Real-time deterministic generation of maximally entangled two-qubit and three-qubit states via bang-bang control

We exploit the notion of SWM-(simultaneous-weak-measurements)-induced quantum state reduction, enabling the use of measurement backaction to produce the desired quantum states. The probabilistic generation of maximally entangled Bell states and the |GHZ > (Greenberger-Horne-Zeilinger) state are then performed as a consequence of this notion. By combining SWM-induced quantum state reduction with feedback control, we are able to deterministically generate any desired Bell state as well as the |GHZ > state, without the knowledge of the initial state. The control-computation time is compensated for by the delay time in the time-delay bang-bang control, through which the real-time implementation of the control scheme is guaranteed. The effectiveness of the proposed scheme is illustrated numerically.