Juan E. Rolon

Coherent control of indirect excitonic qubits in optically driven quantum dot molecules

Department of Physics and Astronomy and Nanoscale and QuantumPhenomena Institute, Ohio University, Athens, Ohio 45701-2979(Dated: July 7, 2010)We propose an optoelectronic scheme to de ne and manipulate an indirect neutral exciton qubitwithin a quantum dot molecule. We demonstrate coherent dynamics of indirect excitons resilientagainst decoherence e ects, including direct exciton spontaneous recombination. For molecules withlarge interdot separation, the exciton dressed spectrum yields an often overlooked avoided crossingbetween spatially indirect exciton states. E ective two level system Hamiltonians are extracted byFeshbach projection over the multilevel exciton con gurations. An adiabatic manipulation of thequbit states is devised using time dependent electric eld sweeps. The exciton dynamics yields thenecessary conditions for qubit initialization and near unitary rotations in the picosecond time scale,driven by the system internal dynamics. Despite the strong inuence of laser excitation, chargetunneling, and interdot dipole-dipole interactions, the e ective relaxation time of indirect excitonsis much longer than the direct exciton spontaneous recombination time, rendering indirect excitonsas potential elemental qubits in more complex schemes.

Förster energy-transfer signatures in optically driven quantum dot molecules

eld dependent opti- cal spectrum of realistic QDMs. In Sec. II the model for the QDM is introduced. An excitonic population map, as function of applied bias and pump laser energy is constructed, resembling the dressed LACS spectra of the QDM. Our main results are presented for two dif- ferent cases. In Sec. III we consider the LACS for a QDM dressed spectrum involving Forster coupling of di- rect single excitons. We show how the coupling is man- ifested in the variation of the amplitude (brightness) of a FRET split satellite as a function of the applied elec- tric

Spin-orbit signatures in the dynamics of singlet-triplet qubits in double quantum dots

We characterize numerically and analytically the signatures of the spin-orbit interaction in a two-electron GaAs double quantum dot in the presence of an external magnetic field. In particular, we obtain the return probability of the singlet state by simulating Landau-Zener voltage detuning sweeps which traverse the singlet-triplet (

Oscillatory acoustic phonon relaxation of excitons in quantum dot molecules

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Förster signatures and qubits in optically driven quantum dot molecules

) resonance. Our results indicate that non-spin-conserving interdot tunneling processes arising from the spin-orbit interaction have well defined signatures. These allow direct access to the spin-orbit interaction scales and are characterized by a frequency shift and Fourier amplitude modulation of the Rabi flopping dynamics of the singlet-triplet qubits

Tunable exciton relaxation in vertically coupled semiconductor InAs quantum dots

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Coherent control of multipartite excitonic entanglement in quantum dot arrays

and

Spin-orbit effects on the full dynamics of double quantum dot qubit states

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Control of exciton relaxation channels in quantum dot molecules

. By applying the Bloch-Feshbach projection formalism, we demonstrate analytically that the aforementioned effects originate from the interplay between spin-orbit interaction and processes driven by the hyperfine interaction between the electron spins and those of the GaAs nuclei.

Charge dynamics and phonon induced oscillatory relaxation rates of indirect excitons in quantum dot molecules

We study electrically tunable self-assembled InAs quantum dot molecules through photoluminescence (PL) and time-resolved PL measurements. For the model we assume quantum dots with cylindrical symmetry, for which the confinement potentials have been modeled as narrow quantum wells in the growth and in-plane directions matched to parabolic potentials. We focus on the hole scattering rates by bulk acoustic phonons, as these rates are the leading contribution for the neutral indirect exciton relaxation rate when the electron localizes primarily on one dot. The hole–phonon scattering structure factor for acoustic phonons is found to contain a phase relationship between the phonon wave and the hole wave function, which can be tuned by an external electric field. The phase relationship leads to interference effects and tunable oscillatory relaxation rates of indirect excitons, in agreement with experiments.