2020/11/11 by Jakob S. Kottmann, Abhinav Anand, Alán Aspuru-Guzik · 2 citations
Physics and Astronomy · #quant-ph #physics.chem-ph #physics.comp-ph
paper · pdf · doi:10.1039/d0sc06627c
arxiv created 2020/11/11 · arxiv updated 2021/01/28
We develop computationally affordable and encoding independent gradient evaluation procedures for unitary coupled-cluster type operators, applicable on quantum computers. We show that, within our framework, the gradient of an expectation value with respect to a parameterized n-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 O(2^(2n)) 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 for electronic ground and excited states.