Hamburg 2009 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 63: Quanteninformation: Quantencomputer
Q 63.9: Talk
Friday, March 6, 2009, 16:00–16:15, VMP 6 HS-A
Interacting electrons, Density Functional Theory, and Quantum Merlin Arthur — •Norbert Schuch1 and Frank Verstraete2 — 1Max-Planck-Institut für Quantenoptik, Garching, Germany — 2Institut für Theoretische Physik, Universität Wien, Wien, Austria
One of the central problems in quantum mechanics is to find the ground state energy of a system of electrons interacting via the Coulomb potential. Since its introduction by Hohenberg, Kohn, and Sham, Density Functional Theory (DFT) has become the most widely used and successful method for simulating systems of interacting electrons, making their original work one of the most cited in physics. In this letter, we show that the field of computational complexity imposes fundamental limitations on DFT, as an efficient description of the associated universal functional would allow to solve any problem in the class QMA (the quantum version of NP) and thus particularly any problem in NP in polynomial time. This follows from the fact that finding the ground state energy of the Hubbard model in an external magnetic field is a hard problem even for a quantum computer, while given the universal functional it can be computed efficiently using DFT. This provides a clear illustration how the field of quantum computing is useful even if quantum computers would never be built.