The intermediate quantum states of multiple qubits, generated during the operation of Shor’s factoring algorithm are analyzed. Their entanglement is evaluated using the Groverian measure. It is found that the entanglement is generated during the preprocessing stage of the algorithm and remains nearly constant during the quantum Fourier transform stage. The entanglement is found to be correlated with the speedup achieved by the quantum algorithm compared to classical algorithms.

• Received 25 August 2005

DOI:https://doi.org/10.1103/PhysRevA.72.062308