Posted in 2015
PhD position in condensed matter theory
I would like to announce a PhD opening with me at the department of Quantum NanoScience at Delft University of Technology. According to Dutch standards, this is a 4-year employment with gross salary up to 2,718 euro.
The project concerns superconducting junctions, topological effects and superconducting qubits. In its short form, it can be found here.
The preferable starting date is 1-1-2016 and can be negotiated. The applications will be considered till 10-11-2015. The applicants are encouraged to send me their CV, motivation letters, and the list of referees. It is also useful to make a test and enclose the results.
Please do not hesitate to ask any questions!
Look forward to a good collaborator!
Keldysh formalism for multiple parallel worlds
this paper with M. Ansari has appeared on arxiv today: see it here. This is our contribution to the forthcoming Special JETP issue dedicated to 85th anniversary of Prof. L. V. Keldysh.
Abstract:
We present here a compact and self-contained review of recently developed Keldysh formalism for multiple parallel worlds. The formalism has been applied to consistent quantum evaluation of the flows of informational quantities, in particular, to evaluation of Renyi and Shannon entropy flows. We start with the formulation of standard and extended Keldysh technique in single world in a form convenient for our presentation. We explain the use of Keldysh contours encompassing multiple parallel worlds In the end, we shortly summarize the concrete results obtained with the method.
FQMT 15
Usually it is quite boring to write about the workshops and conferences, but not about this one. The long title is Frontiers of Quantum and Mesoscopic Thermodynamic and it was held in Prague, 27 July – 1 August 2015. The conference, as all other conferences in series, has been organized with a good care and a warm twist. Among usual things, like meeting many old friends and attending few interesting talks, my mind was rebooted by a plenty of impressions that are best described as surrealistic, almost out-of-world. Just some highlights:
– attended a concert of (well, mostly) classical musics every evening during a week
– heard the vice-president of Czech Academy of Science complaining about unjust separation of physics and musics in the structure of his establishment
– seen Gerard t’Hooft being publicly kissed by a mid-aged lady in an eye-catching garment. She had a medal for him, you see.
– listened to the same Gerard t’Hooft talking about super-determinism in gloomy theatrical environment so the cold horror of predestination grabbed my heart
– signing my book for Marlan Scully, a legend of my student times (have never met him before)
– had a too-much-wine dinner in an establishment that looked like a benedictine monastery from one side and a country-side restaurant from another side. We had a concert in their chapel, so that was the first option for sure
I could go on with the list. Many thanks to the organizers!
Paper to commemorate Markus Buttiker
who has passed away on Oct 4, 2013 in the age of 63. There will be a special issue of Physica E devoted to his memory.
From the conclusions:
“In conclusion, we have provided a technical and comprehensive introduction to the Keldysh action formalism for a multi-terminal scatterer with special emphasis on superconducting leads. We have derived a very general and compact formula and have elaborated on simple important examples to demonstrate the variety of its applications.
I did this to commemorate Markus Buttiker, the pioneer of scattering approach to quantum transport, one of the fathers of this big, prosperous and fruitfully developing research field. I admire not only his research merits: throughout 25 years of our acquaintance I was appreciating much his daring to remain himself, to keep his own research style, research topics and idea sets in times where the close following of a quickly changing scientific fashion seemed to be a must. He was also a charming personality and a good friend.”
The paper can be found here.
Survey Advanced Quantum Mechanics 2
The semester is over – well, almost, we need to prepare the exams, yet it all will happen very soon. The end of the semester was pretty busy so I had no mood neither time for the blog. I shall only do what I ought to – to publish the results of the last survey on Advanced Quantum Mechanics course made on 1-6-2015, during one of the last lectures. Students by this time had very certain opinion about the course, were rather critical, yet could appreciate the good parts of it. That I can also judge from a big number of the students (52) who are going to take the exam.
Ok, questions and answers:
In my opinion, the content of this course is relevant to my education (from -2 to 2) 1.4
This course corresponds well to my prior knowledge (from -2 to 2) 0.8
In relation to the amount of credit points, the actual study load of this course was much higher (from -2 to 2) 0
The lecturer explain the subject matter clearly (from -2 to 2) 0.3
The lecturer discuss the subject matter in a stimulating way (from -2 to 2) 0.2
The instructors give sufficient feedback on student presentations (from -2 to 2 ) 1.53 here we have improved a lot !
The problem-solving sessions are interesting and useful (from -2 to 2 ) -0.22 we need to restructure the problem-solving sessions
English mark for the teacher (from 0 to 10 ) 6.7
English mark for the instructors (from 0 to 10 ) 8.3 good
The lecturer should present the material with more examples . OK
The problem-solving sessions should be with more discussions. OK
This course is well organised (supply of information, scheduling) (from -2 to 2 ) 1.4 much improvement!
I will go on with the course and come to the examination. Majority answered undoubtedly.
What mark do you expect to get at the exam? 6.9
Do you use the book? Majority uses it regulary
The overal mark:
lectures 6.6
problem-solving sessions 6.1 have to do something about
the whole course 7.2 could be better
we wouldn’t mind to score more, yet it’s not a big problem
I have also interesting remarks from the students, to be posted later.
Exact correspondence between Renyi entropy flows and physical flows
has been published today.
Reference: Mohammad H. Ansari and Yuli V. Nazarov, Phys. Rev. B 91, 174307 (2015)
Link: http://journals.aps.org/prb/abstract/10.1103/PhysRevB.91.174307
DOI: http://dx.doi.org/10.1103/PhysRevB.91.174307
Nanofront proposal granted
This happens from time to time with the submitted proposals. The proposal title is “Quantum mixtures of topological and non-topological states realized with superconducting junctions”. I will announce a PhD position soon.
Silence and ERC Advanced Grant proposal
I didn’t write much to the blog for almost a couple of months. An excuse for this is I’ve been busy preparing an important grant proposal. Not that it really took every minute of my working time – yet for me it is psychologically difficult to prepare proposals, and any unrelated activity eventually gives a feeling of guilt – whatever irrational it may be.
Anyway, I’m almost done and will submit the proposal soon. It is in development of the recent ideas about topological properties of superconducting junctions. Below is the title and the abstract.
Higher-dimensional topological solids realized with multi-terminal superconducting junctions (HITSUPERJU)
Recently I revealed a deep operational analogy between an exotic material and an electronic device, i.e. between a 3-dimensional topological solid and a 4-terminal superconducting junction. Specifically, the 3d Weyl singularities revealed in the energy spectrum of this quantum device give rise to quantized trans-conductance in two leads that is typical for 2-dimensional topological Quantum Hall materials. The quantized value can be tuned with the third control phase.
I propose to capitalize on this breakthrough by realizing artificial n-dimensional (topological) solid materials by (n+1)-terminal superconducting junctions. This seemed to be fundamentally forbidden so far. In particular, in the framework of one research direction I will address the realization of higher Chern numbers. The edges and interfaces are important in topological solids, they need to be structured. For the artificial topological materials made with multi-terminal superconducting junctions such structuring is impossible in geometric coordinate space. However, the fact that the charge and superconducting phase are quantum-conjugated quantities provide the unique possibility for the structuring in multi-dimensional charge space that I will access in the framework of another direction. These two research directions will be supplemented by a more technical effort devoted to computational (quantum) dynamics of multi-terminal superconducting junctions.
The proposed way to “conquer” higher dimensions for condensed matter physics is of clear fundamental importance. Exciting applications are at the horizon, too. The exotic quantum states under consideration can be topologically protected and thus useful for quantum information processing. Quantized trans-resistance as well as other topological invariants may be important in metrology. More generally, the research proposed will boost the whole field of electronic devices wherever topology guarantees the discrete stability of device characteristics.
Strong effects of weak ac driving in short superconducting junctions
has been published in PRB couple of days ago.
URL: http://link.aps.org/doi/10.1103/PhysRevB.91.104522
DOI: 10.1103/PhysRevB.91.104522
You can find the preprint here.
Abstract:
We study a short superconducting junction subject to a dc and ac phase bias. The ac modulation changes the occupation of the Andreev bound states formed at the constriction by transitions between bound states and the continuum. In a short junction, the non-equilibrium Andreev bound state population may relax through processes that conserve parity of the occupation number on the same bound state and processes that do not conserve it. We argue that the parity conserving processes occur on a much faster time scale. In this case, even a weak driving may lead to a large deviation of the supercurrent from its equilibrium value. We show that this effect is accompanied by a quasiparticle current which may lead to a measurable charge imbalance in the vicinity of the junction. Furthermore, we study the time evolution of the supercurrent after switching off the ac drive. On a time scale where parity relaxation is negligible, the supercurrent relaxes to a stationary non-equilibrium state. Finally, we briefly outline the regime of ultraweak driving where the ac-induced processes occur on a time scale comparable to parity relaxation.
Self-evaluation AQM: the results of the survey
About a month ago I ask the students to answer some questions regarding the course. We’ve used this feedback. Now the semester break has started: I have time to derive and publish the exact results.
In my opinion, the content of this course is relevant to my education (from -2 to 2) 1.66 good
This course corresponds well to my prior knowledge (from -2 to 2) 0.83 lower than we expected, though not bad
In relation to the amount of credit points, the actual study load of this course was much higher (from -2 to 2) 0.33 very good
The lecturer explain the subject matter clearly (from -2 to 2) 0.33 mmm, point to improve
The lecturer discuss the subject matter in a stimulating way (from -2 to 2) 1.0 rather good
The instructors give sufficient feedback on student presentations (from -2 to 2 ) 0.66 we can improve
The problem-solving sessions are interesting and useful (from -2 to 2 ) 0.88 as expected
English mark for the teacher (from 0 to 10 ) 6.8 mmm…
English mark for the instructors (from 0 to 10 ) 8.0 good
The lecturer should present the material with more examples . OK
The problem-solving sessions should be with more discussions. OK
This course is well organised (supply of information, scheduling) (from -2 to 2 ) 0.9 expected
I will go on with the course and come to the examination. Majority answered undoubtedly or most likely.
What mark do you expect to get at the exam? 7 well, not very ambitious 🙂
Do you use the book? Much worse than expected! A quarter use it regulary, a quater – sometimes. No, that is not good.
The overal mark:
lectures 7.5
problem-solving sessions 6.9
the whole course 7.5
we wouldn’t mind to score more, yet it’s not a big problem
I will make another survey shortly after the semester break.