[Feature]: Virtual Z-gate Loss

[aarontrowbridge]

Feature Description

In certain situations, it is convenient to define a unitary infidelity loss that takes into account the ability of the hardware to easily handle virtual Z-gates. A loss can be written down for this in the form of

$$ \ell(U, \theta) = \mathcal{F}\left( \left(\bigotimes_\alpha Z(\theta_\alpha) \right) U, U_{\text{goal}} \right). $$

Here $\theta$ is a vector of free Z-rotation angles, that are also decision variables. An issue in NamedTrajectories.jl will provide the functionality to store "global" parameters -- parameters that don't depend on time -- to be used as decision variables in the optimizer.

Completing this issue requires:

• implementing functionality to handle global parameters stored in a NamedTrajectory
• implementing the loss defined above with derivatives (either autodiff or tested analytic derivatives)
• documentation for the use of this objective
• a problem template for setting up these types of problems
• test for the problem templates

Importance

3

What does this feature affect?

• quantum system construction
• problem setup
• problem solution
• problem performance
• solution analysis
• plotting
• documentation
• tests
• other (please specify below)

Other information

No response

[andgoldschmidt]

implemented in #149, interface and documentation to come

[andgoldschmidt]

cross reference kestrelquantum/NamedTrajectories.jl#47 for global data