



@article {1371,
	title = {Time Reversal and n-qubit Canonical Decompositions},
	journal = {Journal of Mathematical Physics},
	volume = {46},
	year = {2005},
	month = {2005/01/01},
	pages = {062104},
	abstract = {  For n an even number of qubits and v a unitary evolution, a matrix
decomposition v=k1 a k2 of the unitary group is explicitly computable and
allows for study of the dynamics of the concurrence entanglement monotone. The
side factors k1 and k2 of this Concurrence Canonical Decomposition (CCD) are
concurrence symmetries, so the dynamics reduce to consideration of the a
factor. In this work, we provide an explicit numerical algorithm computing v=k1
a k2 for n odd. Further, in the odd case we lift the monotone to a two-argument
function, allowing for a theory of concurrence dynamics in odd qubits. The
generalization may also be studied using the CCD, leading again to maximal
concurrence capacity for most unitaries. The key technique is to consider the
spin-flip as a time reversal symmetry operator in Wigner{\textquoteright}s axiomatization; the
original CCD derivation may be restated entirely in terms of this time
reversal. En route, we observe a Kramers{\textquoteright} nondegeneracy: the existence of a
nondegenerate eigenstate of any time reversal symmetric n-qubit Hamiltonian
demands (i) n even and (ii) maximal concurrence of said eigenstate. We provide
examples of how to apply this work to study the kinematics and dynamics of
entanglement in spin chain Hamiltonians.
},
	doi = {10.1063/1.1900293},
	url = {http://arxiv.org/abs/quant-ph/0402051v2},
	author = {Stephen S. Bullock and Gavin K. Brennen and Dianne P. O{\textquoteright}Leary}
}
