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.

Quantum cryptography, and quantum communication in general, is built on a set of disruptive concepts and technologies. It is driven by fascinating physics and by promising applications. It requires a new mix of competencies, from telecom engineering to theoretical physics, from theoretical computer science to mechanical and electronic engineering. First applications have already found their way into niche markets, and at the university level, we are already working on futuristic quantum networks, but most of the surprises are still ahead of us. Quantum communication, and more generally quantum information science and technologies, are here to stay and will have a profound impact on the 21st century.Read more...

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...

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...

Single photon detectors are the key components in numerous photonics-related applications such as quantum cryptography, optical time-domain reflectometry, and integrated circuit testing as well as serving diverse applications in metrology, both classical and, more recently, quantum. We are working on several different systems including avalanche photodiodes (APD) superconducting nanowire detectors (SNSPD) and hybrid devices, for various wavelength demands, as well as photon number resolving capabilities. Metrology has a long history at GAP, though our focus has shifted more from telecommunication towards quantum aspects, we continue to take advantage of combining both. A particularly successful area has been in combining single photon detectors and optical time domain reflectometry (OTDR). More recently we have also used the no-cloning theorem as the basis for a practical primary standard for radiated power. 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...