Quantum Technologies with cold Rydberg atoms

Lab website

Atoms excited to Rydberg states with high principal quantum numbers have extraordinary properties such as strong dipole-dipole interaction, large values of polarisability and much longer lifetimes compared to atoms in their ground state. These exotic characteristics and a high degree of controllability make ultra-cold Rydberg atoms versatile atomic building blocks for a variety of Quantum Technologies such as scalable quantum information network using an array of fast quantum gates, precision electrometry and magnetometry as well as a robust single-photon source for secure quantum communications. 

Quantum Entanglement is an important phenomenon in Quantum mechanics in which two or more particles are generated or interact in such a way that their quantum states are correlated and cannot be described independently even though the individual particles may be separated spatially. The correlations exhibited by entangled states have no classical analogue. Quantum entanglement has important applications in emerging quantum technologies such as quantum information processing, quantum cryptography and teleportation.

In this experiment, we focus on Quantum entanglement via long-range dipole-dipole interaction between highly excited Rydberg atoms towards the realisation of quantum entanglement in an array of Rydberg atoms trapped in optical tweezers. 

Recent Publications: 

1. "Observation of effects of inter-atomic interaction on Autler-Townes splitting in cold Rydberg atoms", Silpa B S, Shovan Kanti Barik, Varna Shenoy, Soham Chandak, Rejish Nath Gopinathan Rejani and Sanjukta Roy, New J. Phys. 27 (2025) 083202 (2025). Article

2. “Doppler-Enhanced Quantum Magnetometry with Thermal Rydberg atoms”, Shovan Kanti Barik, Silpa B S, M Venkat Ramana, Shovan Dutta, and Sanjukta Roy, New J. Phys. 26 073036 (2024).   Article 

Media reports: Press Information Bureau, India Today, The Hindu

3.  “Quantum Technologies with Rydberg atoms”, Shovan Kanti Barik, Aishwarya Thakur, Yashica Jindal, Silpa B S and Sanjukta Roy, Frontiers in Quantum Science and Technology 3 1426216 (2024). 

4. “Quantum Technologies with cold Rydberg atoms and atomic spins”, Silpa B S, Sayari Majumder and Sanjukta Roy, Physics News, IPA, 53 53-57 (2023). 

5.  “Quantum Sensing Unveiled: The Power of Rydberg Atoms", Sanjukta Roy, Quantum Vibes, Q3 04 (2023). 

6. "Transition frequency measurement of highly excited Rydberg states of 87Rb for a wide range of principal quantum numbers", Silpa B S, Shovan Kanti Barik, Saptarishi Chaudhuri, and Sanjukta Roy,  Optics Continuum 1 (5), 1176-1192 (2022).

Photograph of the Experimental Setup of our Sodium Potassium Quantum Mixtures (QuMix) experiment

Interactions between bosons and fermions play a vital role in various physical phenomena occurring in nature in diverse energy and length scales. For example, within the Standard model, all the interactions between fermions are mediated by the exchange of a gauge boson and hence all the forces may be described by the interaction of fermions and bosons. In the atomic nuclei, quarks exchange gluons via the strong force. In solid state systems, the electrons are dressed by lattice vibrations to form polarons. In conventional superconductors, phonons induce an attraction between electrons at Fermi energy to form Cooper pairs. This suggests that a mixture of bosons and fermions can be an excellent simulator for such phenomena where the interaction between the fermions is mediated by bosons. Ultra-cold atomic systems provide the possibility of having a mixture of quantum-degenerate bosons and fermions to simulate various quantum many-body and few-body phenomena where the interaction between the bosons and fermions can be tuned via hetero-nuclear Feshbach resonances and dimensionality can be controlled using optical potentials.

Interacting Bose-Bose or Bose-Fermi mixtures can give access to a wealth of physical phenomena which go beyond those accessible with purely bosonic or fermionic systems. Both the bosonic and fermionic atomic species can be simultaneously cooled down to very low temperatures of around a few tens of nK to reach the quantum regime. The physics of Bose-Bose and Bose-Fermi mixtures in periodic optical potentials is extremely rich and yet to be fully understood.

Quantum simulators are coherently controlled quantum systems used to simulate other quantum systems. Based on Feynman's vision of efficient simulation of one quantum system using another, quantum simulators hold promise for tackling problems in quantum many-body physics hitherto intractable on classical computers and exploring new physical phenomena.

In our Quantum Mixtures experiment, we cool down Sodium and Potassium atomic species to ultra-cold temperatures to realise a quantum degenerate mixture for Quantum Simulation using ultra-cold quantum gases in optical lattices and disordered potentials.

Spin Correlation spectroscopy

Random fluctuations or statistical noise is ubiquitous in all physical systems and can provide important information about the characteristic nature and internal structure of the system. Control of the spin state population and its simultaneous non-destructive detection plays a vital role in diverse fields such as atom interferometry, precision magnetometry, atomic clocks as well as in quantum simulators. Spin correlation spectroscopy or Spin noise spectroscopy (SNS) enables such non-invasive detection of spin coherences via measurement of the correlation spectra of the statistical spin noise of the atomic spin ensemble using a far-detuned probe beam. In SNS, a linearly polarised far-detuned probe beam on passing through an ensemble of atomic spins acquires the information of the spin correlations of the system which is extracted using its time-resolved Faraday-rotation noise via polarimetric detection. Due to large detuning of the probe beam from the atomic transition frequency, this detection technique is non-perturbative. Moreover, the inverse scaling of the SNS signal with the

probe size makes it ideal for detection with high spatial resolution. Spin correlation spectroscopy also provides information about the composition of the spin system which are not accessible by traditional absorption spectroscopy. Various atomic,

magnetic and sub-atomic properties, as well as precision magnetometry, can be performed using spin noise spectroscopy in alkali atomic vapour in thermal equilibrium. In our experiment, we measure the spin correlations in coherently driven ensembles of both thermal and cold atoms via Faraday rotation fluctuation measurements. The main objectives of this experiment are to understand the quantum origin of magnetism, precision magnetometry and development of non-invasive detection technique for quantum gases. We have already used this technique to develop high precision magnetometers. 

Publications on Spin Correlation Spectroscopy from our Lab:

1. "Detection of spin coherence in cold atoms via Faraday rotation fluctuations

   Maheswar Swar, Dibyendu Roy, Subhajit Bhar, Sanjukta Roy, and Saptarishi Chaudhuri, Phys. Rev. Research 3, 043171 (2021). Highlighted by DST Mediacell

2.  “Measurements of spin properties of atomic systems in and out of equilibrium via noise spectroscopy”, Maheswar Swar, Dibyendu Roy, Dhanalakshmi D, Saptarishi Chaudhuri, Sanjukta Roy, and Hema Ramachandran, Optics Express 26, 32168 (2018). (Highlighted in Research matters: Spinning our way into the world of atoms)