This work improves upon the best known theoretical limits of phase sensitivity as obtained through intensity measurements in a Mach-Zehnder interferometer.

This work resolves the separability/entanglement issue exactly for a class of bipartite states.

The superposition principle applies to several physical problems. When the problem involves two or more degrees of freedom, the notion of entanglement emerges, as elucidated by Erwin Schroedinger in 1935. Quantum information processing, quantum communication, and quantum computation, have their basis on entanglement, a consequence of the superposition principle. An even more elementary consequence of the superposition principle, as seen in optics

We have found the quadrature operator eigenstates and wavefunctions for the general f-deformed oscillators. We have defined the f-deformed quadrature operator with the help of the homodyne detection method and represented its eigenstates in the f-deformed Fock state basis. This allowed us to produce a recurrence relation for the wavefunctions, which in turn allowed us to discover a new class of orthogonal polynomials. These new polynomials enabled us to represent the excited state wavefunctions of the f-oscillators in terms of the ground state wavefunction.

We have studied the squeezing properties of arbitrary numbers of superpositions of various squeezed states such as squeezed vacuum state, photon-added coherent states, and two mode squeezed vacuum state. We have considered two superpositions: the first kind and the second kind. In the case of the first kind, the superpositions of squeezed states do not show both squeezing and higher-order squeezing of all orders. This is found to be true for any state which has quadrature squeezing and multi-mode squeezed states.

The dynamics of quantum systems play an essential role in quantum information processing and computing. We have studied the dynamics of superposition of wavepackets evolving under different nonlinear Hamiltonians corresponding to Kerr medium, Morse oscillator, and bosonic Josephson junction. We have shown that quantum systems' periodic, quasi-periodic, ergodic, and chaotic dynamics can change drastically if we change just the initial state to its superposition by keeping all other system parameters the same.

[Funded by SERB: Govt. of India: 2016-2019; Project Investigator - S. Jayanthi]

We investigate in detail the underlying spin-dynamics associated with time-dependent Hamiltonians by developing theoretical models in complex spin systems (1H-14N, 1H-35Cl etc.). In a recent work, published in Journal of Magnetic Resonance we employed matrix logarithm and Floquet theory to compute numerically the effective Hamiltonian associated to a time-dependent problem in solid state Nuclear Magnetic Resonance, Cross-Polarization under fast Magic Angle Spinning (MAS) and Double Cross Polarization under fast MAS.

In this work, a novel experiment using selective longitudinal Cross Polarization is proposed and demonstrated that enhances the sensitivity and resolution of homonuclear NOESY correlations by targeting selected 1H–15N spin pairs.The enhanced signal sensitivity (~ 2-5) as well as access to both 15N–1H and 1H–1H NOESY dimensions can greatly facilitate RNA assignments and secondary structure determinations, as demonstrated with the analysis of genome fragments derived from the SARS-CoV-2 virus.

Improvement of heteronuclear transfers through J-driven cross polarization (J-CP), which transfers polarization by spin-locking the coupled spins under Hartmann-Hahn conditions. J-CP provides certain immunity against chemical exchange and other T2-like relaxation effects, a behavior that is examined in depth by both Liouville-space numerical and analytical derivations describing the transfer efficiency.

Figure: Numerical vs analytical solutions for J-CP as a function of contact time.