a buffer zone). The kinetic equation is converted to non-Hermitian field theory in Liouville-Fock space. The general nonequilibrium many-body perturbation theory is developed and applied to the quantum dot with electron-vibronic and electron-electron interactions. Our perturbation theory becomes equivalent to a Keldysh nonequilibrium Green's function perturbative treatment provided that the buffer zone is large enough to alleviate the problems associated with approximations of the Lindblad kinetic equation.     

Nonequilibrium conductance of a nanodevice for small bias voltage

Using nonequilibrium renormalized perturbation theory, we calculate the retarded and lesser self-energies, the spectral density ρ(ω) near the Fermi energy, and the conductance G through a quantum dot as a function of a small bias voltage V, in the general case of electron-hole asymmetry and intermediate valence. The linear terms in ω and V are given exactly in terms of thermodynamic quantities. When the energies necessary to add the first electron (Ed) and the second one (Ed + U) to the quantum dot are not symmetrically placed around the Fermi level, G has a term linear in V if, in addition, either the voltage drop or the coupling to the leads is not symmetric. The effects of temperature are discussed. The results simplify for a symmetric voltage drop, a situation usual in experiment.     

电-声子耦合强度对量子点系统噪声的影响

利用Lang-Firsov正则变换和Keldysh非平衡格林函数方法研究了低温下具有电子-声子相互作用的量子点系统的噪声.我们特别注意了电-声子耦合强度的变化对量子点系统噪声的影响.数值结果表明:随着电-声子耦合强度的增大,系统的噪声增大,同时微分噪声谱中会出现一系列的声子伴带峰,峰的高度和数目对电-声子耦合强度的变化非常敏感.我们也研究了系统的Fano因子,它显示系统噪声对肖特基(Schottky)公式的偏离.在高偏压区,Fano因子随着电-声子耦合强度的增大而增大.     

电-声子耦合强度对量子点系统噪声的影响

利用Lang-Firsov正则变换和Keldysh非平衡格林函数方法研究了低温下具有电子-声子相互作用的量子点系统的噪声。我们特别注意了电-声子耦合强度的变化对量子点系统噪声的影响。数值结果表明：随着电-声子耦合强度的增大,系统的噪声增大,同时微分噪声谱中会出现一系列的声子伴带峰,峰的高度和数目对电-声子耦合强度的变化非常敏感。我们也研究了系统的Fano因子,它显示系统噪声对肖特基(Schottky)公式的偏离。在高偏压区,Fano因子随着电-声子耦合强度的增大而增大。     

Driving rate effects on crackling noise

Many systems respond to slowly changing external conditions with crackling noise, created by avalanches or pulses with a broad range of sizes. Examples range from Barkhausen noise (BN) in magnets to earthquakes. In this Letter, we discuss the effects of increasing driving rate Omega on the scaling behavior of the avalanche size and duration distributions as well as qualitative effects of Omega on the power spectra. We derive an exponent inequality as a criteria for the relevance of Omega. To illustrate these general results, we use recent experiments on BN as a successful example.