Topological Photonics 2025 workshop in San Sebastian: call for abstracts

The Topological Photonics 2025 workshop, to be held at Palacio Miramar in San Sebastian, on 30th June-2nd July 2025. This meeting follows similar workshops held in 2021, 2022 and 2023 and is aimed at gathering a critical mass of people working in the vibrant area of Topological Photonics as well as topology in other wave and quantum phenomena. Abstract submission is now open for contributed talks and posters. 

 The following confirmed keynote and invited speakers are confirmed:

Keynote speakers:

• Andrea Alù (The City College of New York – USA)
• Olga Smirnova (Technical University Berlin, Germany)
• Päivi Törmä (Aalto University, Finland)
  
• Shanhui Fan (Stanford University, CA, USA)
  

Invited speakers

• Alexander Cerjan (Sandia National Laboratory, US)
• Baile Zhang (NTU, Singapore)
• Chiara Devescovi (ETH, Switzerland)
• Clivia Sotomayor-Torres (ICN2, Spain)
• Dario Bercioux (DIPC, Spain)
• Ewold Verhagen (AMOLF, Netherlands)
• Frank Scheffold (University of Fribourg, Switzerland)
• Oded Zilberberg (University of Konstanz, Germany)
• Sylvain Ravets (C2N, France)
• Thomas Christensen (Technical University of Denmark, Denmark)

Please submit your abstracts here before 14th of March 2025. Registration deadline is 30th May 2025. Participants are advised to book rooms as early as possible, hotels fill up quickly at that time of the year. You can find more information at the meeting website.

Postdoctoral Position at Wave Transport in Complex Systems Lab—Wesleyan University

The Wave Transport in Complex Systems (WTICS) Lab at Wesleyan University is
opening a post-doctoral position on wave transport in theory or/and experiment
using microwave and RF analogue circuitry. The candidate must have a basic
knowledge of theory of metamaterials. A knowledge of software packages for
electronic design (such as COMSOL, SPICE etc) is desirable. Specific areas of research that are relevant to the current post include:

(a) Artificial Intelligence and Machine Learning;
(b) Non-Hermitian systems;
(c) Active topological structures;
(d) Asymmetric transport;
(e) Wavefront shaping techniques

The position is for two years with a possible extension of a third year. Information
about the WTICS group can be found here. Interested candidates should send a CV, a short statement of work and three recommendation letters to Prof. T. Kottos at tkottos@wesleyan.edu.

Postdoctoral Positions at Nankai University, Tianjin, China

Applications are solicited for postdoctoral positions in experimental/theoretical optics and photonics in the research group of Prof. Zhigang Chen/Hrvoje Buljan at Nankai University, China, which is one hour away from the capital Beijing and the alma mater of Shiing-Shen Chern. The areas of emphasis are topological photonics, nonlinear optics, optical trapping and manipulation, and machine-learning photonics. A PhD in physics, optics, or related area is required. It is expected that the candidate should have basic numerical skills and/or optical experimental skills and research experience with a good track of record in publications.

The initial appointment will be for three years, with the possibility of extension pending on performance and research funding. If accepted, the salary is competitive (annual gross salary > RMB 500,000, about $70,000), with possible additional merit award depending on academic performance evaluated at the end of each year. Free on-campus apartment is available, and the living cost is very low compared to income. The position will be funded under the China Postdoctoral International Exchange and Introduction Program, with the purpose of attracting outstanding PhD graduates to join the university and conduct postdoctoral research.

Applicant eligibility:
1. In general, applicants shall be under the age of 35. As for key disciplines supported by the university, the limitation on age can be eased to 38 years old.
2. Both Chinese and foreign graduates obtaining their PhD (from overseas top universities or supervised by an internationally recognized scientist) in recent 3~5 years can apply.
3. PhD candidates who meet the above conditions can also apply if they can start the postdoctoral position by June 2025.

Interested candidates are encouraged to contact Professor Chen or Professor Buljan before April 20, 2024 for application this year. However, the starting date is flexible.

Website: https://topo-photonics.nankai.edu.cn/index.htm

Postdoc Opening at Tohoku University: Condensed Matter and AMO Theory

Tomoki Ozawa's group at the Advanced Institute for Materials Research, Tohoku University, has a postdoc opening (the official title would be Specially Appointed Assistant Professor, or Tokunin-Jokyo in Japanese), which can start as soon as the decision is made or from April 1, 2025 at the latest. The position lasts for three years. 

The group works on theoretical condensed matter physics and AMO (atomic, molecular, and optical) physics, in particular on topological phases and/or many-body physics in these systems. A part of the salary of this position will be from the KAKENHI Kiban-B grant, “Geometrical effects in non-Hermitian quantum systems." 

The application deadline is April 30, 2024, and the application should be sent through Academic Jobs Online from the following link:

https://academicjobsonline.org/ajo/jobs/27320

Tomography, topology, and more

Some preprints that caught my attention over the last few weeks:

Attention-based transformer networks for quantum state tomography. The tremendous surge in popularity of transformer-based large language models means that there is a lot of effort towards developing efficient hardware and algorithms for implementing transformer-based neural networks. It is thus timely to understand how this architecture may be useful for solving problems in physics. This preprint proposes a transformer-based model for density matrix reconstruction.

A discrete formulation of the Kane-Mele Z2 invariant. Newcomers to topological materials are often stumped on how to efficiently implement gauge-invariant formulas for topological invariants in numerical calculations; analytical formulas assume a smooth choice of gauge for the eigenfunctions, whereas numerical calculations will return a non-smooth random gauge. The method reported here for calculating Chern numbers without requiring any gauge-fixing greatly simplifies numerical calculations. The present preprint concisely presents a numerical-friendly formulation of the Z2 invariant describing quantum spin Hall phases.

Valley photonic crystal waveguides fabricated with CMOS-compatible process. This work presents valley Hall photonic crystals based on an improved mask design that yields more triangular-shaped holes, improving their performance as valley Hall waveguides. It will be interesting to see measurements of the absolute propagation loss and how it compares to the strong backscattering reported earlier this year.

Photonic Landau Levels. Two groups (from the Netherlands and from the USA) report experiments with strained photonic crystals that emulate Landau levels formed by electrons subjected to uniform magnetic fields. These works show how previous theory and experiments based on weakly-coupled waveguide arrays can be generalized beyond the tight-binding approximation and may serve as a novel platform for achieving high quality factor modes and enhanced light-matter interactions. 

Questions and concerns about Google's quantum supremacy claim. The lead author Gil Kalai is one of the most prominent skeptics of quantum computing. This preprint summarizes efforts to rigorously analyze the raw data behind Google's 2019 quantum supremacy experiments. Since there now exist efficient classical algorithms for reproducing the output of the quantum supremacy circuits, the most important outstanding result from the 2019 paper is that the errors in large scale quantum circuits are uncorrelated to a good approximation, suggesting that quantum error correction can work in principle. This preprint argues that the data underlying this claim is flawed and that more effort should be devoted to understanding noise sources present in NISQ devices.

Suppression of modulational instability in valley-Hall waveguides

Posting has become infrequent due to some urgent deadlines and talk preparations over the last few weeks. Lots of great stuff has appeared on arXiv in May which I'm hoping to read and perhaps post about later. 

In the meantime, we also have a preprint out:

Self-steepening-induced stabilization of nonlinear edge waves at photonic valley-Hall interfaces

Several previous works demonstrated instabilities of topological edge states in the presence of weak nonlinearities, both numerically and analytically, often via reduction to a 1D nonlinear Schrodinger equation (NSE). We show here that if you go to stronger intensities, higher-order nonlinear effects (essentially arising from an intensity dependence of the effective Kerr nonlinearity strength) described by a modified nonlinear Schrodinger equation (MNSE) can stabilize the edge states! The phase diagram below nicely summarizes our central result:

I prepared some slides on this and our earlier analyses of nonlinear Dirac models describing topological edge states. The slides including some background material on photonic crystals and topological photonics are available here!