Professor George Skadron Physics Chair 1986 - 1997
Skadron’s physics niche for ISU challenge: specialization (without too narrow expertise) top notch research agenda solution: Computational Physics => unique education for our undergraduate students
Traditional Physics Nature experiment theory experiment Nature ? ? ? ?
G T W x ( G T W x ( W x ( G T W x ( x W x ( The new problem Laws of nature are established but: we can’t solve the equations.... solution: Computers can calculate numbers example : x = 2 - x => x=0.611857....
Laws of Nature Modern Physics Laws of Nature simulation theory simulation
Structure of the laws of nature know: (t=8 00 ) system at 8 00 goal: (t= 9 00 ) predict future at 9 00 examples for F: Newton Maxwell Dirac = F [ (t) ] rate of change of = function of Continuity of time = unjustified assumption Has mathematics gone too far by requiring t -> 0 Do we really need the strict limit examples for : position temperature field
Discretization of the laws of nature (∞) no limits: => choose t finite ( t = 1 sec) (t+ t) = (t) + F[ (t)] t future 8 00 + 1sec present 8 00 time 8 00 9 00 (t) repeat the forward step 3600 times Computers can do it !
Advantages of Computer Experiments compared to laboratory experiments safer cheaper exactly reproducible all ingredients controllable simultaneous measurements insight into ultrafast mechanisms most importantly: going beyond present technology
Impact of computer experiments on research areas nonlinear dynamics and chaos space-plasma physics solid state physics laser science
3 examples of breakthroughs due to computer simulations 1996 : Adiabatons 2000 : Cycloatoms 2003 : Birth of matter
I. Optical signal transmissionDream: wave = frequency & amplitude change amplitude: pulse can carry information medium input message output (identical to input) Reality: medium input message output (distorted & damped)
Challenge: prevent losses & distortion input medium almost no output Second beam can protect the original field ! input medium output “control the optical properties of medium”
Computer simulations of adiabatons prediction by computer simulation : 1994 experimental verification (Stanford Univ.) : 1996 bodyguard afterbefore input signaloutput signal
Could adiabatons become important? applications in optical switches wavelength converter non-demolition signal replicator pulse-shape controller long distance transmission
storage: recall: Storage and recall of optical information Jennifer Csesznegi and RG, Phys. Rev. Lett. 1997 energy levels medium in ground state medium in excited state
1997: Discovery of this effect in computer simulations 1999: Experimental verification at Harvard: measured speed of light: only 17 m/s (factor of 20 million!) New York Times (Front page on February 18) Glossy article in Time Magazine Appreciation of the value of computer simulations is growing.. Laboratory experiments are presently viewed as important
II. Atom in strong laser fields Laser intensities in W/cm 2 laser pointer: 10 –3 laser welding: 10 6 world record: 10 19 ≈ 1000 lighting bolts
13 Publications 14 Conference presentations Barry Goldwater Scholarship USA All Academic Team Leroy Apker Award in 2002 now a graduate student at Princeton Robert Wagner (Computer Physics Major 1998-2002)
Power and curse of quantum mechanics most accurate description of nature: example: electron’s mag. moment: experiment: 1.0015965219 Dirac: 1.0015965220 "I think I can safely say that nobody understands quantum mechanics." Richard Feynman P.A.M. Dirac When does an atom decay ?............. no answer Where is the electron ?............. no answer
conceptual: provides only probabilities approximate quantum wave function by an ensemble of quasiparticles Difficulties with quantum mechanics technical: difficult to solve Alternative approach use Newtonian mechanics...does it work ?
Quantum mechanics ≈ Classical ensemble ! wave function for an atom ensemble density for the same atom nucleus electron cloud
Patience is better than brute force Trick: use the resonance magnetic field laser field very fast electron strong laser only => fast electrons => electron oscillates magnetic field only => electron orbits in circle + = Past belief:
Use resonance to accelerate electron laser field frequency = cyclotron frequency => no need for expensive high-power lasers electron’s velocity 3 10 8 m/s 10 8 m/s speed of light magnetic field strength 80% of c
Computer simulation of a hydrogen atom in a strong laser and magnetic field magnetic field strengths: earth: 1 magnet: 10 2 neutron star: 10 15 10 13 W/cm 2 10 10 Gauss
Articles from Science Writers about Cycloatoms David Ehrenstein of Physical Review Focus “Fast Electrons on the Cheap” Physical Review Focus 5 (April 6, 2000) Ivars Peterson of Science News “Ring around the Proton” Science News Vol. 157, No.18, 287 (2000) Daniel S. Burgess of Photonics Spectra “Physicists Play Ring-Around-the-Atom” Photonics Spectra 34, 26 (2000) Herczeg János of Élet es Tudomány “Atomi Hulahopp” Élet Tudomány Vol. 18, May 5 (2000)
III. E = mc 2 in space & time resolution Dream: to simulate how a particle is “born” from pure energy 1928 Dirac equation 1932Positrons discovered 1940Progress in interpretation Feynman/Schwinger 1973Application to quarks 1989 First experiment: conversion of laser -> matter 2001Correlated wave function formalism 2003First computer simulations Questions can now be addressed: Where is the electron born? What is its wave function? What are its coherence properties?
Are e _ and e + born at same location? Electron and positron are born “on top of each other” electron & positron’s uncertainty cloud no simultaneous occurence
Collaborators at ISU Students PostDocs Faculty Robert WagnerHarsha Wanare Charles Su Peter PeverlySunish Menon George Rutherford Shannon MandelPiotr Krekora Michael Marsalli Allen Lewis Hiroshi Matsuoka Michael Bell Tony Piraino...... ISU support Honors’ program URG program College of A&S