Sourabh Magare

Publications

Early warning for lensed gravitational wave counterparts from time delays of their host galaxies observed in the optical

Authors: Sourabh Magare, Anupreeta More, Shasvath Kapadia

Journal: Preprint , Year: 2025

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SLICK: Strong Lensing Identification of Candidates Kindred in gravitational wave data

Authors: Sourabh Magare, Anupreeta More, Sunil Choudhary

Journal: Monthly Notices of the Royal Astronomical Society , Year: 2024

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Gear Up for the Action Replay: Leveraging Lensing for Enhanced Gravitational-wave Early Warning

Authors: Sourabh Magare, Shasvath J Kapadia, Anupreeta More, Mukesh Kumar Singh, Parameswaran Ajith, AN Ramprakash

Journal: The Astrophysical Journal Letters, Year: 2023

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Exact time evolution of genuine multipartite correlations for N-qubit systems in a common thermal reservoir

Authors: Abhinash Kumar Roy, Sourabh Magare, Varun Srivastava, Prasanta K Panigrahi

Journal: Quantum Reports, Year: 2022

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1D Ising model using the Kronecker sum and Kronecker product

Authors: Sourabh Magare, Abhinash Kumar Roy, Varun Srivastava

Journal: European Journal of Physics, Year: 2022

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Blogs

Research

Leveraging Lensing for Enhanced Gravitational-wave Early Warning

GW170817 was a 'superstar' event. It was a merger between 2 neutron stars which was detected by Gravitational wave (GW) detectors of LIGO-Virgo Collaboration. Furthermore, after the 2 seconds Gamma rays were detected from the same region of sky and it was established that we have seen the Electromagnetic (EM) counterpart of a GW event. A follow-up search of the same region of sky revealed a Kilo-Nova, which is the remant of the Binary Neutron Star (BNS) merger. Using this multi-messenger data of GWs and EM, we made some fundamental discoveries like putting constraints on the mass of Graviton, Constriants of Lorentz invariance and also fascinating discoveries in Astrophysics like binary neutron star mergers are sources of short gamma ray bursts and, neutron star mergers as source of s- and r- process of nucleosythesis.
However, we observed this event through EM telescopes after the neutron stars have merged i.e. in the post-merger phase. Can we observe such an event even before it is merged?
To observe the premerger implies that we should know the sky-location of the event even before the event has occured. In this work, we show a novel approach to capture the Electromagnetic counterpart of BNS or Neutron star - Black hole (NSBH) mergers with an early warning time of hours and days before the merger, provided the event is strongly lensed. This is orders if magnitude larger than the early warning time we have from the GW low latency piplines.
The idea is that suppose we detect GWs from a BNS/NSBH event. Then, similar to GW170817 by the EM follow-up, we localize host galaxy of the source. If we find that this galaxy is strongly lensed i.e. we observe multiple images of the same galaxy because of gravitaional lensing by an intervening galaxy. Then from the positions of the images of the host galaxy, we can calculate the time-delay between the next images. Now, we know the time when the next image from the merger of BNS/NSBH will reach us and it will be the action replay of the original event.
We just wait and capture that action replay!!

Searching for strong lensing candidates in the gravitational wave data using deep learning algorithms

In this work, we trained a neural network on Q-transform images and Sine-Gaussian images of Gravitational wave (GW) data to distinguish between a pair of lensed GWs and unlensed GWs . We showed that including the Sine-Gaussian maps with Q-transform maps results in a better efficiency than analysing QT maps alone. We also evaluate the performance of our network on real detected GW events detected by LIGO-Virgo collaboration (till O3) and find that our network correctly classifies all of them as unlensed GWs, which is consistent with non-detection of GW lensing.

What exactly is Quantum Entanglement?

We live in a ‘Classical’ world. We call it classical because it follows Newton's Maths. If you throw a ball at a solid wall, it hits the wall and bounces back at you. If you throw that ball as a projectile, it will follow a particular trajectory in the air before it falls. Using Newton's laws, one can accurately calculate the trajectory or path of that ball. However, the laws of physics are different on a small scale. Particles like electrons, protons and neutrons which make up an atom, behave very differently from anything that we see around us. They don't obey Newton's laws; they follow the rules of the quantum world.

In our classical world, a ball has a definite position. It is precisely present at a point. But the same is not correct for an electron. There is some chance for an electron to be found at one point, and some for it to be found at another. One cannot say with absolute certainty that it is at that point; one can only talk about its probability. Furthermore, when you try to measure its position, its probability cloud is lost, and it takes a definite place. Now, the electron is present at one point precisely. Thus, making a measurement makes the electron lose its probability halo and choose an exact location.

If you think in terms of an analogy, it appears to be like throwing a dice. Before you throw a dice, there is a probability of getting any one of the six possible numbers. After you throw the dice, it will give you a particular number. Is the act of electron position measurement the same as that of throwing a regular dice? The answer is No.

The weird thing about ‘Quantum Objects’ like an electron is that before measurement, it behaves as if it is present in many places at the same time, like a ghost. Physicists call it by the jargon 'Quantum Superposition'. And when you attempt to take a measurement, it jumps to one of those many positions. Albert Einstein called this “a spooky action at a distance”.

To see this spooky action at play, let's understand the ‘spin of an electron’, which also shows the same ghostly properties. Spin is a property of the electron, which is measured in two directions: Vertical and Horizontal. After the measurement, there is a 50% chance of getting a spin-up state and a 50% chance of getting a spin-down state. But remember, electron spin has nothing to do with an electron spinning like a ball. Spin is a property of the electron itself, just like the mass and charge of an electron. It's just that scientists are not very good at naming things.
Now let's take two electrons and pass them through a machine we call ‘Entangler’. This machine creates a ‘connection’ between these two electrons. Now, we call these electrons Entangled. In this state, when one electron is measured to have spin-up, then the other electron measured in the same direction, will have spin-down. On measuring the spins of two particles in the same direction, we find that their spins will always be opposite.

So let's consider an experiment with our two scientists- Alice and Bob with each carrying a particle of an entangled pair. We take them hundreds of kilometers away. Now, they decide to measure their spins. Remember, spin can be measured in two directions. Suppose that Alice decides to measure her electron's spin in the vertical direction and finds it to be spin up. Now, by the property of entangled electrons, Bob's electron will be in a spin- down state when measured in a vertical direction. It appears as if Bob's electron has collapsed into a spin-down state, instantly after Alice measured her electron's spin. But this means the two particles are communicating’ at speed faster than speed of light. "Spooky action at a distance !”

But not so fast. Let's consider the same experiment, but this time with a coin instead of electrons. Suppose that we put a coin into either Alice’s or Bob's bag. There is a 50% chance that it is in Alice's bag and a 50% chance that the coin is to be found in Bob's bag. When they are far apart, Alice checks her bag and finds the coin; this immediately fixes that it is not in Bob's bag. Isn't this coin behaving like a Quantum Particle? Isn't the coin also showing the same spooky action at a distance? The answer is No.

To demonstrate this, suppose that Bob always measures spin in the vertical direction, and Alice can measure spin in both directions. If Alice measures spin in the vertical direction and finds it to be spin-up, Bob will always find his electron to be spin-down. On the other hand, if Alice measures spin in the horizontal direction, Bob will measure his electron spin to be spin-up 50% of times and spin- down 50% of times. It is actually the choice of measurement, horizontal or vertical, by Alice, that is affecting Bob's electron's outcome. In the case of a coin, there is no such choice affecting the other partner's result. So I can safely say that coins are not quantum objects.

The two entangled particles don't have spin-up or spin-down in the beginning. They were in the probability halo of up-down spin. Only when one of the spins is measured, is their probability halo lost, and the system takes a particular state. But what makes the quantum particles behave that way? To understand that, let's try a 'Classical Entanglement Experiment.’

Just as before, we have Alice and Bob, but now there is a central machine that throws identical balls towards Alice and Bob. The machine throws four types of balls- Small Red, Small Green, Big Red, and Big Green.
We now make our observers Handicapped: Bob can only know the ball's color and not size. Alice can know both color and size, but only one at a time.
If Alice measures the color of the ball and finds it red, she knows Bob's ball is red with 100% certainty. But if Alice measures the size and finds it small then, there is a 50% chance for Bob to find the ball to be red and 50% chance to be green. We can now ask the same question again- How does Alice's choice of measurement affect Bob's outcomes?

Our Classical Entanglement Experiment works only when our observers - Alice and Bob - have a limited knowledge of the system, that is, they are handicapped. They can know either color or size, but not both. Now, since quantum particles behave in the same way by Quantum Entanglement, does it mean that our understanding of the quantum world and quantum particles is limited? Is our knowledge of the quantum world is handicapped, just as Alice and Bob can measure only the size or color?

This was Einstein's take on Quantum Physics. He stated that quantum physics is incomplete, and one needs a different theory of physics to explain this incompleteness. This started the famous debate between physicists Niels Bohr and Albert Einstein, and paved the way to Quantum Information and Quantum Computation.

Publications

Early warning for lensed gravitational wave counterparts from time delays of their host galaxies observed in the optical

SLICK: Strong Lensing Identification of Candidates Kindred in gravitational wave data

Gear Up for the Action Replay: Leveraging Lensing for Enhanced Gravitational-wave Early Warning

Exact time evolution of genuine multipartite correlations for N-qubit systems in a common thermal reservoir

1D Ising model using the Kronecker sum and Kronecker product

Blogs

About

Research

Leveraging Lensing for Enhanced Gravitational-wave Early Warning

Searching for strong lensing candidates in the gravitational wave data using deep learning algorithms