Project C6

Coherent Control of Electron and Hole Spin Qubits in Quantum Dots and Molecules Using Microwave Fields

PIs: Prof. Dr. J. Finley, Prof. Dr. M. Brandt

The spin of isolated charge carriers (electrons and holes) trapped in semiconductor quantum dots is one of the most attractive systems for solid-state quantum information processing due to the complete motional quantization that strongly suppresses spin relaxation and decoherence processes and, furthermore, since such nanostructures can be electrically manipulated and optically addressed. This project aims to develop electro-optical methods to initialize, control and readout the spin of localized charge carriers in electrically tunable quantum dots and molecules. Previously we have developed techniques to selectively generate electrons and holes in quantum dots by optical excitation of spin orientated excitons and partial ionization, removing either the electron or hole to leave a prepared spin state in the system (figure left panel). We are currently focussing on extending these methods to coherently manipulate the spin state using microwave fields and readout the spin state of the system with high fidelity. The overall goal of the project is to realise a well defined two-qubit system that is optically addressable, electrically tunable and, moreover, can be scaled.

The primary objectives of project C6 are to:

  • Develop and implement sensitive optical and electrical spin readout techniques.

  • Understand the dominant spin relaxation and decoherence mechanisms for electrons and holes in self-assembled quantum dot nanostructures and develop strategies to avoid them

  • Achieve coherent single spin rotations for optically generated electrons using magnetic dipole transitions and holes using electric dipole transitions.

  • Study and utilize interactions between confined electronic and nuclear spin systems.

  • Coherently control of a two electron spin qubit system and integrate with single spin rotations.

C6-fig1

Schematic representation of the optical spin preparation and readout technique.

C6-fig2

long spin lifetimes for electrons and holes in self-assembled quantum dots.

References:

  1. M. Kroutvar, Y. Ducommun, D. Heiss, D. Schuh, M. Bichler, G. Abstreiter and J. J. Finley, Nature 432, 81 (2004)

  2. M. S. Brandt, S. T. B. Goennenwein, T. Graf, H. Huebl, S. Lauterbach and M. Stutzmann, phys. stat. sol. (c) 1, 2056 (2004).

  3. D. Heiss, S. Schaeck, H. Huebl, M. Bichler, G. Abstreiter, J. J. Finley, D. V. Bulaev, and Daniel Loss. Phys. Rev. B 76, 241306 (2007)