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David Edward Pritchard | |
|---|---|
| Born | (1941-10-15)October 15, 1941 (age 84) New York, U.S. |
| Alma mater | California Institute of Technology (MA) Harvard University (PhD) |
| Scientific career | |
| Fields | Atomic physics |
| Institutions | Massachusetts Institute of Technology |
| Thesis | Differential Spin Exchange Scattering: Sodium on Cesium.[1] (1968) |
| Doctoral advisor | Daniel Kleppner |
| Doctoral students | Eric Cornell |
| Other notable students | Jerome Apt (Astronaut) |
| Website | web |
David Edward Pritchard (born October 15, 1941)[2] is a professor at theMassachusetts Institute of Technology (MIT) who specializes inatomic physics andeducational research.
Pritchard completed his PhD in 1968 atHarvard University under the supervision ofDaniel Kleppner. His thesis involved building the first atomic scattering machine with polarized atoms to study differentialspin exchange scattering, a process by which the21 cm hydrogen line manifests.[1]
Pritchard was an early adopter oftunable lasers in physics and chemistry, demonstrating high-resolutionspectroscopy through the simultaneous absorption of two laser photons. He employed both laser and radio-frequency spectroscopy to study weakly boundvan der Waals molecules, such as NaNe[3] and KAr,[4] in cold supersonicmolecular beams.
Pritchard made use of tunable lasers' ability to transfermomentum to atoms, leading to demonstrations of thediffraction of atoms from a standing wave of light (denotedKapitza-Dirac or Raman-Nath regimes) andBragg scattering[5] of atoms fromlight gratings, founding the field of coherentatom optics.[6] This led to the creation of the firstatom interferometer,[7] wherematter waves would propagate on both sides of a metal foil before recombining, so that different interactions on the two sides would result in afringe shift of the atomic interference pattern.[8] This allowed for precise measurements of atomicpolarizability, therefractive index of gaseous matter waves, and fundamental testing ofquantum decoherence, as well as the first demonstration of the ability of atom interferometers to measure angular velocity like agyroscope and to work for complex particles like Na2 molecules in the gaseous phase.[9]
A singularly important development from atom optics is Pritchard's invention of themagneto-optical trap[10] which captures and cools atoms to sub-millikelvin temperatures and of the Dark SPOT MOT, in which atoms are confined in a way such that they do not interact with trapping light.[11] Together with amagnetic atom trap, it can compress ~ 1010 cold atoms into the same small volume (This is sometimes called theIoffe-Pritchard trap to honor its plasma physics origin). These traps are commonly used in the field of cold atom research and are the foundational tools for the MIT-Harvard Center forUltracold Atoms.
In 1990, Pritchard broughtWolfgang Ketterle toMIT as apostdoctoral researcher to work onatom cooling. To encourage Ketterle to stay at MIT, in 1993 Ketterle was given his own experimental cold atom program (with two students and two grants) while Pritchard himself stepped aside from the field to allow Ketterle to be appointed to the faculty. Ketterle pursued atom cooling to achieveBose–Einstein condensation in 1995, a discovery for which Ketterle was awarded theNobel Prize in Physics in 2001, alongside Pritchard's former graduate student,Eric Allin Cornell, andCarl Wieman, who was an informal Pritchard mentee while an undergraduate at MIT.[12]
Ketterle and Pritchard then partnered to study atom optics and interferometry with Bose condensates, demonstrating coherent amplification ofmatter waves,superradiantRayleigh scattering, and the power of Bragg spectroscopy to probe the condensate and used laser light to establish coherence between two condensates that never touch. Pritchard received the 2004Max Born Award, "For creative application of light to new forms of spectroscopy, to manipulation and trapping of atoms, and for pioneering the new fields of atom optics and atom interferometry".[13]
Pritchard is a pioneer in the precise measurement of atomic and molecular masses usingion traps, an advance enabled by his group's developing highly sensitive radio-frequency detectors based onSQUIDs (superconducting quantum interference devices) and techniques to coherently cross-couple the motion of different modes of an ion's oscillation in the trap. These advances culminated in an ion balance in which one each of two different ions were simultaneously confined while theircyclotron frequencies were inter-compared to better than one part in 1011.[14] This led to the discovery of a new type of systematic shift of the cyclotron frequency due to the polarizability of the ion, providing the most accurate measurement of ionic molecule polarizability. It also resulted in a fifty-fold improvement of experimental tests ofAlbert Einstein'smass–energy equivalence that (whereE is the energy,m is the mass andc thespeed of light) – now at ½ part per million.[15]
Precise measurements of the masses ofrubidium andcaesium atoms made with the MIT apparatus have been combined with others' high-precision atom interferometric measurements ofh/m (thePlanck constant divided by the atom mass) to give the most accurate value of the fine structure constant at 0.2 ppb (parts per billion), differing by ~ 2.5 combined errors from measurement based onquantum electrodynamics. This is the most precise comparison of measurements made using entirely different theoretical bases.
In 1998, David Pritchard and his son Alex developed an online Socratic tutor, mycybertutor.com, which provides specific critiques of incorrect symbolic answers, hints upon request, and follow-up comments and questions. This tool has been shown to significantly improve students' ability to answer traditional MIT examination problems, increasing their performance by approximately 2 standard deviations.[16] The software is now marketed as Mastering Physics, Mastering Chemistry, and Mastering Astronomy byPearson Education. It has become a widely used homework tutor in Science and Engineering, with approximately 2.5 million.
Pritchard's education research group, RELATE[17] was started in 2000 with the goal to "Apply the principles and techniques of science and engineering to study and improve learning, especially of expertise". They conduct research using all components in the acronym RELATE - Research in Learning, Assessing, and Tutoring Effectively. They showed that copying online homework is by far the best predictor of a low final exam grade in MIT residential physics,[16] and is the dominant contributor to ~ 5% of the certificates given byedX. They explored new types of instruction (e.g. deliberate practice of critical problem-solving skills) or variations in instruction (adding a diagram, replacing multiple choice questions with more interactive drag and drop questions, etc.) compared with traditional instruction (the control).[18][19]
These experiments, along with other relevant research, indicated an important principle that students were struggling with – strategic thinking – the ability to determine which concepts and procedures are helpful in solving an unfamiliar problem. For this purpose, RELATE developed a Mechanics Reasoning Inventory[20] that measures strategic ability; it served as a benchmark of progress for their new pedagogy: Modeling Approach to Problem-Solving. This pedagogy was shown to greatly improve students' attitudes towards learning science, raise their scores on the Physics 1 final exam retake,[21] and subsequently help them improve their Physics 2 grade by ~ 1/2 standard deviation relative to students who didn't benefit from this intervention.[22]
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