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Ancilla Assisted Quantum Information Processing: General protocols and NMR implementations

While a bit is the fundamental unit of binary classical information, a qubit is the fundamental unit of quantum information. In quantum information processing (QIP), it is customary to call the qubits under study as system qubits, and the additional qubits as ancillary qubits. In this thesis, I describe various schemes to exploit the ancillary qubits to efficiently perform many QIP tasks and their experimental demonstrations in nuclear magnetic resonance (NMR) systems. Particularly, we have showed that, in the presence of sufficient ancillary qubits, it is possible to completely characterize a general quantum state as well as a general quantum dynamics in a single measurement. In addition, it is also possible to exploit ancillary qubits for realizing noninvasive quantum measurements required for several experiments related to quantum physics. I will also illustrate some interesting applications of ancillary qubits in spectroscopy. At last, I describe an experimental study of the efficiency of various dynamical decoupling sequences for suppressing decoherence of single as well as multiple quantum coherences on large spin-clusters. The experiments reveal the superior performance of the recently introduced RUDD sequences in suppressing decoherence.