A lack of empirical evidence has lead to a debate on whether gravity is a quantum entity. Motivated by this, I will present a feasible idea for such a test based on the principle that two objects cannot be entangled without a quantum mediator. I will show that despite the weakness of gravity, the phase evolution induced by the gravitational interaction of two micron size test masses in adjacent matter-wave interferometers can detectably entangle them even when they are placed far apart enough to keep Casimir-Polder forces at bay. A prescription for witnessing this entanglement, which certifies gravity as a quantum coherent mediator, is also provided and can be measured through simple spin correlations. Further, I clarify the assumptions underpinning the above proposal such as our reasonable definition of "classicality", as well as the crucial aspect of the locality of physical interactions. The role of off-shell processes is also highlighted. How the experiment sits within relativistic quantum field theory is clarified. Lastly, the practical challenges are noted. Time permitting other applications of superpositions of nano-crystals, such as in sensing classical gravity and how to detect nonclassicalities of such crystals without preparing superpositions at first, will be discussed.

I will start by introducing a scheme for quantum communication using an unmodulated and unmeasured spin chain. It presents an alternative to converting between static and flying qubits in order to connect up distinct quantum processors. I present some approaches to accomplish perfect quantum communication through a spin chain despite the dispersion of quantum information in the chain. I also discuss the accomplishment of gates between distant spins thorough a spin chain. Apart from transfer, a chain can also be used to simultaneously generate and distribute a maximally entangled state between distant sites, as I illustrate through a chain of coupled qutrits.