Category: paper

Optothermally induced active & chiral motion – a new paper

We have a new paper in Soft Matter

link to the paper (free to access, thanks to IISER Pune library)

We use optical illumination to generate thermal fields, creating non-reciprocal interactions between passive and active colloids. Active colloids absorb light and produce thermal gradients, driving thermo-osmotic forces that induce propulsion and chiral motion. Our Langevin simulations, backed by experimental observation, reveal how to control colloidal behavior. May have implications in light-driven chiral motion and nonlinear dynamics.

Super effort by Rahul, Ashutosh & Sneha from our group, who combined numerical simulations, analytical theory, with experimental observations.

The 2 anonymous reviewers made us think and work hard, and we thank them!

Also, the paper is part of the journal’s themed collection on “Colloidal interactions, dynamics and rheology”

Optical computing – review link and a few thoughts..

“How might optical computers beat electronic computers? …….. There are three main metrics of computing performance for which we might aim to achieve an advantage: latency, throughput and energy efficiency…”

A very readable review by Peter MacMahon of Cornell.

In the immediate future, designing energy-efficient computational platforms will be a necessity. Electronic transport is noisy and dissipative. Optical alternatives can be important, but challenges remain…

Given that the speed of light is the upper limit of information transport and processing, optics will be a vital ingredient in computation. In hindsight, it has already been. But there is more to it than just the speed, as the review article explains elaborately..

Interesting times ahead…

Willow in comparison – Google quantum chip

In scientific research, comparative analysis is an excellent way to objectively quantify two measurable entities. The recent Google quantum chip (named Willow) does that efficiently as it compares its capability with today’s fastest supercomputers. The comparison note on Google’s blog is worth reading.

In scientific analysis, such comparison teaches us three things:

a) how a scientific boundary is claimed to be pushed?

b) how a benchmark problem is used to achieve comparison?

c) what is the current state-of-the-art in that research area?

Some further observations on the work:

  • The theme of the Nature paper reporting this breakthrough is mainly on error correction. Technically, it shows how error tolerance is measured for a quantum device. This device is based on superconducting circuits, which were tested first on a 72-qubit processor and then on a 105-qubit processor.
  • Interestingly, as the authors mention in the paper, the origins of the errors are not understood well.
  • The paper is quite technical to read, and, to my limited understanding as an outsider, it makes a good case for the claim. The introduction and the outlook of the paper are written well, and give more technical information that can be appreciated by a general scientific audience.
  • There is more to come ! It looks like Google has further plans to expand on this work, and it will be interesting to see in which direction they will take the capability. The Google blog shows a roadmap and mentions their ambition as follows: “The next challenge for the field is to demonstrate a first “useful, beyond-classical” computation on today’s quantum chips that is relevant to a real-world application. We’re optimistic that the Willow generation of chips can help us achieve this goal.”
  • In the past 12 months or so, there has been a lot of buzz related to AI tools (thanks to GPTs, Nobels and perplexities :-), which are mainly in the realm of software theoretical development. This breakthrough in the realm of ‘hardware’ tells us how the physical world is still important!

More to learn and explore…interesting times ahead..

Gold nanoparticles in sync – preprint

We have a new preprint: https://arxiv.org/abs/2411.15512

The central circle indicates anchored gold nanoparticles stuck to the glass, and the two moving circles are gold colloids that are trapped synchronously due to the optothermal potential.

Article on Gerhard Herzberg

The October 2024 issue of Resonance, Journal of Science Education

highlights the life and science of Gerhard Herzberg.

He was one of the greatest molecular spectroscopists who laid the foundation of atomic and molecular quantum mechanics and deeply impacted molecular astrophysics and astrochemistry.

He lived an extraordinary life, first in Europe learning quantum mechanics and then escaping 1930s Germany as his wife was of Jewish origin. Then, he settled in Canada to build and lead his lab, which was considered the ‘mecca of spectroscopy’ at NRC, Ottowa.

I wrote a sci-biography article about him in this issue

Link to full edition: https://www.ias.ac.in/listing/articles/reso/029/10

If you don’t know – Resonance is a pedagogical journal published by the Indian Academy of Sciences. It is a true open-access journal. Free to read and does not charge the authors to publish.

Do explore the past editions. There are some absolute gems. https://www.ias.ac.in/listing/issues/reso

Optothermal revolution – preprint

We have an Arxiv preprint on how a mixture of colloids (thermally active + passive particles in water) can lead to the emergence of revolution dynamics in an optical ring trap (dotted line). Super effort by our lab members Rahul Chand and Ashutosh Shukla.

Interestingly, the revolution emerges only when an active and a passive colloid are combined (not as individuals) in a ring potential (dotted line)

the direction (clock or anti-clockwise) of the revolution depends on the relative placement of the colloids in the trap

This revolution can be further used to propel a third active colloid

There are many more details in the paper. Check it out: https://arxiv.org/abs/2409.16792

New paper – Emergence of Directional Rotation

We have a new paper to appear in ACSPhotonics. Great effort by Rahul Chand, Chaudhary Eksha Rani and Diptabrata Paul from our group. We ask : How & why does directional rotation emerge in an optical trap of thermally active (smaller) + passive colloidal combination ?

By combining light absorbing colloid (smaller one) with a normal colloid (bigger ones), we can observe directional rotation in a 2D optical trap. What determines the rotation direction is the relative position of the active colloid in the assembly.

One can switch the direction of rotation, by changing the relative position of active colloid.

For the rotation to emerge, the symmetry of the colloidal arrangement matters. As you see, if there are two active colloids (smaller ones) are symmetrically positions with respect to passive colloids (bigger one), we do not observe rotation.

There is a lot more interesting stuff and explanation of the observed effect discussed in our paper. You can read the pre-print of the our paper in arxiv : https://arxiv.org/abs/2309.12740