[Show abstract][Hide abstract] ABSTRACT: Tunneling in a quantum coherent structure is not restricted to only nearest neighbors. Hopping between distant sites is possible via the virtual occupation of otherwise avoided intermediate states. Here we report the observation of long-range transitions in the transport through three quantum dots coupled in series. A single electron is delocalized between the left and right quantum dots, while the center one remains always empty. Superpositions are formed, and both charge and spin are exchanged between the outermost dots. The delocalized electron acts as a quantum bus transferring the spin state from one end to the other. Spin selection is enabled by spin correlations. The process is detected via the observation of narrow resonances which are insensitive to Pauli spin blockade.
[Show abstract][Hide abstract] ABSTRACT: Tunneling in a quantum coherent structure is not restricted to only nearest
neighbours. Hopping between distant sites is possible via the virtual
occupation of otherwise avoided intermediate states. Here we report the
observation of long range transitions in the transport through three quantum
dots coupled in series. A single electron is delocalized between the left and
right quantum dots while the centre one remains always empty. Superpositions
are formed and both charge and spin are exchanged between the outermost dots.
Detection of the process is achieved via the observation of narrow resonances,
insensitive to the transport Pauli spin blockade.
[Show abstract][Hide abstract] ABSTRACT: Spin qubits based on interacting spins in double quantum dots have been demonstrated successfully. Readout of the qubit state involves a conversion of spin to charge information, which is universally achieved by taking advantage of a spin blockade phenomenon resulting from Pauli's exclusion principle. The archetypal spin blockade transport signature in double quantum dots takes the form of a rectified current. At present, more complex spin qubit circuits including triple quantum dots are being developed. Here we show, both experimentally and theoretically, that in a linear triple quantum dot circuit the spin blockade becomes bipolar with current strongly suppressed in both bias directions and also that a new quantum coherent mechanism becomes relevant. In this mechanism, charge is transferred non-intuitively via coherent states from one end of the linear triple dot circuit to the other, without involving the centre site. Our results have implications for future complex nanospintronic circuits.
[Show abstract][Hide abstract] ABSTRACT: We analyze theoretically the effect of dynamical nuclear spin polarization on the electronic transport through a double quantum dot in the spin blockade (SB) regime in the presence of hyperfine interaction. The electron and nuclei hyperfine interaction produces electron spin flip which partially removes SB. Induced nuclei spin polarization produces a finite magnetic field which acts on the electrons generating an additional Zeeman splitting of the electronic spin up and down levels in each quantum dot. This additional Zeeman splitting changes dynamically with the electronic level occupation. Then, strong feedback between the induced nuclear polarization within each quantum dot and the electronic charge distribution occurs and it produces strong non-linearities in the current as a function of both, external magnetic field and dc voltage. We analyze as well electron spin resonance in a double quantum dot driven by crossed dc and ac magnetic fields. The time dependent magnetic field produces coherent electron spin rotations within each quantum dot. In this configuration, spatial Rabi oscillations due to inter-dot tunnel compete with Rabi oscillations between spin up and down states induced by the time dependent magnetic field, giving rise to a complicated time dependent behavior of the tunneling current.
Physica E Low-dimensional Systems and Nanostructures 01/2010; 42(3):643-648. · 1.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Electronic transport in a triple quantum dot shuttle device in the presence of an ac field is analyzed within a fully quantum mechanical framework. A generalized density matrix formalism is used to describe the time evolution for electronic state occupations in a dissipative phonon bath. In the presence of an ac gate voltage, the electronic states are dressed by photons and the interplay between photon and vibrational sidebands produces current characteristics that obey selection rules. Varying the ac parameters allows to tune the tunneling current features. In particular, we show that coherent destruction of tunneling can be achieved in our device.
[Show abstract][Hide abstract] ABSTRACT: Within the framework of a fully quantum mechanical approach we use the density matrix master equation formalism to study the electronic transport in a triple dot quantum shuttle in the presence of an ac-field. We show that the ac-field induces photo-assisted tunneling which manifests itself as sidebands in the electronic current. We also show that these new tunneling sidebands can be explained in terms of simple sum rules involving the number of absorbed and emitted photons and the oscillator states participating in the process. Finally, we demonstrate that the tunneling channels can be controlled by manipulating the frequency and intensity of the ac-field, giving rise in particular to coherent destruction of tunneling (CDT).