Time-Dependent Coupled-Cluster Formalism for the Propagation of Quantum Superpositions

Predicting the time-evolution of atomic and molecular systems is a well-known challenge in the fields of computational physics and chemistry. Such endeavor includes formulating theories that are compatible with conventional computing architectures and that rely on linked many-body interaction diagrams. Within the context of coupled-cluster theory, in this work we discuss our efforts at developing an electronic structure framework to propagate non-ground-states, with emphasis on multireference systems. The proposed theory is based on the differential analysis of conventional coupled-cluster operators that are subject to modifications in which the ground state is slightly perturbed by an initial state of interest. This leads to a set of dynamical cluster operators and equations that describe the time-evolution of that initial state, which can be an entangled state or a different type of linear superposition. In numerally exact model systems, we observe the proposed formalism reproduces their behavior with high accuracy. Furthermore, we discuss the computation of symmetric quantum mechanical observables, and future directions.