Tempel, DavidAspuru-Guzik, Alan2013-02-112012Tempel, David G., and Alán Aspuru-Guzik. 2012. Quantum computing without wavefunctions: Time-dependent density functional theory for universal quantum computation. Scientific Reports 2:391.2045-2322http://nrs.harvard.edu/urn-3:HUL.InstRepos:10288449We prove that the theorems of TDDFT can be extended to a class of qubit Hamiltonians that are universal for quantum computation. The theorems of TDDFT applied to universal Hamiltonians imply that single-qubit expectation values can be used as the basic variables in quantum computation and information theory, rather than wavefunctions. From a practical standpoint this opens the possibility of approximating observables of interest in quantum computations directly in terms of single-qubit quantities (i.e. as density functionals). Additionally, we also demonstrate that TDDFT provides an exact prescription for simulating universal Hamiltonians with other universal Hamiltonians that have different, and possibly easier-to-realize two-qubit interactions. This establishes the foundations of TDDFT for quantum computation and opens the possibility of developing density functionals for use in quantum algorithms.en-USmagnetic properties and materialstheoretical chemistryinformation theory and computationquantum physicsJournal Article2013-02-1110.1038/srep00391