Interacting Atoms in Optical Lattices

General audience abstract:

The frontier of the technological application of quantum mechanics involves taking advantage of quantum entanglement, where the detailed interactions among particles are of central importance. Such emerging technologies include quantum simulators, quantum computers and quantum communication, as well as advanced versions of older quantum technologies like quantum sensors and clocks. Advancing these technologies requires understanding the dynamics of closed 'quantum many-body systems,' i.e. systems containing many particles which interact with each other and where quantum mechanics is important. The goal of this work is to help develop a universal description of such dynamics. The researchers will experimentally study the quantum many-body system that currently has the most complete equilibrium theoretical description, one-dimensional gases, which they make by putting ultracold atoms into optical lattices (periodic structures made from laser light). By taking these gases out of equilibrium, in situations where entanglement dominates dynamics, they can cleanly test emerging theoretical approaches. The experimental system can be made progressively more complex, so that the theories used to describe them can encompass a wide range of non-equilibrium systems. The largest immediate impact is likely to be in our understanding of the reliability of quantum simulators and the robustness of quantum computers. The training in experimental physics obtained by undergraduates and graduate students working on this experiment is comprehensive and is good preparation for many different types of experimental work.

Technical audience abstract:

The PI and his students will perform a series of measurements on one-dimensional (1D) Bose gases, which consist of ultra-cold 87Rb atoms trapped in a 2D array of tubes that are made with a 2D optical lattice. These interacting many-body systems are integrable, which implies that they are characterized by a large set of extra conserved quantities. The experiments generally involve taking these systems out of equilibrium and studying the ensuing dynamics. Unlike generic many-body quantum systems, the equilibrium properties of 1D gases can be calculated exactly. Their non-equilibrium properties, however, have been a challenge to calculate. A recently developed numerical technique, generalized hydrodynamics (GHD), promises to describe, to within certain approximations, the dynamics of integrable systems. GHD is based upon keeping track of the evolving local distribution of 'rapidities', which are the momenta associated with the quasiparticles that emerge in integrable systems. These important but abstract objects have only recently been measured (by the PI's team) and the team plans to measure them in a much more diverse set of circumstances. With these measurements will come the ability to quantitatively test GHD for the first time in the interesting intermediate and strong coupling regimes. They will also study the border at which GHD becomes applicable, by measuring the evolution of momentum and rapidity distributions after a wavefunction quench. Finally, they propose to extend these studies to a 1D gas in a weak lattice, a non-integrable system for which GHD might also be a useful description, at least at relatively short times. The search for a universal description of dynamics in quantum many-body systems is an important physics frontier, and GHD holds the promise of providing its core.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.