The Group of Applied Physics (GAP) has been a key player in the emerging field of quantum communication and
associated quantum technologies and remains one of the leading groups. We have groups working on both theory and
experiment and addressing topics ranging from the fundamental to the applied.
Nonlocality and Entanglement
Bell inequalities provide a powerful approach for studying both entanglement and nonlocality and have had an enormous impact on the foundations of quantum physics. We are studying, both theoretically and experimentally, fundamental questions about these concepts. Recently, the theoretical work has looked towards multipartite scenarios as well as towards future application such as Device Independent QKD. The experimental effort has previously looked at implementing different tests of quantum mechanics and questions on nonlocality and is following the theoretical move towards more complex, multipartite and distributed systems. We are also developing the techniques for efficiently and coherently coupling multiple quantum systems together to realise these experiments. Read more...
Entanglement is most striking feature of quantum mechanics, but is it limited to the microscopic world only? Is there a fundamental limit to how “macroscopic” entanglement be?
This question is as old as quantum mechanics itself. Recent theoretical and experimental
progress in quantum optics is now opening new and tantalizing ways to explore the ramification of this question. Read more...
Quantum Memories and Repeaters
Quantum Memories are devices that can store the quantum state of a photon, without destroying the volatile quantum information. These will be key components in future quantum networks, such as Quantum Repeaters which can provide a solution for long-distance quantum communication beyond the limit of 200 km using today's technology (see Quantum cryptography above). In addition to future applications, Quantum Memories are fascinating because they provide a way to study how quantum effects such as entanglement can be transferred between physical systems of widely different nature, eg. between light and matter systems. In our research we study light-matter interactions between photons, in the visible and telecommunications wavelength, with rare-earth-metal ions doped into optical crystals. These are highly interesting Quantum Memory materials since they have excellent coherence properties when cooled to below 4 Kelvin. This is crucial in order to avoid destroying the quantum interaction through local interactions such as with phonons. Using ideas developed in our research we have achieved several milestones, for example the first storage of a pseudo single photons, storage of multiple photonic qubits in a single neodymium-doped crystal, and more recently storage of a visible photon entangled with a telecom photon. Read more...
Quantum communication is one of the central themes at GAP. From seminal QKD experiments under lake Geneva to teleportation experiments in real-world communication networks, the GAP in Geneva has become synonomous with quantum communication. Behind these ground breaking experiments has been a steady development of novel quantum photonic technologies, not only for quantum communication but for diverse applications and fundamental tests of Nature. Central to many of these endeavours is entanglement and this provides us with somewhat of a leitmotif - that entanglement is not only fascinating, but also useful – a resource. Read more...