Quantum Simulations with Unitary & Nonunitary Controls: NMR implementations

Abstract: Feynman, in 1982, proposed the idea of using a quantum simulator to perform quantum simulations. A quantum simulator is basically a controllable quantum system that can mimic the dynamics of other quantum systems we wish to study. In this thesis we investigate some aspects of quantum simulation using both unitary and nonunitary controls. In the unitary part, we experimentally simulated the phenomenon of quantum many-body freezing, and also developed a general protocol to decompose an arbitrary unitary operator. In the nonunitary part, we studied phase decoherence by artificially inducing it. We characterized it by noise spectroscopy and quantum process tomography, and also suppressed it by using standard dynamical decoupling techniques. While we use nuclear spin systems in an NMR setup as our quantum testbed, most of the concepts are general and are applicable elsewhere.