ICTS

-

-

-

-

The coherent interaction of the electric fields with the atomic medium which leads to phenomena like electromagnetically induced transparency (EIT) are highly sensitive to the external magnetic fields. Using this fact, magnetic field with good spatial resolution and high sensitivity can be measured. In addition to the magnetic field strength, knowing the direction of the magnetic field is also important. Combining the coherent optical effects like EIT with the longitudinal and transverse magnetic fields create an opportunity for developing an EIT based atomic vector magnetometer which is sensitive to the direction of the magnetic field. In our laboratory, we have developed an apparatus to study the effects of static longitudinal and transverse magnetic fields in a hyperfine -type EIT system. We have shown how the EIT resonance is highly sensitive to the magnetic field direction as well as the polarization direction of the applied electric fields. The selection rules of the EIT resonances can be controlled by controlling the polarization component of the laser fields with respect to the quantization axis. On the theoretical front, apart from developing a numerical solution to support the experimental observation, a toy model consisting of nine level Zeeman sub-system, has been derived in order to analytically understand the phenomena.
Reference:
1. Bankim Chandra Das, Arpita Das, Dipankar Bhattacharya and Sankar De, Journal of the Optical Society of America B, 38, 584 (2021).

Vector beams (VB) have a great advantage over their scalar counterparts, due to their spatially inhomogeneous polarization distribution. Coherent control of polarization, phase and amplitude gives complete freedom to manipulate fully structuring light(FSL). A vector superposition of two orthogonally polarized components can produce VB or FSL  beam. This lecture discusses a scheme to guide a weak vector beam using optically written waveguides inside atomic vapor, whilst controlling its polarization rotation. The polarization rotation control is achieved using the anisotropic property of a four-level tripod atomic system which under a specific configuration, can generate different refractive indices for the left and right circularly polarized components of the vector beam. The refractive indices of the two vector beam components can be varied by changing their detunings. The waveguiding of the vector beam is achieved through a strong control field with an appropriate transverse intensity profile, which generates a ``core and cladding" type refractive index profile inside the medium.

Optical clocks represent the pinnacle of precise timekeeping. Laboratory-based precision atomic clocks which provide the highest level of sensitivity are based on transitions in the microwave/optical domain using neutral atoms or trapped atomic ions and define international timescales, provide a basis for testing the time invariance of fundamental constants and lead to the search for new physics beyond the Standard Model. The other domain is the regime of portable atomic clocks based on warm atomic vapor, that are compact, low power consuming and are field deployable with a multitude of targeted applications in telecommunications, navigation (GPS), sensing and precision timing. With the increasing use of field-deployable atomic clocks and frequency standards, many commercial and strategic applications including sensing,

communications and navigation, are getting a tremendous technological boost. Chip-scale atomic clocks (CSACs) based on Coherent Population Trapping (CPT) have been increasingly popular due to their small size and low power consumption. However, the inherent limitation in frequency sensitivity presented by CSACs stems from the use of microwave-based transitions to derive the frequency reference. Optical transition-based field deployable clocks using two-photon resonances offer a promising alternative with a possibility of surpassing existing commercial clocks (CSACs) by at least a factor of 10 in both short- and long-term stability. Two-photon transitions in alkali and alkaline earth metals are thus considered promising candidates for simple, field-deployable optical frequency references and optical clocks. One may utilize counter propagating beams to drive the two-photon transition in the Doppler-free regime, resulting in narrow lines.

At IIT Tirupati, we are engaged in developing the next generation atomic vapor based portable frequency standards using optical two-photon transitions in Rubidium (Rb) for for quantum sensing and quantum positioning applications. We are working towards development of precision laser sources, electronics, and miniaturized vapor cells for the two-photon frequency standard. We shall present a brief overview of our research activities at IIT Tirupati and discuss some of the challenges, opportunities and commercial benefits related to the development of a portable, precision atomic sensor for a host of quantum technology applications.

-

Exact results for collective behaviour of trapped Fermions have remained elusive.  Apart from mean-field approaches (Local
Density/Thomas-Fermi approximation), there has hardly been any progress on studying collective phenomena. I will give a brief review of some exact results in low dimensions. I will then discuss our recent results [1] for the collective description of noninteracting fermions in a 2D harmonic trap rotating with a constant frequency and in the presence of an additional repulsive central potential. I will show that in the large-N limit, the bulk density has a rich and nontrivial profile with a hole at the center of the trap and surrounded by a multilayered “wedding cake” structure. I will discuss a rich phase diagram that emerges in this system. I will then discuss connections to orthogonal polynomials, unitary evolution of certain quantum spin chains and Random Matrix Theory.

[1] M. Kulkarni, S. N. Majumdar, G. Schehr, Phys. Rev. A 103, 033321 (2021)

In this presentation, I would like to discuss the spontaneous formation of quantum turbulence at the surface (single) and interface (binary) of Bose-Einstein condensate (BEC). I will highlight the physics behind the generation of different oscillating patterns parametrically excited by modulating the scattering lengths. The effective Mathieu equation and Floquet analysis are used here to characterize the patterns [1,2]. The characterizations are supported by experimental observation [2]. I will briefly explain how our theory can predict the generated interfacial tension useful to characterize the condensate. In the end, I will summarize the presentation with the future scopes of these works with different experimental realizations and applications of high-lying collective excitations leading to quantum turbulence.
Reference:
1) Parametrically excited star-shaped patterns at the interface of binary Bose-Einstein condensates; DK Maity, K Mukherjee, SI Mistakidis, S Das, PG Kevrekidis, S Majumder, P Schmelcher; Physical Review A 102 (3), 033320 (2020)
2) Spontaneous Formation of Star-Shaped Surface Patterns in a Driven Bose-Einstein Condensate; Kiryang Kwon, K Mukherjee, SJ Huh, K Kim, SI Mistakidis, DK Maity, PG Kevrekidis, S Majumder, P Schmelcher, J-y Choi; Physical Review Letters, 127, 113001 (2021)

-

We theoretically discuss the isothermal compressibility in the normal state of an ultracold Fermi gas with a tunable pairing interaction associated with a Feshbach resonance. Including strong pairing fluctuations caused by this tunable interaction within the framework of the self-consistent T-matrix approximation (SCTMA), we numerically evaluate this thermodynamic quantity over the entire BCS-BEC crossover region. In the unitary limit, the calculated isothermal compressibility is shown to agree well with the recent experiment on a 6Li Fermi gas. In the strong-coupling BEC regime, we also show that, not only a two-body interaction between Cooper-pair molecules, but also a three-body molecular interaction sizably contribute to the isothermal compressibility. Our results indicate that the isothermal compressibility is a useful quantity for the study of how Cooper pairs are correlated to each other in a strongly interacting Fermi gas. 

Bose-Einstein condensate (BEC) is a highly coherent and tunable quantum matter, which has opened up huge possibility towards emerging areas like quantum simulation and quantum sensing [1,2]. Applications of ultracold atoms as quantum simulator mostly rely on the external trap which can efficiently be engineered to a desired shape due to the unprecedented progress in the experimental front. However, investigating the dynamics of such system through exact theoretical approach becomes quite nontrivial due to its nonlinear nature and the presence of varying external trap upon engineering. Various optical lattices are found to be the most favorable candidates for quantum simulation and the underlying dynamics can exhibit various novel and complex quantum phenomena like Anderson-like localization, negative absolute temperature etc. [3-7]. In this talk, I will present analytical approaches for quasi-periodic optical lattices which can hold and mould matter waves in self similar form like soliton. Applications of BEC under a bi-chromatic optical lattice, engineered superlattices and for quantum precision measurements will be addressed [2,4,6,8].

References:
1. C. Gross and I. Bloch, Science 357, 6355, 995 (2017).
2. J. Bera, S. Ghosh, L. Salasnich, and Utpal Roy, Phys. Rev. A 102, 063323 (2020); S. Ghosh, J. Bera, P. K. Panigrahi and Utpal Roy, Int. J. Quant. Inf. 17, 1950019 (2019).
3. S. Braun et al., Science 339, 52 (2013).
4. A. Nath, J. Bera, S. Ghosh, and Utpal Roy, Sci. Reports 10, 9016 (2020).
5. A. Nath, and Utpal Roy, Laser Phys. Lett 11, 115501 (2014).
6. N. Kundu, A. Nath, J. Bera, S. Ghosh and Utpal Roy, Phys. Lett. A 427, 127922 (2022).
7. A. Nath, J Bera, S Ghosh, P K Panigrahi and Utpal Roy, Eur. Phys. J. D 74, 27 (2020).
8. B. Halder, S. Ghosh, P. Basu, J. Bera, B. Malomed and Utpal Roy, Symmetry 14, 49 (2022). (Special issue on ‘Symmetry in Many-Body Physics’)

Abstract: Rydberg Atoms in highly excited electronic states with n=30-120 can be excited within Bose-Einstein condensates (BECs), and while lifetimes are shorter than in vacuum [1,2], they live long enough to interestingly interact with the BEC [3]. We theoretically study this interaction in the mean-field limit and beyond.

For multiple Rydberg atoms in a single electronic state, we show that the phase coherence of the condensate allows the tracking of mobile Rydberg impurities akin to bubble chambers in particle physics [4,5]. For a single Rydberg atom with multiple electronic states, we provide spectral densities of the BEC as a decohering environment [6], and show that the BEC can image a signature of the entangling evolution that causes Rydberg qu-bit decoherence [7]. Finally, an aggregate of multiple  Rydberg atoms in BEC shows promise for quantum simulations of photosynthetic energy transport, extending [8].

[1] Schlagmüller et al. PRX 6 (2016) 031020.

[2] Kanungo et al. PRA 102 (2020) 063317.

[3] Balweski et al. Nature 502 (2013) 664.

[4] Tiwari et al. PRA 99 (2019) 043616.

[5] Tiwari et al. https://arxiv.org/abs/2111.05031 (2021).

[6] Rammohan et al. PRA 103 (2021) 063307.

[7] Rammohan et al. PRA (Letters) 104  (2021) L06020.

[8] Schönleber, et al. PRL 114 (2015) 123005.

In this talk, I will first give a brief overview of quasi-periodic lattice systems and the nature of single-particle states. I will then discuss how to read out the underlying transport properties of such lattices by coupling them to a qubit that acts as a probe. In the second half of the talk, I will briefly discuss how attaching Buttiker probes to such lattices modifies the charge and energy transport properties.

References:
1. Madhumita Saha, Bijay Kumar Agarwalla, and B. Prasanna Venkatesh, Read-out of Quasi-periodic Systems using Qubits,  Phys. Rev. A  103, 023330 (2021

2. M. Saha, B. Prasanna Venkatesh, and Bijay Kumar Agarwalla, ​​Quantum transport in quasi-periodic lattice systems in presence of Buttiker probes, arXiv: 2202.14033

-

-