Research News
100609: UR Physicists Determine Mass Difference between Top and Antitop Quarks
A team of physicists in the Department has performed the first direct measurement of the mass difference between a quark and its antimatter partner (antiquark). Quarks are the fundamental particles that make up protons and neutrons, the stuff that regular matter is made of. Before antimatter was discovered, Paul Dirac introduced it as a requirement of the laws of quantum mechanics and Einstein's relativity. Scientists have been producing and studying antimatter such as antiprotons, antineutrons and antielectrons (or positrons) for many decades. All antimatter particles are supposed to have the same masses and lifetimes as their matter partners, but with opposite electric charges. Indeed, the masses and lifetimes of antimatter particles have been measured and found to be identical to their normal matter counterparts. Even more complicated objects such as pions, kaons, light nuclei, and hydrogen atoms appear to agree with this matter and antimatter "symmetry."
Studying isolated quarks is challenging because they combine with other quarks to form heavier and more complicated particles very rapidly -- between 10-22 seconds -- before they leave the regions of their creation.
Nonetheless, the heaviest of the quarks, the top quark, behaves differently: it decays so fast -- in around 10-24 seconds -- that it has no time to form any compounds. And that is the quark that the Rochester scientists have used to check the mass difference between a quark and its antiquark.
Emil Wolf Proposes Method to Determine the Phases of X-ray Beams Diffracted by Crystals
092309: In a recent PRL paper, Wilson Professor of Optical Physics and Theoretical Physics Emil Wolf introduces a technique that overcomes the long-standing difficulties relating to measuring phases of diffracted x-ray beams in structure determination of crystals. The current methods incorrectly assume that x-rays are monochromatic, and as Wolf points out in a recent physicsworld.com article, this type of beam does not occur naturally and cannot be created in the lab. He proposes that physicists use spatially coherent x-rays that can be produced in the lab and that they measure beam correlation functions to obtain missing structural data.
NASA Spitzer Space Telescope Moves from Cryogenic to "Warm" Mission
052909: The NASA Spitzer Space Telescope's cryogenic mission is over. At approximately 2:30 PM EDT on Friday, 15 May 2009, precisely as expected, the last of the facility's liquid-helium coolant evaporated. The telescope and instruments began quickly to warm up from the temperature, 1.5 degrees above absolute zero, at which they have been kept for the 5.7-year duration of the mission. The temperature is expected to level off at about 30 degrees above absolute zero, at which the observatory's Infrared Spectrograph and Multiband Imaging Photometer, and half of the detector arrays in the Infrared Array Camera, can no longer function.
The Infrared Spectrograph (IRS) was in use as the helium ran out. University of Rochester Professors Dan Watson and Bill Forrest are members of the team that designed and built the IRS under the leadership of Professor Jim Houck at Cornell University. Watson and Forrest have been among the most frequent users of the IRS.
Weak value measurements by a strong duo
042309: Assistant Professor Andrew Jordan and Associate Professor John Howell teamed up this past year with collaborators to make three strong advances related to weak value measurements and slow light. First, they discovered that gravity can push slow light down by about 1 Angstrom in the lab. Second, they demonstrated an optical pi cross-phase modulation jump. And third, they were able to measure extremely small (560-femtoradian) shifts of an optical beam. Much of this work merged Jordan's theoretical research with weak value measurements and Howell's experimental research with slow light and optical systems.
Publishing three papers between October 2008 and April 2009, their work was jump started when Howell posed an idea about gravitational deflection and slow light. Jordan and graduate student Justin Dressel hammered out the mathematics, then worked with slow light expert Howell and gravity expert Professor Sarada Rajeev to smooth out the details.
Sixty Students Participate in the 2009 Rochester Symposium for Undergraduate Physics Students (RSPS)
April 4, 2009 marked the day of the twenty-eighth Annual Rochester Symposium for Undergraduate Physics Students (RSPS), held this year at the U.S. Military Academy at West Point. Overall, sixty undergraduates from eight colleges and universities participated by either attending or speaking about their research.
NYS APS Spring 2009 Meeting Announced
The April 2009 symposium of the New York State Section of the American Physical Society will take place on April 17-18 at the University of Rochester. This marks the 100th symposium. The topic this year is:
Harnessing the Photon: from Energy to Entanglement
The meeting will begin at 1 pm on Friday April 17th and will end at about 3 pm on Saturday the 18th. After the closing session, we will offer a tour of the Laboratory for Laser Energetics. Following tradition, we will have a poster session for papers contributed by students, and we will select several papers for oral presentations.
Download the symposium poster.
The Death of Entanglement: Life Without Half-Life
020309: All Natural Processes Follow a Half-Life Rule when Decaying--Except Entanglement
Quantum entanglement, a type of correlation peculiar to quantum objects, has been found to disregard completely the "half-life" rule that is obeyed by all natural processes, such a radioactive decay.
In the current issue of the journal Science, Joseph Eberly, professor of physics at the University of Rochester, with his colleague Ting Yu, reviews four years of investigation into what is now called "the sudden death of entanglement," which they first reported in 2004.
"Our original paper on this triggered an explosion of interest because it attacks an issue that is so fundamental, the natural dying away of physical order," says Eberly. "Entanglement is at the heart of quantum computing, cryptography, teleportation--all these weird effects that physicists are just starting to exploit in labs around the world. And now we have to face that for some reason entanglement doesn't follow the rules."
Eberly and Yu discovered that entanglement--a quantum mechanical phenomenon that exists only when shared--weakens and disappears completely in the face of any common environmental "noise" such as heat or random vibration. In contrast, other known processes under similar circumstances get weaker by half in each successive time interval without ever quite disappearing.
First Laboratory Experiment to Accurately Model Stellar Jets Explains Mysterious "Knots"
020909: Some of the most breathtaking objects in the cosmos are the jets of matter streaming out of stars, but astrophysicists have long been at a loss to explain how these jets achieve their varied shapes. Now, laboratory research detailed in the current issue of Astrophysical Journal Letters shows how magnetic forces shape these stellar jets.
"The predominant theory says that jets are essentially fire hoses that shoot out matter in a steady stream, and the stream breaks up as it collides with gas and dust in space--but that doesn't appear to be so after all," says Adam Frank, professor of astrophysics at the University of Rochester, and co-author of the paper. "These experiments are part of an unusal international collaboration of plasma physicists, astronomers and computational scientists. It's a whole new way of doing astrophysics. The experiments strongly suggest that the jets are fired out more like bullets or buckshot. They don't break into pieces--they are formed in pieces."
Predicted Planet Seen--First Since Neptune 162 Years Ago
120908: In 2006, astronomer Alice Quillen of the University of Rochester predicted that a planet of a particular size and orbit must lie within the dust of a nearby star. That planet has now been photographed by the Hubble Space Telescope, making it only the second planet ever imaged after an accurate prediction. The only other planet seen after an accurate prediction was Neptune, discovered more than 160 years ago.
Dusty Shock Waves Create Raw Materials for Planets
120608: A team of astronomers led by Professor William Forrest and graduate student Ben Sargent have discovered that "[s]hock waves around dusty, young stars might be creating the raw materials for planets," according to a recent NASA press release. Using NASA's Spitzer Space Telescope, the researchers found the first evidence of cristobalite and tridymite crystals around several stars just beginning to transition into planets. These particular crystals require "flash heating events, such as shock waves, to form."
A type of silica, the crystals develop only under temperatures of approximately 1,220 Kelvin (1,740 degrees Fahrenheit). The disks that eventually become planets are too cold to enable creation of the cristobalite and tridymite crystals. The disk temperatures range from 100 to 1,000 Kelvin (minus 280 to positive 1,340 degrees Fahrenheit). Hence, Forrest and his team concluded that heating followed by rapid cooling -- perhaps shock waves -- might be responsible for creating the newly found crystals.
University of Rochester to Host Frontiers in Optics/Laser Science 2008
100908: From October 19-23, the University of Rochester will host this year's annual Frontiers in Optics/Laser Science 2008 at the Rochester Riverside Convention Center. The Chairs of the conference include Professor of Optics and Professor of Physics Lukas Novotny (photo left) and Professor of Chemistry and Professor of Physics Lewis Rothberg (photo right), as well as Karl Koch of Corning, Inc. and John Kitching of NIST.
The plenary speakers will be John C. Mather, Senior Astrophysicist, NASA Goddard Space Flight Center, whose topic is "From the Big Bang to the Nobel Prize and on to James Webb Space Telescope"; and Anton Zeilinger Professor of Physics, University of Vienna, and Director, Institute of Quantum Optics and Quantum Information of the Austrian Academy of Sciences, whose topic is "Photonic Entanglement and Quantum Information."
James Bergquist of NIST will receive the 2008 Arthur L. Schawlow Prize in Laser Science and speak about "Single-Atom Optical Clocks." Peter Knight of Imperial College in London will receive the 2008 Frederic Ives Medal/Jarus W. Quinn Endowment Award and speak about "Light, Photons and Nonclassicality."
For details, see the main conference webpage, the conference program page, and the student information page.
Upgrade to the Advanced Lab (PHY 243): Positon Tomography Teaching Laboratory
062508: By far, the course that our undergraduates like the most is the Advanced Lab (PHY 243), which they take in the fall of senior year. This course is a centerpiece of the curriculum leading to a BS in Physics, enabling students to perform sophisticated experiments, where they apply everything they've learned.
Thanks largely to Physics alumnus Dr. Chris Lirakis, a board member of the Donaldson Trust, the Department is adding an interdisciplinary experiment to the Advanced Lab in the emerging frontier of bio-medical physics. Because Dr. Lirakis enjoyed the Advanced Lab during his undergraduate years at the University of Rochester, he has enabled the Department to purchase a high-resolution germanium detector for use in the study of positron tomography. Future upgrades are also in the works.
The Advanced Lab has been heavily focused on optics experiments for years, having been run by quantum optics specialists Chair and Professor Nicholas Bigelow and Assistant Professor John Howell. Professor Frank Wolfs, who is in charge of our undergraduate program, has always wanted to give the Advanced Lab a medical twist because, as he says, "a lot of physics students want to do graduate work in medical applications. This is a burgeoning field." After talking with Dr. Lirakis during Meliora Weekend, Professor Wolfs devised a new experiment, one that focuses on nuclear radiation. (lhg)
Twenty Students Present Results at 2008 Rochester Symposium for Undergraduate Physics Students (RSPS)
040508: April 4, 2008 marked the day of the twenty-seventh Annual Rochester Symposium for Undergraduate Physics Students (RSPS), where twenty Physics, Astronomy, and Optics majors presented their research findings. The northeast regional RSPS conference is typically held each year during the Spring semester. This year's participants represented the University of Rochester, Houghton College, Rochester Institute of Technology, Colgate College, West Point Military Academy, Binghamton University, Siena College, and SUNY at Oswego.
Three University of Rochester undergraduates gave 15-minute presentations:
- Elizabeth Pollock, "Cosmic Ray Muon Imaging and Decay and Capture Process Detection," Advisor: Udo Schröder
- Zhengqing Qi, "Hadronic Jets and Clustering Algorithms in CMS," Advisor: Professor Regina Demina
- Jordan Webster, "Analysis of Momentum Resolution in VLE Beamlines," Advisor: Professor Regina Demina
The first twenty-four RSPS conferences were hosted from 1981 through 2005 by the University of Rochester. In 2006, the twenty-fifth RSPS conference was held at Houghton College, New York. In 2007 and 2008, the conference returned to Rochester, and in 2009, it will be hosted by the United States Military Academy at West Point, New York. (lhg)
Slowing and Stopping Images
020608: Associate Professor John Howell reported in January of 2007 that his group showed how to slow images down to "300 times lower than the speed of light" and preserve the amplitude and phase of the image. He also stated that, "we're working on systems that slow images down to 10 million times lower than the speed of light." Howell and his Quantum Optics team of Ryan Camacho, Curtis Broadbent, and Irfan Ali Khan used a technique known as slow light. When close to a narrow resonance feature, the group velocity of the light can be very slow. His team used naturally-occurring resonances in a cesium vapor to precisely slow images and delayed them for about 10 nanoseconds while retaining their properties.
Now the group (above from left to right: Ryan Camacho, Praveen VudyaSetu, and John Howell) has stopped images in a hot gas of Rubidium atoms for about 10 microseconds and is working toward a goal of a millisecond (Phys. Rev. Lett. 100, 123903). The new process changes the light field into an atomic excitation, then reads out that atomic excitation and converts it back into a light field. This differs from the method used in January of 2007, in which the light propagated slowly through a dilute vapor. In the stored light technique, the light field is interconverted into a coherence in the atoms and then read out at a later time. Remarkably, the storage process remains robust even given the diffusion of the rapidly moving atoms. (lhg)
Nobelist Steven Weinberg Praises Professor Carl Hagen and Collaborators for Higgs Boson Theory
030308: In October 2007, Nobel Prize Winner Steven Weinberg reminded a new generation of physicists about the crucial contribution regarding the Higgs boson theory made by Professor Carl Hagen of the University of Rochester and his collaborators. Weinberg's comments were part of his invited presentation at a conference celebrating the fiftieth anniversary of John Bardeen, Leon Cooper, and J. Robert Schrieffer's (BCS) theory of superconductivity.
The method suggested by Professor Hagen and others gives mass to vector bosons and is an essential ingredient in the unified electroweak theory for which Sheldon Lee Glashow, Abdus Salam, and Weinberg shared the 1979 Nobel Prize in Physics. In their acceptance speeches, they all gave equal prominence to the contributions of three independent teams who had predicted the existence of the Higgs boson, as it is now commonly called.
Three independently formulated papers describing the theoretical mechanism appeared in Volume 13 of Physical Review Letters in 1964. They were by Gerald Guralnik, Carl Hagen, and Tom Kibble; by Peter Higgs; and by Francois Englert and Robert Brout. All three papers were written from different perspectives, and each made a distinct contribution. (lhg)
Building Super-Amplifiers in Nano-Electric Systems using Strange Weak Values
020508: In a recent Physical Review Letters (PRL 100, 026804) article, Assistant Professor Andrew Jordan and third-year PhD student Nathan Williams describe how to implement one of the most bizarre predictions in quantum mechanics: a strange weak value in a nano-electric system. For a quantum system, their proposed method could provide an electrical current that exceeds the current supplied by the analogous classical system by factors of hundreds or thousands; that is, their device could boost a nano-amp to one amp or even to ten amps. This new method could also be used to determine whether an experimental system is a quantum mechanical device. (lhg)
Finally, the 'Planet' in Planetary Nebulae?
Astronomers at the University of Rochester, home to one of the world’s largest groups of planetary nebulae specialists, have announced that low-mass stars and possibly even super-Jupiter-sized planets may be responsible for creating some of the most breathtaking objects in the sky.
The news is ironic because the name "planetary" nebula has always been a misnomer. When these objects were discovered 300 years ago, astronomers couldn't tell what they were and named them for their resemblance to the planet Uranus. But as early as the mid-19th century, astronomers realized these objects are really great clouds of dust emitted by dying stars.
Now, Rochester researchers have found that planets or low-mass stars orbiting these aged stars may indeed be pivotal to the creation of the nebulae's fantastic appearance.
Embryonic Solar System Assembly Seen for the First Time
082907: Using NASA's Spitzer Space Telescope, a team of astronomers led by Professor Dan M. Watson of the University of Rochester has observed the onset of planetary-system formation, a process nobody has seen until now. The group's exciting first look at the creation of an embryonic solar system yields many new insights about the physics and chemistry of evolving astronomical objects.
Publishing their results in the August 30, 2007 issue of Nature, the researchers note that the Spitzer Space Telescope enabled them to see water, in the form of ice, "raining" from a cloud enveloping the infant star NGC 1333-IRAS 4B approximately 1,000 light years away from Earth. The ice is vaporizing as it lands supersonically on a dense, dusty disk surrounding the baby star, a long-sought phenomenon called a disk-accretion shock. In time, planets will form within the dusty disk. (lhg)
Assistant Professor Andrew Jordan Discovers How to Save Schrodinger's Cat
091707: The feature story of the May 14, 2007 issue of New Scientist features Assistant Professor Andrew Jordan's work on reversing quantum measurements, published with co-author Alexander Korotkov in Physical Review Letters 97, October 2006. Jordan defines experiments to physically undo a measurement of an unknown quantum state. In the case of Schrodinger's cat, this means that he has figured out how to monitor the state (dead or alive) of the classic "cat in a box," then undo any damage caused by the monitoring. (lhg)