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Decoherence and fidelity of single-electron spin states in quantum dots: effects of nuclear hyperfine coupling and double occupancy

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Title Decoherence and fidelity of single-electron spin states in quantum dots: effects of nuclear hyperfine coupling and double occupancy
 
Creator RAJAGOPAL, AK
D MAHANTI, S
JHA, SS
 
Subject dynamical semigroups
 
Description The decoherence and fidelity of spin states in a localized single-electron quantum dot in the presence of a dc magnetic field, arising either from the nuclear hyperfine interaction within the dot or due to its coupling with another localized quantum dot, are examined in detail. A general framework for determining the time evolution of the reduced density matrix. for a single dot is presented, which is exact up to the second order in interaction with any reservoir. In particular, it is applied to the problem of nuclear hyperfine coupling, and approximate estimates of coherence decay time are made when the nuclear spins are either polarized or unpolarized and the internal dynamics of nuclear spins is determined mainly by the nuclear magnetic dipole-dipole interaction. The fidelity of a pure unperturbed electronic one-qubit spin state is obtained as a function of time, which is exact even on a very short timescale of logic gate operations. The time variation of the fidelity of the same one-qubit state on the localized dot as a part of the direct product with another one-qubit state on another localized dot arising because of coupling between these quantum dots is also calculated in this paper. In this case, we include both the single-particle tunnelling between the dots as well as the direct and exchange Coulomb interactions, including on-site Coulomb repulsion. This allows for the double occupation of a single dot. It is found that the loss of fidelity of such two-qubit states due to double occupancy and additional phase errors in the presence of appreciable dot-dot coupling can become a more severe limiting factor than that due to the hyperfine interaction in individual dots.
 
Publisher IOP PUBLISHING LTD
 
Date 2011-08-03T15:05:47Z
2011-12-26T12:54:16Z
2011-12-27T05:41:54Z
2011-08-03T15:05:47Z
2011-12-26T12:54:16Z
2011-12-27T05:41:54Z
2006
 
Type Article
 
Identifier JOURNAL OF PHYSICS-CONDENSED MATTER, 18(47), 10677-10691
0953-8984
http://dx.doi.org/10.1088/0953-8984/18/47/013
http://dspace.library.iitb.ac.in/xmlui/handle/10054/9070
http://hdl.handle.net/10054/9070
 
Language en