N. Bose National Centre for Basic Sciences (SNBNCBS) is an autonomous research institute dedicated to basic research in mathematics sciences under the Department of Science and Technology of Government of India. It is located in West Bengal, Salt Lake, Kolkata. This institute was named after the Indian scientist Satyendra Nath Bose and established in 1986. Chanchal Kumar Majumdar was the founder director of this institute.As this is a research institute, mainly Ph.D. program is done here. From 2001 Integrated Ph.D. (M.Sc.+Ph.D.) program was started. After completion of two years of study, a M.Sc. degree is given by University of Calcutta. Formerly, this degree was given by West Bengal University of Technology. Students of this institute can submit their Ph.D. thesis to Jadavpur University, the University of Calcutta, West Bengal University of Technology or any other university which allows students to do so.
Spin mixing conductance (SMC) determines spin angular momentum transfer across ferromagnet/nonmagnet (FM/NM) interfaces and directly controls spin pumping-induced damping. While SMC is well understood in bilayer systems, its quantitative behaviour in multilayers with multiple spin-sink interfaces remains unclear. Here, we report an all-optical study of spin pumping in a Ta/Co20Fe60B20 (CoFeB)/W trilayer, where a single ferromagnetic CoFeB layer is coupled to two nonmagnetic spin sinks. Time-resolved magneto-optical Kerr effect measurements are used to extract the effective Gilbert damping and corresponding effective SMC, which are benchmarked against reference Ta/CoFeB and CoFeB/W bilayers. Although the damping enhancement in the trilayer is not strictly additive, the extracted composite effective SMC quantitatively follows a series-sum relation of the SMCs of the constituent interfaces. This result demonstrates that spin transport in the trilayer is governed by independent spin pumping contributions from each interface, establishing composite SMC as a useful metric for engineering damping in multilayer spintronic heterostructures.
Teleportation of quantum information over long distances requires robust entanglement on the macroscopic scale. The construction of highly energetic eigenstates with tunable long-range entanglement can provide a new medium for information transmission. Using a symmetric superposition of the antipodal triplet states, we construct polynomially many exact zero-energy eigenstates for a class of nonintegrable spin-1/2 Hamiltonians with two-body interactions. These states exhibit nonthermal correlations, and hence, are genuine quantum many-body scars. By tuning the distribution of triplets, we induce extensive, logarithmic, or area-law entanglement and can observe a second-order entanglement phase transition. Quasiparticle excitations in this manifold converge to be exact quantum many-body scars in the thermodynamic limit. This framework has a natural extension to higher dimensions, where entangled states controlled by lattice geometry and internal symmetries can result in new classes of correlated out-of-equilibrium quantum matter. Our results provide a new avenue for entanglement control and quantum state constructions.
The Kirkwood-Dirac (KD) distribution has recently emerged as a powerful quasiprobability framework with wide-ranging applications in quantum information processing tasks. In this work, we introduce an experimentally motivated criterion for detecting nonclassical signatures of the KD distribution using its statistical moments and demonstrate its effectiveness through explicit examples. We further show that this approach extends naturally to identifying other quantum resources, such as quantum coherence and nonclassical extractable work -- that are intrinsically connected to the KD distribution. Our criteria involves the evaluation of simple functionals, making it well-suited for efficient experimental implementation.
In this paper, we study the motion of a massless, chargeless particle in Schwarzschild-de Sitter spacetime, revealing exponential radial growth and potential chaos in an integrable system. Poincaré sections show regular Kolmogorov–Arnold–Moser (KAM) tori when black hole and cosmological horizons are distant, but distortions and chaos emerge as they converge. As the horizons coincide, the Poincaré sections fully contract and vanish, marking the system’s transition to Nariai spacetime. Our analysis also suggests that, within the parameter range explored, the event horizon exerts a comparatively more substantial chaotic influence on the system, primarily due to its consistent proximity. Additionally, we analyze the Lyapunov exponents to quantify the degree of chaos in the system. Our findings indicate that as the closeness of the two horizons increases, the most prominent Lyapunov exponent also increases, signifying a rise in chaotic behavior. By examining the long-term saturation values of the Lyapunov exponents, we confirm that they consistently comply with the Maldacena–Shenker–Stanford (MSS) bound.
The interaction of fermion spin with spacetime can be non-universal, leading to a new interaction beyond the Standard Model, independent of gravitation. Fermions generate spacetime torsion, which can be integrated out in favor of a four-fermion interaction in a torsion-free background. This is a current-current interaction which involves all fermions and generically has different coupling constants for different chiralities and species of fermions. It does not vanish when curvature goes to zero, so accelerator experiments should be able to see its effect. We calculate the contribution of this geometrical interaction to parity nonconservation in e^-e^- and e^-D scattering and compare with known observations. This provides an estimate of an upper bound on the coupling constants, suggesting that the strength of the “new physics” can be as large as only one order of magnitude smaller than that of weak interactions.
