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Posts in category Research

Renyi entropy in quantum engines

has been published in Physical Review B,
Phys. Rev. B 91, 104303 ā€“ Published 18 March 2015.
It has been submitted in August last year, the preprint is available here here.

We evaluate Renyi entropy flows from generic quantum heat engines (QHE) to a weakly-coupled probe environment kept in thermal equilibrium. We show that the flows are determined not only by heat flow but also by a quantum coherent flow that can be separately measured in experiment apart from the heat flow measurement. The same pertains to Shanon entropy flow. This appeals for a revision of the concept of entropy flows in quantum nonequlibrium thermodynamics.

Mikhail Titov

has been visiting on Wednesday to give the Quantum Nanoscience seminar among other things. I know him from 2000 when he was a post doc with Carlo Beenakker. Now he is a faculty in Nijmegen.

His work now is mostly in bulk transport, graphene being the most popular and useful application. The talk was about linear magnetoresistance and sign-reversed Coulomb drag in compensated Hall regime. This may sound involved, however, it was quite a fun to follow and understand that all miracles of experiment can be solved if you think clearly, simply but beyond a beaten track.

I even had an urge to do some Coulomb drag: I used to like the phenomenon, yet last time I look at it was 1999.

Exact correspondence

Me and Mohammad Ansari have submitted a paper that concludes a nice piece of research on Renyi entropies. We have found an exact relation, like fluctuation-dissipation theorem, that relates physical and unphysical quantities: you can guess the implications:))))

Here is the link

Exact correspondence between Renyi entropy flows and physical flows
Mohammad H. Ansari, Yuli V. Nazarov

We present a universal relation between the flow of a Renyi entropy and the full counting statistics of energy transfers. We prove the exact relation for a flow to a system in thermal equilibrium that is weakly coupled to an arbitrary time-dependent and non-equilibrium system. The exact correspondence, given by this relation, provides a simple protocol to quantify the flows of Shannon and Renyi entropies from the measurements of energy transfer statistics.

Charles Markus

from Copenhagen, a brilliant experimentalist who has now mostly concentrated on Majoranization of semiconducting nanowires by connecting those to superconductors – has given a talk on Thursday.

He started with reporting successes in nanowire growth: nanowires can be better contacted with superconductors, and can be made in t and h shapes. He has shown “hard gap” – looked good, finally in place after years of technological search.

Then we got the report on experimental results – some fresh, right from the oven. The results in “Delft geometry” seemed clean but I did not quite see the gap as hard as promised. The results in “Copenhagen geometry” were a superconducting island has been attached to the nanowire seemed more fun – I will have to revise those carefully.

Wilfred van der Wiel

from Twente University gave a Nanoscience seminar on Wednesday. I vividly remember him as an outstanding PhD student, have not seen him for years and was delighted to see no significant change: in the position of full professor, he reminds sharp, handsome, nice and does outstanding research.

There were two topics. First one: Wilfred has investigated the conductance (well, if you can call inverse GigaOhm a conductance) of molecular wires thread in zeolyte crystal. The conductance could be changed by order of magnitude by tiny magnetic field in millitesla range. The mechanism of the effect must be related to nuclear spins and as such is the same as for the spin-blockade lifting in double quantum dots. The details remain unclear for me: yet the effect is there and is a record-strong.

The second topic has fascinated me even more. The physics was rather simple: Coulomb blockade in a pile of gold nanoparticles carelessly collected between a multitude of electrodes. A neat physical realization of complete and hopelessly incomprehensible mess. Yet it appears that that it is the mess that motivated the researcher. Wilfred managed to demonstrate that with the proper tuning (based on genetic algorithm) the pile can work as any of the logical gates! I reckon this work will have a big philosophical impact (seriously). It proves that electronic components can be made from anything (substitute “anything” with a stronger word if you like).

Mutli-terminal Josephson junctions as topological materials

This is the title of the manuscript I have submitted on Tuesday with my Grenoble friends Julia Meyer, Roman Riwar and Manuel Houzet. Mmm, perhaps I exaggerate in excitation, but this looks the most significant piece of research I accomplished for last years. The preprint is not available yet, but I expect this to happen soon šŸ™‚

Christian Glattli

from Saclay has visited us on Wednesday this week. We have had an opportunity to chat about his research on graphene plasmonics and his plans to utilize edge channels in graphene, as well as about my plans with chiral electrons.

His talk was about “levitons”, his recent research on noise in quantum point contact. This drew me very philosophical: I began to think about most general definition of a particle and even ask Christian about)).

Eduard Driessen

who is presently a postoc in Grenoble with Claude Chapelier has given a talk yesterday. He reported very recent results on low-temperature STM experiments with superconducting nanowires. It is a tremendous technical challenge he has overcame.

The results were many and various. Some were pretty familiar and irritating like the incomplete gap in this disordered superconductor: the thing that has an explanation, yet the explanation so primitive and far-fetched that you feel yourself ashamed that you can’t do it better. Some were generation-binding: the hot spots in superconducting wires have been hot topic in 70s when Eduard’s former supervisors Hans Mooij and Teun Klapwijk were at his stage of the career, and STM experiments of Eduard just neatly visualized the intimate structure of these spots.

Some were teasingly interesting. Eduard pushed a 1nA – tiny – current to the STM and observed a gigantic suppression of the critical current in the nanowire. It is like you add an extra droplet to a river stream – and it does not flow anymore. These droplets must be quasiparticles.
The result suggests that the quasiparticles accumulate being added at a rate of 10^7 per second. This is thus about slow quasiparticle dynamics – a topic of my long interest

Happy New Year

to you, dear reader. Let peace and harmony prevail every aspect of your life!

Today seems a good day to restart my business blog. Since I’m alive, it must go on too. Let me outline my main challenges for 2015 and wish you to confront your challenges as well.

In education, I restart the course on Advanced Quantum Mechanics after five-something year break. That used to be a success, yet the students have changed ever since – so I feel a thrill. The course will be based on my book with Jeroen Danon. Albert Gonzales and Michael Wimmer will help me this year with exercises, so I hope we’ll do it fine.

In research, I need to complete to the papers the ideas of 2014 that came to me and my co-authors – some of them are quite striking and eye-opening. I will apply for a relatively big grant of European Research Council which hopefully gives me some means to work on novel topological effects in multi-terminal Josephson junctions.

As to organization, my role would be modest – conform to my age, I will try to resist most if not all (bureaucratic)changes in the group and the department šŸ™‚ The idea is that the changes that you cannot resist are really useful and necessary šŸ˜‰ while the others …

In addition, have to confront a way more personal challenge: to cope with a long-standing emotional disbalance that, among other things, seriously affects my business efficiency. 2014 has brought the idea of solving this problem, and hopefully the solution can be implemented in 2015.

Actually, my promotion is pending now: I don’t know if or when it happens. In case it will, I’d get a very useful emotional boost.

PhD opening in NanoFront

Iā€™m looking for a PhD student to work on linear quantum measurements with delays. Many thanks to NanoFront initiative!

More info:
PhD position in quantum theory of dissipative measuring environments.
Can we predict quantum jumps? A common opinion is that we cannot. Is this opinion correct? Full project description can be found here .
Job description
4 years phd position
Kavli institute of Nanoscience, department of quantum nanoscience

The applicant should bear MSc title in theoretical physics or its equivalent. Experience in condensed matter physics and quantum information theory is appreciated.
Conditions of Employment
When fulfilling a PhD position , you will get the status of junior scientist.
You will get a contract for 4 years. Your salary will be up to a maximum of 2,636 euro gross per month.The salary is supplemented with a holiday allowance of 8% and an end-of-year bonus of 8.33%.
You are supposed to have a thesis finished at the end of your four year term.

Yuli V. Nazarov

Please send your CV and recommendation letters


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