Optically Pumping Nuclear Magnetic Spin

M.R.Ross, D.Morris, P.H. Bucksbaum, T. ChuppPhysics Department, University of Michigan

J. Taylor, N. GershenfeldMIT

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.

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.

Circularly Polarized light

Chemical sample

B

Strong Magnetic field

Genetic AlgorithmWe can improve the effectiveness of the pulses used to pump the liquid by applying a genetic algorithm.

Goal!

Experimental Setup

Coumarin 500Chosen 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 AbsorptionAfter 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.

AbstractOptically 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, indicating why ultrafast measurement is necessary.