Field Theory of Open Quantum Systems

This book tackles questions of central importance for the continued development of quantum computers. As current devices have reached qubit counts large enough to warrant treating them as genuinely many-particle collective systems, understanding their behavior requires moving beyond conventional microscopic quantum mechanics. Each qubit is a macroscopic object strongly coupled to its environment—a kind of Schrödinger cat—so the governing principles differ markedly from those of isolated quantum systems. This book takes important steps toward formulating a theory for the evolution of such many-body open systems, constructing a general formalism which applies field theory methods to study the Lindbladian evolution of many-body open quantum systems, and deriving several highly non-trivial consequences. Most notably, the author shows that the collective properties of large arrays of open quantum systems differ qualitatively from both their classical counterparts and their closed, purely quantum analogs.