Quantum Hamiltonian Complexity

Constraint satisfaction problems are a central pillar of modern computational complexity theory. This monograph provides an introduction to the rapidly growing field of Quantum Hamiltonian Complexity (QHC), which includes the study of quantum constraint satisfaction problems. Over the past decade and a half, this field has witnessed fundamental breakthroughs, ranging from the establishment of a Quantum Cook-Levin Theorem to deep insights into the structure of 1D low-temperature quantum systems via so-called area laws. Quantum Hamiltonian Complexity provides the reader with a computer science-oriented introduction to the subject in order to help bridge the language barrier between computer scientists and physicists in the field. As such, it includes the following: (1) The motivations and history of the field, (2) a glossary of condensed matter physics terms explained in computer-science friendly language, (3) overviews of central ideas from condensed matter physics, such as indistinguishable particles, mean field theory, tensor networks, and area laws, and (4) brief expositions of selected computer science-based results in the area. For example, as part of the latter, it provides a novel information theoretic presentation of Bravyi's polynomial time algorithm for Quantum 2-SAT. Quantum Hamiltonian Complexity reviews some of the most fundamental results in QHC and is an ideal reference for computer scientists with little or no background in quantum information.