  Entanglement has been termed a critical resource for quantum information
processing and is thought to be the reason that certain quantum algorithms,
such as Shor's factoring algorithm, can achieve exponentially better
performance than their classical counterparts. The nature of this resource is
still not fully understood: here we use numerical simulation to investigate how
entanglement between register qubits varies as Shor's algorithm is run on a
quantum computer. The shifting patterns in the entanglement are found to relate
to the choice of basis for the quantum Fourier transform.
