Condensed Matter Theory - Massoud Borhani

Address:	Office 4.6 Department of Physics and Astronomy University of Basel Klingelbergstrasse 82 CH-4056 Basel, Switzerland
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Vitaly N. Golovach, Massoud Borhani, Daniel Loss
Phys. Rev. B 74, 165319 (2006) (cond-mat/0601674 )

An alternating electric field, applied to a ``spin 1/2'' quantum dot, couples to the electron spin via the spin-orbit interaction. We analyze different types of spin-orbit couplings known in the literature and find that an electric dipole spin resonance (EDSR) scheme for spin manipulation can be realized with the up-to-date experimental setups. In particular, for the Rashba and Dresselhaus spin-orbit couplings, a fully transverse effective magnetic field arises in the presence of a Zeeman splitting in the lowest order of spin-orbit interaction. Spin manipulation and measurement of the spin decoherence time T_2 are straightforward in lateral GaAs quantum dots through the use of EDSR.

Massoud Borhani, Vitaly N. Golovach, Daniel Loss
Phys. Rev. B 73, 155311 (2006) (cond-mat/0510758 )

We consider a mechanism of spin decay for an electron spin in a quantum dot due to coupling to a nearby quantum point contact (QPC) with and without an applied bias voltage. The coupling of spin to charge is induced by the spin-orbit interaction in the presence of a magnetic field. We perform a microscopic calculation of the effective Hamiltonian coupling constants to obtain the QPC-induced spin relaxation and decoherence rates in a realistic system. This rate is shown to be proportional to the shot noise of the QPC in the regime of large bias voltage and scales as "a^-6" where "a" is the distance between the quantum dot and the QPC. We find that, for some specific orientations of the setup with respect to the crystallographic axes, the QPC-induced spin relaxation and decoherence rates vanish, while the charge sensitivity of the QPC is not changed. This result can be used in experiments to minimize QPC-induced spin decay in read-out schemes.

Massoud Borhani, Daniel Loss
Phys. Rev. A 71, 034308 (2005) (quant-ph/0410145)

We show that a special type of entangled states, cluster states, can be created with Heisenberg interactions and local rotations in 2d steps where d is the dimension of the lattice. We find that, by tuning the coupling strengths, anisotropic exchange interactions can also be employed to create cluster states. Finally, we propose electron spins in quantum dots as a possible realization of a one-way quantum computer based on cluster states.

Massoud Borhani, Reza Mansouri, Samad Khakshournia
Int. J. Mod. Phys. A 19, 4687 (2004) (hep-th/0301228 )

We consider a spherical thick 3-brane immersed in a five-dimensional bulk spacetime. We demonstrate how the thick brane equation of motion expanded in powers of the thickness of the brane can be obtained from the expected junction conditions on the boundaries of thick brane with the two embedding spacetimes. It is shown that the finite thickness leads to a faster collapse of the spherical shell.