Strongly Driven 2,3,6 Level Quantum Systems

                 
   

Principal Investigator

John P. D. Martin

Research School of Physical Sciences and Engineering

Projects

w08 - PC

       
The nitrogen vacancy (NV) defect centre in diamond is an experimental system that the Solid State
Spectroscopy group of the Laser Physics Centre has been investigating. It has radio frequency (rf) transitions that exhibit many novel nonlinear effects such as lasing without inversion and electromagnetically induced transparency. Such nonlinear effects suggest the possibility of tailoring the properties of materials by controlled application of electromagnetic fields. Since the number of quantum levels strongly driven by electromagnetic fields in the NV centre can be from 2 to 6 levels it is important to understand the change in the nonlinear processes as more levels become involved. Calculation of the nonlinear signals from multilevel quantum systems driven by multiple strong electromagnetic fields requires significant computing power.
   
     
     
         
                 

     

 

 

What are the results to date and the future of the work?

In our previous calculations of the strongly driven 6 level quantum system the relative intensities of the various spectral features were not in sufficient agreement with experiment. The difference was attributed to incorrect modelling of the optically induced spin polarization known to occur in the NV centre of diamond. This process of spin polarization was known to significantly improve the signal strength but through this computational project its quantitative dependence on the spin structure of the NV centre is now being realised. This year modelling of data on the two laser holeburning and electron paramagnetic resonance experiments has greatly improved understanding of the spin polarization process and the excited state fine structure in this optical centre. Figure 1, shows the comparison between observed two laser holeburning and modelling.

Simulations of the multiple strong electromagnetic field excitation experiments will now be resumed. This recent resolution of the role of the spin polarization process should lead to better quantitative agreement with experiment.

What computational techniques are used?

The two laser holeburning modelling shown in Figure 1 was performed on the Power Challenge using the mathematical package Mathematica. The two lasers simultaneously excite transitions from the six ground state levels to an inhomogenously broadened excited state. Decay from

                 
- Appendix A

 
                 

 
           

the excited states involves loss of memory of the original ground state and includes the uncommon spin polarization process. Mathematica provides an excellent platform for setting up the coupled equations describing the competition between optical pumping, excited state decay, spin polarization and ground state relaxation. Inclusion of the effect of inhomogeneous broadening requires summing of the contribution from different homogeneous subgroups. Mathematica also provides easy access to extracting the required calculated components.

Publications

J.P.D. Martin, Fine structure of excited 3E state in nitrogen-vacancy centre of diamond, (accepted for publication by J. Luminesence)

 

 

Figure 1:

   
     

 

 

 

 

 

 

 

 

 

 

Appendix A -