Geometrical phases for the G(4,2) Grassmannian manifold

We generalize the usual abelian Berry phase generated for example in a system with two non-degenerate states to the case of a system with two doubly degenerate energy eigenspaces. The parametric manifold describing the space of states of the first case is formally given by the G(2,1) Grassmannian manifold, while for the generalized system it is given by the G(4,2) one. For the latter manifold which exhibits a much richer structure than its abelian counterpart we calculate the connection components, the field strength and the associated geometrical phases that evolve non-trivially both of the degenerate eigenspaces. A simple atomic model is proposed for their physical implementation.Comment: 7 pages, 1 figure, REVTEX, minor typos corrected, to appear in Jour. Math. Phy

Stability of holonomic quantum computations

We study the stability of holonomic quantum computations with respect to errors in assignment of control parameters. The general expression for fidelity is obtaned. In the small errors limit the simple formulae for the fidelity decrease rate is derived.Comment: 7 page

Quantum Holonomies for Quantum Computing

Holonomic Quantum Computation (HQC) is an all-geometrical approach to quantum information processing. In the HQC strategy information is encoded in degenerate eigen-spaces of a parametric family of Hamiltonians. The computational network of unitary quantum gates is realized by driving adiabatically the Hamiltonian parameters along loops in a control manifold. By properly designing such loops the non-trivial curvature of the underlying bundle geometry gives rise to unitary transformations i.e., holonomies that implement the desired unitary transformations. Conditions necessary for universal QC are stated in terms of the curvature associated to the non-abelian gauge potential (connection) over the control manifold. In view of their geometrical nature the holonomic gates are robust against several kind of perturbations and imperfections. This fact along with the adiabatic fashion in which gates are performed makes in principle HQC an appealing way towards universal fault-tolerant QC.Comment: 16 pages, 2 figures, REVTE

(1+1)-Dimensional SU(N) Static Sources in E and A Representations

Here is presented a detailed work on the (1+1) dimensional SU(N) Yang-Mills theory with static sources. By studying the structure of the SU(N) group and of the Gauss' law we construct in the electric representation the appropriate wave functionals, which are simultaneously eigenstates of the Gauss' operator and of the Hamiltonian. The Fourier transformation between the A- and the E-representations connecting the Wilson line and a superposition of our solutions is given.Comment: 10 pages, no figures, REVTEX, as in Phys. Rev.

Quantum computation with abelian anyons on the honeycomb lattice

We consider a two-dimensional spin system that exhibits abelian anyonic excitations. Manipulations of these excitations enable the construction of a quantum computational model. While the one-qubit gates are performed dynamically the model offers the advantage of having a two-qubit gate that is of topological nature. The transport and braiding of anyons on the lattice can be performed adiabatically enjoying the robust characteristics of geometrical evolutions. The same control procedures can be used when dealing with non-abelian anyons. A possible implementation of the manipulations with optical lattices is developed.Comment: 4 pages, 3 figures, REVTEX, improved presentation and implementatio

The Coulomb Branch of Yang-Mills Theory from the Schroedinger Representation

The Coulomb branch of the potential between two static colored sources is calculated for the Yang-Mills theory using the electric Schroedinger representation.Comment: 4 pages, no figures, REVTEX, as in Phys. Lett.