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

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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