arXiv subjects

Akash Mitra

Publications and source records attributed to Akash Mitra.

6 recordsLinked to original sources

arXiv2026

Dynamical quantum phase transitions through the lens of mode dynamics

We study the mode dynamics of a generic quadratic fermionic Hamiltonian under a sudden quench protocol in momentum space. Modes with zero energy at any given time, $t$, are referred to as dynamical critical modes. Among all zero-energy modes, spin-flip symmetry is restored in the eigenvector corresponding to selected zero-energy modes. This symmetry restoration is used to define the dynamical quantum phase transition (DQPT). This shows that the occurrence of these dynamical critical modes is necessary but not sufficient for a DQPT. We show that the conditions on the quench protocol and time for such dynamical symmetry restoration are the same as the divergence of the rate function and integer jump in the dynamical topological order parameter, which have been the traditional identifiers of a DQPT. This perspective also naturally explains when one or both of DQPT and ground-state quantum phase transitions will occur.

cond-mat.stat-mech↗

arXiv2025

Sunburst quantum Ising battery under periodic delta-kick charging

Most quantum batteries studied so far with notable exception of Sachdev-Ye-Kitaev (SYK) batteries are based on integrable models, where superlinear scaling of charging power and hence a quantum advantage can be achieved, but at the cost of unstable stored energy due to integrability. Here, by considering the sunburst quantum Ising battery driven by periodic delta-kicks, we show that in the quantum chaotic regime a quantum advantage is achieved for number of batteries $n_b\leq 4$, together with excellent stability of energy storage. In the integrable regime optimal energy storage and extraction are possible irrespective of the initial state of the charger. Finally, we show that the observed advantage does not originate from multipartite entanglement within the battery subsystem and is therefore classical in nature.

quant-ph↗

arXiv2024

Quantum criticality and universality in stationary state of long-range Kitaev model

We investigate the signature of quantum criticality in the long-time stationary state of the long-range Kitaev chain by performing various quench protocols. In this model, the pairing interaction decays with distance according to a power law with exponent $\alpha$. Using quantum information-theoretic measures, such as mutual information and logarithmic negativity, we show that, irrespective of the values of $\alpha$, critical-to-critical quench displays quantum criticality even in the stationary state. Remarkably, in the presence of long-range pairing interactions, where fermionic correlators decay algebraically even at non-critical points, signature of quantum criticality persists in the stationary state. Furthermore, the effective central charge, calculated from both mutual information and logarithmic negativity of stationary state following a critical-to-critical quench, agrees with the central charge of the corresponding ground states for both $\alpha = 0$ and $\alpha = 2$. Therefore, information of the universality class can be inferred from the stationary state.

quant-ph↗

arXiv2024

Bound energy, entanglement and identifying critical points in 1D long-range Kitaev model

We investigate the entanglement structure of a bipartite quantum system through the lens of quantum thermodynamics in the absence of conformal symmetry. Specifically, we consider the long-range Kitaev model, where the pairing interaction decays as a power law with exponent $\alpha$, with broken conformal symmetry for $\alpha<3/2$. We analytically show that the bound energy, a quantum thermodynamical quantity, is linearly proportional to the square of entanglement entropy per unit system size for $\alpha=1$ where conformal symmetry is broken. We further show that for all values of $\alpha$, bound energy, in the thermodynamic limit, shows a pronounced minimum at the critical point, which enables the identification of $\mu=1$.

cond-mat.str-el↗

arXiv2024

Sunburst quantum Ising battery

We study the energy transfer process in the recently proposed sunburst quantum Ising model, which consists of two interacting integrable systems: a transverse Ising chain with a very small transverse field and a finite number of external isolated qubits. We show that in this model of the quantum battery, coupling between the battery and charger can be used to optimize the ergotropy, which is the maximum amount of energy that can be extracted from the battery. At the same time, maximum charging power increases with the coupling strength, allowing for the simultaneous optimization of both ergotropy and charging power in the strong coupling limit. Furthermore, we show that both ergotropy and charging power are independent of the initial state of the charger.

quant-ph↗

arXiv2022

Sunburst quantum Ising model under interaction quench: entanglement and role of initial state coherence

We study the non-equilibrium dynamics of an isolated bipartite quantum system, the sunburst quantum Ising model, under interaction quench. The pre-quench limit of this model is two non-interacting integrable systems, namely a transverse ising chain and finite number of isolated qubits. As a function of interaction strength, the spectral fluctuation property goes from Poisson to Wigner-Dyson statistics. We chose entanglement entropy as a probe to study the approach to thermalization or lack of it in post-quench dynamics. In the near-integrable limit, as expected, the linear entropy displays oscillatory behavior while in the chaotic limit, it saturates. Along with the chaotic nature of the time evolution generator, we show the importance of the role played by the coherence of the initial state in deciding the nature of thermalization. We further show that these findings are general by replacing the Ising ring with a disordered $XXZ$ model with disorder strength putting it in the many-body localized phase.

quant-ph↗