Creating sufficiently strong entanglement between exciton-polaritons is a step of utmost importance towards the exploitation of these systems in quantum information processing with continuous variables. The generation of entanglement relies on the strength of the nonlinearity, which is weak for semiconductor microcavities. Recently, a way to essentially amplify the nonlinearity strength in these systems using two coherent laser fields was suggested, leading in theory to the creation of a fair amount of entanglement between exciton-polaritons in coupled cavities and networks in general. Throughout this process, the Josephson coupling and the enhanced nonlinearity in the two coupled cavities are held constant, with the former always larger. In this work we show that the entanglement generated with the above procedure can be substantially enhanced with the appropriate on-off switching of Josephson coupling between the cavities. Furthermore, we show that if we consider a time-dependent enhanced nonlinearity, through the modulation of the corresponding coherent laser fields, and allow it to attain larger values than the Josephson coupling, then we can generate larger values of entanglement using shortcuts to adiabaticity, a method developed to accelerate quantum adiabatic dynamics. The suggested methodologies are not restricted to exciton-polaritons but are expected to find applications in a wide spectrum of physical contexts, where nonlinear interacting bosons are encountered.
We consider a pair of coupled spins with Ising interaction in z-direction and study the problem of generating efficiently the triplet Bell state. We initially analyze the transitionless quantum driving shortcut to adiabaticity method and point out its limitations when the available duration approaches zero. In this short time limit we explicitly calculate the fidelity of the method and find it to be much lower than unity, no matter how large the available control fields become. We find that there is a lower bound on the necessary time to complete this transfer, set by the finite value of the interaction between the spins. We then use numerical optimal control to find bang-bang pulse sequences, as well as, smooth controls, which can generate high levels of the target Bell state in the minimum possible time. Finally, we explain how this method can be adapted for the efficient generation of general quantum entanglement in the system. The results of the present work are not restricted only to spin systems, but is expected to find also applications in other physical systems which can be modeled as interacting spins, such as, for example, coupled quantum dots.