# Posts in category Research

## PRB about 4 kinds of topology in a single device

Published about a month ago, actually.

**Order, disorder, and tunable gaps in the spectrum of Andreev bound states in a multiterminal superconducting device**

*Tomohiro Yokoyama, Johannes Reutlinger, Wolfgang Belzig, and Yuli V. Nazarov*

Phys. Rev. B 95, 045411 (2017) – Published 12 January 2017

## PRB details omega-squid

I thought for a while I made a record publishing two independent papers on the same day – no such luck, still a day difference

**Coherent transport properties of a three-terminal hybrid superconducting interferometer**

*F. Vischi, M. Carrega, E. Strambini, S. D’Ambrosio, F. S. Bergeret, Yu. V. Nazarov, and F. Giazotto*

Phys. Rev. B 95, 054504 – Published 13 February 2017

## PRB transconductance quantization

**Topological transconductance quantization in a four-terminal Josephson junction**

*Erik Eriksson, Roman-Pascal Riwar, Manuel Houzet, Julia S. Meyer, and Yuli V. Nazarov*

Phys. Rev. B 95, 075417 – Published 14 February 2017

## A postdoc/PhD student position in Germany (quantum information theory versus physics)

A fully-funded postdoc/PhD student position is available to work at

Peter Gruenberg Institute (PGI-2) in Forschungszentrum Juelich, near

Aachen in Germany. For students the degree will granted by RWTH

university in Aachen. The researcher will work with Dr. Mohammad H.

Ansari. The purpose of the project is to further develop the

mathematical relations between quantum information theory and physics.

Our findings will be used to explore new phenomena in quantum

thermodynamics and biology. The project requires that you have basic

knowledge about quantum physics, e.g. density matrix, Bloch equation,

correlations, the statistics of fermions and bosons, etc.

We will collaborate with some theoretical and experimental research

groups. One of our main collaborators will be Prof. Yuli Nazarov from

Delft University of Technology in the Netherlands, whom the researcher

will have the opportunity to visit and work with.

Everyone from all around the world are welcome to apply. For full

consideration, please apply as soon as possible, by sending your

documents in one pdf file to “mansari AT gmail DOT com”:

1. your academic CV,

2. your list of publications,

3. your short research interests (no more than 300 words ~ two paragraphs)

4. the names, affiliation, and email addresses of 2 or 3 referees,

(make sure they are willing to send letters on time)

More information about the research can be found on:

https://sites.google.com/site/mansari

## Quantum measurements made predictable

This is the first submission by Albert.

See it here.

**Probability distributions of continuous measurement results for conditioned quantum evolution**

A. Franquet, Yuli V. Nazarov

(Submitted on 24 Aug 2016)

ABSTRACT: *We address the statistics of continuous weak linear measurement on a few-state quantum system that is subject to a conditioned quantum evolution. For a conditioned evolution, both the initial and final states of the system are fixed: the latter is achieved by the post-selection in the end of the evolution. The statistics may drastically differ from the non-conditioned case, and the interference between initial and final states can be observed in the probability distributions of measurement outcomes as well as in the average values exceeding the conventional range of non-conditioned averages. We develop a proper formalism to compute the distributions of measurement outcomes, evaluate and discuss the distributions in experimentally relevant setups. We demonstrate the manifestations of the interference between initial and final states in various regimes. We consider analytically simple examples of non-trivial probability distributions. We reveal peaks (or dips) at half-quantized values of the measurement outputs. We discuss in detail the case of zero overlap between initial and final states demonstrating anomalously big average outputs and sudden jump in time-integrated output. We present and discuss the numerical evaluation of the probability distribution aiming at extend- ing the analytic results and describing a realistic experimental situation of a qubit in the regime of resonant fluorescence. *

## New submission: one device, 3 distinct topologies :)

This is possible: see it on cond-mat

**Order, disorder and tunable gaps in the spectrum of Andreev bound states in a multi-terminal superconducting device**

*Tomohiro Yokoyama, Johannes Reutlinger, Wolfgang Belzig, Yuli V. Nazarov*

(Submitted on 18 Sep 2016)

ABSTRACT: *We consider the spectrum of Andreev bound states (ABSs) in an exemplary 4-terminal superconducting structure where 4 chaotic cavities are connected by QPCs to the terminals and to each other forming a ring. Such a tunable device can be realized in 2DEG-superconductor structures.
We concentrate on the limit of a short structure and large conductance of the QPCs where a quasi-continuous spectrum is formed. The energies can be tuned by the superconducting phases. We observe the opening and closing of gaps in the spectrum. This concerns the usual proximity gap that separates the levels from zero energy as well as less usual “smile” gaps that split the levels of the spectrum.
We demonstrate a remarkable crossover in the overall spectrum that occurs upon changing the ratio of conductance of the inner and outer QPCs. At big values of the ratio, the levels exhibit a generic behavior expected for the spectrum of a disordered system manifesting level repulsion and “Brownian motion” upon changing the phases. At small values of the ratio, the levels are squeezed into narrow bunches separated by wide smile gaps. Each bunch consists of almost degenerate ABSs.
We study in detail the properties of the spectrum in the limit of a small ratio, paying special attention to the crossings of bunches. We distinguish two types of crossings: i. with a regular phase dependence of the levels and ii. crossings where the Brownian motion of the levels leads to an apparently irregular phase-dependence. We work out a perturbation theory to explain the observations.
The unusual properties of the spectrum originate from unobvious topological effects. Topology of the first kind is related to the winding of the semiclassical Green’s function. It is responsible for the proximity gaps. Topology of the second kind comes about the discreteness of the number of modes and is responsible for the smile gaps. *

## Nature Nanotechnology: how to engineer topology

The engineering efforts reported in March made their way to Nature Nanotechnology on Sep. 12,

**The ω-SQUIPT as a tool to phase-engineer Josephson topological materials**

* E. Strambini, S. D’Ambrosio, F. Vischi, F. S. Bergeret, Yu. V. Nazarov & F. Giazotto*

Nature Nanotechnology (2016) doi:10.1038/nnano.2016.157

Full text can be accessed via this link

## PRL quasiparticles

The attempt to unveil quasiparticle mysteries has been finally published in PRL

**Theoretical Model to Explain Excess of Quasiparticles in Superconductors**

*Anton Bespalov, Manuel Houzet, Julia S. Meyer, and Yuli V. Nazarov*

Phys. Rev. Lett. 117, 117002 – Published 9 September 2016

ABSTRACT: Experimentally, the concentration of quasiparticles in gapped superconductors always largely exceeds the equilibrium one at low temperatures. Since these quasiparticles are detrimental for many applications, it is important to understand theoretically the origin of the excess. We demonstrate in detail that the dynamics of quasiparticles localized at spatial fluctuations of the gap edge becomes exponentially slow. This gives rise to the observed excess in the presence of a vanishingly weak non-equilibrium agent.

## Supercurrents in chiral channels originate from upstream information transfer: a theoretical prediction

This is the title of (relatively) new arxiv submission, first with Xiao-Li Huang.

It can be found here.

**Abstract:**

*It has been thought that the long chiral edge channels cannot support any supercurrent between the superconducting electrodes. We show theoretically that the supercurrent can be mediated by a non-local interaction that facilitates a long-distance information transfer in the direction opposite to electron flow. We compute the supercurrent for several interaction models, including that of an external circuit. *

## Nature news and views

Quite unexpectedly, I’ve published something in Nature, specifically in News ans Views:

**Quantum physics: Destruction of discrete charge**

*Electric charge is quantized in units of the electron’s charge. An experiment explores the suppression of charge quantization caused by quantum fluctuations and supports a long-standing theory that explains this behaviour. See Letter p.58*

Yuli V. Nazarov

*Nature 536, 38–39 (03 August 2016) | doi:10.1038/536038a*

Full text can be seen here.