Physics is fascinating because of the intellectual excitement it provides and because of the applications it offers. In the Group of Applied Physics (GAP) at Geneva University we get our inspiration from both of these motivations. Optics, in this respect, has a privileged place. Indeed, in modern optics, experiments and theory progress hand-in-hand, and practical applications are close behind. Consequently, we can work both on conceptual issues and on applications. Moreover, it is a very good time for optics! The fascinating new insight about quantum mechanics brought about by recent quantum optics experiments on one side, and the tremendous development of optical communications on the other, illustrates our privileged position!
The American Research Council has recently declared optics as the technology of the 21st century. In contrast, a famous physicist, Michael Berry, has declared that the 21st century will be shaped by quantum physics, in a way similar to electrodynamics, which shaped the 20th century. Our position in GAP-Optique, at the crossroads between optics and quantum physics, ensures our participation to both challenges.
Prof. Nicolas Gisin, Group Leader
Quantum mechanics predicts microscopic phenomena with undeniable success. Nevertheless, current theoretical and experimental efforts still do not yield conclusive evidence that there is or is not a fundamental limitation on the possibility to observe quantum phenomena at the macroscopic scale.
In a recent publication in Physical Review Letters, we report on the generation of entangled state which involves the superposition of two macroscopically distinguishable solid-state components composed of several tens of atomic excitations.
Our experiment is clearly demonstrating micro-macro light-matter entanglement.
The Nature News highlights the discussion about arXiv screening policies which was triggered by the blog post written by Prof. Nicolas Gisin in December 2015. It describes the incident of an unsuccessful publication by two of his students on arXiv. The preprint was rejected by the moderators without reasonable justification. Professor Gisin indicates that such practice can have a big impact on young researchers’ careers.
Popular article "Teleporting light" written by Felix Bussieres was selected to be a part of a book "Inspired by Light: Reflections from the International Year of Light 2015". It comprises various contributions to the blog devoted to the International Year of Light (IYL 2015) and was published by SPIE in January 2016.
Communication through optical fibers has revolutionized the way people access information and has given rise to the network of connected computer nodes known as the internet. The photons that traverse the fibers are also nearly ideal carriers of quantum information. Today physicists are developing the technologies needed for a quantum version of the information network, which might be used for, among other applications, long-distance cryptography, distributed quantum computing, and remote sensing.
Quantum memories, another key building block, would act as the nodes where the photons—or rather, their quantum states—are temporarily stored while the system completes some other processing in the network. The quantum state of a photon can be transferred to a single trapped atom or to a bunch of atoms in a gas or solid and be stored for later release on demand. The spectacular progress in this field is discussed in our recent article published in Physics Today journal.
Many conceptual difficulties of quantum mechanics can be nicely illustrated by Schrödinger's cat being in a superposition of dead and alive. In particular, Bohr's famous transition between quantum and classical world is challenged. The measurement problem shows up as well: Is the cat an observer or part of the (quantum mechanical) system? The recent experimental developments in quantum optics and atomic ensembles allow us nowadays to coherently control larger and larger systems. The creation of Schrödinger cat states is more and more in reach, even if its size is not at all at the level of real cats.
Astonishingly, the question which quantum mechanical states should be considered as cat states is still open. Traditionally, in photonic states, superposition of two coherent states are the archetypal cat states. In a recent contribution, we suggest to consider a much larger class of optical states to be called cat states and discuss their creation and analysis. This work was published in the Journal of the Optical Society of America B and was highlighted by the editors with a "Spotlight on Optics" on the journal's web page.