Bartlomiej Szafran AGH University of Science and Technology, Kraków(Poland)Driven spin transitions in quantum dots at the interface between SrTiO3and LaAlO3Abstract:The talk focuses on the results of the tight-binding modeling of single-and two-electron statesin a quantum dot and a double quantum dot and on the simulations of the spin transitionsdriven by periodic electric field. The symmetry of the states in the context of harmonic andsubharmonic transitions is discussed. The talk reports on the optimization of the drivensinglet-triplet transitionsby the asymmetry of the double quantum dot. Rabi vs Landau-Zenertransition regimes are discussed.
Bartlomiej Szafran AGH University of Science and Technology, Kraków(Poland)Driven spin transitions in quantum dots at the interface between SrTiO3and LaAlO3Abstract:The talk focuses on the results of the tight-binding modeling of single-and two-electron statesin a quantum dot and a double quantum dot and on the simulations of the spin transitionsdriven by periodic electric field. The symmetry of the states in the context of harmonic andsubharmonic transitions is discussed. The talk reports on the optimization of the drivensinglet-triplet transitionsby the asymmetry of the double quantum dot. Rabi vs Landau-Zenertransition regimes are discussed.
The spin dynamics in two electron double quantum dots embedded in a two-dimensional electron gas at the interface between SrTiO3 and LaAlO3 is studied by an exact numerical solution of the time-dependent Schr\"odinger equation in the context of the electric-dipole-spin-resonance experiment. On the basis of the three-band model of 3d electrons localized at Ti ions on the square lattice, we analyze in detail the singlet-triplet transition induced by the ac electric field, in the magnetic field range close to the avoided crossing that appears as a result of the spin-orbit coupling. For symmetric double quantum dots the single-photon spin-flip transition is prohibited due to the parity symmetry, and the transition can occur only by the higher-order two-photon processes. For a weakly asymmetric system, when the first-order singlet-triplet transitions are released due to the parity symmetry breaking, the spin-flip transition has a character of the Rabi oscillations for a low electric field amplitude. As the amplitude is increased, the frequency of the transition is blueshifted (redshifted) for the magnetic field below (above) the single-triplet avoided crossing. For a sufficiently high magnetic field and high ac-field amplitude, the electric field drives the system across the avoided crossing, inducing the spin flip by the Landau-Zener-Stueckelberg-Majorana effect. Finally, the optimization of the geometrical parameters of the system with respect to the time of spin flip of its fidelity is also presented.
Electrical spin manipulation in double SrTiO3/LaAlO3 quantum dots
The spin dynamics in two electron double quantum dots embedded in two dimensional electron gas at the interface between SrTiO3 and LaAlO3 is studied by an exact numerical solution of the time-dependent Schrödinger equation, in the context of the electric dipole spin resonance experiment. Based on the three band model of 3d-electrons localized at Ti ions on the square lattice we analyze in details the singlet-triplet transition induced by the AC electric field, in the magnetic field range close to the avoided crossing which appears as a result of the spin-orbit coupling. Our calculations show that for symmetric double quantum dots the single photon spin-flip transitions is prohibited due to the parity symmetry and the transition can occur only by the higher order two-photon processes. For a weakly asymmetric system, when the first order singlet-triplet transitions are released due to the parity symmetry breaking, the spin-flip transition has a character of the Rabi oscillations for a low electric field amplitude. As the amplitude is increased the frequency of the transition is blueshifted (redshifted) for the magnetic field below (above) the single-triplet avoided crossing. Interestingly, for a sufficiently high magnetic field and high AC field amplitude the electric field drives the system across the avoided crossing inducing the spin-flip by the Landau-Zener-Stueckelberg-Majorana transitions with 100\% spin flip probability for a slow sweep. Finally, the optimization of the geometrical parameters of the system with respect to the time of spin-flip of its fidelity is also presented.
Progress in the fabrication of nanoscale transition-metal-oxide heterostructures makes these platforms promising candidates for the realization of spin qubits, mainly due to the d-character of their electronic structures, which could potentially result in a reduction of hyperfine interactions and spin decoherence. Here, we present a systematic study of spin control within the SWAP operation in double quantum dots embedded in a two-dimensional electron gas at the LaAlO3/SrTiO3 interface. Our analysis starts with a study of single-electron spin dynamics, focusing on the influence of spin-orbit and interorbital coupling on the spin evolution. In this case, our findings are supported by semiclassical calculations based on the Bloch equations, which show good agreement with full quantum mechanical simulations. We then simulate the SWAP operation by analyzing the crossover between two regimes: (i) large quantum dots, where the electronic structure is dominated by the dxy orbitals and the spin dynamics is affected primarily by Rashba-type spin-orbit interaction; and (ii) small quantum dots, where higher-energy orbitals dxz/yz contribute to the electronic structure, leading to a significant reduction in the SWAP fidelity. In the first regime, particularly relevant from the application point of view, we analyze in detail the anisotropy of the SWAP operation induced by the spin-orbit coupling.
We investigate the energy spectrum of a single- and two-electron quantum dot (QD) embedded in two-dimensional electron gas at the interface between SrTiO3 and LaAlO3, in the presence of the external magnetic field. For this purpose, the three-band model of 3d electrons defined on the square lattice of Ti ions was utilized. We demonstrate that, for the weak parabolic confinement potential, the low-energy spectrum is sufficiently well described by the effective Hamiltonian reduced to the one dxy orbital with the spin-orbit interaction originating from the coupling to the dxz and dyz bands. This is not the case for stronger confinement where contribution of the states related to the dxz/yz orbital is relevant. Based on the time-dependent calculations, we discuss in detail the manipulation of the electron spin in a QD by external AC voltages, in the context of the electric dipole spin resonance. The allowed and forbidden transitions are discussed in detail with respect to the parity selection rule. Our calculations show that, for a single-electron QD, the spin flip in the ground state has the character of a Rabi resonance, while for two electrons, the singlet-triplet transition is forbidden by the parity symmetry. For the two-electron QD, we demonstrate that the spin-flip transition can still be accomplished via a second-order, two-photon process that has a two-state Rabi character for low AC field amplitude. The violation of the parity symmetry on the spin-flip transitions is also analyzed.
We consider a double dot system of equivalent, capacitively coupled semiconducting quantum dots, each coupled to its own lead, in a regime where there are two electrons on the double dot. Employing the numerical renormalization group, we focus here on single-particle dynamics and the zero-bias conductance, considering in particular the rich range of behaviour arising as the interdot coupling is progressively increased through the strong coupling (SC) phase, from the spin-Kondo regime, across the SU(4) point to the charge-Kondo regime; and then towards and through the quantum phase transition to a charge-ordered (CO) phase. We first consider the two-self-energy description required to describe the broken symmetry CO phase, and implications thereof for the non-Fermi liquid nature of this phase. Numerical results for single-particle dynamics on all frequency scales are then considered, with particular emphasis on universality and scaling of low-energy dynamics throughout the SC phase. The role of symmetry breaking perturbations is also briefly discussed.
Abstract. We consider a double dot system of equivalent, capacitively coupled semiconducting quantum dots, each coupled to its own lead, in a regime where there are two electrons on the double dot. Employing the numerical renormalization group, we focus here on single-particle dynamics and the zerobias conductance, considering in particular the rich range of behaviour arising as the interdot coupling is progressively increased through the strong coupling (SC) phase, from the spin-Kondo regime, across the SU(4) point to the charge-Kondo regime; and then towards and through the quantum phase transition to a charge-ordered (CO) phase. We first consider the two-self-energy description required to describe the broken symmetry CO phase, and implications thereof for the non-Fermi liquid nature of this phase. Numerical results for single-particle dynamics on all frequency scales are then considered, with particular emphasis on universality and scaling of low-energy dynamics throughout the SC phase. The role of symmetry breaking perturbations is also briefly discussed.