Augment the Rotosolve optimizer to support Rotoselect

[ValentinS4t1qbit]

Issue: Feature Request

The Rotosolve optimizer is a straightforward method to obtain the optimal value for a single qubit rotation in variational quantum algorithms. The current implementation in Tangelo supports its use in ongoing research involving the Qubit Coupled Cluster algorithm where typically only a single rotation axis is considered. This feature can be easily augmented to the Rotoselect optimizer, which chooses both the optimal angle and axis of single qubit rotation.

• Paper describing Rotoselect: https://arxiv.org/pdf/1905.09692
• Implementation of Rotosolve in Tangelo: https://github.com/goodchemistryco/Tangelo/blob/main/tangelo/toolboxes/optimizers/rotosolve.py

Describe the solution you'd like

The solution would include a separate solver called Rotoselect which modifies the rotation axis (RX, RY, RZ) of the gates in the variational circuit. For each rotation axis, it could call rotosolve_step to find the optimal angle.

Finish line

Testing for this feature should be analogous to the rotosolve tests. The test would require an input variational circuit, and a Hamiltonian to minimize. These should be constructed such that the output optimized circuit has a different rotation axis for at least one rotation gate.

[cburdine]

Hi Valentin,

I'm here for UnitaryHack and thought this might be a good problem for me to tackle. Could you assign me to this issue? Thanks!

[ValentinS4t1qbit]

Game on, @cburdine ! Do your best :)

I recommend you work on something that has the desired behaviour and tries to reuse some Rotosolve code, and then ping @elloyd-1qbit and I to have a quick look at it and give you feedback. Then you should be able to have a clear checklist to take you to the finish line and earn the bounty :)

[ValentinS4t1qbit]

Solved by #392 by @cburdine