arXiv subjects

Christian Flindt

Publications and source records attributed to Christian Flindt.

112 records · Page 7Linked to original sources

arXiv2004

Current noise spectrum of a quantum shuttle

We present a method for calculating the full current noise spectrum for the class of nano-electromechanical systems (NEMS) that can be described by a Markovian generalized master equation. As a specific example we apply the method to a quantum shuttle. The noise spectrum of the shuttle has peaks at integer multiples of the mechanical frequency, which is slightly renormalized. The renormalization explains a previously observed small deviation of the shuttle current compared to the expected value given by the product of the natural mechanical frequency and the electron charge. For a certain parameter range the quantum shuttle exhibits a coexistence regime, where the charges are transported by two different mechanisms: shuttling and sequential tunneling. In our previous studies we showed that characteristic features in the zero-frequency noise could be quantitatively understood as a slow switching process between the two current channels, and the present study shows that this interpretation holds also qualitatively at finite frequency.

cond-mat.mes-hall↗

arXiv2004

Modeling of quantum electromechanical systems

We discuss methods for numerically solving the generalized Master equation GME which governs the time-evolution of the reduced density matrix of a mechanically movable mesoscopic device in a dissipative environment. As a specific example, we consider the quantum shuttle -- a generic quantum nanoelectromechanical system (NEMS). When expressed in the oscillator basis, the static limit of the GME becomes a large linear non-sparse matrix problem (characteristic size larger than 10^4 by 10^4) which however, as we show, can be treated using the Arnoldi iteration scheme. The numerical results are interpreted with the help of Wigner functions, and we compute the current and the noise in a few representative cases.

cond-mat.mes-hall↗

arXiv2004

Shot Noise of a Quantum Shuttle

We formulate a theory for shot noise in quantum nanoelectromechanical systems. As a specific example, the theory is applied to a quantum shuttle, and the zero-frequency noise, measured by the Fano factor F, is computed. F reaches very low values (F~0.01) in the shuttling regime even in the quantum limit, confirming that shuttling is universally a low noise phenomenon. In approaching the semiclassical limit, the Fano factor shows a giant enhancement (F~100) at the shuttling threshold, consistent with predictions based on phase-space representations of the density matrix.

cond-mat.mes-hall↗

arXiv2004

Current noise in a vibrating quantum dot array

We develop methods for calculating the zero-frequency noise for quantum shuttles, i.e. nanoelectromechanical devices where the mechanical motion is quantized. As a model system we consider a three-dot array, where the internal electronic coherence both complicates and enriches the physics. Two different formulations are presented: (i) quantum regression theorem, and (ii) the counting variable approach. It is demonstrated, both analytically and numerically, that the two formulations yield identical results, when the conditions of their respective applicability are fulfilled. We describe the results of extensive numerical calculations for current and current noise (Fano factor), based on a solution of a Markovian generalized master equation. The results for the current and noise are further analyzed in terms of Wigner functions, which help to distinguish different transport regimes (in particular, shuttling vs. cotunneling). In the case of weak inter-dot coupling, the electron transport proceeds via sequential tunneling between neighboring dots. A simple rate equation with the rates calculated analytically from the P(E)-theory is developed and shown to agree with the full numerics.

cond-mat.mes-hall↗