  The standard method of Quantum State Tomography (QST) relies on the
measurement of a set of noncommuting observables, realized in a series of
independent experiments. Ancilla Assisted QST (AAQST) proposed by Nieuwenhuizen
and co-workers (Phys. Rev. Lett., 92, 120402 (2004)) greatly reduces the number
of independent measurements by exploiting an ancilla register in a known
initial state. In suitable conditions AAQST allows mapping out density matrix
of an input register in a single experiment. Here we describe methods for
explicit construction of AAQST experiments in multi-qubit registers. We also
report nuclear magnetic resonance studies on AAQST of (i) a two- qubit input
register using a one-qubit ancilla in an isotropic liquid-state system and (ii)
a three-qubit input register using a two-qubit ancilla register in a partially
oriented system. The experimental results confirm the effectiveness of AAQST in
such many-qubit registers.
