arXiv subjects

Nitesh Jaiswal

Publications and source records attributed to Nitesh Jaiswal.

8 recordsLinked to original sources

arXiv2026

Emergent Hawking Radiation and Quantum Sensing in a Quenched Chiral Spin Chain

We investigate the emergence and detection of Hawking radiation (HR) in a 1D chiral spin chain model, where the gravitational collapse is simulated by a sudden quantum quench that triggers a horizon-inducing phase transition. While our previous work Jaiswal [2025] established that this model mimics BH formation conditions even when the Hoop conjecture is seemingly violated, we here focus on the resulting stationary radiation spectrum and its detectability. By mapping the spin chain dynamics to a Dirac fermion in a curved (1 + 1)-dimensional spacetime, we analyze the radiation using two complementary approaches: field-theoretic modes and operational quantum sensors. First, using localized Gaussian wave packets to model realistic detectors, we find that the radiation spectrum exhibits deviations from the ideal Planckian form, analogous to frequency-dependent greybody factors, while retaining robust Poissonian statistics that signal the loss of formation-scale information. Second, we introduce a qubit coupled to the chain as a stationary Unruh-DeWitt detector. We demonstrate that the qubit functions as a faithful quantum sensor of the Hawking temperature only in the weak-coupling regime, where its population dynamics are governed solely by the bath spectral density. In the strong-coupling limit, the probe thermalizes with the global environment, obscuring the horizon-induced thermal signature. These results provide a clear operational protocol for distinguishing genuine analog HR from environmental noise in quantum simulation platforms.

cond-mat.stat-mech↗

arXiv2025

Analog charged black hole formation via percolation: Exploring cosmic censorship and Hoop conjecture

We investigate an analog model of charged black hole (BH) formation using the framework of classical percolation. By analyzing the scaling behavior of key quantities, including surface gravity and Komar mass, we establish a robust correspondence between this analog system and gravitational collapse in general relativity. Our numerical simulations of the lattice model show excellent agreement with analytical predictions for the continuum limit, highlighting the potential of analog systems to capture essential features of BH physics. Interestingly, we find that while geometric criteria related to the hoop conjecture are necessary, they are not sufficient for BH formation in our model. Instead, the exponential growth of energy and cluster size emerges as the key indicator, suggesting a novel interpretation of the hoop conjecture and providing further support for cosmic censorship within our analog framework by ensuring horizon formation. This work offers a fresh perspective on the organization of matter within BH event horizons and lays the groundwork for future quantum extensions that could shed light on Hawking radiation and the BH information paradox by linking entanglement entropy in quantum percolation models to BH entropy.

gr-qc↗

arXiv2023

Spread complexity evolution in quenched interacting quantum systems

We analyse time evolution of spread complexity (SC) in an isolated interacting quantum many-body system when it is subjected to a sudden quench. The differences in characteristics of the time evolution of the SC for different time scales is analysed, both in integrable and chaotic models. For a short time after the quench, the SC shows universal quadratic growth, irrespective of the initial state or the nature of the Hamiltonian, with the time scale of this growth being determined by the local density of states. The characteristics of the SC in the next phase depend upon the nature of the system, and we show that depending upon whether the survival probability of an initial state is Gaussian or exponential, the SC can continue to grow quadratically, or it can show linear growth. To understand the behaviour of the SC at late times, we consider sudden quenches in two models, a full random matrix in the Gaussian orthogonal ensemble, and a spin-1/2 system with disorder. We observe that for the full random matrix model and the chaotic phase of the spin-1/2 system, the complexity shows linear growth at early times and saturation at late times. The full random matrix case shows a peak in the intermediate time region, whereas this feature is less prominent in the spin-1/2 system, as we explain.

quant-ph↗

arXiv2023

Spread Complexity in free fermion models

We study spread complexity and the statistics of work done for quenches in the three-spin interacting Ising model, the XY spin chain, and the Su-Schrieffer-Heeger model. We study these models without quench and for different schemes of quenches, such as sudden quench and multiple sudden quenches. We employ the Floquet operator technique to investigate all three models in the presence of time-dependent periodic driving of parameters. In contrast to the sudden quenched cases, the periodically varying parameter case clearly shows non-analytical behaviour near the critical point. We also elucidate the relation between work done and the Lanczos coefficient and how the statistics of work done behave near critical points.

quant-ph↗

arXiv2023

FOTOC complexity in an extended Lipkin-Meshkov-Glick model

We study fidelity out-of-time-order correlators (FOTOCs) in an extended Lipkin-Meshkov-Glick model and demonstrate that these exhibit distinctive behaviour at quantum phase transitions in both the ground and the excited states. We show that the dynamics of the FOTOC have different behaviour in the symmetric and broken-symmetry phases, and as one approaches phase transition. If we rescale the FOTOC operator with time, then for small times, we establish that it is identical to the Loschmidt echo. We also compute the Nielsen complexity of the FOTOC operator in both phases, and apply this operator on the ground and excited states to obtain the quasi-scrambled state of the model. The FOTOC operator introduces a small perturbation on the original ground and excited states. For this perturbed state, we compute the quantum information metric to first order in perturbation, in the thermodynamic limit. We find that the associated Ricci scalar diverges at the phase transition on the broken-symmetry phase side, in contrast to the zeroth order result. Finally, we comment upon the Fubini-Study complexity in this model.

quant-ph↗

arXiv2022

Complexity and quenches in models with three and four spin interactions

We study information theoretic quantities in models with three and four spin interactions. These models show distinctive characteristics compared to their nearest neighbour counterparts. Here, we quantify these in terms of the Nielsen complexity in static and quench scenarios, the Fubini-Study complexity, and the entanglement entropy. The models that we study have a rich phase structure, and we show how the difference in the nature of phase transitions in these, compared to ones with nearest neighbour interactions, result in different behaviour of information theoretic quantities, from ones known in the literature. For example, the derivative of the Nielsen complexity does not diverge but shows a discontinuity near continuous phase transitions, and the Fubini-Study complexity may be regular and continuous across such transitions. The entanglement entropy shows a novel discontinuity both at first and second order quantum phase transitions. We also study multiple quench scenarios in these models and contrast these with quenches in the transverse XY model.

quant-ph↗

arXiv2021

Complexity, Information Geometry, and Loschmidt Echo near Quantum Criticality

We consider the Nielsen complexity ${\mathcal C}_N$, the Loschmidt echo ${\mathcal L}$, and the Fubini-Study complexity $τ$ in the transverse XY model, following a sudden quantum quench, in the thermodynamic limit. At small times, the first two are related by ${\mathcal L} \sim e^{-{\mathcal C}_N}$. By computing a novel time-dependent quantum information metric, we show that in this regime, ${\mathcal C}_N \sim dτ^2$, up to lowest order in perturbation. The former relation continues to hold in the same limit at large times, whereas the latter does not. Our results indicate that in the thermodynamic limit, the Nielsen complexity and the Loschmidt echo show enhanced temporal oscillations when one quenches from a close neighbourhood of the critical line, while such oscillations are notably absent when the quench is on such a line. We explain this behaviour by studying the nature of quasi-particle excitations in the vicinity of criticality. Finally, we argue that the triangle inequality for the Nielsen complexity might be violated in certain regions of the parameter space, and point out why one should be careful about the nature of the interaction Hamiltonian, while using this measure.

quant-ph↗

arXiv2020

Complexity and information geometry in spin chains

We study Nielsen complexity and Fubini-Study complexity for a class of exactly solvable one dimensional spin systems. Our examples include the transverse XY spin chain and its natural extensions, the quantum compass model with and without an external magnetic field. We obtain the scaling behaviour of both complexities near quantum phase transitions in the thermodynamic limit, as a function of the system parameters. We provide analytical proofs of these, in an information geometric framework, which verify our numerical analysis. The scaling of the Nielsen complexity with the system size is also established, close to criticality. We also obtain analytic expressions for the Fubini-Study complexity in some special cases for all the models, while a numerical analysis in more generic situations is carried out. Our study clearly demonstrates the differences in the two notions of complexity in quasi-free fermionic systems.

cond-mat.stat-mech↗