A simple Example of Definitions of Truth, Validity, Consistency, and   Completeness in Quantum Mechanics
  Besides their use for efficient computation, quantum computers are a base for studying quantum systems that create valid physical theories using mathematics and physics. An essential part of the validation process for quantum mechanics is the development of a coherent theory of mathematics and quantum mechanics together. Such a theory should combine mathematical logical concepts with quantum mechanics. That this might be possible is shown here by defining truth, validity, consistency, and completeness for a quantum mechanical version of a simple classical expression enumeration machine described by Smullyan. It is seen that for an interpretation based on a Feynman path sum over expression path states, truth, consistency, and completeness have different properties than for the classical system. For instance the truth of a sentence S is defined only on the paths containing S. It is undefined elsewhere. Also S and its negation can both be true provided they appear on separate paths. This satisfies the definition of consistency. It is seen that validity and completeness connect the system dynamics to the truth of the sentences. It is proved that validity implies consistency. The requirements of validity and maximal completeness strongly restrict the possible dynamics of the system. Aspects of the existence of a valid, maximally complete dynamics are discussed. An exponentially efficient quantum computer is described that is also valid and complete. 
Paul Benioff (Physics Division, Argonne National Laboratory)