Free-Time and Fixed End-Point Multitarget Optimal Control Theory Applied to Quantum Computing

Abstract

Quantum computing and quantum information science are expected to be one of the newest technologies in the next generation. In this article, we focus on theoretical and numerical studies on quantum computing and entanglement generation using molecular internal degrees of freedom (electronic, vibrational, and rotational). We have proposed one method of creating the Bell states and arbitrary linear superposition states in molecular vibrational–rotational modes by using sequential chirped laser pulses. In addition, the numerical simulations of Deutsch–Jozsa algorithm using several combinations of the molecular internal states are reported and compared them from the viewpoint of fidelity of the measurement results of the sender. It turned out that rotational modes of polar molecules coupled by dipole–dipole interaction are the most promising candidates for molecular quantum computing. In connection with quantum computing and entanglement manipulation by external laser fields, we have constructed free-time and fixed end-point optimal control theories (FRFP-OCTs) for the quantum systems without and with dissipation. Using the theories, we have performed simulations of entanglement generation and maintenance. From the numerical results, we have found that FRFP-OCT is more efficient than the conventional fixed-time and fixed end-point optimal control theory (FIFP-OCT) because the optimal time duration of the external laser fields can also be determined exactly using FRFP-OCT.