Quantum computation and quantum spin dynamics

We analyze the stability of quantum computations on physically realizable q uantum computers by simulating quantum spin models representing quantum com puter hardware. Examples of logically identical implementations of the cont rolled-NOT operation are used to demonstrate that the results of a quantum computation are unstable with respect to the physical realization of the qu antum computer. We discuss the origin of these instabilities and discuss po ssibilities to overcome this, for practical purposes, fundamental limitatio n of quantum computers.