Condensed Matter Physics Seminar

Wednesday, September 15, 1999, 4 p.m.
Physics Building, Room 1219

Quantum Computing and Quantum Communication with Electrons in Quantum Dots

Daniel Loss

(Department of Physics, University of Basel, Switzerland)

Abstract:  I review our proposed quantum dot architecture for a quantum computer, which is based on electron spins in coupled semiconductor quantum dots[1-3]. The fundamental XOR quantum gate is operated by dynamically coupling the spins of neighboring dots. We have determined the exchange coupling in the effective Heisenberg model as a function of magnetic and electric fields within the Heitler-London and Hund-Mulliken approximation. The influence of nuclear spins on the dephasing of the electron spin in the quantum dot will be discussed[2]. Addressing the feasibilty of quantum communication with entangled electrons[3] we consider electronic EPR pairs and show that the entanglement of two electrons in a double-dot can be detected in mesoscopic transport and noise measurements[4,5]. In the Coulomb blockade and cotunneling regime of a double-dot (attached to leads) the singlet and triplet states of the double-dot lead to phase-coherent current and noise contributions of opposite signs and to Aharonov-Bohm and Berry phase oscillations in response to magnetic fields[5]. These oscillations are a genuine two-particle Aharonov-Bohm effect and provide a direct measure of non-locality in entangled states. The ratio of zero-frequency noise to current (Fano factor) is universal and equal to the electron charge.

[1] D. Loss and D.P. DiVincenzo, Phys. Rev. A  57 (1998) 120; cond-mat/9701055.
[2] G. Burkard, D. Loss, and D.P. DiVincenzo, Phys. Rev. B 59 (1999) 2070; condmat/9808026.
[3] D.P. DiVincenzo and D. Loss, cond-mat/99011137.
[4] G. Burkard, D. Loss, and E. Sukhorukov, cond-mat/9906071.
[5] D. Loss and E. Sukhorukov, cond-mat/9907129..

Host: Xuedong Hu

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