International Conference on Quantum Science & Technology (6-9th October, 2025) - call for abstracts

The main aim of the conference, to be held in Quy Nhon, Vietnam, is to develop links between physicists in Vietnam and those in France and around the world who are contributing to the advances of quantum physics. The scientific programme features eminent invited speakers including Serge Haroche. The following themes are envisaged:

• quantum optics, quantum communication and quantum computation
• topics where condensed matter, atomic physics and chemical physics overlap
• high precision experiments involving spectroscopy and metrology
• cold atoms and simulation of materials
• theory and methods in quantum mechanics
• quantum high energy physics and cosmology
• quantum technologies and energy production

A focus on inter-generational exchanges will be planned between top level invited senior physicists and young students, opening new scientific horizons to them. Tutorials will be given (half a day before the colloquium) to provide the basis of the fields which will be covered by the speakers. Time will be given to young PhDs and postdocs to present their work. Round tables will allow informal discussions raised by the presentations and identify opportunities to develop scientific cooperative projects between Vietnamese and foreign laboratories. 

For more details and registration information, please visit the conference website. The abstract submission and registration deadline is September 7th, 2025. Registration is free, but participants must cover their own travel and accommodation expenses.

Upcoming ICTP Asian Network Schools and Related Events

Joint Thailand-Cambodia Mini-School on Quantum Materials: Theory and Experimentation

June 18 - 20, 2025, SC45 Building, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand

https://physics.sci.ku.ac.th/conference/minischool2025/

Open to all, but focused on participation of graduate students and early career researchers from Thailand and Cambodia. Potential participants should register online as soon as possible.

Asian Network School and Workshop on Complex Condensed Matter Systems

November 10 - 14, 2025, National Institute of Physics, University of the Philippines Diliman, Quezon City 1101, Philippines

https://pcs.ibs.re.kr/ICTP_Asian_Network/ICTP_Events.html

Open to all ICTP Asian Network participants. A dedicated web page will appear soon.

Advanced School on Topological Quantum Matters
June 30 - July 5, 2025, ICISE, Quy Nhon, Vietnam

https://icisequynhon.com/conferences/2025/toposchool2025/ 

This school is supported by APCTP. In principle it is open to all students and early career researchers, but places and support may be limited. Interested participants are encouraged to contact the organisers and register online.

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.

The 17th Annual Meeting Photonic Devices, Zuse Institute Berlin, Germany

Call for abstracts for the 17th Annual Meeting Photonic Devices (AMPD2025), taking place at Zuse Institute Berlin, Germany.

Topics include nanophotonic devices and related simulation methods. The organisers aim for open discussions between experiment, theory, and numerical methods.

Invited talks will be given by:

Anna Tasolamprou, National and Kapodistrian University of Athens
Bumki Min, Korea Advanced Institute of Science and Technology (KAIST), Daejeon
Costantino De Angelis, University of Brescia
Costanza Toninelli, European Laboratory for Non-Linear Spectroscopy in Florence
Haejun Chung, Hanyang University, Seoul
Humeyra Caglayan, Tampere University
Jesper Mork, Technical University of Denmark, Lyngby
Kurt Busch, Humboldt University of Berlin
Mohsen Rahmadi, Nottingham Trent University
Nahid Talebi, Kiel University
Olivier Martin, EPFL, Lausanne
Thomas Pertsch, Friedrich Schiller University Jena
Tim Schröder, Humboldt University of Berlin
Further invited speakers to be confirmed.

Please consider joining this workshop as either a speaker (poster or talk) or as an audience member. The workshop is free of registration fees.

Important dates:

Abstract submission deadline: January 31, 2025
Decision about acceptance: February 15, 2025
Registration deadline: March 25, 2025
Workshop: April 02-04, 2025 

Further information is available at https://www.zib.de/workshop-photonic-devices/ampd2025.html

IPS Meeting 2024 and Nobel Week

Last week I attended the IPS Meeting 2024, held this year at Nanyang Technological University, and gave a plenary talk on flatband lattices, covering material we recently published in an invited review in Nanophotonics. Among the many interesting talks this year, the plenary presentation by Antonio Castro Neto on the creation of carbon thin films and liquid crystals via oxidation of graphene (see e.g. this paper).

This week the Nobel Prizes were announced, with machine learning and AI dominating the Physics and Chemistry prizes. It's quite remarkable that one of the Physics laureates (Hopfield) published his prize-winning work as a single author theory paper in 1982, when he was already 49 years old! It's never too late to do your most impactful work!

Asian Network Mini-School on Quantum Materials 2024

Last week I visited the University of Indonesia to present two lectures on topological photonics at the Asian Network Mini-School on Quantum Materials 2024. This is one of a series of events held in South East Asian countries held by the ICTP Asian Network. The school attracted 95 participants from Indonesian universities, the majority being advanced undergraduates or graduate students. Meetings such as these provide valuable opportunities for early career scientists to learn about cutting-edge research areas and build collaborations with others in the region. I was impressed by the level of engagement from the audience - even though I ended my first lecture 20 minutes early, the remaining time was fully occupied by questions! Many thanks to the local organizers for putting together such an enjoyable meeting! Two more schools will be held this year, both in Thailand, on complex condensed matter systems and magnetism and spectroscopy, with more planned for next year.

IPS Meeting 2023

A few things I learned attending the first two days of this year's IPS Meeting, held right here at NUS:

Prof. Giovanni Vignale gave a plenary talk on bulk currents and edge accumulation in anomalous Hall systems. In the conventional quantum Hall effects, accumulation of charge at the edges of the sample are driven by the bulk quantized Hall conductivity. Anomalous quantum Hall systems, on the other hand, do not show an accumulation of spin or valley densities at their edges, despite their corresponding bulk spin or valley Hall conductivities being nonzero. In the case of spin Hall systems it's because bulk electrons will flip their spin when reflecting off the edge of the sample. Thus, the edges accumulate a nonzero charge density, but their spin density remains zero. Interestingly, a similar argument does not hold for the case of valley Hall systems because the applied electric field that drives the current also induces coupling between the valleys in the bulk. Further details can be found here.

The second plenary talk by Prof. Silvija Gradecak focused on the use of imperfect or novel materials to develop new components. A striking example given was the use of 2D materials as diffusion barriers in nanoscale metal contacts in integrated circuits, which promises the ability to further miniaturize electronic components.

Dr. Sen Mu talked about Kardar-Parisi-Zhang (KPZ) physics in the Anderson localization of two-dimensional wavepackets. The KPZ equation describes fluctuations that arise in the density fluctuations of expanding waves in the presence of disorder. These fluctuations are universal and arise in a variety of wave systems, including the spreading of coffee poured out onto a napkin, which he demonstrated for us live! arXiv preprint

Weitao Chen discussed critical dynamics in one-dimensional disordered systems with long range coupling. In critical systems the eigenstates exhibit multifractality, meaning that the different moments of the eigenstates scale with different non-integer exponents with the system size. This is a bit abstract and hard to measure directly in an experiment, but remarkably this multifractality can also be observed by exciting a single site of the lattice and measuring the time-dependent return probability! arXiv preprint

Prof. Di Zhu in another plenary surveyed integrated photonics for the generation, manipulation, and detection of quantum states of light. A recurring theme was that many of the improvements required to scale up integrated quantum photonic systems can be found by looking back to scientific literature from the 1960s! One neat example he gave was scaling up superconducting nanowire single photon detectors: Putting many of them one one chip is hard, because each coaxial microwave read-out line also conducts heat in - if you have too many you will no longer be able to keep the chip cool enough for the detectors to work. The solution? Move from detection based on a lumped circuit model to a transmission line detector, which can (with a bit of signal processing) perform spatially-resolved detection of multiple single photons. A demonstration of this idea was published this year in Physical Review Applied after spending quite some time under peer review by the looks of it.

There were many other interesting talks and posters that I didn't take enough notes on to write about, but it was nevertheless great to see the breadth of physics being done at the different universities and research institutes in Singapore.

International Workshop on Polaritons in Emerging Materials

Last week I had the pleasure of attending an IBS PCS International Workshop on Polaritons in Emerging Materials held in Daejeon, Korea. Smaller workshops such a this one (~40 participants) with a more relaxed schedule (40 minutes per speaker and generous coffee/lunch breaks) are great for getting a more in-depth and candid picture of an unfamiliar research field!

One of the hot topics was polaritons in transition metal dichalcogenides - a rapidly-maturing family of two-dimensional graphene-inspired materials. Prof. Myung-Ki Kim from Korea University talked about plasmon resonances in multi-layer TMDs, Prof. Deep Jariwala from the University of Pennsylvania presented experiments with cavity-free polaritonic structures. The high refractive index of 2D materials such as molybdenum disulphide means that they can already exhibit strong light-matter coupling without requiring embedding in a microcavity. Thanks to the different localization of the photonic and electronic degrees of freedom one can form ultra-thin multilayer structures either as thin sheets of the 2D material (with the thickness controlling the electronic band structure), or as lattices formed by multiple non-interacting single sheets. Prof. Su-Hyun Gong (Korea University) presented waveguides based on multilayer tungsten disulphide can achieve tight (nanoscale) light confinement with lower losses compared to conventional plasonic materials such as gold. Expect to see many more works in this area as high-quality and large-area samples of these exotic materials start to become commercially available.

Another active area was optically-driven rotation and localization of exciton-polariton condensates. Dr. Michael Fraser (RIKEN) presented experiments in which a condensate is stirred via incoherent pumping with two slightly-detuned Laguerre-Gaussian layer beams, leading to an asymmetric reservoir density that undergoes a rotation, producing condensates with vortices. Theoretical analyses of vortex generation and turbulence in stirred exciton-polaritons were presented by Dr. Alexey Yulin (ITMO) and Dr. Helgi Sigurðsson (Warsaw), and Dr. Sergei Koniakhin (IBS PCS). Prof. Alberto Amo (Lille) showed that the dynamics of resonantly-driven condensates in lossy lattices can be remarkably counterintuitive - the strongest localization occurs between the pumped sites, not at them!

While not the main theme of the workshop, topological photonics was represented in talks by Profs. Sven Höfling, Sebastian Klembt (both from Würzburg University), Dr. Xingran Xu (NTU), who focused on lasing and non-Hermitian topological phenomena, and Dr. Alexander Cerjan (Sandia National Labs), who showed how real-space topological markers can be used to quantify the robustness of nonlinear topological edge states.

Prof. Fabrice Laussey (Wolverhampton) gave a captivating talk on quantum light and the importance of taking detector bandwidth into account when modelling quantum light sources. Since quantum light is so weak, signals measured using a finite bandwidth filter will inevitably be dominated by the tails of the much stronger pump beam unless homodyne detection is used. Look for quantum correlations in the spectral minima, not the dips! In related talks, Prof. Andrey Moskalenko (KAIST) analyzed entanglement between cavities generated by coherent optical driving, and Prof. Hyang-Tag Lim (KIST) covered experimental generation of multi-mode N00N states.

Most of the talks should become available to watch on the PCS Youtube account at some point.

Conferences in Ukraine

The first two international physics conferences I had the pleasure of attending, way back in September 2011, were held in Ukraine. This was also my first time travelling outside Australia. 

After 30 hours and 4 flights I landed in Kharkiv for the first conference, the International Workshop on Nonlinear Photonics (NLP*2011), held at the Kharkiv National University, located at the picturesque Svobody Square in the city centre.

Svobody Square. The statue of Lenin was torn down in 2014, replaced by a fountain in 2020, and presumably shelled in 2022.

Kharkiv was the home and origin of many great theoretical physicists. Landau and Lifschitz began writing their classic textbook series Course of Theoretical Physics there. Outside the auditorium in which the conference was held, attendees were greeted by an impressive Soviet-era mural.

The entrance to the conference auditorium. The university buildings were destroyed by Russian army shelling in March 2022.

This workshop was my first chance to meet many leading researchers working on nonlinear optics and singular optics, including the late Marat Soskin, who gave a memorable talk on the creation and destruction of topological defects in nematic liquid crystals. One afternoon my then-colleague and future Ignobel Prize Laureate Ivan Maksymov showed me around the city, which was where he had completed his physics studies.

 The following week I attended the Tenth International Conference on Correlation Optics, held at Chernivsti National University on the other side of the country, two flights and a train ride away.

 

The beautiful grounds of the Chernivsti National University, a UNESCO World Heritage Site, constructed between 1864 and 1882.

The Correlation Optics conference series is still going strong, with the next edition planned to be held in hybrid mode in September 2023. As one attendee aptly put it, "No one really knows what correlation optics is precisely, so its themes can continuously adapt to changes in research trends." At the time, one trend was the increasing availability of nanofabrication facilities leading to a transition from micro-optics to nano-optics.

Before dawn on the morning after the end of the conference, what seemed like all of the international attendees converged on the tiny Chernivsti Airport to catch the only international flight running that day. After "checking in" our baggage, we had to wheel it ourselves onto the tarmac to be loaded onto the small jet plane while we considered holding a post-conference session during the flight. 

I travelled onwards to Germany to visit collaborators at the University of Münster. Due to a chance encounter at ICOAM last year, we resumed our collaboration leading to a paper soon to be published in Photonics Research. But that's another story.

TDA Week 2023

TDA Week is a five-day conference on topics related to topological data analysis, held this year in person at Kyoto University from July 31 (Mon) to August 4 (Fri). It follows last year's conference, which was held online due to covid restrictions.

The abstract submission deadline for poster presentations is 14th April. Presenting authors may request partial support for travel expenses.

Snippets from the topological data analysis workshop

 I had the pleasure of visiting KIAS last week to attend their Workshop on Topological Data Analysis: Mathematics, Physics, and Beyond.

The programme featuring so many pure mathematics-focused talks was daunting at first, but ultimately I learnt a lot more than I would have by presenting the same work at a physics conference. This serves as a nice reminder: When we become experts at a highly specialised topic in our PhD studies (and beyond), it is easy to lose sight of the bigger picture. Changing fields or even attending a wide range of seminars outside our own expertise sparks new ideas.

Some useful tidbits from the talks:

• The Vietoris-Rips complex is not stable with respect to outliers. For example, adding a few points to a middle of a circular point cloud will completely change the form of the 1D persistence diagram (replacing the single high persistence cycle with low-persistence cycles). Stability theorems for persistence diagrams refer to small perturbations of a fixed set of point.
• Similar persistence diagrams do not imply similar data, in fact datasets with an arbitrarily large Hausdorff distance can have the same persistence diagrams.
• Mathematicians like TDA because it involves interesting problems with elegant solutions. But not all these elegant methods end up being useful in practice.
• The chemical and biological sciences benefit from having large datasets publicly available for benchmarking and standardised scoring of new machine learning / data analysis methods including TDA. This allows demonstrations of new heuristic methods to be convincing. 
• TDA can be used to estimate geometric features of data, including their (fractal) dimension, which is useful for understanding the performance of neural networks.
• The generators of 0-dimensional persistence diagrams give the minimal spanning tree for the data. This widely-used "folklore" was only rigorously proved in 2020!
  

Workshop on Topological Data Analysis: Mathematics, Physics and beyond

Next month I'll be speaking at a workshop on topological data analysis (TDA) organized by the Korean Institute for Advanced Study, to be held on February 8-10 in Seoul. I'm quite excited because this will be my first chance to attend an in-person meeting dedicated to this topic! From the workshop website: 

"This workshop aims to share our knowledge about topological data analysis from the viewpoint of mathematics and physics. We are trying to make this event in-person with a relaxed schedule, so that we can discuss each other more freely. We hope this event help us widen our perspectives on mathematical and physical backgrounds about data analysis."

In other TDA news, there is an article on TDA published in the January issue of Physics Today which gives an overview of applications to condensed matter and soft matter physics using the "shape" of Jigglypuff as a pedagogical example!

IBS-APCTP Conference on Advances in The Physics of Topological and Correlated Matter

Last month I attended the IBS-APCTP Conference on Advances in The Physics of Topological and Correlated Matter. It was great to be attending a conference in-person after so long! Slides from many of the talks are available here. Summaries of some of the talks from the notes that I took:

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Prof. Changyoung Kim (IBS/SNU) spoke about tunable anomalous Hall conductivity in correlated electron systems. The anomalous Hall effect is a Hall effect that occurs in the absence of an external magnetic field in materials exhibiting a spontaneous magnetization of the electron spins. An extreme example of this is half-metals, where the energy bands are completely filled (insulating) for one spin and partially-filled (conducting) for the other spin. 

One way to potentially enhance the anomalous Hall conductivity is to dope the material to tune the Fermi level of the partially-filled band to a region of high Berry curvature, but in some cases this kind of perturbation picture will fail due to the doping-inducing a reconstruction of the band structure to form a distinct phase. It is important to distinguish the intrinsic anomalous Hall conductivity from (potentially much larger) extrinsic (disorder-induced) contributions.

Another approach applicable to thin film materials is substrate-induced magnetization, which can lead to interesting thickness-dependent material properties including the magnitude and even sign of the anomalous Hall conductivity changing as single layers are added or removed. These changes can be resolved using spin-resolved ARPES.

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Prof. Masatoshi Sato (Kyoto University) talked about Majorana fermions in topological superconductors, particularly differences between spinless and spinful Majorana fermions; the latter require additional symmetries for protection. The symmetry requirements will likely make it quite extremely challenging to carry out robust braiding operations required for topological quantum computation. Another application of Majorana particles outside of quantum computing is to use them to probe the properties of the underlying superconductor, since they share the same symmetries as the underlying superconducting gap function.

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Prof. Takashi Oka (University of Tokyo) covered Floquet engineering of topological bands and novel topological nonlinear optical effects, including Hall response dependent on a nonlinear gauge-invariant curvature term, related to theoretical analysis published in Nature Physics at the end of last year. Floquet engineering of topological bands has of course been a very influential idea since the late 2000s (Oka and Aoki's 2009 paper has amassed more than 1000 citations!), with a variety of linear (and nonlinear) phenomena occurring sensitive to the period and strength of the periodic Floquet driving.

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Prof. Gil-Ho Lee (POSTECH) discussed his group's experimental work on Floquet engineering of graphene using microwaves. The effective strength of the Floquet-induced band structure modifications scales as \( E / \omega^2 \), where \( E \) is the (normalized) field strength of the drive and \( \omega \) is its frequency. By using a lower frequency microwave drive (instead of more conventional optical pumping), the required field strength is reduced, making it practical to study continuous wave driving while maintaining a sufficiently low temperature. The catch, however, is that the lower drive frequency is accompanied by smaller Floquet band gaps that require scanning tunneling microscopy to resolve. Ongoing work aims to observe Floquet topological bands induced by polarized microwave driving, and to improve the coupling between the microwave antenna and the graphene sheet to probe higher Floquet drive strengths.

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Dr. Andrew Pierce (Harvard -> Cornell?) talked about thermodynamic measurements of topological states in magic angle graphene, the subject of his PhD studies and three (!) Nature Physics papers published in the last year ([1], [2], [3]). He mentioned that bilayer graphene is an extremely fickle system - every sample is different and it is very hard to reproduce experimental results. Trilayer graphene, on the other hand, can offer a more reliable platform for exploring moire phenomena including twist-induced superconductivity. 

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Dr. Robert-Jan Slager (Cambridge University) talked about unconventional multi-gap topological phases. In the conventional topological band theory we usually consider a single band gap whose topological properties (and the existence or absence of robust edge states) is determined by topological invariants of all the bands below the gap, leading to the well-known periodic table of topological insulators. Interestingly, the topological band theory can be generalized to novel multi-gap topological phases which are trivial under the conventional topological band theory, involving partitions of the band structure into three or more sectors. One example of non-trivial multi-gap topological invariant is the Euler class. These ideas are now being generalized to Floquet systems.

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Prof. Aris Alexandradinata (UC Santa Cruz) presented a topological principle in photovoltaics. Bulk photovoltaic effects known as shift currents are attracting interest as a potential route towards making more efficient solar cells. A nonzero shift current requires a material with broken inversion symmetry. Beyond this necessary condition it is not clear what is the best way to maximize the strength of the shift current. New classes of topological phases may provide a route to finding materials with stronger shift currents. He currently as a few PhD and postdoctoral research fellow positions open!

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Prof. Emil Bergholtz (Stockholm University) talked about fractional Chern insulators and quantum geometry in moire materials. A long-standing goal in the field of topological materials has been the search for fractional Chern insulators, which are hoped to exhibit high temperature fractional quantum Hall states. The "simple" picture of a fractional Chern insulators is that they are lattice systems exhibiting nearly flat bands with nonzero Chern numbers that form a lattice analogue of the Landau levels underlying the conventional quantum Hall and fractional quantum Hall effects. In practice, however, the physics is more complicated. Even if the energy dispersion is relatively flat, other properties of the band including its quantum metric and Berry curvature can be strongly non-uniform, disrupting the analogy with continuum Landau levels and destroying the fragile fractional quantum Hall states. This seems to also be the case with the nearly flat topological bands arising in twisted bilayer graphene: although the single particle band structure is flat, interactions combined with the non-trivial momentum-dependence of the quantum metric lead to self-consistent (Hartree-Fock) bands with strong dispersion, inhibiting the formation of fractional quantum Hall states. He also has some postdoc openings!

Quantum Africa Conference (QA6)

Quantum Africa is a conference covering quantum information and quantum computing running next week (Monday 12th to Friday 16th of September 2022).

It will be held in hybrid mode with a mix of in-person and online talks.

The talks should be quite pedagogical and will be given by outstanding researchers from academia and industry, including Steve Girvin (Yale, USA), Francesco Petruccione (UKZN, South Africa), Pedram Roushan (Google Quantum), and Terry Rudolph (PsiQuantum).

Talks will be recorded for later on-demand viewing for registered participants. Registration is free for online attendance!

The 2nd POSTECH MINDS Workshop on Topological Data Analysis and Machine Learning

Resuming (hopefully) semi-regular posting after a few weeks finishing revisions to a few manuscripts:

POSTECH in Korea is hosting another workshop on the intersection between topological data analysis (TDA) and machine learning at the end of September [Sep. 26 (Monday) ~ Sep. 29 (Thursday)]. From the conference website:

This workshop will bring together researchers and students working on TDA and machine learning and provide an opportunity where they present their recent research and share ideas. Further, this workshop will also provide tutorial sessions that will introduce various TDA computational tools and provide practical hands-on tutorials. This is a sequel to the workshop of the same name held in 2021 - ILJU POSTECH MINDS Workshop on Topological Data Analysis & Machine Learning, 2021.

I attended (virtually) last year's workshop and found it quite interesting. As a newcomer to the field it gave a good picture of some of the cutting-edge questions being pursued in TDA. There is no registration fee, but registration is required for access to the workshop live stream.

ICOAM 2022 - live stream

The 6th International Conference on Optical Angular Momentum is running this week, featuring an impressive lineup of invited speakers including Sir Michael Berry (of geometric/Berry phase fame), who will be giving a public lecture on Friday.

The organisers have kindly provided a zoom livestream of the sessions so those who unable to attend in person can still watch the talks.

I will be giving my talk remotely on Wednesday morning. Here are my slides. My aim is to provide an accessible introduction to topological data analysis and offer some potentially-interesting directions for future research.

Unfortunately the review article we've been working on is not yet finished - I was hoping to have an arXiv link ready in time for my talk.

ICOAM 2022 - call for abstracts

6th International Conference on Optical Angular Momentum
12–17 June 2022
Tampere University, Finland

ICOAM covers topics broadly related to the fields of structured light and singular optics. The conference was supposed to be held last year, but was postponed due to covid. The organisers are optimistic it can be held in person this year. The submission deadline for contributed abstracts is 1st March.

I did not yet have a chance to attend any conference from this series, but I've met many of the committee members at other events (SOILM13, Singular Optics, BIRS) and I'm sure they will put together a very thought-provoking and inspiring series of talks!

IPS Meeting Day 2

Some highlights from Day 2 of the IPS Meeting:

• Prof. Javier G. Fernandez (SUTD) gave a plenary talk about bio-inspired manufacturing, including the 3D printing of low density yet strong structures inspired by cellulose and chitin. His main take-home message was that nature finds a way to make the most of available materials using intricate multi-scale design principles; details from the nanoscale up to hundreds of micrometers all contribute to bulk structural properties. We need to follow a similar paradigm to develop next-generation sustainable materials, and for colonies on other planets to be viable.
• Prof. José Ignacio Latorre (NUS) covered the fundamentals and future of quantum technologies in his plenary talk. He emphasised how quantum algorithms will be very different from the classical algorithms we are more familiar with. For example, computing 2 x 3 = 6 is easy for a classical computer, but such a computation cannot be performed using unitary quantum evolution (making it hard for quantum computers) because it is a non-invertible operation. For example, since 1 x 6 = 6 as well, the inverse transformation is ill-defined. Another important principle is the no-cloning theorem, meaning that it is impossible to save or copy quantum data. Finally, measurements are intrinsically random. These differences make it hard to find useful quantum algorithms. The known quantum algorithms with exponential speed-ups compared to classical algorithms are specific to problems with special structure (such as periodicity), which allows quantum interference to be tailored to find the solution faster.
• Prof. Cesare Soci (NTU) talked about the fabrication of superconducting single photon detectors and efforts to develop detectors for infrared frequencies using microbridge designs. Conventional nanowire detectors are based on an incident photon breaking a Cooper pair, resulting in a cascade of Joule heating which destroys the superconducting state. On the other hand, in microbridge detectors the incident photon creates vortex-antivortex pairs in the superconducting order parameter; this differing mechanism allows for designs more compatible with lower frequency detectors. 
• Ximeng Zheng (NTU) discussed hollow core fibre-based atomic vapor cells. The idea is that by placing atoms inside the hollow fibre core, the strong light confinement can be used to enhance the light-matter interactions. One challenge is that since the fibre core is so small, it takes a long time (weeks or months!) for the atoms to be loaded into the fibre. On the other hand, once they are in there they can remain for a few years...
• Prof. Murray Barret (NUS) gave an overview of his team's efforts to integrate ion clocks into silicon chips, an essential step towards making them more practical and affordable. For example, commercially-available ion traps cost hundreds of thousands of dollars, whereas mass-produced integrated ion chips could be as cheap as $350 each. But getting comparable performance (i.e. timing precision of 10^-18!) in integrated devices is challenging, due to the shallower confining potentials and stronger thermal effects.
• The QEP 2.0 panel discussion emphasised the need for outreach and involvement of stakeholders and potential industry end-users in order to discover more potential use-cases of quantum technologies. Development of open-source frameworks such as QIBO will be essential to get full value out of future quantum devices.
  

Overall, despite all the social distancing requirements it was an enjoyable conference. Definitely being in the room watching the talks live makes it easier to stay focused on the presentations and avoid distractions. Watching some of the presentations (particularly the poster pitch session) was a good reminder that, when presenting your work to a general physics audience, less is more. It is hard to distill your months or years of work down to a few minutes, but essential to get your message across. In hindsight, even after cutting my talk heavily I still tried to include too much. Something to remember for the next conference...

IPS Meeting Day 1

Today was the first day of the IPS Meeting, an annual conference organised by the Institute of Physics Singapore. For many of us in Singapore, this was the first in-person conference we have been able to attend since the pandemic started. The many covid restrictions mean that it's not the same as the pre-pandemic times (mingling between participants not allowed, must stick to the same session room for the whole day), but is still a lot better than online conferences. Big thanks to the organisers for making it run smoothly despite the recent changes to the covid restrictions.

Here are the slides for my talk on applications of persistent homology to physics. I think for many of us (me included) it will take some time to get used to presenting in person again...

Some highlights from Day 1:

• Prof. Jie Yan (NUS) talked about his group's work on developing more sensitive covid antigen and antibody testing, sharing data on how his and his team's antibodies are decaying with time following their vaccination doses...
• Prof. Ranjan Singh (NTU) gave an overview of the importance of terahertz interconnects for 6G communication technologies, including work from last year on terahertz waveguides based on topological edge modes published in Nature Photonics.
• Weikang Wu (NTU) explained how higher-order band crossings (i.e. parabolic and cubic crossings) can emerge in certain two-dimensional systems. For example, cubic crossings can be induced by spin-orbit coupling. arXiv preprint.
• Jeremy Lim (SUTD) on how 3D Dirac semimetals can provide orders of magnitude more efficient high harmonic generation compared to 2D materials, limited mainly by propagation-induced dephasing of the light-induced current. arXiv preprint.
• Xingran Xu (NTU) - Interaction-induced skin effect in exciton-polaritons. The non-Hermitian skin effect (extreme sensitivity of eigenvalues to boundary conditions) most often arises in Hamiltonians with non-reciprocal couplings, which are tricky to realize. By suitably pumping a polariton condensate (such that it exhibits the same nonlinear mode profile for open and periodic boundary conditions), one can also observe the non-Hermitian skin effect in the fluctuation modes of the condensate!
• Udvas Chattopadhyay (NTU, now NUS) - Mode delocalization in a disordered photonic Chern insulator. The most well-known feature of Chern insulators is their protected edge edge states that traverse the bulk band gaps. Interestingly, nonzero Chern numbers also lead to bulk modes protected against localization in the presence of disorder, which can be observed using arrays of coupled microring resonators.
• Anna Paterova (A*STAR) talked about quantum imaging, which enables measurement of objects in troublesome spectral regions (such as the moleculer fingerprint region) using cheaper optical or infrared cameras, based on quantum interference between photon pairs generated by nonlinear crystals. Paper in Science Advances.

Looking forward to attending the Quantum Engineering sessions tomorrow!

Metanano 2021

Last week I attended the virtual Metanano 2021 conference and presented an invited talk in the "Topological states in classical and quantum systems" session. Here are my talk slides. The conference organisers have kindly made the session recordings available on YouTube until 3rd October (link to schedule of talks).

The topological session allowed me to catch up on some recent developments in topological photonics that I haven't had time to closely follow. Highlights from the Thursday session I attended:

Baile Zhang reported on the observation of antichiral edge states using microwave gyromagnetic photonic crystals. In conventional topological photonic crystals, the chiral states on opposite edges propagate in opposite directions, ensuring local conservation of energy. A 2018 PRL paper showed how to design antichiral edge states that propagate in the same direction on both edges, with energy conservation provided by counter-propagating bulk modes. The antichiral edge states do not support topologically-protected transport (since they do not reside in a complete band gap), but they are nevertheless interesting as a means of extending the possibilities offered by chiral edge states.

Yidong Chong discussed topological defect states in photonic and acoustic lattices. By introducing defects such as dislocations and disclinations into the bulk of topological photonic crystals, one can create free-form waveguides with near-arbitrary trajectories. This enables the flexible creation of topological analogues of regular photonic crystal waveguides. Extending to 3D structures enables the design of topological waveguides for orbital angular momentum modes, with the propagation direction controlled by the handedness of the mode vorticity.

Jian-Hua Jiang reported on a closely related idea - the experimental observation of bulk-disclination correspondence in topological crystalline insulators. What's really interesting about this work is that bulk topological defects can be sensitive to exotic topological invariants (e.g. higher order topological phases associated with fractional charge modes) that cannot be distinguished using the more familiar bulk-edge correspondence. He also mentioned a recent preprint on multi-band topological pumping using magnetic defects in acoustic metamaterials.

Daniel Sievenpiper presented recent work on coupling light between topological and non-topological photonic crystal waveguides, and using terminations of topological waveguides to create collimated far-field radiation. This opens avenues in the direction of topological antennas.

There are other interesting-sounding talks that I missed due to other commitments and time zone differences that I hope to catch up on while the recordings are available.