Decoherence in quantum computers is formulated within the semigroup approach. The error
generators are identified with the generators of a Lie algebra. This allows for a
comprehensive description which includes as a special case the frequently assumed spin …

Various physical implementations of quantum computers are being investigated, although
the requirements 1 that must be met to make such devices a reality in the laboratory at
present involve capabilities well beyond the state of the art. Recent solid-state approaches …

Quantum random walks on graphs have been shown to display many interesting properties,
including exponentially fast hitting times when compared with their classical counterparts.
However, it is still unclear how to use these novel properties to gain an algorithmic speedup …

Light-harvesting components of photosynthetic organisms are complex, coupled, many-body
quantum systems, in which electronic coherence has recently been shown to survive for
relatively long timescales, despite the decohering effects of their environments. Here, we …

Universal quantum computation on decoherence-free subspaces and subsystems (DFSs) is
examined with particular emphasis on using only physically relevant interactions. A
necessary and sufficient condition for the existence of decoherence-free (noiseless) …

Decoherence is the phenomenon of non-unitary dynamics that arises as a consequence of
coupling between a system and its environment. It has important harmful implications for
quantum information processing, and various solutions to the problem have been proposed …

We study nonlocal two-qubit operations from a geometric perspective. By applying a Cartan
decomposition to su (4), we find that the geometric structure of nonlocal gates is a 3-torus.
We derive the invariants for local transformations, and connect these local invariants to the …

Two-particle calculations, which include the electron-hole Coulomb interaction
nonperturbatively, are performed for excitons in surface passivated Si nanocrystals. The
calculated exciton energies agree quantitatively with photoluminescence data. The exciton …

Spectroscopic experiments on molecules embedded in free clusters of liquid helium reveal a
number of unusual features deriving from the unique quantum behavior of this nanoscale
matrix environment. The apparent free rotation of small molecules in bosonic 4 He clusters is …

Quantum clusters are van der Waals aggregates of light atomic and molecular species
whose behaviour is dominated by quantum delocalization and exchange effects. We
summarize here recent theoretical and experimental studies of helium and molecular …