  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.
