Taming the world of atoms and photons


  • Guido W. Fuchs

This year in October the Humboldt Foundation invited its award winners, fellows, alumni, top league scientists and young researchers to discuss problems and successes in quantum optics. It was the third Humboldt Award Winners‘ Forum held in Bonn from 9–12 October. The first one “Frontiers in Macromolecular and Material Science” was held in 2011, followed by “The New Desire for Metaphysics” the year after. This year, about 180 participants from all over the world attended the forum “Frontiers in Quantum Optics: Taming the World of Atoms and Photons – 100 Years after Niels Bohr” which took place at the Hotel Bristol and, partly, at the University of Bonn, Germany.

Jürgen Fohrmann, rector of the university in Bonn, opened the conference with his welcome address, followed by Jürgen Nimptsch, the Lord Mayor of the City of Bonn, and Helmut Schwarz, President of the Alexander von Humboldt Foundation. The first keynote lecture was given by Serge Haroche (Collège de France, Paris) titled “Controlling photons in a box to explore the quantum world”. His talk outlined his Nobel Prize winning work and new developments (see Fig. 1).1

Figure 1.

Serge Haroche (left) and Helmut Schwarz.

Figure 2.

Participants listening to the presentation. In the front row (from left): V. Sandoghdar J. M. Raimond, W. Ketterle, D. Meschede, J. Nimptsch, J. Fohrmann; in the second row (left): E. Giacobino.

The next day (Thursday, 10), further welcome and introduction speeches were given by Enno Aufderheide, Secretary General of the Alexander von Humboldt Foundation, Wolfgang Sandner, Vice-President of the Deutsche Physikalische Gesellschaft, and Dieter Meschede from the University Bonn who organized the meeting. The forum was organized in four panels. The first one “Exploring the Quantum World with Atoms and Photons” was introduced and chaired by Jean-Michel Raimond. Howard J. Carmichael held a keynote lecture about 100 years of quantum jumps, outlining the history from Bohr and Einstein's A and B coefficients to the works by Haroche's group and beyond. Vahid Sandoghdar talked about the efficient coupling of single photons and single quantum emitters in a cavity-free way, Nir Davidson continued the session by talking about long coherence times in dense ultracold atomic ensembles, and Atac Imamoglu finished the session by outlining recent developments in solid-state quantum optics.

The panel “Cold Atoms and Many Body Physics” was chaired by Wolfgang Ketterle who also introduced the topic in a brief presentation. Ketterle showed how physics is interconnected and that the study of cold atoms can indeed help solving problems in many-body (solid-state) physics. There is a quest for new materials, like high-temperature superconductors, new carbon-based materials (e.g. nanotubes or graphene) or materials revealing colossal magnetoresistance, to name just a few. There will be more materials needed in the future. To newly discover or to further understand these materials “we like to use paradigmatic models”, he said, “some sort of atomic ‘legos’ that help us understand complex systems”. We are now in a process of quantum “engineering” that will most likely guide future progress in the field. The following lectures further outlined this vision. Georgii V. Shlyapnikov talked about many-body physics of quantum gases in disorder. Of special interest was his discussion about work based on D.M. Basko, I.L. Aleiner, B.L. Altshuler (the AAH model) in which fluid–insulator transitions of disordered quantum gases were discussed. In these systems a surprising effect can occur. Shlyapnikov said: “Imagine you boil a pot of water and then discover that you got ice cubes as a result”, i.e. phase transitions can occur that are unique and do not appear in other systems or materials. Massimo Inguscio continued the session with a discussion about ultracold fermions and novel one-dimensional matter, and Michael Köhl talked about photonic coupling of atoms and solid-state quantum systems, asking the question “Can we make different quantum systems communicate with each other?” – a theme that will keep many scientists busy over the next few years or decades. Finally, Tilman Pfau showed the potential of using electrons of Rydberg atoms to probe Bose–Einstein condensates (BEC). As he showed, the electrons of Rydberg atoms with very high principal quantum numbers (e.g. around n = 100 to 200) can enclose up to several thousand atoms of a Bose–Einstein condensate – a remarkable achievement which allows the investigation of electron–phonon scattering in the BEC. After a full day of science William A. Kinderman gave a lecture on Ludwig van Beethoven's 1823 composed Diabelli variations and completed his presentation with a first-class performance of the piano sonata in C minor, Opus 111, at the Beethovenhaus in Bonn.

The next day (Friday, 11) started with the panel “Quantum Information Science”, which was introduced and chaired by Michael Fleischhauer. Arno Rauschenbeutel talked about the possibilities to trap and investigate ions using an optical nanofiber, a technique that has potential as a quantum memory and processing device for quantum computing. Jian-Wei Pan discussed recent experimental progress in quantum manipulation with photons and cold atoms, specifically in quantum information processing (QIP). He showed that linear system equations of the form math formula; math formula can be solved faster using QIP (with O(log(N)) steps) than in a classical way (with O(N) steps), but that the scalability of QIP is still a challenge as it requires quantum repeaters and quantum memories. He also showed the latest achievements in long-range free-space quantum communication of around 100 km in China and other places and noted that the next step would be to cover a 1200-km distance via satellite. The ultimate aim is to enable and set up large-scale, long-range quantum communication networks. Andrea Alberti discussed transport phenomena in quantum systems. Using quantum walks with neutral atoms as an example he showed that classical and quantum systems differ strongly in their behavior. The last session contribution was by David DiVincenzo talking about prospects for superconducting qubits including some outlook for “Moore's law” of coherence times, and surface code error correction using resonators or cavities.

Elisabeth Giacobino then introduced the panel “Precision Measurements and Hot Topics”, with keynote lecturer Jun Ye talking about probing exotic quantum matter (e.g. many-body quantum spin dynamics in which quantum fluctuations become correlated) with clock precision. Edward A. Hinds discussed how cold atoms can be used to test fundamental physics, and Gerald Gabrielse continued in this direction with his talk about measured and calculated properties of elementary particles. For example: Is there an electron electric dipole moment? According to the current standard model it is nearly nonexistent (around math formula). Gabrielse and his coworkers want to challenge this by going beyond the current experimental limit of math formula by one or more orders of magnitude. A positive result would have tremendous effect on the standard model and could help to decide on recent predictions by supersymmetric and technicolor models. Quantum optomechanics on various scales, from nano- to macromechanics was discussed by Markus Aspelmeyer. He also showed that this research field has potential to make contributions at the absolute limit of the physical realm, testing fundamental physical aspects where quantum and space–time (i.e. gravity) aspects become relevant.

In the evening, Hans Bachor (Australian National University, Wamboin) gave the dinner speech, or what he called “the after soup” speech as he was placed between the starter and the main course. Among other things, Bachor recalled how science was done in the early times of quantum mechanics and pointed to the central role of personal relationships and friendships among scientists. Bohr was put forward as a memorable example who brought forward many of the central ideas of quantum mechanics by walking and discussing matters with his colleagues, like Heisenberg and Einstein. It is this deep, sometimes controversial, but continuous thinking that enables us to solve sheer insurmountable problems jointly as an interactive science community.

The Alexander von Humboldt (AvH) foundation sets great value on promoting excellent scientists, but it does not stop with a one-time support. It goes beyond the usual sponsorship by continued fostering of its award winners, fellows and alumni. It is the networking aspect that makes the foundation a key player in Germany's scientific landscape and unique among international science founders. Steffan Mehlich (AvH representative) emphasized that the family aspect of the Alexander von Humboldt foundation is key to its success and helps strengthen the links within the network. Consequently, the forum did not end with the scientific talks but continued with a cultural program. Here, the participants could visit the castle “Burg Satzvey”, the Radio Telescope Effelsberg at Bad Münstereifel-Effelsberg (Max Planck Institute for Radio Astronomy), and the winery “Kloster Marienthal” (Bad Neuenahr), thus getting into closer contact with each other. Helmut Schwarz formulated it at the beginning of the meeting: “Science is made by individuals, not by projects”. In the end it needs both – individuals and projects – but the meeting showed that without a strong focus on the researcher as a person there will be no progress. This meeting was in the right spirit to bring together outstanding individuals and to make them think and work together.

  1. 1

    The talk was partially based on his Nobel lecture from the year before that has been published in Annalen der Physik recently, see [1].