Quantum over breakfast Quantum over breakfast

Quantum Happy Hour (Fall 2011)

Research I, Room 202, 3pm



Announcement:

We invite you to join us for informal lectures, presented by one of our physics faculty or an outside guest scientist, engaged in research in frontiers of quantum physics. These stimulating discussion style lectures will be followed by happy hour where we will continue our conversation on various current topics in quantum physics. We encourage our graduate and advanced undergraduates, particularly those interested in Quantum Physics, to participate and contribute to the excitement.



September 23

Bunching-Antibunching of Quantum Particles:
from Astrophysics to AMO

Indu Satija, GMU

Young’s double slit setup, introduced about two hundred years ago, is one of the most versatile tools to demonstrate the interference phenomena for both the light and the matter waves in physics. In contrast to this amplitude interferometry, there is also an intensity interferometry, discovered by Hanbury Brown and Twiss (HBT) about half a century ago, where correlations of signal intensities, rather than amplitudes was used to measure the angular sizes of astronomical objects. Instead of the two slits, the intensity interferometry involves two detectors and measures the probability of simultaneous arrival of particles in the detectors. In view of the strange unclassical character of the identical particles, this detection probability is enhanced for bosons (bunching) and diminished for fermions (antibunching) compared to the corresponding values for the particles whose trajectories obey classical laws of physics. This interferometry, is now an exquisite tool in particle physics on a scale of 10−10, just the opposite of the astronomical scale of 1010 in original HBT effect, in addition to its applications in AMO and condensed matter physics.

This talk will covers the historical journey that begins with the work of Dirac, Heisenberg, Pauli and Fermi and others, and encounters the celebrated work of Hanbury Brown Twiss in astronomy and focus on one of the most exciting new frontiers, namely the physics of ultracold atoms that is revolutionizing physics.

November 4

Building the Most Precise Atomic Clocks in the World by Studying Many-Body Physics

Ana Maria Rey, University of Colorado in Boulder and JILA

About 60 years ago, the second was defined by the Earth’s rotation. However, with the discovery of quantum mechanics and the quantized nature of the atomic energy levels, it became clear that atomic clocks could be more accurate and more precise than any mechanical or celestial reference previously known to man. Thus, in 1967 the second was redefined in terms of atomic transitions in the microwave domain between two energy levels of cesium atoms. The new generation of frequency standards, however, are optical clocks based on single trapped ions or neutral atoms with optical transition frequencies, i.e. up to six orders of magnitude higher than microwaves. While currently the single trapped ion clocks are at the forefront, neutral atom optical clocks have the potential to outperform the latter due to the possibility to simultaneously interrogate a large number of neutral atoms; This will be however only possible if we can understand and control atom-atom interactions. In this talk I am going to describe our recent progress towards the understanding of the atomic collisions during clock operation. I will also explain why a precise characterization of the many-body physics could be extremely useful towards the further application of clock technology on quantum information sciences.

November 18

Ultracold Atoms: Understanding Complex Systems Through Simplicity

Ian Spielman, NIST

What is the origin of complexity? This simple question underlies some of the must fundamental problems in science: how can simple chemical components organize themselves into living cells and organisms? What governs order on the astronomical scale? While these examples involve numerous distinct interacting components, similar order appears in systems of identical particles all with the same interactions. Complexity from simplicity: this is fundamental physics.

Nowhere is such complexity more common than in solids where innumerable electrons interact with the familiar Coulomb law, yet scaling up we can get different materials such as semiconductors, metals, superconductors, magnets, and so forth. How do these work? Some we understand, and some like high-temperature superconductors, we do not.

Seemingly simple, electrons moving in a crystal are still moving in a complicated environment; an intricate crystal structure, random imperfections, and a myriad of other details make it difficult to formulate simple laws that predict behavior.

In contrast, systems of ultra-cold atoms -- tenuous vapors of atoms cooled to just a billionth of a degree above absolute zero -- truly allow us to ask and answer the question "how does order appear from simplicity?" In a realm where quantum mechanics rules, we create atomic systems that are analogous to more complex material systems, allowing us to better understand the fundamental reason for physical effects. In my talk I will answer such common party questions as: How neutral atoms can experience the Lorentz force? And, what can cold atoms tell us about spintronics?