Anna Grodecka

Partly noiseless encoding of quantum information in quantum dot arrays against phonon-induced pure dephasing

We show that pure dephasing of a quantum dot charge (excitonic) qubit may be reduced for sufficiently slow gating by collectively encoding quantum information in an array of quantum dots. We study the role of the size and structure of the array and of the exciton lifetime for the resulting total error of a single-qubit operation.

Phonon-induced decoherence for a quantum-dot spin qubit operated by Raman passage

We study single-qubit gates performed via stimulated Raman adiabatic passage (STIRAP) on a spin qubit implemented in a quantum dot system in the presence of phonons. We analyze the interplay of various kinds of errors resulting from the carrier-phonon interaction as well as from quantum jumps related to nonadiabaticity and calculate the fidelity as a function of the pulse parameters. We give quantitative estimates for an InAs/GaAs system and identify the parameter values for which the error is considerably minimized, even to values below

Phonon-assisted tunneling between singlet states in two-electron quantum dot molecules

10^{-4}

Indirect spin dephasing via charge-state decoherence in optical control schemes in quantum dots

per operation.

Phonon-induced dephasing of optical spin control in single-charged quantum dots

We study phonon-assisted electron tunneling in semiconductor quantum dot molecules. In particular, singletsinglet relaxation in a two-electron-doped structure is considered. The influence of Coulomb interaction is discussed via comparison with a single-electron system. We find that the relaxation rate reaches similar values in the two cases but the Coulomb interaction shifts the maximum rates toward larger separations between the dots. The difference in electron-phonon interaction between deformation potential and piezoelectric coupling is investigated. We show that the phonon-induced tunneling between two-electron singlet states is a fast process, taking place on the time scales of the order of a few tens of picoseconds.

Reducing pure dephasing of quantum bits by collective encoding in quantum dot arrays

We demonstrate that an optically driven spin of a carrier in a quantum dot undergoes indirect dephasing via conditional optically induced charge evolution even in the absence of any direct interaction between the spin and its environment. A generic model for the indirect dephasing with a three-component system with spin, charge, and reservoir is proposed. This indirect decoherence channel is studied for the optical spin manipulation in a quantum dot with a microscopic description of the charge-phonon interaction taking into account its non-Markovian nature.

Phonon impact on the coherent control of quantum states in semiconductor quantum dots

Within a density-matrix approach, we study the phonon-induced decoherence effects on the nonlinear dynamics and pump-probe spectra for the optical control of a spin in a single-charged quantum dot proposed recently.

Optical control and decoherence of spin qubits in quantum dots

We show that phonon-induced pure dephasing of an excitonic (charge) quantum bit in a quantum dot (QD) may be reduced by collective encoding of logical qubits in QD arrays. We define the logical qubit on an array of 2, 4 and 8 QDs, connecting the logical |0 state with the presence of excitons in the appropriately chosen half of dots and the logical |1 state with the other half of the dots occupied. We give quantitative estimates of the resulting total error of a single qubit operation for an InAs/GaAs system.