Posted in October 2012
Inaugural speech prof. Pieternel Levelt
has taken place today. If I understood correctly, she mostly works at Royal Netherlands Meteorological Institute and is in charge of important task: she monitors the trace gases in air with the aid of sattelite-based spectrometers and thereby watches the climate changes and air quality over the globe. Important job, this contibutes to unbelievable stability of her research: the plans are made till 2030.
It was a good lecture, and I’ve learnt a couple of funny things. The struggle to impove the quality of air can contribute to global warming if done without thinking: some trace gases help to cool. Air pollution is not limited to (compact) industrial regions: major ship routes are clearly seen on a map that shows NO2 concentration in athmosphere.
Alina Hriscu
has obtained her PhD title today by defending the thesis entitled Theoretical Proposals of Quantum Phase-slip Devices. I had a pleasure to promote her.
Alina Hriscu was my first female PhD student, and four years with her were full of unforgettable experiences. In my speech I compared these years to a rough cross-country ride that brought three very good publications.
FOM projectruimte 2012
In the context of our national grant competition I have applied with Leo Kouwenhoven for a project meant to facilitate the further exploration of recently discovered Majorana particles.
Spin-blockade qubit in a superconducting junction
is a title of our new cond-mat submission with Ciprian. You can find it here .
Below is the abstract:
We interpret a recent pioneering experiment [Zgirski M. et al., Phys. Rev. Lett., 106 (2011) 257003] on quasiparticle manipulation in a superconducting break junction in terms of spin blockade drawing analogy with spin qubits. We propose a novel qubit design that exploits the spin state of two trapped quasiparticles. We detail the coherent control of all four spin states by resonant quantum manipulation and compute the corresponding Rabi frequencies. The read-out technique is based on the spin-blockade that inhibits quasiparticle recombination in triplet states. We provide extensive microscopic estimations of the parameters of our model.
Andrea Caviglia
has become a new member of our department of Quantum Nanoscience. He will start from January 1st and will make nanostructures on conducting interfaces of complex oxides. Welcome!
Yaroslav Blanter
of our section Theoretical Physics by decision of College van Bestuur of our university has Yaroslav Blanter has been promoted to the rank of full professor, Antoni van Leeuwenhoek hoogleraar . Well-deserved and long-awaited promotion. This decision, although irreversible, is not yet officially announced and will be implemented by steps, the last one will be an official speech of Yaroslav in about a year. Congratulations!
QNM-12: Monday * October 2012
The workshop on quantum noise and measurement we are organizing in Dresden is up and running. Initially I wanted to make a collective blog for all participants but after thinking a while I decided to blog my personal impressions: emphasis is on personal, the account on the talks presented is by no means accurate and was not checked with the speakers as it should be for publication in more representative media. I’ll present my reports with a delay of couple of days.
The workshop is held at Max Planck Institute for Physics of Complex Systems (mpi-pks). Frank Jülicher, managing director of the institute, has welcomed us giving some general info about the place that makes science, runs 15-20 workshops per year and collaborates with other two MP institutes in the city, those are in chemistry and biology.
Wolfgang Belzig, our main organizer, has started the workshop providing necessary technical info.
Markus Buttiker discussed the distribution of waiting times between the events of electron transfers and its unobvious relation to full counting statistics. He discussed it first for simple electron counters and single particle emmiters where it can be easily accessed experimentally. He presented theoretical resuts for distribution of waiting times for the generic case of quantum point contact and denonstrated the crossover from wigner-dyson distribution for high transparencies to poissonian one expected at low transparencies.
Leonid Levitov has actually given two talks in one. In the first part he discussed the noiseless electron sources where a special form of control pulse produces states with “no splash” : electron is transferred without extra electron-hole pairs generated. For a quantum point contact, such pulses are Lorentian.In the second part, he talked about spin qubits and nuclear spin effect in there that determine decoherence of the practical qubits. He concentrated on a long-standing experimental puzzle of ultra-slow oscillations, much slower than heart beats, observed in the qubits but only in the vertical dots. He has developed a minimal model to solve the puzzle. 3 crucial ingredients are: nuclear spin diffusion, nuclear polarisation inside the barrier separating the dots, energy dependence of triplet decay rates.
Robert Schoelkopf shortly reviewed the research on transmon qubits (slightly non-linear josephson junctions) in Yale and summarized new results. Althouth the number of qubits in the device still does not follow Moore’s law as function of time, there is almost exponential progress in combatting decoherence sources: T1, T2 have been improved with 3d cavity resonantors and filterinng techniques to 100 microsec range and are still improving. The main attraction of circuit QED setups is the simplicity, everything is described with Jaynes–Cummings Hamiltonian. Operation in strongly dispersive regime enables QND measurement of photon states in the cativy and provides a toolbox for manipulating light. Robert has concentrated on Kerr effect: frequency shift proportional to the square of photon number. The device has two cavities: one for storage and another for qubit readout. They produce coherent states and measure those doing Wigner tomography. Kerr effect provides a spectacular evolution of the states that is revealed by the measurements. Ideas for future have been discussed: to entangle the qubit and the photons in the cavity.
Jukka Pekola talked about experimental progress in investigating fluctuation relations in driven electron tunneling. He oulined fluctuation theorem that has been investiated recently in ETH with double-dot electron counter and related it to the entropy production. He outlined Jarzynski inequality als well as the problems related to the defintion of work. Experiment was made with a split SE box where charge has been monitored. Jarzynski relation is fullfilled with 3 per cent accuracy, the error is perhaps due to non-equilibrium conditions (difference of phonon and electron temperature). Better accuracy can be achived for the general equality, or integral fluctuation theorem that is known in markovain statistics and is valid for classical systems. What about quantum? There is no consistent definition of work. Rather we will talk about calorimetry quantifying fluctuations of energy flows. The plan is to study a simple two-level system and LZ tunneling. The simulation shows that the calorimetry can work in this setup. The experiment is under way.
Klaus Mølmer gave a rather review-like talk entitled “Quantum state control by quantum measurements or what you see is what you get”. He indicated he belongs to AMO (Atomic molecular optics) community and soon proved that this community is a way more jovile and friendly than condensed matters. His rather traditional introduction of interpretation and collapse of the quantum state he has ended with a dithyrambe to quantum dynamics noting that the dithyrambe also provide a perfect description of his wife (thinking back, I recognized that we have probably married twins). He has attributed the discovery of second quantization to Shakespire who has been constantly talking of “a dagger” and switched to Glauber and Kraus and repetative measurements and heterodyne detection of quantum noise. y the end we all got convinced that measurement provides better entanglement than any interaction: a point that actually never came to my non-AMO mind.
Jan van Ruitenbeek talked about his experiments on inelastic noise in nanowires that he attributed to a two-electron effect. His wires were rather short upon my taste: typically, a two-atom molecule hanging in a gap in a metallic break junction. They have resonant mechanical modes. Jan has demonstrated good characterization and understanding of the processes forming I-V curves in the wires in various conductance regimes, from tunnel to transparent. Most important feature is the threshold of inelastic process at voltage matching the resonant mode frequency. The results on noise in this regime are fresh and intriguing: Jan said they do not match any theory. Since I was also involved with one theory he has mentioned I felt a bit disrupted. Yet the experiment is still rather fresh…
Steven Girvin gave a colloquium talk: a special talk that is intended for a larger MaxPlanck community and should be accessible for biologist. Basically, it was a compherensive introduction to quantum-limited amplifiers starting from the basics of Heisenberg uncertainty. Actually many things and particular details of the Steve’s interpretation looked pretty new and fascinating to me: it’s like as a gifted piano player discovers new sounds in a thousand-times-heard piece of classical musics. Steve has finished the talk with a copy of a postcard to Bohr from Gerlach that reported this famous experiment. He mentioned that the interpretation of the experiment was wrong by the time.
And we got to dinner and poster session.
Han Keijzers
has been declared PhD yesterday by his promotor Leo Kouwenhoven. The PhD thesis was entitled “Josephson effects in carbon nanotube mechanical resonators and graphene”. I was naturally present as a member of the committee. If I were not I would have come anyway since a big chunk of the (already relatively) recent research of me and Ciprian has originated from occasional chat with Han by the bicycle stall three years ago. Since that we have had many chats, yet the only solid conclusion we have drawn and confirmed by hard theoretical work and numerous experiments is that the physics of Josephson nanotube resonators is far more complicated and less spectacular than we have assumed three years ago.
Han did impressive work and his PhD thesis is a way thicker than an average one. I find it remarkable that the opponents spoke during the defence almost as long as the candidate: their questions were long and sometimes complex-structured while the answers came quickly and to the point.
Han has now switched from nanotubes to gigatubes: he has found his way in Dutch industry. Somebody else should go about the superconducting nanotube resonators, that’s it.
And today, the day after the defense, we have received an acceptance note of our
http://lanl.arxiv.org/abs/1112.5807, the work done in collaboration with Han.
Quantum Noise and Measurement in Engineered Electronic Systems
This international workshop we have organized with Wolfgang Belzig and Michel Devoret has ended succesfully, mostly because of local organizer Katrin Lantsch. We got quite some enthousiastic responses and are basically satisfied. Time allows I will blog the notes I made last week.