QUROPE Quantum Information Processing and Communication in Europe

As part of their ongoing effort to chart and shape the evolving landscape of future and emerging technologies, FET have launched a public consultation to identify promising and potentially game-changing directions for future technological research. QUTE-EUROPE WP2 has submitted an idea regarding Quantum Technologies.

We explore the existence of entangling dynamics in a large family of theories which contains quantum theory as a special case. We classify all continuously-reversible and locally-tomographic theories for bipartite systems where each subsystem has a state space with the geometry of a Euclidean ball (like the Bloch ball of a qubit but with dimension not necessarily equal to three). We show that the only theory in this family which has interacting dynamics is quantum theory, and all the other theories do not allow for entanglement nor violation of Bell inequalities.

In recent years, the use of information principles to understand quantum correlations has been very successful. Unfortunately, the programme is limited by the fact that all principles considered so far have a bipartite formulation, but intrinsically multipartite principles, yet to be discovered, are necessary for reproducing quantum correlations. In this work, we introduce the principle of Local Orthogonality, an intrinsically multipartite principle which states that events involving different outcomes of the same local measurement must be exclusive, or orthogonal.

Does information play a significant role in the foundations of physics? Information is the abstraction that allows us to refer to the states of systems when we choose to ignore the systems themselves. The viability of this can be formalized by postulating the existence of an information unit such that the state of any system can be reversibly encoded in a sufficient number of such units (bits/qubits in the classical/quantum case). This property of classical and quantum theory is not true in general, so we promote it to a postulate.

Quantum mechanics dramatically differs from classical physics, allowing for a wide range of genuinely quantum phenomena. The goal of quantum information is to understand information processing from a quantum perspective. In this mindset, it is thus natural to focus on tasks where quantum resources provide an advantage over classical ones, and to overlook tasks where quantum mechanics provides no advantage. But are the latter tasks really useless from a more general perspective?

Discrete-time quantum walks (QWs) represent robust and versatile platforms for the controlled engineering of single particle quantum dynamics, and have attracted special attention due to their algorithmic applications in quantum information science. Even in their simplest 1D architectures, they display complex topological phenomena, which can be employed in the systematic study of topological quantum phase transitions [1].

We study the fractional quantum Hall phases of a pseudospin-1/2 Bose gas in an artificial gauge field. In addition to an external magnetic field, the gauge field also mimics an intrinsic spin-orbit coupling of the Rashba type. While the spin degeneracy of the Landau levels is lifted by the spin-orbit coupling, the crossing of two Landau levels at certain coupling strengths gives rise to a new degeneracy. We therefore take into account two Landau levels, and perform exact diagonalization of the many-body Hamiltonian.

Existing techniques for synthesizing gauge fields are able to bring a two-dimensional cloud of harmonically trapped bosonic atoms into a regime where the occupied single-particle states are restricted to the lowest Landau level. Repulsive short-range interactions drive various transitions from fully condensed into strongly correlated states. In these different phases we study the response of the system to quasihole excitations induced by a laser beam.

Existing techniques for synthesizing gauge fields are able to bring a two-dimensional cloud of harmonically trapped bosonic atoms into a regime where the occupied single-particle states are restricted to the lowest Landau level (LLL). Repulsive short-range interactions drive various transitions from fully condensed into strongly correlated states. In these different phases we study the response of the system to quasihole excitations induced by a laser beam.

The concentration and distribution of quantum entanglement is an essential ingredient in emerging quantum information technologies. Much theoretical and experimental effort has been expended in understanding how to distribute entanglement in one-dimensional networks. However, as experimental techniques in quantum communication develop, protocols for multi-dimensional systems become essential.