Transcript NMRTalk - University of Michigan

Optically Pumping Nuclear
Magnetic Spin
M.R.Ross, D.Morris, P.H. Bucksbaum, T. Chupp
Physics Department, University of Michigan
J. Taylor, N. Gershenfeld
MIT
Goals
Show that short laser pulses can add
angular momentum, or Quantum spin,
to electrons in a liquid sample.
Transfer this Quantum spin to nuclei of
the sample molecules.
Evaluate this NMR system for
applications to Quantum Computers or
detailed structure studies.
Optically Pumping Nuclear Spin
1. Laser light pulses
are circularly
polarized.
B
Chemical sample
Circularly Polarized light
Strong Magnetic field
2. A sample molecule
absorbs the photon the
electron receives one unit
of angular momentum.
3. Relaxation
of interacting
states or
microwave
pulses in a
strong
magnetic field
transfer
electron spin to
nuclear spin.
Genetic Algorithm
Goal!
We can
improve the
effectiveness of
the pulses used
to pump the
liquid by
applying a
genetic
algorithm.
Experimental Setup
Coumarin 500
Chosen because…
Has known singlet to triplet
transition
The three Fluorine atoms can
provide a clean NMR signal
Has a strong absorbance in an
accessible region of the
spectrum
Measuring Spin Absorption
After the pump of circularly polarized light is absorbed,
giving electron spin. We can use linear polarized light to
detect the absorption, or we can use the NMR machine.
NMR Magnet
Mirror
This is one of several boxes used to transfer the light to the NMR machine
safely. It contains two small stepper motors that are used to change the
angle of the mirror to ensure the light reaches it’s intended target.
Initial Results
Conclusions and Future
Experimentation
We have preliminary evidence that electron spin can be
optically pumped by short laser pulses. This polarization
has a relatively fast decay time, on the order of a
hundred picoseconds. Transfer or this electron spin to
nuclear spin may extend the polarization substantially.
Experimental runs with the NMR magnet are ongoing.
More work will be done to improve the pulse shape that
is sent into the sample.
Abstract
Optically pumping angular momentum, or
quantum spin, into a liquid system for studies
in Nuclear Magnetic Resonance (NMR).
Previous work done in solids was limited by
the length of laser pulses. Using ultrafast laser
technology we should be able to optically
pump nuclear polarization into a liquid sample
and study the properties of this polarization.
Using ultrafast circularly polarized light,
electronic spin can be polarized and relaxation
gives nuclear polarization. Early results
indicate that the decay of electron polarization
is on the order of the expected time for
molecular rotations or about 150 picoseconds,