Adiabatic transfer of electrons in coupled quantum dots

Brandes, Tobias; Vorrath, T.

doi:10.1103/physrevb.66.075341

Cited by 104 publications

(140 citation statements)

References 51 publications

(106 reference statements)

Supporting

Mentioning

137

Contrasting

Order By: Relevance

“…By assuming Ohmic spectral density for simplicity, the spin-boson model predicts the decoherence rate Γ sb = π 4 g∆ coth(∆/2k B T lat ) for ε = 0, where g = 0.03 is the dimensionless coupling constant that was chosen to fit with the temperature dependence data [see dashed line in Fig. 3(c)] [13,14]. This g is a reasonable value to explain the inelastic current [13], and thus phonon emission seems to be significant in our system.…”

Section: (B)]mentioning

confidence: 99%

Coherent Manipulation of Electronic States in a Double Quantum Dot

et al. 2003

View full text Add to dashboard Cite

We investigate coherent time-evolution of charge states (pseudo-spin qubit) in a semiconductor double quantum dot. This fully-tunable qubit is manipulated with a high-speed voltage pulse that controls the energy and decoherence of the system. Coherent oscillations of the qubit are observed for several combinations of many-body ground and excited states of the quantum dots. Possible decoherence mechanisms in the present device are also discussed.Initiated by various experiments on atomic systems, studies on coherent dynamics have been extended to small-scale quantum computers [1]. Nano-fabrication technology now allows us to design artificial atoms (quantum dots) and molecules (coupled quantum dots), in which atomic (molecular)-like electronic states can be controlled with external voltages [2,3,4]. Coherent manipulation of the electronic system in quantum dots and a clear understanding of decoherence in practical structures are crucial for future applications of quantum nanostructures to quantum information technology.In this Letter, we describe the coherent manipulation of charge states, in which an excess electron occupies the left dot or the right dot of a double quantum dot (DQD). The coherent oscillations between the two charge states are produced by applying a rectangular voltage pulse to an electrode. Although this scheme is analogous to experiments on a superconducting island [5], our qubit is effectively isolated from the electrodes during the manipulation, while it is influenced by strong decoherence during the initialization due to the coupling with the electrodes. This controlled decoherence provides an efficient initialization scheme.We consider a DQD consisting of left and right dots connected through an interdot tunneling barrier. The left (right) dot is weakly coupled to the source (drain) electrode via a tunneling barrier [see Fig. 1(a)]. The conductance through the device is strongly influenced by the onsite and interdot Coulomb interactions [6]. In the weakcoupling regime at a small source-drain voltage, V sd , a finite current is only observed at the triple points, where tunneling processes through the three tunneling barriers are allowed. Under an appropriate condition where only the interdot tunneling is allowed, Coulomb interactions effectively isolate the DQD from the source and drain electrodes. In this case, we can consider two charge states, in which an excess electron occupies the left dot (|L ) or the right dot (|R ) with electrochemical potentials E L and E R , respectively. In practice, each charge state involves (many-body) ground and excited states. When the two specific states are energetically close to each other and the excitation to other states can be neglected, the system can be approximated as a two-level system (qubit). It is characterized by the energy offset, ε ≡ E R − E L , and the interdot tunneling, which gives an anti-crossing energy, ∆ [3]. The effective Hamiltonian iswhere σ x and σ z are the Pauli matrices for pseudo-spin bases of |L and |R . When E L and E R of ...

show abstract

Section: (B)]mentioning

confidence: 99%

Coherent Manipulation of Electronic States in a Double Quantum Dot

et al. 2003

View full text Add to dashboard Cite

show abstract

“…In some examples given later-on, we will phenomenologically parameterize [31,32] the density of states as…”

Section: Bath Correlation Functionsmentioning

confidence: 99%

Preservation of positivity by dynamical coarse graining

2008

View full text Add to dashboard Cite

We compare different quantum Master equations for the time evolution of the reduced density matrix. The widely applied secular approximation (rotating wave approximation) applied in combination with the Born-Markov approximation generates a Lindblad type master equation ensuring for completely positive and stable evolution and is typically well applicable for optical baths. For phonon baths however, the secular approximation is expected to be invalid. The usual Markovian master equation does not generally preserve positivity of the density matrix. As a solution we propose a coarse-graining approach with a dynamically adapted coarse graining time scale. For some simple examples we demonstrate that this preserves the accuracy of the integro-differential Born equation. For large times we analytically show that the secular approximation master equation is recovered. The method can in principle be extended to systems with a dynamically changing system Hamiltonian, which is of special interest for adiabatic quantum computation. We give some numerical examples for the spin-boson model of cases where a spin system thermalizes rapidly, and other examples where thermalization is not reached.

show abstract

“…The time-dependent spin-boson problem is in general characterised by the fact that both ε(t) and T c (t) are timedependent. One can then investigate interesting effects such as adiabatic charge pumping, dissipative LandauZener tunneling 78 , or for the closed system (no coupling to the leads) the control of quantum superpositions 79 . Although this general time-dependence offers the richest spectrum of possible physical phenomena, one is clearly strongly restricted by the fact that nearly no analytical solutions are available.…”

Section: A Model Hamiltonianmentioning

confidence: 99%

Charge transport through open driven two-level systems with dissipation

2004

View full text Add to dashboard Cite

We derive a Floquet-like formalism to calculate the stationary average current through an AC driven double quantum dot in presence of dissipation. The method allows us to take into account arbitrary coupling strengths both of a time-dependent field and a bosonic environment. We numerical evaluate a truncation scheme and compare with analytical, perturbative results such as the Tien-Gordon formula.

show abstract

Adiabatic transfer of electrons in coupled quantum dots

Cited by 104 publications

References 51 publications

Coherent Manipulation of Electronic States in a Double Quantum Dot

Coherent Manipulation of Electronic States in a Double Quantum Dot

Preservation of positivity by dynamical coarse graining

Charge transport through open driven two-level systems with dissipation

Contact Info

Product

Resources

About