QUROPE Quantum Information Processing and Communication in Europe

Quantum communication, the transfer of quantum superposition states over long distances, is presently limited to about 200km (both in optical fibre and free space) due to unavoidable photon absorption losses. For this reason, theoretical schemes to extend this distance using “entanglement swapping” and “teleportation” have been established. By concatenating short entanglement swapping sub-sections it is in principle possible to generate entangled (correlated) bits over very long distances with bit rate only limited by the losses in one short section.

Trapped cold ions are among the most advanced systems to implement quantum information processing. In current experiments entanglement of the qubits, represented by long lived internal atomic states, is achieved via quantum control of the (collective) motion of the ion crystal.

Quantum Information Processing and Quantum Communication brought a radical, paradigmatic change in our understanding of the nature of information and of its use. Progress in efficient quantum computation and communication will be possible provided we gain a significantly improved comprehension of the underlying principles of quantum physics, have scalable analysis tools available to study the dynamics, decoherence, as well as the applicability of large quantum states, and, last but not least, have reliable and robust quantum technology components available.

The QScale project focuses on the development of advanced quantum communication technologies, specifically of quantum repeater architectures, which represent a major and timely challenge for the field of quantum information science and technology.

Quantum repeaters are needed in order to overcome losses and errors in the transmission of quantum data. It allows the distribution of entanglement at arbitrary large distances, which is a universal resource for quantum information applications, including quantum cryptography and quantum teleportation.

The aim of QINVC is to exploit the superior quantum coherence of the spins of the negatively charged Nitrogen-Vacancy (NV) colour centres in diamond, at both room and low temperature, for quantum information processing (QIP). This system is indeed among the best solid-state quantum systems in terms of coherence, ease of manipulation by ESR, and addressability down to the single spin using optical microscopy. Our project first focuses on two hybrid strategies for QIP (WP1).

Coherent optics has been known since the 1960’s to be, in principle, the best tool to achieve very high bandwidths and bit rates in optical communication. While the development of fiber optical amplifiers in the 1980’s has reduced the need for developing such a technology, the advent of quantum information sciences has triggered a renewed interest in using coherent optics to realize high-rate quantum communication systems.

Device-Independent Quantum Information Processing represents a new paradigm for quantum information processing: the goal is to design protocols to solve relevant information tasks without relying on any assumption on the devices used in the protocol. For instance, protocols for device-independent key distribution aim at establishing a secret key between two honest users whose security is independent of the devices used in the distribution.

The power of information theory – classical as well as quantum – originates in the abstraction of information from its physical carrier. On this level of discussion, every process, every time evolution and every operation is described by a quantum channel – an input-output relation abstracting from the microscopic origin of the physical dynamics. Quantum channels are therefore central objects and basic building blocks in quantum information theory. The composition of quantum channels is a very natural operation arising in most physical situations.