Quantum Control and Entanglement in a Strongly Interacting Spin Ensemble

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

This research will investigate quantum phase transitions using ultracold atomic gases cooled close to absolute zero temperature. Phase transitions play important roles in many areas of physics including cosmology, particle physics and condensed matter. The freezing of water to ice provides a familiar example: the motion of water molecules undergo a phase transition upon crystallization as the temperature falls below the freezing point. In cosmology, it is conjectured that the large scale structure of the universe is a vestige of defects (e.g. "cosmic strings") formed as the Universe cooled through a phase transition (via the so-called "Higgs mechanism") shortly after the Big Bang. This research will explore quantum phase transitions and associated phenomena in an unexplored regime at the opposite end of the temperature scale, close to absolute zero on the Kelvin temperature scale (or nearly 460 degrees below zero on the Fahrenheit temperature scale). The experiments will use ultracold atomic Bose-Einstein condensates (a quantum state of matter that forms at extremely low temperatures) to explore phase transitions in which the behavior of the transition is determined by quantum effects rather than thermal effects. In addition to providing new insight to the fundamental quantum science of many-particle systems, these experiments have potential applications to quantum information science and to the development of new quantum sensors for inertial guidance and measurement of gravity and magnetic fields. This experimental research will study strongly interacting ensembles of spin-1 atoms in a Bose-Einstein condensate to explore the nature of quantum phase transitions in the neighborhood of the critical point and to investigate creation, control and characterization of non-classical highly entangled states of the ensembles. The investigations use small rubidium-87 atomic Bose-Einstein condensates containing just a single spin domain, such that the dynamic evolution occurs only in the internal spin degrees of freedom. These condensates feature a well-characterized Hamiltonian with a tunable quantum phase transition that allow exploration of both ferromagnetic and polar (nematic) ground states of the spins. The combination of an exactly solvable Hamiltonian with a quantum phase transition together with demonstrated dynamics in the quantum regime provide a unique combination of tools to explore important topics including high precision studies of a second order quantum phase transitions, exploration of excitations across a quantum critical point, and the generation of massively entangled states. A common theme in all of these studies is the role of finite size effects that manifest in the quantum fluctuations of the system. This research will provide insight into fundamental principles of many-particle quantum mechanics that are important to many areas of physics and will point the way to future explorations of quantum many-body spin systems including thermalization and ergodicity crossing a quantum phase transition, investigations of Hamiltonian quantum chaos and other non-linear phenomena, and finite temperature effects.