Deterministic one-way logic gates on a cloud quantum computer

One-way quantum computing is a promising candidate for fault-tolerant quantum computing. Here, we propose new protocols to realize a deterministic one-way CNOT gate and one-way $X$-rotations on quantum-computing platforms. By applying a delayed-choice scheme, we overcome a limit of most currently available quantum computers, which are unable to implement further operations on measured qubits or operations conditioned on measurement results from other qubits. Moreover, we decrease the error rate of the one-way logic gates, compared to the original protocol using local operations and classical communication (LOCC). In addition, we apply our deterministic one-way CNOT gate in the Deutsch-Jozsa algorithm to show the feasibility of our proposal. We demonstrate all these one-way gates and algorithms by running experiments on the cloud quantum-computing platform IBM Quantum Experience

Multi-photon entanglement and interferometry

Multi-photon interference reveals strictly non-classical phenomena. Its applications range from fundamental tests of quantum mechanics to photonic quantum information processing, where a significant fraction of key experiments achieved so far comes from multi-photon state manipulation. We review the progress, both theoretical and experimental, of this rapidly advancing research. The emphasis is given to the creation of photonic entanglement of various forms, tests of the completeness of quantum mechanics (in particular, violations of local realism), quantum information protocols for quantum communication (e.g., quantum teleportation, entanglement purification and quantum repeater), and quantum computation with linear optics. We shall limit the scope of our review to "few photon" phenomena involving measurements of discrete observables.Comment: 71 pages, 38 figures; updated version accepted by Rev. Mod. Phy

Simulation of open quantum dynamics and investigation of quantum correlations in finite systems

This thesis reports a series of theoretical studies regarding the dynamics of fewbody controllable quantum systems. Generally speaking, the main focus is on the behavior of correlations in open quantum systems and how these could be used both for applications to quantum technologies and investigations of more fundamental phenomena. The general physical setting for most of the results presented is trappedion systems. These have been proven to be an almost prefect practical platform for realizing a quantum computer. Furthermore, thanks to their exceptional degree of controllability, trapped ions have been lately employed to also simulate basic physics, ranging from condensed-matter to high-energy physics. Although the ndings in this manuscript are theoretical, real experimental parameters have been taken into account in order to provide a more realistic modeling. To this aim, a mixed of analytical and numerical methods have been extensively utilized. Concluding, we do believe that the theory developed in this thesis could be experimentally tested to give a more insightful view on open quantum system dynamics, both from a foundational and applicative point of view