Posts in category Research
Phenomenology and Dynamics of Majorana Josephson Junction
is a title of new submission we made with Dima Pikulin. Interesting and simple dymanical effect in a Josephson qubit that we called any-pi Josephson effect. Please find it here.
The abstract is as follows:We derive a generic phenomenological model of a Majorana Josephson junction that accounts for avoided crossing of Andreev states, and investigate its dynamics at constant bias voltage to reveal an unexpected pattern of any-pi Josephson effect in the limit of slow decoherence.
The Effect of Mechanical Resonance on Josephson Dynamics
is a title of new arxiv submission made with Ciprian and Han Keijzers, PhD student from Quantum Transport group. This summarizes our long activity in course of which we strove to be close to experiment and the experiment strove for perfectness. This has not quite work yet, however the results are interesting and useful: certainly, they are for generations to come. Please read it here
The abstract: We study theoretically dynamics in a Josephson junction coupled to a mechanical resonator looking at the signatures of the resonance in d.c. electrical response of the junction. Such a system can be realized experimentally as a suspended ultra-clean carbon nanotube brought in contact with two superconducting leads. A nearby gate electrode can be used to tune the junction parameters and to excite mechanical motion. We augment theoretical estimations with the values of setup parameters measured in the samples fabricated.
We show that charging effects in the junction give rise to a mechanical force that depends on the superconducting phase difference. The force can excite the resonant mode provided the superconducting current in the junction has oscillating components with a frequency matching the resonant frequency of the mechanical resonator. We develop a model that encompasses the coupling of electrical and mechanical dynamics. We compute the mechanical response (the effect of mechanical motion) in the regime of phase bias and d.c. voltage bias. We thoroughly investigate the regime of combined a.c. and d.c. bias where Shapiro steps are developed and reveal several distinct regimes characteristic for this effect. Our results can be immediately applied in the context of experimental detection of the mechanical motion in realistic superconducting nano-mechanical devices.
Statistics of radiation at Josephson parametric resonance
I have not written to the blog for about a month. A fact which is not a direct consequence of this, but related to this is that Ciprian, Fabian Hassler and me have finally accomplished a long paper entitled as above. You can find it on the Arxiv.
The topic is hot, and the paper could have been short, yet we have discovered on time that a part of our results have been already obtained in optical context.
The abstract is as follows:Motivated by recent experiments, we study theoretically the full counting statistics of radiation emitted below the threshold of parametric resonance in a Josephson junction circuit. In contrast to most optical systems, a significant part of emitted radiation can be collected and converted to an output signal. This permits studying the correlations of the radiation.
To quantify the correlations, we derive a closed expression for full counting statistics in the limit of long measurement times. We demonstrate that the statistics can be interpreted in terms of uncorrelated bursts each encompassing 2N photons, this accounts for the bunching of the photon pairs produced in course of the parametric resonance. We present the details of the burst rates. In addition, we study the time correlations within the bursts and discuss experimental signatures of the statistics deriving the frequency-resolved cross-correlations.
Josephine van Leeuwen
graduated today. She was the first master student of Leo Di Carlo in his function as prof in Delft, and of Diego Riste in his function as phd student. So all three received deserved congratulations today.
Josephine was instumental in desinging, checking and measuring 3d superconducting cavities that serve as unbelievably high-quality resonators to play qubit games with. I never saw Lorentian shapes that fit so tightly. The cavities hosted already some qubits of a record-long decay time and they promise to revolutionize the field.
Good luck to Josephine with her future. When her grandson boasts with his last acquision,a supercool quantum ipad, she may be able to recognize her desing and he may believe her.
A manifestly strong fluctuation
has occurred today: the paper with Matti Laakso and Tero Heikkillä, entitled correspondingly (see this post ), has been accepted for Physical Review Letters today, without any revisions, within a first round of the referee reports and in three weeks upon submission. I cannot recall this happenning to me before, at least not in the last 15 years.
Workshop with Keio University
On Monday and Tuesday we have had a special event: a workshop for PhD students where experimentalists and theorists from Delft come together with their colleagues from Keio University. Japanese goverment provides financial support (or, given the present state of affairs, perhaps provided) to Japanese students to attend such workshops.
Prof. Mikio Eto thus came to us bringing Takashi Kashimura and Ryota Watanabe, and Tomohiro Yokoyama was already these. Guess it was interesting for everybody since the program was really various.
Here it is for your information:
Monday
10:15-10:30 Opening: Profs. Yuli V. Nazarov (TUD) and Mikio Eto (Keio)
10:30-11:00 Takashi Kashimura (Ohashi group, Keio) “π-Josephson junction in a spin-polarized Fermi gas”
11:00-11:30 Ciprian Padurariu (TUD, Theory group)
“Superconducting spin qubits”
11:30-12:00 Peng Yan (TUD, Theory group)
“All-magnonic spin-transfer torque and domain wall propagation”
13:30-14:00 Ryota Watanabe (Ohashi group, Keio)
“Pseudogap effects on photoemission spectra in the BCS-BEC crossover regime of
atomic Fermi gases”
14:00-14:30 Vlad Pribiag (TUD, Quantum Transport group)
"The spin-orbit interaction in InAs and InSb nanowire quantum dots."
14:30-15:00 Tomohiro Yokoyama (Eto group, Keio)
“Spin-polarized current generation in quantum dot with spin-orbit interaction”
Tuesday
9:15-10:15 Prof. Mikio Eto (Keio)
“Kondo effect in quantum dot embedded in Aharonov-Bohm ring”
10:30-11:00 Mohammad Shafiel (TUD, Quantum transport group)
“Single-shot correlations and two-qubit gate of solid-state spins”
11:00-11:30 Mireia Alos Palop (TUD, Theory group)
“Adiabatic quantum pumping through surface states in 3D
topological insulators”
11:30-12:00 Dmitri Pikulin (Leiden/TUD, Theory group)
"Influence of topology on transport properties of superconducting junctions"
Ewold Verhagen
is an 31-year-old Dutch physicist with merits in optomechanics, a recently emerged brusting field exploiting the coupling of laser light and high-quality mechanical resonators. He’s visited our department today to check the opportunities.
Ewold looks yonger than he is till he starts talkinig: then you recognize he’s actually a mature scientist deeply devoted to his subject, and is ready to explain the importance of the subject for others. He’s got quite a number of prizes and awards: normally, this would corrupt a person of his age irreversibly. However, Ewold appeared to sucsessfully withstand the bait and is able to talk about with an ironic smile.
The talk was both clear and exciting. I was pleased to see a speaker who starts with Hamiltonians: he made clear that optics along with atomic/molecular physics still enjoyes an innocent harmomy between experiment and theory, a paradise long lost in the field of quantum transport. I wish him a full sucsess.
Re-flows
my article on the flows of Reneyi entropy has finally appeared in press, this is the link to Physical Review B.
Nicolas Gisin
has continued yesterday a tradition of star talks in our Department. Prof. Gisin is a pioneer of commercial use of quantum technologies and one of selected scientists who manage to enforce his own research agenda upon the rest of the world.
Yet it remains its own research agenda, and he has clearly demonstrated this in the course of his talk. For me, the most fascinating and valueable part was the first one where he talked about device-independent Quantum Key Distribution. Two other topics seem more optics-bound.
Manifestly non-Gaussian fluctuations
in superconductor-normal metal tunnel nanostructures is a title of a new arXiv submission of me and my thrusted Finnish collaborators Matti Laakso and Tero Heikkillä. You can read it here.
In short, the paper is about making a commandable Maxwell daemon in SNS structures. Here is a detailed abstract:
We propose a mesoscopic setup which exhibits strong and manifestly non-Gaussian fluctuations of energy and temperature when suitably driven out of equilibrium. The setup consists of a normal metal island (N) coupled by tunnel junctions (I) to two superconducting leads (S), forming a SINIS structure, and is biased near the threshold voltage for quasiparticle tunneling. The fluctuations can be measured by monitoring the time-dependent electric current through the system, which makes the setup suitable for the realization of feedback schemes which allow to stabilize the temperature to the desired value.
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