Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 44: Semiconductor Microcavities and Entangled States in Quantum Dots

HL 44.8: Invited Talk

Thursday, March 29, 2007, 17:45–18:15, H15

Coupled Quantum Dots for Quantum Information — •Tom Reinecke — Naval Research Laboratory, Washington, DC USA

Spins in quantum dots (QDs) are attractive candidates for quantum bits (qubits) for quantum information technologies. A key need is for coherent coupling between qubits that can be manipulated in two-qubit gates needed for quantum logic. Recent advances in the understanding of two different physical systems for this purpose made in joint work involving fabrication, experiment and theory will be discussed.

Vertically coupled InAs quantum dots are formed by Stanski-Krastanov MBE growth on adjacent GaAs layers. We have shown that the quantum tunnel coupling between QDs can be manipulated by an external electric field [1,2]. Electron states, hole states or excitons can be brought into and out of resonance with fields and appropriate sample design [3]. Exchange interactions between spins in coupled QDs have been elucidated, including a novel ’kinetic exchange’ interaction [4]. A novel mechanism to turn on interactions between spins optically has been found. Strongly tunable biexciton-exciton cascades of interest in quantum optics have been demonstrated [5]. An electric field dependent g-factor for spin splitting has been found, which provides opportunities for single qubit and two qubit operations with fast electric fields [6].

Coherent (’strong’) interactions between QD excitons and cavity photon modes have long been sought as a basis for fast optical coupling between distant QDs and for distributed quantum computing. We have demonstrated this strong coupling with high finesse pillar microcavities and large dipole moment In_.30Ga_.70As/GaAs QDs [7]. Recently we have also found strong coupling between two quantum dots within the linewidth of a single cavity mode [8].

[1] G. Ortner, M. Bayer, Y. B. Lyanda-Geller T. L. Reinecke and A. Forchel, Phys. Rev. Lett. 94, 157401 (2005).

[2] E.A. Stinaff, M. Scheibner, A.S. Bracker, I. Ponomarev, V.L. Korenev, M.E. Ware, M.F. Doty, T.L. Reinecke and D. Gammon , Science 311, 627 (2005).

[3] A. S. Bracker, M. Sheibner, M. F. Doty, E. A. Stinaff, I. V. Ponomarev, J. C. Kim, L. J. Whitman, T. L. Reinecke and D. Gammon, Appl. Phys. Lett. 89, 233110 92006)

[4] M. Scheibner, M. F. Doty, I. V. Ponomarev, A. S. Bracker, E. A. Stinaff, V. L. Korenev, T. L. Reinecke and D. Gammon, condmat 0607241

[5] M. Scheibner, M.F. Doty, I.V. Ponomarev, A.S. Bracker, E.A. Stinaff, T.L. Reinecke, C. S. Hellberg, D. Gammon (to be published)

[6] M. F. Doty, M. Scheibner, I. V. Ponomarev, E. A. Stinaff, A. S. Bracker, V. L. Korenev, T. L. Reinecke and D. Gammon, Phys. Rev. Lett. 97, 197202 (2006)

[7] J.-P. Reithmaier, G. S*k, A. Löffler, C. Hofmann, S. Kuhn , S. Reitzenstein, L. Keldysh, V.Kulakovskii, T.L. Reinecke, and A. Forchel, Nature 432, 197 (2004).

[8] S. Reitzenstein, A. Löffler, C.Hofmann, J.-P. Reithmaier, M. Kamp, , V.D. Kulakovskii, L.V. Keldysh , T. L. Reinecke and A. Forchel, Optics Letters 31, 1738 (2006)