  We introduce string-bond states, a class of states obtained by placing
strings of operators on a lattice, which encompasses the relevant states in
Quantum Information. For string-bond states, expectation values of local
observables can be computed efficiently using Monte Carlo sampling, making them
suitable for a variational abgorithm which extends DMRG to higher dimensional
and irregular systems. Numerical results demonstrate the applicability of these
states to the simulation of many-body sytems.
