Abstract An effective scheme is proposed for preparing large-scale maximally entangled W states by fusing arbitrary-size polarization entangled W or W -like states via polarization-dependent beam splitter (PDBS). In our scheme, W m + n −1 state can be generated from an n -qubit W state and an m -qubit W state, and W m + n + t −2 state can be generated from W m , W n and W t states. The fusion process can start with Bell states too. Because PDBS has selective transmission rates for different polarization states, our fusion has a distinct property, i.e. a large-scale maximally entangled W state can be generated by fusing small-size W -like states, and the cost analyses indicate that our fusion scheme is more efficient than the previous one in fusing W -like states. In addition, there is no need for any controlled quantum gate and any ancillary photon in our scheme, so it is simple and feasible.
Greenberger-Horne-Zeilinger (GHZ) state is a typical maximally entangled state which is pursued in both fundamental research and emerging quantum technologies. Preparing large-scale GHZ states in lattice spin systems is particularly appealing for quantum advantages, but conventional schemes face great challenges in scalability. Here we propose a universal and scalable scheme to generate large-scale GHZ-like states, which share similar entanglement and metrological properties with standard GHZ states, in lattice spin systems through global Floquet engineering. Our scheme requires only global operations and shows great advantage for large particle number. It is applicable to systems with arbitrary interaction ranges, offering a practical pathway for large-scale implementation of many-body entangled states in various systems.
We show that when $N\ensuremath{\gg}1$ the geometric entanglement measure of general
N-qubit
W states, except maximally entangled
W states, is a one-variable function and depends only on the Bloch vector with the minimal
z component. Hence one can prepare a
W state with the required maximal product overlap by altering the Bloch vector of a single qubit. Next we compute analytically the geometric measure of large-scale
W states by describing these systems in terms of very few parameters. The final formula relates two quantities, namely the maximal product overlap and the Bloch vector, that can be easily estimated in experiments.