David E. Pritchard

Last updated
David Edward Pritchard
Born (1941-10-15) October 15, 1941 (age 82)
New York, New York
CitizenshipAmerican
Alma mater California Institute of Technology (A.M.)
Harvard University (Ph.D.)
Scientific career
Fields Physics
Atomic Physics
Physics Education Research
Institutions MIT
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.mit.edu/physics/people/faculty/pritchard_david.html

David Edward Pritchard (born October 15, 1941) [2] is a professor at the Massachusetts Institute of Technology (MIT), working on atomic physics and educational research.

Contents

Career

Early work

Pritchard completed his PhD in 1968 at Harvard University under the supervision of Daniel Kleppner. For his thesis, he built the first atomic scattering machine with polarized atoms to study differential spin exchange scattering - the process that excites the 21 cm hydrogen radiation. [1]

Pritchard was a pioneer in the application of tunable lasers to physics and chemistry, being the first to demonstrate high resolution spectroscopy when two laser photons are absorbed simultaneously. He used both laser and radio-frequency spectroscopy to study weakly bound van der Waals molecules like NaNe [3] and KAr [4] made in cold supersonic molecular beams.

Atom optics, atom traps, and atom interferometers

Exploiting the ability of tunable lasers to transfer large amounts of momentum to atoms, Pritchard performed classic demonstrations of the diffraction of atoms from a standing wave of light (denoted Kapitza-Dirac or Raman-Nath regimes) and Bragg scattering [5] of atoms from light gratings, founding the field of coherent atom optics. [6] This led to the first atom interferometer. [7] Where the atom wave passed on both sides of a metal foil before recombining, so that different interactions on the two sides produced a fringe shift of the atomic interference pattern. [8] This allowed precise measurements of atomic polarizability, the refractive index of gasses for atom waves, and fundamental tests of quantum decoherence, as well as the first demonstration of the power of atom interferometers to measure rotation like a gyroscope and to work for complex particles like Na2 molecules. [9]

A singularly important development from atom optics is Pritchard’s invention of the magneto-optical trap [10] that captures and cools atoms to sub-milikelvin temperatures and the “dark spot MOT”. [11] That can compress ~ 1010 cold atoms in the same small volume. Together with a magnetic atom trap, Pritchard independently re-invented (sometimes called the Ioffe-Pritchard trap to honor its plasma physics origin). These traps are the workhorses in the field of cold atom research and are the foundational tools for the MIT-Harvard Center for Ultracold Atoms .

In 1990, he brought Wolfgang Ketterle to MIT as a postdoctoral researcher to work on atom cooling. To induce Ketterle to stay at MIT, in 1993 he gave him his experimental cold atom program (with two students and two grants) and stepped aside from that field to allow Ketterle to be appointed to the faculty. Ketterle pursued atom cooling to achieve Bose–Einstein condensation in 1995, a discovery for which Ketterle was awarded the Nobel Prize in Physics in 2001, along with Pritchard’s former graduate student, Eric Allin Cornell and Carl Wieman who was an informal Pritchard mentee as an undergraduate at MIT. [12]

Ketterle and Pritchard then partnered to study atom optics and interferometry with Bose condensates, demonstrating coherent amplification of matter waves, superradiant Rayleigh scattering, the power of Bragg spectroscopy to probe the condensate, and even used laser light to establish coherence between two condensates that never touch.

Precise measurements of atomic masses

Pritchard is a pioneer in the precise measurement of atomic and molecular masses using ion traps, an advance enabled by his group’s developing highly sensitive radio-frequency detectors based on SQUIDs (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 their cyclotron frequencies were inter-compared to better than one part in 1011. [13] 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 of Albert Einstein’s mass–energy equivalence that (where E is the energy, m is the mass and c the speed of light)– now at ½ part per million. [14]

Precise measurements of the masses of rubidium and caesium (Cesium) atoms made with the MIT apparatus have been combined with others’ high-precision atom interferometric measurements of h/m (Planck’s 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 on quantum electrodynamics. This is the most precise comparison of measurements made using entirely different theoretical bases.

Teaching and education software

In 1998, he and his son Alex developed an online Socratic tutor, mycybertutor.com, that offers specific critiques of incorrect symbolic answers as well as hints upon request and follow-up comments and questions. It increases students’ ability to answer traditional MIT examination problems by ~ 2 standard deviations [15] and is now marketed as Mastering Physics.com, MasteringChemistry and …Astronomy by Pearson Education. It has been the dominant homework tutor in Science and Engineering for over a decade, with ~ 2.5M users annually.

Pritchard’s education research group RELATE [16] was started in 2000 with a 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, [15] and is the dominant contributor to ~ 5% of the certificates given by edX. 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 by more interactive drag and drop questions, etc.) are compared with traditional instruction (the control). [17] [18]

These experiments, along with other relevant research, indicated an important principal that students were struggling in – strategic thinking – the ability to determine which concepts and which procedures are helpful in solving an unfamiliar problem. For this purpose, RELATE developed a Mechanics Reasoning Inventory [19] 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, raised their scores on the Physics 1 final exam retake, [20] and subsequently helped them improve their Physics 2 grade by ~ ½ standard deviation relative to students who didn’t benefit from this intervention. [21]

Related Research Articles

<span class="mw-page-title-main">Ionization</span> Process by which atoms or molecules acquire charge by gaining or losing electrons

Ionization is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion. Ionization can result from the loss of an electron after collisions with subatomic particles, collisions with other atoms, molecules and ions, or through the interaction with electromagnetic radiation. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs. Ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected.

<span class="mw-page-title-main">Laser cooling</span> Class of methods for cooling atoms to very low temperatures

Laser cooling includes several techniques where atoms, molecules, and small mechanical systems are cooled with laser light. The directed energy of lasers is often associated with heating materials, e.g. laser cutting, so it can be counterintuitive that laser cooling often results in sample temperatures approaching absolute zero. Laser cooling relies on the change in momentum when an object, such as an atom, absorbs and re-emits a photon. For example, if laser light illuminates a warm cloud of atoms from all directions and the laser's frequency is tuned below an atomic resonance, the atoms will be cooled. This common type of laser cooling relies on the Doppler effect where individual atoms will preferentially absorb laser light from the direction opposite to the atom's motion. The absorbed light is re-emitted by the atom in a random direction. After repeated emission and absorption of light the net effect on the cloud of atoms is that they will expand more slowly. The slower expansion reflects a decrease in the velocity distribution of the atoms, which corresponds to a lower temperature and therefore the atoms have been cooled. For an ensemble of particles, their thermodynamic temperature is proportional to the variance in their velocity. More homogeneous velocities between particles corresponds to a lower temperature. Laser cooling techniques combine atomic spectroscopy with the aforementioned mechanical effect of light to compress the velocity distribution of an ensemble of particles, thereby cooling the particles.

<span class="mw-page-title-main">Wolfgang Ketterle</span> German physicist

Wolfgang Ketterle is a German physicist and professor of physics at the Massachusetts Institute of Technology (MIT). His research has focused on experiments that trap and cool atoms to temperatures close to absolute zero, and he led one of the first groups to realize Bose–Einstein condensation in these systems in 1995. For this achievement, as well as early fundamental studies of condensates, he was awarded the Nobel Prize in Physics in 2001, together with Eric Allin Cornell and Carl Wieman.

Resolved sideband cooling is a laser cooling technique allowing cooling of tightly bound atoms and ions beyond the Doppler cooling limit, potentially to their motional ground state. Aside from the curiosity of having a particle at zero point energy, such preparation of a particle in a definite state with high probability (initialization) is an essential part of state manipulation experiments in quantum optics and quantum computing.

<span class="mw-page-title-main">Rydberg atom</span> Excited atomic quantum state with high principal quantum number (n)

A Rydberg atom is an excited atom with one or more electrons that have a very high principal quantum number, n. The higher the value of n, the farther the electron is from the nucleus, on average. Rydberg atoms have a number of peculiar properties including an exaggerated response to electric and magnetic fields, long decay periods and electron wavefunctions that approximate, under some conditions, classical orbits of electrons about the nuclei. The core electrons shield the outer electron from the electric field of the nucleus such that, from a distance, the electric potential looks identical to that experienced by the electron in a hydrogen atom.

An atom interferometer is an interferometer which uses the wave character of atoms. Similar to optical interferometers, atom interferometers measure the difference in phase between atomic matter waves along different paths. Today, atomic interference is typically controlled with laser beams. Atom interferometers have many uses in fundamental physics including measurements of the gravitational constant, the fine-structure constant, the universality of free fall, and have been proposed as a method to detect gravitational waves. They also have applied uses as accelerometers, rotation sensors, and gravity gradiometers.

Atomic coherence is the induced coherence between levels of a multi-level atomic system.

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Atom optics "refers to techniques to manipulate the trajectories and exploit the wave properties of neutral atoms". Typical experiments employ beams of cold, slowly moving neutral atoms, as a special case of a particle beam. Like an optical beam, the atomic beam may exhibit diffraction and interference, and can be focused with a Fresnel zone plate or a concave atomic mirror.

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<span class="mw-page-title-main">Electron beam ion trap</span>

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<span class="mw-page-title-main">Trojan wave packet</span> Wave packet that is nonstationary and nonspreading

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<span class="mw-page-title-main">Magic wavelength</span>

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<span class="mw-page-title-main">Penning–Malmberg trap</span> Electromagnetic device used to confine particles of a single sign of charge

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References

  1. 1 2 "Harvard Physics PhD Theses, 1954-1970" (PDF). Harvard University Department of Physics. Archived from the original (PDF) on 18 May 2014. Retrieved 26 July 2019.
  2. ↑ "Biography on APS". Archived from the original on 2016-03-07. Retrieved 2012-07-14.
  3. ↑ Ahmad-Bitar, Riad; Lapatovich, Walter P.; Pritchard, David E.; Renhorn, Ingemar (1977-12-26). "Laser Spectroscopy of Bound NaNe Molecules". Physical Review Letters. 39 (26): 1657–1660. Bibcode:1977PhRvL..39.1657A. doi:10.1103/PhysRevLett.39.1657. ISSN   0031-9007.
  4. ↑ Mattison, Edward M.; Pritchard, David E.; Kleppner, Daniel (1974-03-11). "Spin-Rotation Coupling in the Alkali---Rare-Gas Van der Waals Molecule KAr". Physical Review Letters. 32 (10): 507–509. Bibcode:1974PhRvL..32..507M. doi:10.1103/PhysRevLett.32.507.
  5. ↑ Martin, Peter J.; Oldaker, Bruce G.; Miklich, Andrew H.; Pritchard, David E. (1988-02-08). "Bragg scattering of atoms from a standing light wave". Physical Review Letters. 60 (6): 515–518. Bibcode:1988PhRvL..60..515M. doi:10.1103/PhysRevLett.60.515. PMID   10038570.
  6. ↑ Wieman, Carl E.; Pritchard, David E.; Wineland, David J. (1999-03-01). "Atom cooling, trapping, and quantum manipulation". Reviews of Modern Physics. 71 (2): S253–S262. Bibcode:1999RvMPS..71..253W. doi:10.1103/RevModPhys.71.S253.
  7. ↑ Keith, David W.; Ekstrom, Christopher R.; Turchette, Quentin A.; Pritchard, David E. (1991-05-27). "An interferometer for atoms". Physical Review Letters. 66 (21): 2693–2696. Bibcode:1991PhRvL..66.2693K. doi:10.1103/physrevlett.66.2693. ISSN   0031-9007. PMID   10043592.
  8. ↑ Ekstrom, Christopher R.; Schmiedmayer, Jörg; Chapman, Michael S.; Hammond, Troy D.; Pritchard, David E. (1995-05-01). "Measurement of the electric polarizability of sodium with an atom interferometer". Physical Review A. 51 (5): 3883–3888. Bibcode:1995PhRvA..51.3883E. doi:10.1103/physreva.51.3883. ISSN   1050-2947. PMID   9912059.
  9. ↑ Cronin, Alexander D.; Schmiedmayer, Jörg; Pritchard, David E. (2009-07-28). "Optics and interferometry with atoms and molecules". Reviews of Modern Physics. 81 (3): 1051–1129. arXiv: 0712.3703 . Bibcode:2009RvMP...81.1051C. doi:10.1103/revmodphys.81.1051. hdl: 1721.1/52372 . ISSN   0034-6861. S2CID   28009912.
  10. ↑ Pritchard, D. E.; Raab, E. L.; Bagnato, V.; Wieman, C. E.; Watts, R. N. (1986-07-21). "Light Traps Using Spontaneous Forces". Physical Review Letters. 57 (3): 310–313. Bibcode:1986PhRvL..57..310P. doi:10.1103/physrevlett.57.310. ISSN   0031-9007. PMID   10034027. S2CID   42773639.
  11. ↑ Ketterle, Wolfgang; Davis, Kendall B.; Joffe, Michael A.; Martin, Alex; Pritchard, David E. (1993-04-12). "High densities of cold atoms in adarkspontaneous-force optical trap". Physical Review Letters. 70 (15): 2253–2256. Bibcode:1993PhRvL..70.2253K. doi:10.1103/physrevlett.70.2253. ISSN   0031-9007. PMID   10053514.
  12. ↑ "The Nobel Prize in Physics 2001". NobelPrize.org. Retrieved 2024-02-03.
  13. ↑ Rainville, Simon; Thompson, James K.; Pritchard, David E. (2004-01-16). "An Ion Balance for Ultra-High-Precision Atomic Mass Measurements". Science. 303 (5656): 334–338. Bibcode:2004Sci...303..334R. doi: 10.1126/science.1092320 . ISSN   0036-8075. PMID   14671311. S2CID   10927619.
  14. ↑ Rainville, Simon; Thompson, James K.; Myers, Edmund G.; Brown, John M.; Dewey, Maynard S.; Kessler, Ernest G.; Deslattes, Richard D.; Börner, Hans G.; Jentschel, Michael; Mutti, Paolo; Pritchard, David E. (2005). "A direct test of E=mc2". Nature. 438 (7071): 1096–1097. doi:10.1038/4381096a. ISSN   0028-0836. PMID   16371997. S2CID   4426118.
  15. 1 2 Morote, Elsa-Sofia; Pritchard, David E. (2009-08-01). "What course elements correlate with improvement on tests in introductory Newtonian mechanics?". American Journal of Physics. 77 (8): 746–753. Bibcode:2009AmJPh..77..746M. doi:10.1119/1.3139533. hdl: 1721.1/51717 . ISSN   0002-9505.
  16. ↑ "Relate | Research in Learning, Assessing and Tutoring Effectively" . Retrieved 2023-08-03.
  17. ↑ Chen, Zhongzhou; Chudzicki, Christopher; Palumbo, Daniel; Alexandron, Giora; Choi, Youn-Jeng; Zhou, Qian; Pritchard, David E. (2016). "Researching for better instructional methods using AB experiments in MOOCs: results and challenges". Research and Practice in Technology Enhanced Learning. 11 (1): 9. doi: 10.1186/s41039-016-0034-4 . ISSN   1793-7078. PMC   6302917 . PMID   30613242.
  18. ↑ Chudzicki, Christopher; Pritchard, David E.; Chen, Zhongzhou (2015-03-14). "Learning Experiments Using AB Testing at Scale". Proceedings of the Second (2015) ACM Conference on Learning @ Scale. New York, NY, USA: ACM. pp. 405–408. doi:10.1145/2724660.2728703. hdl: 1721.1/99202 . ISBN   9781450334112. S2CID   42124185.
  19. ↑ Pawl, Andrew; Barrantes, Analia; Cardamone, Carolin; Rayyan, Saif; Pritchard, David E.; Rebello, N. Sanjay; Engelhardt, Paula V.; Singh, Chandralekha (2012). "Development of a mechanics reasoning inventory". AIP Conference Proceedings. 1413 (1). AIP: 287–290. Bibcode:2012AIPC.1413..287P. doi:10.1063/1.3680051. hdl: 1721.1/78556 .
  20. ↑ Pawl, Andrew; Barrantes, Analia; Pritchard, David E.; Sabella, Mel; Henderson, Charles; Singh, Chandralekha (2009). "Modeling Applied to Problem Solving". AIP Conference Proceedings. 1179 (1). AIP: 51–54. Bibcode:2009AIPC.1179...51P. doi:10.1063/1.3266752. hdl: 1721.1/76354 .
  21. ↑ Rayyan, Saif; Pawl, Andrew; Barrantes, Analia; Teodorescu, Raluca; Pritchard, David E.; Singh, Chandralekha; Sabella, Mel; Rebello, Sanjay (2010). "Improved Student Performance In Electricity And Magnetism Following Prior MAPS Instruction In Mechanics". AIP Conference Proceedings. 1289 (1). AIP: 273–276. Bibcode:2010AIPC.1289..273R. doi:10.1063/1.3515221. hdl: 1721.1/63094 .
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