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Department of Physics

Professor Calvin W. Johnson

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   What does a computational quantum mechanic do?

     I have two overarching goals:

     Firstbetter numerical solutions of the many-body Schrodinger equation, especially for atomic nuclei. These primarily come as large-scale diagonalization of Hamiltonian matrices, with dimensions up to a billion or more, often carried out on cutting-edge parallel supercomputers.  Because such brute-force solutions are so difficult to come by, I also explore and test common approximations to the many-body problem, such as Hartree-Fock and the random phase approximation. I also explore random matrix models of many-body physics.

     What this boils down to is writing efficient computer codes, mostly in modern Fortran (with parallelization via MPI and OpenMP), most of which either involved finding eigensolutions of very large matrices, using the BIGSTICK code written with Erich Ormand and others, or approximations to those eigensolutions. 

      Because of this, I often have Ph.D students in SDSU's Joint Doctoral Program in Computational Science, which I think of as science with big computers.  The two are not separate; being a good coder is not enough.  In order to write efficient code you have to understand the science. For example, the BIGSTICK code achieves an enormous compression of a large, sparse matrix by utilizing quantum numbers (conserved quantities).   If you like both physics and computing, you should think about working with me.

     Second, to apply those solutions and use nuclei as a laboratory for fundamental physics and astrophysics.  Some of the questions I explore include:

* What is the nature of the forces between nucleons?

* How do neutrinos interact with matter? How do those interactions affect astrophysical phenomena, such as core-collapse supernova and nucleosynthesis?  How can we use neutrinos to probe astrophysical events?

* What is the nature of the weak nuclear force?

* What is the nature of the neutrino mass?

* What is dark matter, and how can we detect it? 

* Nuclei exhibit many complex behaviors, such as collective deformation and clustering. At high energy nuclei can be modeled by random matrices, but at low energies they exhibit quite orderly behavior. How can we understand that order? Does it depend sensitively upon the details of the nuclear force, or is there something more fundamental how order arises in many-body systems?

    Overview of my research

    Some of my current projects

    Recent and current student research

    Research projects for prospective students