A feasible approach for automatically differentiable unitary coupled-cluster on quantum computers. Issue 10 (27th January 2021)

• Record Type: Journal Article
• Authors: Kottmann, Jakob S.; Anand, Abhinav; Aspuru-Guzik, Alán
• Is Part Of: Chemical science. Volume 12:Issue 10(2021)
• Page Start: 3497
• Page End: 3508
• Publication Date: 2021-01-27
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d0sc06627c
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : We develop computationally affordable and encoding independent gradient evaluation procedures for unitary coupled-cluster type operators, applicable on quantum computers. Abstract : 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 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.