Philip Bucksbaum

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Chapter 2Control of Electrons and Nuclei in
Atoms, Molecules, and Materials

• Philip Bucksbaum
• Stanford PULSE Center

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Fundamental science challenges Coherence and
Control

• Chapter 2 describes the challenge of
  understanding and controlling coherence in new
  ways.
• Main concepts Coherence and Control
• Quantum coherence in materials control new
  phenomena
• Quantum degeneracy and quantum coherence
• Quantum coherence in photochemistry
• Quantum coherence and information science
• Coherence properties of novel light sources to
  control new materials
• Chemical composition and chemical bond control
• Laser-driven materials properties
• Imaging materials in important new ways

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We know there can be strong connections between
materials and quantum coherence
Superconductivity is just one of a number of
phases related to quantum coherence of electrons
at low temperatures in certain materials.
Sophisticated magnetic materials are used widely
(information storage, nanoscale sensors, and in
the future for spintronics
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The quantum state of matter at low temperatures
Quantum simulators
Vortex arrays in superfluids made of atoms,
molecules, and BCS pairs (Ketterle, MIT)
Challenges Quantum spin liquid at T ? 0 A
triangular antiferromagnetic spin lattice
(Physics Today, February 2007)
The future simulating Quantum Chromodynamics?
((F. Wilczek, Nat. Phys 3, 375 (2007).)
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Excited state chemistry requires a new description
Avoided crossings of spaghetti of states of
diatomics becomes a puff pastry of conical
intersections in polyatomic molecules.
H2O anion - D. Haxton
NH3
H3 - C. H. Greene
The Born-Oppenheimer approximation may be
irrelevant. We dont yet have a language to
describe the physics these experiments can probe
-- W. Kohn
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Why we cant just calculate this stuff
Moores original graph predicting Moores Law in
1965. Chip capacity will double every two years.
This must fail soon (2007). Too bad for us,
because we need much more computing power
Kohns law Traditional multiparticle
wave-function methods when applied to systems of
many particles encounter an exponential wall when
the number of atoms N exceeds a critical value
which currently is in the neighborhood of N10
(to within a factor of about 2) (W. Kohn, Nobel
Prize Address, 1999)
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Quantum simulators, or some other new computing
paradigm, is required
Analog logic? 17nm featureson a crossbar
circuit, showingatomic-scale bumpiness. Analog
circuit elements like memristors may be able to
use such circuits more effectively.
Quantum computing? (Quantum entanglementas a
resource.)
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Intense coherent sub-picosecond x-ray light
sources will be able to track matter at extremes
MD simulation of FCC copper
Periodic features ? average distance
between faults
Diffuse scattering from stacking fault
Peak diffraction moves from 0,0 due to relaxation
of lattice under pressure
0
S. K. Saxena L. S. Dubrovinsky, American
Mineralogist 85, 372 (2000). J. C. Boettger D.
C. Wallace, Physical Review B 55, 2840 (1997). C.
S. Yoo et al., Physical Review Letters 70, 3931
(1993).
0
X-ray diffraction image using LCLS probe of the
(002) shows in situ stacking fault information
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Coherent Control

• The control of quantum phenomena takes
  engineering control principles into the realm of
  quantum mechanics
• Time scales are picoseconds to attoseconds, and
  the size of objects under direct control are
  Angstroms to nanometers.
• The intellectual pay-off of this field is vast
  essentially all dynamics events start with the
  atomic and molecular scale, including all of
  chemistry, and much of materials science.

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COHERENT CONTROL IN MOLECULAR SYSTEMS

• Pulse Shaping the optimal field discovered by
  OCT often has a broad bandwidth, with its phases
  adjusted to give a highly structured pulse.
• Learning Control The learning loop brings the
  same feedback used in optimal control algorithms
  into the laboratory.

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Connections to nature photosynthesisElectron
motion drives nuclear motion
The retinal molecule (light blue) in the center
of rhodopsin bends after absorbin light, to help
move a proton across a membrane. Coherence
enhancement?
Some molecules appears to utilize quantum
coherence in the process of photosynthesis.
Challenges 1. Discover the general principles
for control 2. Real-time feedback for quantum
control
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New Experiments are showing us attosecond
electron dynamics for the first time
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QUANTUM ELECTRON SCATTERING
Figure Collecting an image of a nitrogen
molecule as it undergoes strong-field ionization
and recollision (cartoon at left). The image
collected from the radiation produced in the
recollision is shown at the top right, and a
calculation of the most loosely bound ground
state electron in nitrogen is shown on the bottom
right. (from AMO2010 Controlling the Quantum
World. Original artwork from D. Villeneuve, NRC,
Ottawa.
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X-ray laser science
Figure 13 The LCLS, Linac Coherent Light
Source, when it is completed in 2009 at Stanford
University, will be one-billion times brighter
than currently existing synchrotrons.
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Imaging with XFELs

• XFEL light will be a billion times more brilliant
  than current sources, in bursts shorter than the
  movement of the atoms in a molecule.
• Fundamental mechanisms of damage at such high
  intensities are not well understood.
• Can the coherence of the x-ray laser change the
  character of the damage?

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Questions that frame the challenges in this
chapter

• A. Materials and coherence
• 1. How does electronic quantum coherence affect
  the properties of materials?
• 2. What is the role of quantum coherence in
  dynamics, especially photo-chemistry?
• B. Coherence and control
• 1. How can we control the quantum states of
  matter by applying coherent fields? (Coherent
  control)
• 2. How does matter behave on the timescale of
  electron motion? (Attoscience)
• 3. How can we utilize new generations of coherent
  sources for materials science and chemical
  science?