  We study time-dependent coupled-cluster theory in the framework of nuclear
physics. Based on Kvaal's bi-variational formulation of this method [S. Kvaal,
arXiv:1201.5548], we explicitly demonstrate that observables that commute with
the Hamiltonian are conserved under time evolution. We explore the role of the
energy and of the similarity-transformed Hamiltonian under real and imaginary
time evolution and relate the latter to similarity renormalization group
transformations. Proof-of-principle computations of He-4 and O-16 in small
model spaces, and computations of the Lipkin model illustrate the capabilities
of the method.
