Indian Scientists Design New Algorithm That Can Produce Better Images To Help In Study Of Ultracold Atoms

A team of Indian scientists have designed a new image-correction technique capable of getting better images during the study of cold atoms or atoms at absolute zero temperature.  

This technique reduces the unwanted interference fringes in images by half, which is crucial for a more accurate understanding of the quantum mechanics governed properties of these cold atoms.

At temperatures approaching absolute zero, atoms exhibit behaviours governed by quantum mechanics rather than classical mechanics.

They hold potential to offer a possibility to study and better understand the atomic properties at such low temperatures.

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The commonly used techniques for the study of ultracold atoms is by deploying magneto-optical traps with high-power laser cooling techniques.

Cold atoms of elements like sodium, potassium, and rubidium are commonly examined using detection techniques, namely the fluorescence, absorption, or phase-contrast imaging techniques, with fluorescence and absorption being the most widely used.

However, images obtained from these imaging techniques often suffer from interference fringes - unwanted dark and bright patterns that degrade the image quality.

These fringes can hinder the precise calculation of critical parameters like atom number, temperature, and dynamics over short timescales.

To combat this issue, a research group at the Raman Research Institute (RRI), an autonomous institute of the Department of Science and Technology, has developed an image-correction solution.

This new algorithm couples existing eigen-face recognition with smart masking technique to minimise interference fringes in the images.

Eigen-face recognition, similar to technology in smartphones, identifies correct images from a set based on object features.

“While dealing with the cold atoms, it is necessary to calculate the Optical Density (OD) from which one can determine the temperature, size, density and other useful parameters,” said Gourab Pal, a PhD student at the QuMix lab, RRI.

In this algorithm, researchers need to calculate an important parameter known as the Optical Density, which is the logarithmic subtraction of two frames -- one containing the cold cloud (denoted as S) and other is the probe light (denoted by L).

Ideally, both frames would have identical interference fringes, allowing for easy subtraction and fringe removal.

“But in reality, while working in lab, these frames do not showcase identical interference fringes, making the situation challenging and requiring a de-fringing method to obtain a clean Optical Density,” explained Pal, who is first author of the paper titled ‘Efficient denoising of cold atom images using optimised eigenface recognition algorithm’.

The RRI team's research paper, published in Applied Optics, shows that this technique can reduce interference fringes in cold atom absorption imaging by about 50 per cent.

It also improves the accuracy of temperature measurements in cold Rubidium atoms by a similar margin.

In the paper published recently in the journal Applied Optics, RRI team has claimed that the proposed technique could reduce the interference fringes in the absorption imaging of cold atoms by nearly 50 percent.

Scientists argue that the absorption imaging technique is popular in the cold atom community and has a wide range of applications.

“This is particularly useful where the number of atoms is fewer. Absorption imaging can be used to find the density profile of cold and ultracold atoms. In this technique, we find the temperature of a cold atom cloud via time-of-flight measurements. The basic of the quantum gas microscopy is the absorption imaging. In addition, this method is used to perform in-situ measurements of trapped atoms,” said co-author of the paper, Saptarishi Chaudhuri, head QuMix laboratory, RRI.

The absorption imaging technique is best suited when atom numbers under study are small.

Thereby, it can be deployed to calculate the density profile of cold and ultracold atoms and the temperature of a cold atom cloud via time-of-flight measurements, he said.

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