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Atoms, Lasers and Computers
Rainer Grobe
Intense Laser Physics Theory Unit
Illinois State University
seea factor 2
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
experiment
Nature Nature
Nature ?
? ?
?
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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 o
f Natu
re
Laws o
f Natu
re
Law
s of Nature
simulation
theorysimulation
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
lim
t 0
(t t) (t)
t
Continuity of time = unjustified assumptionHas mathematics gone too far by requiring t -> 0Do we really need the strict limit
examples for : position temperature field
limits ∞No
Discretization of the laws of nature (∞)
no limits: => choose t finite (t = 1 sec)
(t+t) = (t) + F[(t)] t
future8 00 + 1sec
present 8 00
time
8 00 9 00
(t)
repeat the forward step 3600 times
Computers can do it !
Advantages of Computer Experimentscompared 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 transmission
Dream:Dream:
wave = frequency & amplitude
change amplitude: pulse can carry information
medium
input message output(identical to input)
Reality: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
after before
input signal output 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 levelsmedium 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/cm2
• laser pointer: 10–3
• laser welding: 106
• world record: 1019
≈ 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
it ic mc2 V(r)
(r, t)0
"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 functionfor an atom
ensemble densityfor the same atom
nucleus
electroncloud
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
0.4
0.6
0.8
1
0.8 0.9 1 1.1 1.2 1.3
electron’s velocity
3 108 m/s
108 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: 102
• neutron star: 1015
1013 W/cm2 1010 Gauss
Time evolution of a cycloatom
QuickTime™ and aApple Motion JPEG Format A decompressor
are needed to see this picture.
Articles from Science Writers about Cycloatoms
David Ehrenstein ofPhysical Review Focus“Fast Electrons on the Cheap”Physical Review Focus 5 (April 6, 2000)
Ivars Peterson ofScience News“Ring around the Proton”Science News Vol. 157, No.18, 287 (2000)
Daniel S. Burgess ofPhotonics Spectra“Physicists Play Ring-Around-the-Atom”Photonics Spectra 34, 26 (2000)
Herczeg János ofÉlet es Tudomány“Atomi Hulahopp”Élet Tudomány Vol. 18, May 5 (2000)
Half resonance
QuickTime™ and aGIF decompressor
are needed to see this picture.
Could cycloatoms become important?
cycloatoms generate new light with very high frequencies
L
1
L
2
Laser input
Evolution of the electron’s spin
III. E = mc 2 in space & time resolution
Dream: to simulate how a particle is “born” from pure energy
1928 Dirac equation1932 Positrons discovered1940 Progress in interpretation Feynman/Schwinger1973 Application to quarks1989 First experiment: conversion of laser -> matter2001 Correlated wave function formalism2003 First computer simulations
Questions can now be addressed:Where is the electron born?What is its wave function?What are its coherence
properties?
The birth of an electron-positron pair
The birth of an electron-positron pair
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 FacultyRobert Wagner Harsha Wanare Charles SuPeter Peverly Sunish Menon George RutherfordShannon Mandel Piotr Krekora Michael MarsalliAllen Lewis Hiroshi MatsuokaMichael BellTony Piraino......
ISU supportHonors’ program URG program College of A&S