arXiv subjects

Sinchan Ghosh

Publications and source records attributed to Sinchan Ghosh.

3 recordsLinked to original sources

arXiv2026

Generating pairwise entanglement in periodically driven quantum spin chains with stochastic resetting

We show that stochastic resetting may lead to finite entanglement between individual, spatially separated spins (pairwise entanglement) in the steady state of the spin chains driven periodically with frequency $\omega_D$. We find the presence of a critical resetting rate $r_c$ below which the steady state pairwise entanglement, measured via concurrence $C$, vanishes. We also identify an optimal resetting rate $r_m$ at which $C$ becomes maximum. These critical and optimal rates exhibit a non-monotonic dependence on $\omega_D$. Our analysis demonstrates the existence of special drive frequencies at which $r_c$ vanishes and $r_m$ attains minima. We compute $C$ in the presence of stochastic resetting using exact diagonalization for both the integrable XY model and non-integrable Rydberg spin chains, which demonstrate these features. Our numerical results match perturbative analytical expressions for the special drive frequencies in the large drive amplitude regime.

quant-ph↗

arXiv2025

Index-theoretic route to the subgap Andreev bands and topological response in Josephson junctions

We demonstrate that the subgap Andreev bound states in a transparent Josephson junction, comprising of either chiral or non-chiral superconductors, can be viewed as a consequence of the index theorem in supersymmetric quantum mechanics. We provide an exact solution for these states starting from the Bogoliubov-de Gennes (BdG) equations describing quasiparticles in such junctions. We demonstrate that the dispersion of these subgap states depends only on the asymptotic properties of the pair-potential and not on its local spatial variation. Our study reveals the crucial distinction between junctions of non-chiral $p$-wave superconductors and those of $s$-wave or chiral superconductors by analyzing the wavefunction of their subgap bound states. We find a stable topological response leading to the well-known $4\pi$ periodic Josephson effect protected against weak disorder potential for the non-chiral $p$-wave junctions; no such protection is found for junctions of $s$-wave or chiral superconductors. We supplement our analytic results with numerical computation of the Josephson currents in such junctions using exact numerical Green functions and starting from a lattice model of an itinerant altermagnet which is expected to host triplet $p$-wave superconductivity with equal-spin-pairing. We also discuss the implications of our results for Josephson junctions away from the transparent limit.

cond-mat.mes-hall↗

arXiv2021

Experimental realization of BB84 protocol with different phase gates and SARG04 protocol

Cryptography in the modern era is very important to prevent a cyber attack, as the world tends to be more and more digitalized. Classical cryptographic protocols mainly depend on the mathematical complicacy of encoding functions and the shared key, like RSA protocol in which security depends upon the fact that factoring a big number is a hard problem to the current computers. This means that high computing power can help you crack traditional encryption methods. Quantum machines claim to have this kind of power in many instances. Factorization of big numbers may be possible with Shor's algorithm with quantum machines in considerable time. Apart from this, the main problem is key sharing i.e., how to securely share the key the first time to validate the encryption. Here comes quantum key distribution. Two parties who are interested in communication with each other, create a process, which claims considerable security against an eavesdropper, by encoding and decoding information in quantum states to construct and share a secret key. Quantum key distribution may be done in a variety of ways. This paper begins with experimental verification of the BB84 procedure utilizing four bases (using phase gates) followed by the experimental realization of the SARG04 protocol which was derived from BB84 Protocol to overcome PNS attack. The possibility of a third-party attack and the effect of noise is considered and implemented. The IBM Quantum Experience platform was used for all of the implementations.

quant-ph↗