  Quantum control of large spin registers is crucial for many applications
ranging from spectroscopy to quantum information. A key factor that determines
the efficiency of a register for implementing a given information processing
task is its network topology. One particular type, called star-topology,
involves a central qubit uniformly interacting with a set of ancillary qubits.
A particular advantage of the star-topology quantum registers is in the
efficient preparation of large entangled states, called NOON states, and their
generalized variants. Thanks to the robust generation of such correlated
states, spectral simplicity, ease of polarization transfer from ancillary
qubits to the central qubit, as well as the availability of large
spin-clusters, the star-topology registers have been utilized for several
interesting applications over the last few years. Here we review some recent
progress with the star-topology registers, particularly via nuclear magnetic
resonance methods.
