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.