Entanglement area law in superfluid 4He

Area laws were first discovered by Bekenstein and Hawking(1,2), who found that the entropy of a black hole grows proportional to its surface area, and not its volume. Entropy area laws have since become a fundamental part of modern physics, from the holographic principle in quantum gravity(3-5) to ground-state wavefunctions of quantum matter, where entanglement entropy is generically found to obey area law scaling(6). As no experiments are currently capable of directly probing the entanglement area law in naturally occurring many-body systems, evidence of its existence is based on studies of simplified qualitative theories(6-8). Using new exact microscopic numerical simulations of superfluid He-4, we demonstrate for the first time an area law scaling of entanglement entropy in a real quantum liquid in three dimensions. We validate the fundamental principle that the area law originates from correlations local to the entangling boundary, and present an entanglement equation of state showing how it depends on the density of the superfluid.