Photonic Quantum Science and Technologies: Interference at the heart of quantum

Quantum mechanics is a cornerstone of modern physics. Just as the 19th century was called the Machine Age and the 20th century the Information Age, the 21st century promises to go down in history as the Quantum Age. Quantum Computing promises unprecedented speed in solving certain classes of problems while Quantum Cryptography promises unconditional security in communications.

In this talk, I will discuss the world of single and entangled photons and also discuss ongoing work towards quantum communications, quantum information and quantum computing in our Quantum Information and Computing lab at the Raman Research Institute, Bengaluru, India.

I will primarily focus on four recent experiments from our lab, all of which use quantum interference as a resource but for very different end goals. The first experiment [1] discusses a new quantum state estimation method "Quantum State Interferography" which promises tremendous resource advantage over the more conventional quantum state tomography approaches. The second uses interference in a specific quantum information processing task, wherein we demonstrate the first loophole free violation of the Leggett Garg Inequality using a photonic architecture [2]. The third uses interference for a quantum communication advantage [3] whereas the final work demonstrates the first unambiguous Quantum Cheshire Cat phenomenon, again using interference, while bringing in a new understanding of Bohr's Complementarity principle[4].

I will end with our broad vision for the future, which includes establishment of long distance secure quantum communications in India and beyond involving satellite based, fibre based as well as integrated photonics based approaches towards the global quantum internet.

1. S. Sahoo, S. Chakraborti, A. K. Pati, U. Sinha, 'Quantum State Interferography', Phys. Rev. Lett. 125 123601, (2020).
2. K. Joarder, D. Saha, D. Home and U.Sinha, 'Loophole free interferometric test of macrorealism using heralded single photons,', PRX Quantum, 3, 010307, (2022).
3. S. Chatterjee, K. Goswami, R. Chatterjee and U.Sinha, 'Polarization correction towards satellite-based QKD without an active feedback', Communications Physics 6, 116 (2023).
4. S. N. Sahoo, S. Chakraborti, S. Kanjilal, S. R. Behera, D. Home, A. Matzkin and U. Sinha, 'Unambiguous joint detection of spatially separated properties of a single photon in the two arms of an interferometer', Communications Physics 6, 203 (2023).