Colloquium Archives (before June 2017)

More recent colloquia are posted on the Physics & Astronomy Colloquia page.

Gregory Fuchs, Faculty Candidate, Center for Spintronics and Quantum Computation, University of CA-Santa Barbara

Topic: "Gigahertz Dynamics of a Strongly Driven Single Spin in Diamond"  (Video)

Abstract: Nitrogen vacancy (NV) center spins in diamond have emerged as a promising solid-state system for quantum information and communication. Techniques to manipulate a single spin have been used to study the long room temperature spin coherence times of NV centers as well as their interactions with nearby electron and nuclear spins. There remain major challenges, however, both in understanding the physics of these defects and in the development of technologies based on their quantum properties. We extend coherent control of individual spins to the chip level by fabricating coplanar waveguide structures on diamond substrates to apply high-intensity microwave fields. Within large driving fields, conventional models of spin dynamics break down, enabling reproducible spin flips in less than 1 nanosecond. These results represent an important step toward quantum error correction and time-optimal quantum control.

Dartmouth GreenCube: Umair Siddiqui '10, Amanda Slagle '12, Max Fagin '11, Sean Currey '11 for the GreenCube Team

Topic: "Multiple Balloon Measurements of Gravity Waves over New Hampshire"  (Video)

ABSTRACT:   The undergraduate GreenCube group, with mentorship from professors and engineering staff, have designed and constructed a payload conforming to CubeSat standards. A CubeSat is a small satellite package standard established by CalPoly and Stanford Universities for standardized secondary spacecraft design.   The GreenCube is a 30cm x 10cm x 10cm payload which contains a 3-axis magnetometer, a GPS receiver, a ham radio system, and and digitized sensors. For the GreenCube II gravity wave mission flown this August, the sensors were thermistors for ambient atmospheric temperature observations.  Together with the GPS data, these thermistors were used in an attempt to measure atmospheric gravity waves over Mt Washington.

Jeevak Parpia, Cornell University

Topic: "Dissipative Mysteries-Experiments on Glasses at Low Temperatures"  (Video)

Abstract: I will discuss two recent experiments on glasses at Cornell. The first shows signatures (in the acoustic response) for the presence of interactions between two level systems that comprise the "building blocks" of glasses. The temperature dependence tracked down to below 3 mK shows a linear T behavior in dissipation (in contrast to the T3 behavior predicted by the standard tunneling model). The second examines a disordered material (silicon nitride) that incorporates a high internal stress and that displays extraordinarily high Qs at room temperature and down to the "plateau" region between 0.1 and 10K, where it is found that almost all glasses show a dissipation that is on the order of 3_10-3. High stress nitride deviates from this behavior displaying a dissipation that is almost 1000 _ smaller. Stress relieved structures (cantilevers) fabricated from the same material show a dissipation in closer agreement to the universal behavior. Future work will be discussed.

Samuel A. Werner, Physics Laboratory, NIST Gaithersburg, Maryland

Topic: "Observation of Aharonov-Bohm Effects by Neutron Interferometry"  (Video)

ABSTRACT:  The special and unique techniques of neutron interferometry have been used to observe a number of topological and geometrical effects. These include the phase shift of a particle carrying a magnetic moment (a neutron) encircling a line charge (the Aharonov-Casher effect), and the Scalar Aharonov-Bohm effect, observed with a pulsed magnetic field solenoid and time-of-flight neutron detection. On the occasion of the 50th anniversary of the Aharonov-Bohm paper, I provide an overview of the neutron interferometry technique and a description of these two historic experiments.

Elisha Huggins,Dartmouth College, Department of Physics and Astronomy Emeritus Faculty

Topic: "Introductory Contemporary Physics"  (Video)

ABSTRACT:  What laws of physics apply to everything, and have no known exceptions?  We can think of two--the principle of relativity and the uncertainty principle.  Our goal has been to construct an introductory physics course with emphasis on these two laws.  To do this, we begin with the principle of relativity, a law understood by Galileo, and end with the uncertainty principle after focusing on the particle-wave nature of matter.

In our talk we will start with the way we handle the time-energy form of the uncertainty principle, and then describe some of the steps we took to get there.  The most important step was introducing special relativity in week one.

Mariangela Bernardi, University of Pennsylvania

Topic: Topic: "Massive Galaxies in Massive Datasets"  (Video)

ABSTRACT:  Understanding why massive early-type galaxies are red and dead has proved to be difficult. This has been the source of tension with hierarchical formation models, such as the Cold Dark Matter model, in which massive objects are formed from mergers of smaller ones which existed at early times. The problem is to arrange for star formation to occur at higher redshift than the actual assembly of the stars into a single massive galaxy.  The most recent galaxy formation models arrange for this to happen by a combination of two processes:dry mergers and AGN feedback. I will discuss a number of results on massive galaxy formation that are based on analyses of Brightest Cluster Galaxies and other extreme objects in the SDSS and other recent astrophysical datasets. These suggest that at z < 2, in addition to being dry, the mergers should have been minor.