arXiv subjects

Saikat Sur

Publications and source records attributed to Saikat Sur.

17 recordsLinked to original sources

arXiv2026

Quantum state localization in dipole-dipole interacting disordered networks

We study the localization of excitations in positionally disordered spin or atom networks coupled via the realistic resonant dipole-dipole interaction (RDDI), which does not conform to a simple power law, as the spatial dependence and dissipative character distinguish it from conventional short or long-range models. Despite its partially long-ranged and radiative nature, positional disorder in the RDDI coupling leads to strong spatial localization of excitations. The interplay between coherent and dissipative couplings gives rise to nontrivial interference effects that stabilize localized modes even in open geometries. Our results uncover a photon wavelength-induced transition from extended to localized excitation dynamics, establishing RDDI networks as a unique setting to explore the emergence of localization in realistic quantum optical systems. Our analysis of the localized modes induced by RDDI has potential applications in coherent photovoltaics, excitonic circuits, quantum memory, and quantum sensors.

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arXiv2026

Volume Law and Universality of Entanglement Entropy in Random Graph Fermi Systems

We study the ground-state entanglement entropy of free fermions on random graphs. We first establish a general criterion for the volume law on random graphs, based on the spectral characteristics of the Hamiltonian. We then apply this criterion to the Erd\H{o}s--R\'enyi random graph, where each of the possible edges is present independently with some probability. Using random matrix theory and asymptotic freeness, we show that the ground-state entanglement entropy obeys an exact volume law in Erd\H{o}s--R\'enyi graphs in the thermodynamic limit, with a universal coefficient that is independent of the edge probability of the graph. This coefficient is confirmed numerically to take the value approximately $0.3863$ nats, strictly below the Page value. The volume law therefore reflects the absence of geometric locality in the random graph.

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arXiv2026

Automorphism-Induced Entanglement Bounds in Many-Body Systems

We derive an upper bound on the maximum balanced bipartite entanglement entropy of ground states of many-body Hamiltonians defined on a graph, agnostic to any particular model, that possesses a nontrivial automorphism group. We show that the entropy is bounded by the logarithm of a weighted sum of multiplicities of irreducible representations of the bipartition-preserving automorphism subgroup. This bound complements the known degeneracy-based bound, with neither universally dominating the other. For the complete graph $K_n$, the new bound yields an exponential improvement from linear to logarithmic scaling in the system size, consistent with the exact value of the entropy.

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arXiv2026

Collective purification of interacting quantum networks beyond symmetry constraints

Following any quantum information processing protocol, it is essential to reset a mixed state of a many-body interacting spin-network to the computational-zero pure state. This task is challenging, both theoretically and experimentally, because of the quantum correlations. There is currently no effective cooling strategy for both high and low temperatures in such networks. Here we put forth a universal cooling strategy for multi-spin interacting networks. The strategy is based on the collective coupling of the system to an ancilla spin that intermittently dumps part of its entropy into an ultracold bath. Yet this strategy should overcome the symmetry-imposed correlations that impede the cooling. To avoid the prohibitive complexity of computing the dynamics, we resort to graph analysis of the network. %To approach the desired state, We show that a unique choice of alternating, non-commuting system-ancilla interaction Hamiltonians exists that breaks the symmetry constraints and allows the network to approach the desired pure state. We illustrate this universal purification strategy in diverse experimental settings.

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arXiv2026

Control of Multipartite Entanglement through Anisotropy against Thermal Noise

Preserving multipartite entanglement in open many-body quantum systems is fundamentally limited by unavoidable environmental noise. We study the open-system dynamics of multipartite entanglement in an anisotropic XXZ spin chain interacting with a thermal spin bath, focusing on two states with distinct types of multipartite entanglement: the generalized GHZ and the generalized W state. Using a master-equation approach combined with the Bethe ansatz technique, we show analytically that robustness of multipartite entanglement at low temperatures can be enhanced by suitably tuning the anisotropy of the system. Our results highlight interaction-induced spectral control as a mechanism for stabilizing multipartite entanglement in quantum computing platforms.

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arXiv2025

A Mathematical Framework for Misinformation Propagation in Complex Networks: Topology-Dependent Distortion and Control

Misinformation is pervasive in natural, biological, social, and engineered systems, yet its quantitative characterization remains challenging. We develop a general mathematical framework for quantifying information distortion in distributed systems by modeling how local transmission errors accumulate along network geodesics and reshape each agent's perceived global state. Through a drift-fluctuation decomposition of pathwise binomial noise, we derive closed-form expressions for node-level perception distributions and show that directional bias induces only a uniform shift in the mean, preserving the fluctuation structure. Applying the framework to canonical graph ensembles, we uncover strong topological signatures of misinformation: Erd\H{o}s-R\'enyi random graphs exhibit a double-peaked distortion profile driven by connectivity transitions and geodesic-length fluctuations, scale-free networks suppress misinformation through hub-mediated integration, and optimally rewired small-world networks achieve comparable suppression by balancing clustering with short paths. A direct comparison across regular lattices, Erd\H{o}s-R\'enyi random graphs, Watts-Strogatz small-world networks, and Barab\'asi-Albert scale-free networks reveals a connectivity-dependent crossover. In the extremely sparse regime, scale-free and Erd\H{o}s-R\'enyi networks behave similarly. At intermediate sparsity, Watts-Strogatz small-world networks exhibit the lowest misinformation. In contrast, Barab\'as-Albert scale-free networks maintain low misinformation in sparse and dense regimes, while regular lattices produce the highest distortion across connectivities. We additionally show how sparsity constraints, structural organization, and connection costs delineate regimes of minimal misinformation.

physics.soc-ph↗

arXiv2025

Molecular Processes as Quantum Information Resources

In this contribution to Abraham Nitzan's Festschrift, we present a perspective of theoretical research over the years that has pointed to the potential of molecular processes to act as quantum information resources. Under appropriate control, homonuclear dimer (diatom) dissociation (half-collision) and the inverse process of atom-pair collisions are shown to reveal translational (EPR-like) entanglement that enables molecular wavepacket teleportation. When such processes involve electronic-state excitation of the diatom, the fluorescence following dissociation can serve as an entanglement witness that unravels the molecular-state characteristics and evolution. Such entangling processes can also exhibit anomalous quantum thermodynamic features, particularly temperature enhancement of a cavity field that interacts with dissociated entangled diatoms.

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arXiv2025

Generic Two-Mode Gaussian States as Quantum Sensors

Gaussian quantum channels constitute a cornerstone of continuous-variable quantum information science, underpinning a wide array of protocols in quantum optics and quantum metrology. While the action of such channels on arbitrary states is well-characterized under full channel knowledge, we address the inverse problem, namely, the precise estimation of fundamental channel parameters, including the beam splitter transmissivity and the two-mode squeezing amplitude. Employing the quantum Fisher information (QFI) as a benchmark for metrological sensitivity, we demonstrate that the symmetry inherent in mode mixing critically governs the amplification of QFI, thereby enabling high-precision parameter estimation. In addition, we investigate quantum thermometry by estimating the average photon number of thermal states, revealing that the transmissivity parameter significantly modulates estimation precision. Our results underscore the metrological utility of two-mode Gaussian states and establish a robust framework for parameter inference in noisy and dynamically evolving quantum systems.

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arXiv2024

Sensing multiatom networks in cavities via photon-induced excitation resonance

We explore the distribution in space and time of a single-photon excitation shared by a network of dipole-dipole interacting atoms that are also coupled to a common photonic field mode. Time-averaged distributions reveal partial trapping of the excitation near the initially excited atom. This trapping is associated with resonances of the excitation at crossing points of the photon-dressed energy eigenvalues of the network. The predicted photon-induced many-atom trapped excitation (PIMATE) is sensitive to atomic position disorder which broadens the excitation resonances and transforms them to avoided crossings. PIMATE is shown to allow highly effective and accurate sensing of multi-atom networks and their disorder.

quant-ph↗

arXiv2024

Many-body quantum thermal machines in a Lieb-kagome Hubbard model

Quantum many-body systems serve as a suitable working medium for realizing quantum thermal machines (QTMs) by offering distinct advantages such as cooperative many-body effects, and performance boost at the quantum critical points. However, the bulk of the existing literature exploring the criticality of many-body systems in the context of QTMs involves models sans the electronic interactions, which are non-trivial to deal with and require sophisticated numerical techniques. Here we adopt the prototypical Hubbard model in two dimensions (2D) in the framework of the line graph Lieb-kagome lattice for the working medium of a multi-functional QTM. We resort to a non-perturbative, static path approximated (SPA) Monte Carlo technique to deal with the repulsive Hubbard model. We observe that in a Stirling cycle, in both the interacting and non-interacting limits, the heat engine function dominates and its performance gets better when the strain is induced from the kagome to the Lieb limit, while for the reverse the refrigeration action is preferred. Further, we show that the QTM performs better when the difference between the temperatures of the two baths is lower and the QTM reaches the Carnot limit in this regime. Further, we extensively study the performance of the QTM in the repulsive Hubbard interacting regime where the magnetic orders come into the picture. We explore the performance of the QTM along the quantum critical points and in the large interaction limit.

quant-ph↗

arXiv2023

Repeated quantum game as a stochastic game: Effects of the shadow of the future and entanglement

We present a systematic investigation of the quantum games, constructed using a novel repeated game protocol, when played repeatedly ad infinitum. We focus on establishing that such repeated games -- by virtue of inherent quantum-mechanical randomness -- can be mapped to the paradigm of stochastic games. Subsequently, using the setup of two-player--two-action games, we explore the pure reactive strategies belonging to the set of reactive strategies, whose support in the quantum games is no longer countably finite but rather non-denumerably infinite. We find that how two pure strategies fare against each other is crucially dependent on the discount factor (the probability of occurrence of every subsequent round) and how much entangled the quantum states of the players are. We contrast the results obtained with the corresponding results in the classical setup and find fundamental differences between them: e.g, when the underlying game is the prisoner's dilemma, in the quantum game setup, always-defect strategy can be beaten by the tit-for-tat strategy for high enough discount factor.

quant-ph↗

arXiv2023

Quantum Advantage of Thermal Machines with Bose and Fermi Gases

In this article, we show that a quantum gas, a collection of massive, non-interacting, indistinguishable quantum particles can be realized as a thermodynamic machine as an artifact of energy quantization and hence bears no classical analog. Such a thermodynamic machine depends on the statistics of the particles, the chemical potential, and the spatial dimension of the system. Our detailed analysis demonstrates the fundamental features of quantum Stirling cycles from the viewpoint of particle statistics and system dimensions that helps us to realize desired quantum heat engines and refrigerators by exploiting the role of quantum statistical mechanics. In particular, a clear distinction between the behavior of a Fermi gas and a Bose gas is observed in one dimension than in higher dimensions, solely due to the innate differences in their particle statistics indicating the conspicuous role of a quantum thermodynamic signature in lower dimensions.

quant-ph↗

arXiv2022

Information scrambling and redistribution of quantum correlations through dynamical evolution in spin chains

We investigate the propagation of local bipartite quantum correlations, along with the tripartite mutual information to characterize the information scrambling through dynamical evolution of spin chains. Starting from an initial state with the first pair of spins in a Bell state, we study how quantum correlations spread to other parts of the system, using different representative spin Hamiltonians, viz. the Heisenberg Model, a spin-conserving model, the transverse-field XY model, a non-conserving but integrable model, and the kicked Harper model, a spin conserving but nonintegrable model. We show that the local correlations spread consistently in the case of spin-conserving dynamics in both integrable and nonintegrable cases, with a strictly nonnegative tripartite mutual information. In contrast, in the case of non-conserving dynamics, tripartite mutual information is negative and local pair correlations do not propagate.

quant-ph↗

arXiv2019

Quantum counterpart of Measure synchronization: A study on a pair of Harper systems

Measure synchronization is a well-known phenomenon in coupled classical Hamiltonian systems over last two decades. In this paper, synchronization for coupled Harper system is investigated in both classical and quantum contexts. The concept of measure synchronization involves with the phase space and it seems that the measure synchronization is restricted in classical limit. But, on the contrary, here, we have extended the aforesaid synchronization in quantum domain. In quantum context, the coupling occurs between two many body systems via a time and site dependent potential. The coupling leads to the generation of entanglement between the quantum systems. We have used a technique, which is already accepted in the classical domain, in both the contexts to establish a connection between classical and quantum scenarios. Interestingly, results corresponding to both the cases lead to some common features.

quant-ph↗

arXiv2018

Loschmidt echo of local dynamical processes in integrable and non integrable spin chains

The Loschmidt echo is investigated to track the effect of the local QDP. It is also quite sensitive to whether the background dynamics is integrable or not. For the integrable case, viz. the Heisenberg model, the Loschmidt echo depends on the parameters operators corresponding to the QDP as well as the time of QDP. The probability of reviving the system to its initial state is higher for incoherent QDPs occurring at large time intervals. Whereas each time coherent QDP occurs certain probability of reviving the state is always lost. For For the non-integrable case, viz. a kicked Harper model, it exhibits a decaying behaviour when contrasted with integrable dynamics. The decay rate is slower when the corresponding classical Hamiltonian is non chaotic. The Loschmidt echo also distinguishes the integrable and the nonintegrable dynamics when a QDP occurs.

quant-ph↗

arXiv2018

Interference of the signal from a local dynamical process with the quantum state propagation in spin chains

The effect of a local instantaneous quantum dynamical process (QDP), either unitary or non-unitary, on the quantum state transfer through a unitary Hamiltonian evolution is investigated for both integrable and non-integrable dynamics. There are interference effects of the quantum state propagation and the QDP signal propagation. The state transfer fidelity is small for further sites, from the site where the information is coded, indicating a finite speed for the propagation of the quantum correlation. There is a small change in the state transfer fidelity for the case of non- unitary QDP intervening the background unitary dynamics. In the case of unitary QDP, the change is more pronounced, with a substantial increase in the fidelity for appropriate sites and times. For the non-integrable case, viz. a kicked Harper model, the state transfer fidelity is quite large for further sites for short times, indicating a finite speed for the propagation of the quantum correlation cannot be defined.

quant-ph↗

arXiv2017

Remotely detecting the signal of a local decohering process in spin chains

We study the dynamics of a one dimensional quantum spin chain evolving from unentangled or entangled initial state. At a given instant of time a quantum dynamical process (ex. measurement) is performed on a single spin at one end of the chain, decohering the system. Through the further unitary evolution, a signal propagates in the spin chain, which can be detected from a measurement on a different spin at later times. From the dynamical unitary evolution of the decohered state from the epoch time, it is possible to detect the occurrence of the dynamical process. The propagation of the signal for the dynamical process, and the speed of the signal are investigated for various spin models, viz. using the Ising, Heisenberg, and the transverse-XY dynamics.

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