In this work we experimentally demonstrate that the I. Mastroserio, et al., Paper appeared as back cover on Advanced Quantum Technologies 12/2022. |

A quantum embedding is a map that can be trained to separate and embed classical data points into a much larger Hilbert space. In the case of binary classification problems, this quantum protocol achieves a geometrical representation of the data in which they are easier to be classified. In the era of big data, this algorithm can provide a remarkable simplification of the intensive preprocessing often necessary for Machine Learning algorithms to perform efficiently. We have developed an extensive experimental study of quantum embedding by implementing a parametrized quantum circuit on two complementary experimental platforms: atomic and photonic. We have compared the results with a similar analysis conducted on the cloud-available Rigetti superconducting quantum processor. The successful results support the promising idea of hybrid quantum technologies for future Quantum Machine Learning applications. (Front cover on Adv. Quantum Technol. Volume 5, Issue 8, August 2022) I. Gianani, et al., |

The ideal quantum Zeno effect is a robust method to protect the coherent dynamics of a quantum system. In particular , in the weak quantum Zeno regime, repeated quantum projective measurements can allow the sensing of semi classical field fluctuations. We report our proposal and demonstration, both theoretical and experimental, of a novel noise sensing scheme enabled by the weak quantum Zeno regime. We experimentally tested these theoretical results on a Bose Einstein Condensate of 87Rb atoms realized on an atom chip, by sensing ad hoc introduced noisy fields. H.–V. Do et al., |

A closed-trajectory evolution of a quantum state generally imprints a phase that contains both dynamical and geometrical contributions. While dynamical phases depend on the reference system, geometric phase factors are uniquely defined by the properties of the outlined trajectory. Here, we generate and measure geometric phases in a Bose-Einstein condensate of H.–V. Do et al., |

We demonstrate a tomographic reconstruction algorithm that relies on data collected during the evolution of an unknown quantum state. We estimate the state density matrix as well as the dephasing noise present in the system by assuming complete knowledge of the hamiltonian evolution. Our scheme therefore realizes quantum state tomography but could readily be modified to perform quantum process tomography by assuming complete knowledge of the input states. C. Lovecchio et al., |

Driving the complex dynamics of physical systems to perform a specific task is extremely useful but challenging in several fields of science, and especially for fragile quantum mechanical systems. Even harder, and often unfeasible, is to invert the time arrow of the dynamics, undoing some physical process. We theoretically and experimentally drive forth and back through several paths in the five-level Hilbert space of a Rubidium atom in the ground state. We achieve such an objective applying optimal control strategies to a Bose-Einstein condensate on an Atom chip via a frequency modulated RF field. We further prove that backward dynamical evolution does not correspond to simply inverting the time arrow of the driving field neglecting the only-system part of the dynamics. Apart from the relevance for the foundations of quantum mechanics, these results are important steps forward in the manipulation of quantum dynamics that is crucial for several physical implementations and very promisingly powerful quantum technologies. C. Lovecchio et al., |

It is generally impossible to probe a quantum system without disturbing it. However, it is possible to exploit the back-action of quantum measurements and strong couplings to tailor and protect the coherent evolution of a quantum system. This is a profound and counterintuitive phenomenon known as quantum Zeno dynamics (QZD). Here we demonstrate QZD with a rubidium Bose-Einstein condensate in a five-level Hilbert space. We harness measurements and strong couplings to dynamically disconnect different groups of quantum states and constrain the atoms to coherently evolve inside a two-level subregion. In parallel to the foundational importance due to the realization of a dynamical superselection rule and the theory of quantum measurements, this is an important step forward in protecting and controlling quantum dynamics and, broadly speaking, quantum information processing. F. Schӓfer et al., S. Gherardini et al., |