Quantum-dot Cellular Automata (QCA) provides a basis for classicalcomputation without transistors. Many simulations of QCA rely upon theso-called Intercellular Hartree Approximation (ICHA), which neglects thepossibility of entanglement between cells. Here, we present computationalresults that treat small groups of QCA cells with a Hamiltonian analogous to aquantum mechanical Ising-like spin chain in a transverse field, including theeffects of intercellular entanglement. When energy relaxation is included inthe model, we find that intercellular entanglement changes the qualitativebehaviour of the system, and new features appear. In clocked QCA, isolatedgroups of active cells experience oscillations in their polarization states asinformation propagates. Additionally, energy relaxation tends to bring groupsof cells to an unpolarized ground state. This contrasts with the results ofprevious simulations which employed the ICHA. The ICHA is a valid approximationin the limit of very low tunneling rates, which can be realized inlithographically defined quantum-dots. However, in molecular and atomicimplementations of QCA, entanglement will play a greater role. The degree towhich entanglement poses a problem for memory and clocking depends upon theinteraction of the system with its environment, as well as the system'sinternal dynamics.
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