IQI Weekly Seminar

Abstract: The emergence of classical behavior from a many-body wavefunction is determined by its entanglement structure, in the form of redundant classical information shared between many local subsystems. We show how this structure can be generated via cosmological dynamics from the vacuum state of a massless field, causing the wavefunction to branch into classical field configurations on large scales.  An accelerating epoch first excites the vacuum into a superposition of classical fields as well as a highly sensitive bath of squeezed super-horizon modes. Gravitational interactions allow these modes to collect information about (and decohere) longer-wavelength fluctuations. During a subsequent decelerating epoch, this information is amplified and propagates spatially, creating long-range redundant correlations in the wavefunction. The resulting classical observables, preferred basis for decoherence, and system/environment decomposition emerge from the translation invariant wavefunction and Hamiltonian, rather than being fixed by hand.  We discuss the role of phase information in the wavefunction, and the relation between decoherence and wavefunction branching.