0000000000013904
AUTHOR
Paweł Machnikowski
showing 8 related works from this author
Spin-Based Quantum Information Processing in Magnetic Quantum Dots
2005
We define the qubit as a pair of singlet and triplet states of two electrons in a He-type quantum dot (QD) placed in a diluted magnetic semiconductor (DMS) medium. The molecular field is here essential as it removes the degeneracy of the triplet state and strongly enhances the Zeeman splitting. Methods of qubit rotation as well as two-qubit operations are suggested. The system of a QD in a DMS is described in a way which allows an analysis of the decoherence due to spin waves in the DMS subsystem.
Anharmonicity-induced polaron relaxation in GaAs/InAs quantum dots
2002
The anharmonicity-induced relaxation of a polaron in a quantum dot is analyzed using the Davydov diagonalization method, including the coherent renormalization of the relevant third-order phonon interaction. The resulting relaxation time for a small GaAs/InAs self-assembled quantum dot turns out to be a few times longer than that found previously by a perturbative method.
Fast Control of Quantum States in Quantum Dots: Limits due to Decoherence
2005
We study the kinetics of confined carrier-phonon system in a quantum dot under fast optical driving and discuss the resulting limitations to fast coherent control over the quantum state in such systems.
Decoherence of the Exciton and Decay of the Excitonic Polaron in Quantum Dots
2005
Bulk-phonon mechanisms of decoherence of an exciton confined in a quantum dot (QD) are considered in order to establish time limitations for the coherent control of the exciton with relevance to its application in quantum information processing. These are the formation and decay of the excitonic polaron. The estimations of characteristic dephasing times for the InAs/GaAs QD are discussed.
Coherent and incoherent phonon processes in artificial atoms
2003
Carrier-phonon interaction in semiconductor quantum dots leads to three classes of phenomena: coherent effects (spectrum reconstruction) due to the nearly-dispersionless LO phonons, incoherent effects (transitions) induced by acoustical phonons and dressing phenomena, related to non-adiabatic, sub-picosecond excitation. Polaron spectra, relaxation times and dressing-related decoherence rates are calculated, in accordance with experiment.
Magnetopolaron in a weakly elliptical InAs/GaAs quantum dot
2003
We study theoretically the properties of a polaron formed in a shallow, weakly elliptical, disk-shaped InAs/GaAs quantum dot in the presence of a magnetic field by using the Davydov's canonical transformation. Special attention is paid to the energy-level splitting due to the Frohlich interaction of an electron in a quantum dot with optical phonons near resonance. The polaron relaxation rates, including the anharmonicity induced channel, are analyzed for various confinement energies and magnetic field magnitudes, taking into account coherent polaronic effects.
Relaxation and decoherence of orbital and spin degrees of freedom in quantum dots
2002
The phonon induced mechanisms of relaxation/decoherence in quantum dots are analysed. A non-perturbative technique - a modification of the Davydov transformation appropriate to the localised particles is applied for solving the electron-phonon eigenvalue problem in a quantum dot at magnetic field presence. The decay rates for polaron relaxation via the anharmonicity induced channel are analysed in details. In particular, it is indicated that previous, of perturbative type, estimations of the anharminicity induced relaxation rates were too severe and after including the coherence effects they are of, at least, one order longer. The process of exciton dressing with phonons is also analysed as…
Unavoidable decoherence in semiconductor quantum dots
2005
Phonon-induced unavoidable decoherence of orbital degrees of freedom in quantum dots is studied and the relevant time scales are estimated. Dephasing of excitons due to acoustic phonons and, in a polar medium, to optical phonons, including anharmonic effects and enhancement of the effective Fr\"ohlich constant due to localization, is assessed for typical self-assembled quantum dots. Temporal inefficiency of Pauli blocking due to lattice inertia is predicted. For quantum dots placed in a diluted magnetic semiconductor medium a magnon-induced dephasing of a spin is also estimated in accordance with experimental results.