A feasible approach for automatically differentiable unitary coupled-cluster on quantum computers
Jakob S. Kottmann, Abhinav Anand, Alán Aspuru-Guzik · Chemical Science · 2021
-fold fermionic excitation can be evaluated by four expectation values of similar form and size, whereas most standard approaches, based on the direct application of the parameter-shift-rule, come with an associated cost of expectation values. For real wavefunctions, this cost can be further reduced to two expectation values. Our strategies are implemented within the open-source package Tequila and allow blackboard style construction of differentiable objective functions. We illustrate initial applications through extended adaptive approaches for electronic ground and excited states.