2007-2008 Academic Year
All colloquia are Thursdays at 4:45 pm in Merrill lecture room 3 unless otherwise noted.
Tea and cookies are served in Merrill 204 beginning at 4:15 pm.
The Quantum Limit for Electrical Amplifiers: Can We Reach It?
Any scientific instrument, including an electrical amplifier, necessarily adds noise in the process of performing a measurement. As might be expected from knowledge of Heisenberg's uncertainty principle, quantum mechanics sets strict limits on how little noise a measurement can add. There is a great deal of current interest in performing measurements at the quantum limit on such systems as qubits and nanomechanical resonators. This talk will introduce the notion of quantum limited electrical measurement, and discuss recent progress toward this goal at Dartmouth.
Welcome (back) pizza party. (Student lounge - Merrill 114-116)
David Haviland, KTH (
Sweden) and Universityof Massachusetts
Nonlinearities, Parametric Amplification and Noise Squeezing in Superconducting Microresonators
Superconducting microresonators are key components in the emerging field of Circuit Quantum Electrodynamics (QED). These circuits are made with planar lithography, and their electrodynamics can be well described by the simple model Hamiltonians of QED, where both field and “atom” degrees of freedom must be treated quantum mechanically. The talk will discuss the intrinsic non-linear properties of coplanar microresonators, demonstrating how this non-linearity can be controlled and used to realize parametric amplification of microwave signals. A brief introduction to parametric amplifiers will be given, and results on squeezing of a microwave signal with the phase-sensitive parametric amplifier will be shown. It is also possible to squeeze noise, and even quantum zero-point fluctuations, creating squeezed vacuum states. Such states can be used for noise-free measurement.
Oct. 4 (Note unusual time: 4 p.m.)
Subcellular surgery and nanosurgery
We use femtosecond laser pulses to manipulate sub-cellular structures inside live and fixed cells. Using only a few nanojoules of laser pulse energy, we are able to selectively disrupt individual mitochondria in live bovine capillary epithelial cells, and cleave single actin fibers in the cell cytoskeleton network of fixed human fibro-blast cells. We have also used the technique to micromanipulate the neural network of C. Elegans, a small nematode. Our laser scalpel can snip individual axons without causing any damage to surrounding tissue, allowing us to study the function of individual neurons with a precision that was not achievable before.
Oct. 4 (Note unusual time and location: 8 p.m. in Merrill 2)
(Phi-Beta-Kappa Lecture) Harvard University
How the mind tricks us: visualizations and visual illusions
Neurobiology and cognitive psychology have made great progress in understanding how the mind processes information - in particular visual information. The knowledge we can gain from these fields has important implications for the presentation of visual information and student learning.
Eric Mazur's web site: http://mazur-www.harvard.edu/
John Doyle, Harvard University
Cold Molecules the Old Fashioned Way
Over the past ten years we have developed the technique of buffer-gas cooling and loading of atoms and molecules into magnetic traps. Buffer-gas cooling relies solely on elastic collisions (thermalization) of the species-to-be-trapped with a cryogenically cooled helium gas. This makes the cooling general and potentially applicable to any species trappable at the temperature of the buffer gas (as low as 240 mK). Using buffer-gas loading, paramagnetic atoms and polar molecules were trapped at temperatures around 300 mK. In conjunction with evaporative cooling, buffer-gas loaded magnetic traps offer a means to further lower the temperature and increase the density of the trapped ensemble. Future directions include the production of polar molecule chips for quantum information.
Probing the Foundations of Quantum Mechanics with Mechanical Objects
Over the past 10 years, researchers have made enormous progress in the area of quantum measurement in quantum optics and condensed matter settings. This has transformed what scientists have thought was impossible and absurd to the ordinary and routine; for instance it is now common-place to produce coherent superposition states in electronic circuits. Recently there has been a wave of progress in the efforts to produce and measure the quantum properties of mechanical objects. I will discuss recent measurements in my lab and others which approach the Heisenberg Uncertainty Principle and the quantum ground state, and efforts around the world to produce a superposition in space of a mechanical structure: an object located in two places simultaneously. These experiments are designed to shed light on the boundaries of quantum mechanics and the quantum decoherence of macroscopic objects.
How Your Brain May End Up in My Computer: Modeling Cerebrovascular Physiology in Functional Neuroimaging
Neuroimaging technologies have revolutionized our ability to noninvasively image the dynamics brain function but our ability to interpret these data still lags behind. A specific challenge with functional magnetic resonance imaging (fMRI) and near-infrared spectroscopy (NIRS) is to isolate an evoked response from significant background physiological fluctuations. Data analysis approaches typically use averaging or linear regression to remove this physiology with varying degrees of success. An alternative solution is to apply biophysical models of the underlying physiology to interpret the data. In the present study, we compare model-based predictions of cerebrovascular physiology with NIRS measurements from 10 human subjects measured at rest. We found significantly higher correlations with the NIRS data for our model predictions compared to linear regression with the blood pressure fluctuations (multifactor ANOVA, p<0.0001). This finding supports the further development and use of physiological models for neuroimaging analysis. Future extensions of this work could model changes in cerebrovascular physiology that occur during development, aging and disease.
Hunting for the Evidence of Time Reversal Symmetry Breaking: An electric dipole moment search using a paramagnetic insulator
The physics that generates a permanent electric dipole moment (EDM) in fundamental particles, like electrons, requires breaking of both parity and time reversal symmetries. While parity violation has been verified in a wide range of experiments, the direct time reversal process seems much rarer. A non-zero result of the electric dipole moment measurement will provide insights into mechanisms that produce T violation, which is believed to link intimately to the physics of CP violation. I will discuss one such EDM searches at Indiana University. This experiment looks for an induced magnetization in a garnet sample polarized by an external electric field. The technique complements the ongoing EDM search at Amherst.
Fred Cooper, National Science Foundation
Nov. 27 at 7 pm. (Note unusual day and time)
Stanford University( "What's New in Physics" lecture) Five College
Dec. 4, 6 and 11
Senior Honors Thesis Talks
Laura Cadonati, University of Massachusetts
Gravitational Waves and LIGO: a new Probe into the Universe
The Laser Interferometer Gravitational-wave Observatory (LIGO) has the ambitious goal of the first direct detection of gravitational waves. As predicted by General Relativity, gravitational waves are ripples in the fabric of space-time generated by accelerating masses: black hole and neutron star collisions, supernova explosions, rotating systems and the Big Bang itself. Their detection will provide a fundamental new tool for the understanding of the universe. To achieve this goal, LIGO uses three Michelson laser interferometers, two in Hanford, WA, and one in Livingston, LA. Each interferometer monitors changes in the relative separation of mirrors at the ends of each of two perpendicular arms of km-scale length, in response to the space-time distortions induced by the passage of gravitational waves. The goal for the initial phase of LIGO is to measure differences in length of one part in 1021, or 10-18 m, one thousand times smaller than the nuclear diameter. The LIGO detectors have successfully completed a 2-year run at design sensitivity and the LIGO Scientific Collaboration is actively searching for gravitational wave signatures in the interferometers' data, while upgrades have started to improve the detectors' sensitivity by one order of magnitude over the next decade. This talk will give an overview of the status and the science of LIGO, with current results and the expected reach of the initial and advanced LIGO configuration.
Dmitry Garanin, CUNY Lehman College
Zvonimir Dogic, Brandeis University
Anthony Dinsmore, University of Massachusetts
Jenny Ross, University of Massachusetts
Danny Greenberger, City College of New York
Tatsu Takeuchi, Virginia Tech
Thomas Powers, Brown University
Kiko Galvez, Colgate University
Ian Gregory, Evergreen Solar
Lee Lynd, Dartmouth College
May 1, 6 and 8
Senior Honors Thesis Talks