Condensed Matter Physics Seminar
Wednesday, September 15, 1999, 4 p.m.
Physics Building, Room 1219
Quantum Computing and Quantum Communication with Electrons in Quantum
(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. Addressing the feasibilty of quantum
communication with entangled electrons 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. 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.
 D. Loss and D.P. DiVincenzo, Phys. Rev. A 57 (1998) 120; cond-mat/9701055.
 G. Burkard, D. Loss, and D.P. DiVincenzo, Phys. Rev. B 59 (1999)
 D.P. DiVincenzo and D. Loss, cond-mat/99011137.
 G. Burkard, D. Loss, and E. Sukhorukov, cond-mat/9906071.
 D. Loss and E. Sukhorukov, cond-mat/9907129..
Host: Xuedong Hu
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