主 题：Almost quantum correlations
The correlations achievable between distant observers living in a quantum universe exhibit a very peculiar correlation structure. Different authors have tried to capture this structure through reasonable physical principles; the working hypothesis being that "the world is quantum not by chance, but because there is just no other way". To counter this claim, in this talk I will introduce the almost quantum set, a theoretical set of multipartite supra-quantum correlations. The almost quantum set is not only physically consistent, but also happens to satisfy all physical principles proposed so far to single out the set of quantum correlations. My results therefore suggest that our world might not be quantum after all.
主 题：Resetting uncontrolled quantum systems
We consider a scenario where we wish to bring a closed system of known Hilbert space dimension dS (the target), subject to an unknown Hamiltonian evolution, back to its quantum state at a past time t0. The target is out of our control: this means that we ignore both its free Hamiltonian and how the system interacts with other quantum systems we may use to influence it. Under these conditions, we prove that there exist protocols within the framework of non-relativistic quantum physics which reset the target system to its exact quantum state at t0. Each "resetting protocol" is successful with non-zero probability for all possible free Hamiltonians and interaction unitaries, save a subset of zero measure. When the target is a qubit and the interaction is sampled from the Haar measure, the simplest resetting circuits have a significant average probability of success and their implementation is within reach of current quantum technologies. Finally, we find that, in case the resetting protocol fails, it is possible to run a further protocol that, if successful, undoes both the natural evolution of the target and the effects of the failed protocol over the latter. By chaining in this fashion several such protocols, one can substantially increase the overall probability of a successful resetting.
主 题：Chunking quantum networks
As quantum technologies develop, we acquire control of an ever-growing number of quantum systems. Unfortunately, current tools to certify non-classical properties of quantum states, such as entanglement and nonlocality, are just practical for systems of a very modest size, of around 4 sites. Our approach to solve this “many-body quantum information problem” consists in devising linear witnesses which admit an exact tensor network state representation. The resulting method, connector theory, allows us to certify entanglement, Bell nonlocality and supra-quantum Bell nonlocality in networks with hundreds of sites in a matter of seconds.
编辑：杨棋凌 / 审核：罗莎 / 发布者：陈伟