Download or read book Multi-qubit Entanglement and Spin Squeezing in Cavity QED Via Two-photon Driving written by Catherine Leroux and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "We present a generic cavity quantum electrodynamics (QED) set-up that can generate different types of strong multipartite entanglement. The proposed system is already accessible at the experimental level in different cavity QED architectures as it only involves a spin ensemble weakly coupled to a two-photon driven cavity. The first entangling scheme we propose, the dark-mode assisted protocol (DMAP), consists in transferring the squeezing from the cavity to the spin ensemble. The resulting spin squeezed state (with a Kitawaga spin squeezing parameter on the order of 10−2) has strong pairwise entanglement that is especially useful for quantum metrology. In a relatively short timescale (inversely proportional to the collective coupling strength), our scheme can almost reach the quantum Heisenberg limit (with a Wineland spin squeezing parameter close to 2/N), even for a few spins. Unlike one-axis twisting and two-axis countertwisting, the amount of spin squeezing generated by our scheme is not constrained by the number of spins. Our scheme is faster and doesn't suffer the oscillatory dynamics of one-axis twisting. We will also demonstrate how the DMAP can be analyzed as an adiabatic evolution even though achieving adiabaticity might seem impossible in our gapless system. In the second part of the thesis, we build on our previous work which showed that a two-photon drive can be used to simulate ultra-strong coupling in a standard cavity QED system where the cavity is weakly coupled to a single qubit. We extend this approach to a cavity weakly interacting with a spin ensemble and simulate the Dicke model, which is known to exhibit interesting quantum features such as strong entanglement and quantum phase transitions. The other entangling schemes we propose, make use of the simulated Dicke model: the realization of a Molmer-Sorenson gate, closely related to one-axis twisting, and the generation of large multipartite entangled cat-states. We demonstrate how our scheme can be used to prepare a remote entanglement protocol, a key ingredient in quantum information, where the weakly interacting Hamiltonian is used to grow a Greenberger-Horne-Zeilinger state which will then be transformed into an entangled-cat state by the simulated Dicke Hamiltonian. Finally we illustrate how our system can become an interesting platform to study superradiant phase transition and as well as the effects of squeezed input noise." --