Custom Fidelity Computer Question

[Matthew Belzer]

Hello,

I am working on a problem where I am interested in doing Quantum Optimal Control on a subsystem of a large Hamiltonian that is comprised of two coupled systems. To do this numerically in QuTiP, as I understand it, I would have to use a custom Fidelity Computer with CRAB/GRAPE and use it to take a partial trace of the wave vector to get the wave vector of the subsystem that I am interested in. And then, I would have to optimize that using CRAB/GRAPE.

After searching the forum, I have found one thread on custom Fidelity Computers, but it is not recent and the code it links to has errors when I run it. I have tried to update the code (see attached Jupyter File), and I am now getting an error that says:

UsageError: 'No fid_computer (Fidelity computer) set. A default should be assigned by the Dynamics subclass'

Any help on solving this issue and/or implementing a custom fidelity would be appreciated.

Thanks,

Matthew

[Simon Cross]

Hi Matthew,

It might be worthwhile looking at qutip-qoc -- https://github.com/qutip/qutip-qoc. This is a relatively new package in the QuTiP family that provides a more general interface to optimal control problems.

It seems to have an open issue to add support for exactly your use case -- https://github.com/qutip/qutip-qoc/issues/10. If you could comment there, it might be easier for one of the interested developers to implement the feature than to explain / debug the at times quirky interface for the fidelity computers in qutip-qtrl.

Regards,

Simon

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[Matthew Belzer]

Hi Simon, thanks for pointing me in the right direction! I asked the question there.