Observation of Zitterbewegung in a Degenerate Quantum GasDecember 19, 2012
American Center for Physics
College Park, MD
Date: Wednesday, December 19, 2012
Speaker: Ian B. Spielman, Joint Quantum Institute, NIST and the University of Maryland
Time and Location: 1:00 PM, with Q&A to follow, in a 1st floor conference room at the American Center for Physics, 1 Physics Ellipse, College Park, MD-- off River Rd., between Kenilworth Ave. and Paint Branch Parkway.
Abstract: Here I present our experimental work on Bose-Einstein condensates, systems of ultra-cold charge neutral atoms at a temperature of about 100 nano-Kelvin: one billion times colder than room temperature. These condensates - quantum gases - are nearly perfect quantum mechanical systems, and here we demonstrate a technique by which these charge neutral particles have artificial spin-orbit coupling, of a form more well known in material systems.
In one limit, this spin-orbit coupled system is described by the 1D relativistic Dirac equation. Among the earliest predictions of relativistic quantum mechanics is Schrödinger's suggestion that a relativistic quantum particle, such as an electron, should undergo a microscopic trembling -Zitterbewegung - is it moves. For the electron, the f = mc2/h ≈ 1× 1020 Hz frequency and δx = h/mc ≈ 2 pm amplitude of this motion is below any foreseeable threshold for detection. This desperate situation can be happily resolved by working with artificial relativistic systems such as graphene, or as here with ultracold atoms where c can be vastly decreased and where the mass m is tunable. In our experiment, where c ≈ 6 mm/s, f ~ 1 kHz and δx ~ 0.5 μm, Zitterbewegung is easily observed.
In our engineered system, we observed Zitterbewegung and directly measured the frequency and amplitude of this microscopic motion, and find it to be in agreement with our relativistic model.
Biography: Ian B. Spielman is a Fellow at the Joint Quantum Institute (National Institute of Standards and Technology and the University of Maryland). He received his B.S. in Physics and Mathematics at the University of Oklahoma and his Ph.D. in Physics at the California Institute of Technology. He was then a National Research Council Postdoctoral Associate at NIST and went on to join the NIST staff.
His current experiments lie at the intersection of condensed matter and atomic physics, realizing many-body systems with systems of ultra-cold atoms. His current projects include: (1) creating magnetic/optical configurations leading to synthetic gauge fields, for example, making the charge neutral bosons move like charged particles in a magnetic field, or act as if they experience the classic Rashba and Dresselhaus spin-orbit couplings; (2) using Feshbach resonances in 87Rb to control interaction term in model Hamiltonians; (3) studying ultracold 87Rb in an optical lattice, thus realizing the 2D Bose-Hubbard model; and (4) building a new experiment to study Bose-Fermi mixtures of 87Rb and 6Li.