Last year we published together with the Schmiedmayer group a paper on the creation of twin atoms from a one-dimensional degenerate Bose gas. At that time our task was to design an optimal control ramp for bringing the condensate into a (transversally) excited state, although the main point of the work was the ensuing relaxation process where two atoms in the excited state decay via a two-body process into paired, propagating modes with identical population and opposite momenta (twin atoms).

In late 2010, when we were close to submission of our first paper, I attended a rather boring workshop in Vienna and I skipped the last afternoon session to meet with the atomchip group and to discuss (with great excitement) the physics involved in twin atom creation. Later in the evening I returned with Julian, who at that time was working at the Atominstitut, to Graz, and I remember that in the train I first realized that with our experience in the field of atom interferometry we should be able to describe the process of twin atom production (at least in principle). The next day I started to work on the problem and devised a simple two-mode model whose results were in surprisingly good agreement with experiment.

As always in the collaborations with Jörg and his group, this was the beginning of a long (but pleasant) story. It soon turned out that it was necessary to change to a density matrix description to cope with more modes and to include many additional features relevant for the experiment, and I soon began to realize that I was running into a kind of endless story. At some point Robert took over with the simulations. It may be due to his youth, his strong faith in the strength of our model (as theoreticians we seem to be more attracted by the weak points), or simply the larger amount of time he was investing, in any case, it was amazing to see to which level of perfection he was pushing the agreement between experiment and theory. It is fair to say that Robert is the true hero of this work, considering also the mere 35 iterations it took to bring the paper to its final form. I think that we finally succeeded to compile a beautiful piece of work. Thanks a lot to all collaborators!

Back in 2003, when virtually every system was considered as a viable candidate for quantum computation, we published a PRL about STIRAP-based quantum gates, building upon a beautiful proposal of Kis and Renzoni. Later in the same year I met Zsolt Kis in Kaiserslautern, where he was working at that time and where I gave a talk.

In 2008, several years later, Zsolt suggested to apply for a bilateral project between Austria and Hungary, together with Gabor Demeter and Gagik Djotyan. The summer of the next year brought me for the first time in my life to Budapest, a beautiful city with a lot of history, and I was enjoying the hospitality of Zsolt and Gabor. From a physics point of view my stay was successful, and we figured out a number of topics for possible collaborations.

In what followed Zsolt, Gabor, and Gagik visited me twice in Graz. We had a lot of discussions and our collaboration made significant progress, mainly due to Gabor and Zsolt. I feel a littly guilty that I was not contributing more, but, honestly speaking, I was completely stuck with other things. We finally submitted a beautiful piece of work, which had the smoothest refereeing process I have ever seen. The referee was extremely polite and concluded that "This is a very well written paper on pulse propagation in a multi-resonant medium. The field of pulse propagation, although perhaps not in the forefront of current theoretical and experimental interest, is an evergreen". So thanks a lot to Gabor, Zsolt, as well as to the unknown referee!

Crossing the Tote Gebirge with skis has been on my wish list for several years. The Tote Gebirge is located between the provinces Styria and Oberösterreich, and is one of the most remote areas in Austria. It typically takes two to three days to cross the entire region.

In the last years my son Moritz and me had tried (and failed) twice: in 2010 we started too late and finally had to return to our starting point at the Loser in Altausee, in 2011 we gave up because of foggy conditions. This year we were lucky with the weather, the forecast promised two sunny days, and we started early enough to reach the Applehaus early in the afternoon where we spent a cold night in the winter room.

On the next day we finished our tour-de-force with a 11 hour walk, passing through one of the most beautiful and lonesome regions I have ever seen. I owe a big thank to Moritz, who was pushing me and who was bravely leading the final part of our tour. In the last glimpse of the sunlight we arrived at our final destination Tauplitz. 

On friday our solid state group, which is partially more condensed than solid, went for a ski day to the Präbichel. The weather and snow conditions were perfect, and we had a lot of fun and surprisingly little physics discussions. The picture above shows (from left to right): Jürgen Waxenegger, Jakob Ebner, Robert Schütky, me, Andi Trügler, Rene Hammer, Georg Jäger, Miriam Mutici, and Christian Ertler (middle on right picture, photographer of the left picture). It is good to see that there are other great things in life except of physics ...

In a nonlinear optical process light interacts with matter and a photon is transformed into several photons of lower frequency (energy), or, in a reversed process, several photons are transformed into one photon of higher frequency. Third harmonic generation (THG) describes the process where three low-energy photons generate, in presence of a polarizable medium, one high-energy photon. In a work, which just has been accepted for publication in Nano Letters, we demonstrate that such conversion is significantly enhanced for metallic nanoantennas, where surface plasmons can be excited and the nonlinear process becomes boosted by the strongly localized plasmon fields.

About two years ago we started to perform simulations for experiments that were performed by Tobi Hanke in the group of Alfred Leitenstorfer and Rudi Bratschitsch. I know both Alfred and Rudi from the very early days of my physics career, when all of us were working in the field of coherent semiconductor optics, and it was a great experience collaborating again on a new topic. Andi Trügler spent a huge amount of time with the simulations, which were challenging both from the computational and methodology point of view. On the one hand, our MNPBEM toolbox is not optimal for large particles (since we are currently using a pure collocation method), while on the other hand it turned out to be necessary to model the full coherent THG emission process.

At the end we could deliver a message that is as simple as a message can be: the amount of emitted THG radiation is directly linked to the dephasing properties of the nanoantennas -- the smaller the dephasing, the larger the THG intensity. I think that the final manuscript describes a beautiful piece of work. The collaboration was longish but nevertheless most rewarding, including both physics as well as a beautiful ski tour (Preber) together with Tobi at the Mauterndorf winter school. So thanks a lot to everybody!

Our MNPBEM Toolbox made it into the selection of the most downloaded Computer Physics Communications articles. We hope that people come along well with the programs and enjoy the toolbox!

For 2012 we plan a few improvements. First, we would like to add a more user-friendly interface where the different options and simulation modes (static and retarded) can be set via a single mnpbemset function, similar to the odeset function of the ODE Matlab solver. Second, we will add plot functions for compstruct objects (such as sig). Most importantly, we will implement an interpolation of the curved particle boundaries, using shape functions for the triangles and quadrilaterals. With this, the closed argument of the comparticle objects will become obsolete and the Green functions can be integrated more accurately over the face elements, which should be beneficial for larger nanoparticles.

So these are our plans, not very much has been done so far.  In any case, stay tuned -- we hope to have something ready in the second half of 2012.

Last friday Christof Weber passed the final exam of his diploma studies.  Christof's thesis deals with electron energy loss spectroscopy (EELS) and microscopy of plasmonic nanoparticles, in particular for situations where the electron beam passes through the nanoparticle. The critical thing is how to describe within our boundary element method (BEM) approach the crossing point of the electron beam with the nanoparticle boundary, as one has to be rather careful in dealing with the diverging potentials and fields close to the beam. To be sure that things are done properly we decided to compare the results with Mie theory where analytic solutions are available.

Christof succeeded half way and obtained reasonable agreement between the BEM and analytic results. Yet, it appears that more work is needed to properly implement EELS into our MNPBEM toolbox. Nevertheless, at some point it was time for Christof to write up things and finish. I wish him all the best whatever his future will bring.

A paper describing our MNPBEM toolbox for the simulation of plasmonic nanoparticles, as well as the program files, have been accepted for publication in Computer Physics Communications, and can now be downloaded here. We ask all users to cite the Comp. Phys. Commun. paper.

There exists also an extended version of the toolbox, which includes symmetry and layer structures, whose download requires a password. These additional features are still somewhat experimental and under development.

From 23.08 – 01.09.2011 me and my son Moritz, now 16 years old, were biking through the Dolomites and the mountains close to the Swiss border. After our tours Austria–Paris (2009) and Swiss mountains (2010), this was our third tour in a row. Again we were extremely lucky with the weather (hot and sunny, with the exception of two rainy days), and we climbed in ten days approximately 17000 hm. Highlights were the beautiful Sella round, the Passo Giau and the Stilfserjoch, just to name a few. Altogether it was a beautiful experience, exhaustive but in many ways rewarding. A more detailed tour description (in german) can be found here.

Just in case someone is interested: 2011 is the 305th prime number (the next one is 2017). You can check this in Matlab with primes(2011).

After 3 years of PhD work, today Andi Trügler passed his final Rigorosum exam with distinction. Within the last few years Andi has been the key person and backbone for the plasmonics activities of my research group. He has successfully handled a large number of projects, mostly with experimental groups, and I think that the output of his thesis of about ten papers is quite remarkable.

Andi is a relaxed person (with the only exception of the last days before his final exam) who does his work quietly but with great care. Through all the years we have worked together I have been fully satisfied with his performance and output, and I am sure that Andi will make his way whatever he approaches in the future. The original plan was that he would continue a Postdoc for another two years,  but since the project for which we applied was not funded in the first round we now have to improvise, and I hope that we will find a solution. In any case, the next few weeks Andi will travel through the Suisse mountains, relaxing from physics and hopefully being stressed by other things.

Last friday it was time again for the yearly Kleeblattlauf, a relay race organized by our university that has to be finished within one hour. The solid state group started with two teams, namely me, Christof Weber, Jürgen Waxenegger, and Miriam Mutici (team #158) and Peter Senekowitsch, Christian Ertler, Rene Hammer, and Walter Pötz (team #160). As regarding my performance, I was suffering from a complete lack of running workout and thus opted for the shorter distance, which gave me at least the great feeling of finishing the course among the first. At the end, both teams were equally strong, and the final runners came in simultaneously after about 50 minutes. Congratulations to everyone!

Measuring a quantum-mechanical wavefunction is a popular and not so difficult Gedanken experiment in quantum mechanics, but to actually measure it in experiment remains a hard endeavor. In the past, my interest as a theoretical physicist has been somewhere in between: we have suggested and analyzed experiments that could do the job. A technique of particular interest is scanning nearfield optical microscopy (SNOM). Here light is quenched through the tip of an optical fiber, which allows to probe optical excitations in semiconductors (excitons) with nanometer resolution, and opens the possibility to map out the exciton wavefunction.

In a recent work, that is based on the diploma thesis of Jürgen Waxenegger and which has now been accepted for publication in Physical Review B, we extended the analysis to the mapping of excitons in carbon nanotubes with a metallic nanosphere using a so-called apertureless SNOM setup. This approach appears to be quite feasible in experiment, at least this is how it seems from a theoretician's perspective. Although we initially advertised our work as a "wavefunction mapping" in carbon nanotubes, a referee rightly pointed out that the simulated experiment rather gives information about the coupled exciton-nanosphere system than the exciton wavefunction itself, so we finally weakened our claims. In any case, we hope that our work will stimulate further experiments in this direction.

At the beginning of my career it happened once that a paper of mine did not make it through the refereeing process. It was not that the referee reports were particularly bad, rather I felt disappointed that the work, which I considered to be fine work, did not receive the perception I was expecting, and I never re-submitted. Later I realized that this was a mistake, but it was too late to change back. This experience tought me to fight papers through, unless there is something deadly wrong in them, and I have done this without exception since then.

Now it has almost happened again that I lost a paper. It is based on the diploma work of Gabi Jaritz, which is excellent work that certainly deserves publication. Gabi is a relaxed person and was not pushing me hard enough, so it already took ages before I wrote up the paper. We submitted and received two reports where the referees asked for minor modifications. At that time I was occupied with too many other things, and I postponed the revision. A few months later I was still postponing, although I had carried the paper with me to a number of meetings and conferences where I had hoped to find time to work on it, and I slowly started to realize that I was running into something unpleasant.

To make the long story short, more than one year after receiving the reports I finally brushed up the paper and submitted it to the European Physical Journal B, where it had a smooth refereeing and was finally accepted. I must say that it is a big relief for me, and I am happy that I could defeat the demons of my scientific youth. I owe a big excuse to Gabi for my unduly laziness,  and I truly hope she will accept.

Twin-atom beams is the paper with the shortest title I have ever published, but it's the paper that fills me with the highest joy. Yesterday it was published online in Nature Physics. For a long time in my career I never even thought about publishing in the prestigious Nature and Science journals. The first time I realized that they are not restricted area was back in 2000, when I published my first PRL, a beautiful work together with the group of Eli Kapon which received the highest number of citations of all my papers, while at the same time a work of similar quality was published in Nature.

In the following years more and more of my colleagues succeeded in publishing in Nature and Science, and I was not even chasing the train. It was time to change things. My first attempt failed miserably. The second one was much better, with hindsight I must say that the paper would have deserved it, but we failed closely. All good things go three. Together with the atomchip group of Jörg Schmiedmayer we submitted a beautiful piece of work, which already made it into my news section on 10.12.2010, and I was confident from the beginning that things would work out, as they indeed did in the end.

I am too old to believe that many other occasions will come for reaching science's heaven, and my experience tells me to take a breath and enjoy the moment. My deep thanks go to Julian, Robert, Thorsten and Jörg, as well as to all other coworkers. It was great pushing for this final success.

Presseaussendung KFU Graz    Presseaussendung TU Wien

MNPBEM is a Matlab toolbox for the simulation of metallic nanoparticles (MNP), using a boundary element method approach (BEM), which we have developed and used over the last few years. A first release of the MNPBEM toolbox is now ready, which can be made available on the basis of scientific collaborations. The toolbox includes exhaustive demo and help features. It is still in the testing phase and subject to frequent changes, so we advice all users to check the main product page on a regular basis.

Today we received the information that our paper Atom interferometry with trapped Bose-Einstein condensates has been selected as one of the Best of 2010 of the New Journal of Physics. According to the journal, this special collection of papers "represents the breadth and excellence of the work published in the journal last year. The articles were selected for their presentation of outstanding new research, receipt of the highest praise from our international referees and the highest number of downloads last year."  There remains nothing for me to amplify this appraisal. I am happy to be part of this exclusive collection of articles, and I thank all co-authors, in particular Jörg for his numerous ideas and suggestions as well as Julian for his tremendous efforts and for compiling everything.

As there are no striking news at the moment (but hopefully approaching), I take the opportunity to recommend two books I stepped over recently and which are worth reading. The first one is by my uncle Gottfried Schatz, one of the key persons in the discovery of the mitochondrial DNA. In Feuersucher (NZZ Buchverlag, Zürich, 2011) he describes both the life of a young scientist coming from post-war Austria as well as the race for the discovery of the working principle of ATP synthesis in living cells, that resulted in two nobel prizes (1978 and 1997). The other book, which is real fun to read, is the classical Double Helix by James D. Watson where he gives an autobiographical and very personal account of the discovery of the DNA double helix structure (nobel prize in 1962). Both books imposingly demonstrate how easy science can be if one has the right ideas -- and how tedious otherwise.

The influence of surface roughness on the optical properties of particle plasmons is the topic of both a paper that was just accepted by Phys. Rev. B as a rapid communication, and of a research project funded by the FWF that started a while ago. Andi Trügler and Jean-Claude Tinguely from the nanooptics group are working on this project. At the end of 2009 Andi performed the first simulations by adding through a stochastic procedure, that we adapted from simulations for interface roughness in semiconductor quantum wells, surface height fluctuations to a nanosphere. The results were astonishing: virtually nothing happened in the spectra! We tried the same thing with nanorods and the results were extremly similar, although shifts of the plasmon peaks were now at least visible.

It was time to start experiments. Things are more complicated in the experiments because surface roughness is related to the grainy composition of the gold nanoparticles, which not only adds roughness but can also have an impact on the shape of the particles. Nevertheless, we observed again only small deviations between spectra of particles that were identically designed but differ due to the unavoidable surface roughness.

On top of simulation and experiment, we finally added a theoretical description, based on a perturbation theory for surface plasmons, which completed our analysis. The refereeing process was rather rough than smooth, but what else could one expect for a topic like this? I think that we finally delivered a nice piece of work, with many possible extensions, and I am grateful to all collaborators.

A few weeks ago we have been asked by PRL to highlight an article reporting the first observation of trions in carbon nanotubes. I consider myself an expert on excitons in semiconductors and a semi- expert on carbon nanotubes, so writing the highlight was OK for me and my co-author Guido Goldoni from Modena university. We tried our best to describe things as clearly as possible and finally delivered something hopefully accessible to a broad community. You may read and judge yourself ...

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