Namaste, Hola & Welcome from G.V. Pavan Kumar.
I am a Professor of Physics at the Indian Institute of Science Education and Research, Pune, India.
My research interests are :
(1) Optics & Soft Matter: Optically Induced Forces – Assembly, Dynamics & Function;
(2) History and Philosophy of Science – Ideas in Physical Sciences.
I am interested in the historical and philosophical evolution of ideas and tools in the physical sciences and technology. I research the intellectual history of past scientists, innovators, and people driven by curiosity, and I write about them from an Indian and Asian perspective. My motivation is to humanize science.
In the same spirit, I write and host my podcast Pratidhvani – Humanizing Science.
The Indian Express recently reported that “Author Helen DeWitt’s refusal to accept the prestigious Windham-Campbell Prize is a reminder that in a noisy world, the most imaginative stance may well be to let the book stand on its own.”
To quote: “DeWitt’s refusal, like Ferrante’s silence, is a reminder that in a noisy world, the most imaginative stance may well be to let the book stand on its own.” This kind of thinking and action is rare nowadays. Good to see this still persists. Perhaps, such people should be called ‘de-influencers’.
I have to add that DeWitt is already an established name in her field. By established, I mean, by name and perhaps by income too.
2 questions:
1) It may be relatively easier for a person of fame to reject further recognition. Will an upcoming writer (or equivalent in other fields) be able to do this?
2) The same person in a different situation may have reacted differently, and a different person in the same situation, too. In the human context, do we fully understand what an incentive is?
Binay Panda is a Professor at JNU’s School of Biotechnology. The Oxford-educated scientist specializes in genome science, cancer genomics, and data integration, while advocating for open science and Indian biofoundries. He is also an avid long-distance cyclist.
In this freewheeling conversation, we discuss his intellectual journey and his thoughts on doing science, particularly in India.
The world, irrespective of the location, can adapt a lot more to the ‘creative commons’ principle than it has done over the years.
When it comes to knowledge generation and sharing, open source has great value to the world. Think Internet in its early days. The motivation for its propulsion was to connect the nodes of knowledge (www stands for World Wide Web).
Having said that, I acknowledge that commercialization is important, but it has its relevance in certain domains downstream of knowledge, especially where engineering has to interface with the scale, scope and demands of the market. Not at the origins, learning and coupling with the society.
If anything, open source knowledge, harnessed properly with fair markets, may lead to far more commercialization and entrepreneurial opportunities.
For the scale and variety of India, open source has a lot to offer. Are we ready to adopt and adapt?
My previous blog discussed some historical papers related to the intensity interferometer and its connection to quantum optics. Here, I explain the basic physics of an intensity interferometer.
In the context of spatial coherence, the coherence theory expresses the degree of spatial coherence as,
with \( U_i(t) \) representing the fields of sources \( i = 1 \) and \( 2 \).
An intensity interferometer measures the intensity correlation function between such sources. If \( I_1(t) \) is the intensity of source 1 and \( I_2(t) \) is the intensity of source 2, then the intensity correlation function is given by:
If one ignores the background (the first term in the sum of the above equation) and considers only the fluctuations in the signal (the second term), then the term of relevance will be:
The signal in the intensity interferometer is thus proportional to \( \left| \gamma_{12} \right|^2 \).
A conventional interferometer measures a signal that is proportional to \( \left| \gamma_{12} \right| \), which includes the amplitude and phase, whereas an intensity interferometer measures a signal proportional to \( \left| \gamma_{12} \right|^2 \), which is not sensitive to the phase.
Intensity interferometers have certain advantages compared to conventional interferometers (such as the Michelson interferometer). Below is a partial list:
Intensity measurements (unlike amplitude or phase) can be done directly using optoelectronic instruments.
They do not require precise, sub-wavelength optical alignment, unlike amplitude- or wavefront-dividing interferometers.
They can be used with two detectors that are placed far apart, thereby improving the spatial resolution of the measurement (relevant in astronomy).
A constraint of an intensity interferometer is that the intensity of the participating source should be bright.
Many students outside IISER Pune have been following my course blog on Quantum Optics, so I thought I would share some lectures too. I have recorded some discussion related to statistical optics, and will eventually connect them to quantum optics in a few lectures.
Lecture 1 – Quantum Optics via Statistical Optics
topics discussed: Temporal coherence function Degree of temporal coherence function Coherence time Coherence length Power spectral density Spectral width
There is an important connection between quantum optics and radio astronomy. Hanbury Brown and Twiss in the 1950s devised the intensity interferometer.
Particularly, they were interested in measuring the ‘diameter of discrete radio sources’. The title of their seminal paper reads “A new type of interferometer for use in radio astronomy”. As the authors claimed in their paper: “The principle of the instrument is based upon the correlation between the rectified outputs of two independent receivers at each end of a baseline, and it is shown that the cross-correlation coefficient between these outputs is proportional to the square of the amplitude of the Fourier transform of the intensity distribution across the source.”(Brown and Twiss, 1954)
First, they tested their technique in a laboratory situation and followed it up with a measurement of the diameter of Sirius. Their technique was a game-changer in measuring the diameter of bright stars.
As the intensity interferometers were being developed, the laser was realized in the early 1960s. Unlike conventional light sources, laser light is coherent, and this brings in unique features that can be used to understand the nature of light. In the context of laser optics, intensity interferometers had immediate utility in studying coherence through correlation measurement. It was logical to combine lasers with intensity interferometers and study the correlation. This combination is what led to the discovery of some fascinating aspects of quantum properties of light, including anti-bunching.
If the book by Born and Wolf is considered a classic on the electromagnetic theory of light, the quantum extrapolation is the book by Leonard Mandel and Emil Wolf titled Optical Coherence and Quantum Optics.
This book discusses the interface of statistical optics, optical coherence, and quantum optics. The core argument of the book starts with probability theory and its connection to fluctuations of light and builds optical coherence, polarization, and eventually quantum optical effects of light. It is a well-written treatise on light with a flavor of experiments (Mandel did some pioneering experiments in quantum optics) and theoretical explanation (a hallmark of Wolf).
In the preface of the book, they bring together the importance of intensity interferometers and the discovery of lasers and explain how and why it led to a deeper understanding of quantum optics:
“Prior to the development of the first lasers in the 1960s, optical coherence was not a subject with which many scientists had much acquaintance, even though early contributions to the field were made by several distinguished physicists, including Max von Laue, Erwin Schrodinger and Frits Zernike. However, the situation changed once it was realized that the remarkable properties of laser light depended on its coherence. An earlier development that also triggered interest in optical coherence was a series of important experiments by Hanbury Brown and Twiss in the 1950s, showing that correlations between the fluctuations of mutually coherent beams of thermal light could be measured by photoelectric correlation and two-photon coincidence counting experiments. The interpretation of these experiments was, however, surrounded by controversy, which emphasized the need for understanding the coherence properties of light and their effect on the interaction between light and matter.” (Mandel and Wolf, 1995, p. 1)
This further led to a series of studies on light-matter interaction from a coherence perspective, and included analysis of the fluctuation of light by understanding the randomness and the associated statistics of the fluctuations. Mandel, Wolf, Glauber, E.C.G. Surdarshan and many others across the world laid the foundation and connection between optical coherence and quantum optics. What started as a technical development in radio astronomy turned out to be a vital tool in quantum optics.
Brown, R. Hanbury, and R. Q. Twiss. ‘LXXIV. A New Type of Interferometer for Use in Radio Astronomy’. Philosophical Magazine 45, no. 366 (1954): 663–82. https://doi.org/10.1080/14786440708520475.
Brown, R. Hanbury, and R. Q. Twiss. ‘Correlation between Photons in Two Coherent Beams of Light’. Nature 177, no. 4497 (1956): 27–29. https://doi.org/10.1038/177027a0.
Hanbury Brown, R., and R. Q. Twiss. ‘A Test of a New Type of Stellar Interferometer on Sirius’. Nature 178, no. 4541 (1956): 1046–48. https://doi.org/10.1038/1781046a0.
Sanjit Mitra is a Senior Professor at IUCAA, Pune, and explores gravitational wave astronomy. Serving as the science spokesperson, Laser Interferometer Gravitational-Wave Observatory (LIGO)-India and project coordinator, his research focuses on stochastic backgrounds, detector noise, and CMB analysis.
In this episode, we discuss the science and technology behind LIGO and its Indian expansion.
I have been studying quantum mechanics for almost 30 years now. Every time I go back to study and understand something, it reminds me of a quote by Nelson Mandela: “There is nothing like returning to a place that remains unchanged to find the ways in which you yourself have altered” ~ Long Walk to Freedom (1994)
On further contemplation, I find the same with other branches of physics and certain aspects of mathematics, too.
