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Subhashish Banerjee

Publications and source records attributed to Subhashish Banerjee.

At least 37 records · Page 2Linked to original sources

Supervised Machine Learning for Predicting Open Quantum System Dynamics and Detecting Non-Markovian Memory Effects

We present a \emph{novel} and scalable supervised machine learning framework to predict open-quantum system dynamics and detect non-Markovian memory using only local ancilla measurements. A system qubit is coherently coupled to an ancilla via a symmetric XY Hamiltonian; the ancilla interacts with a noisy environment and is the only qubit we measure. A feedforward neural network, trained on short sliding windows of supplementary data from the past, forecasts the observable system $\langle Z_{(S)}(t)\rangle$ without state tomography or knowledge of the bath. To quantify memory, we introduce a normalized revival-based metric that counts upward 'turn-backs' in \emph{predicted} $\langle Z_{(S)}(t)\rangle$ and reports the fraction of evaluated samples that exceeds a small threshold. This bounded score provides an interpretable, model-independent indicator of non-Markovianity. We demonstrate the method on two representative noise channels, non-unital amplitude damping and unital dephasing from random telegraph noise (RTN). Under matched conditions, the model accurately reproduces the dynamics and flags memory effects, with RTN exhibiting a larger normalized revival score than amplitude damping. Overall, the approach is experimentally realistic and readily extensible, enabling real-time, interpretable non-Markovian diagnostics from accessible local measurements.

quant-ph↗

Satellite-based communication for phase-matching measurement-device-independent quantum key distribution

This study investigates the feasibility of the phase-matching measurement-device-independent quantum key distribution (PM-MDI QKD) protocol proposed by Lin and Lütkenhaus for satellite-based quantum communication. The protocol's key rate, known to exceed the repeaterless bound, is evaluated in the asymptotic limit under noisy conditions typical of satellite communications, including loss-only scenarios. The setup involves two ground-based parties connected via fiber (lossonly or noisy) and a space-based third party linked to one of these two ground-based parties through free-space communication. Simulations using the elliptic-beam approximation model the average key rate (AKR) and its probability distribution (PDR) across varying zenith angles and fiber distances. Down-link free-space communication is assessed under day and night conditions, with intensity optimization for each graphical point. Dynamic configurations of satellite and ground stations are also considered. Results indicate that AKR decays more slowly under loss-only conditions, while PDR analysis shows higher key rates produce more concentrated distributions. These findings demonstrate the potential of PM-MDI QKD protocols for achieving reliable key rates in satellitebased quantum communication.

quant-ph↗

Quantum spread complexity as a probe of NSI, $CP$ Violation, and mass ordering in neutrino oscillations in matter

Quantum spread complexity characterizes how a quantum state evolves and becomes distributed over the Hilbert space under unitary dynamics. In this work, we employ a cost function as a quantitative measure of spread complexity. We investigate this cost function within the framework of three-flavor neutrino oscillations in vacuum and matter, incorporating the $CP$-violation phase and Non-Standard Interaction (NSI) effects, under both normal and inverted mass ordering scenarios. The cost function is evaluated for each scenario and analyzed with the corresponding neutrino transition probabilities for both initial muon neutrino and muon antineutrino flavor states. The results are presented using the energy where the first oscillation is maximum and baseline lengths of ongoing long-baseline accelerator neutrino experiments, including T2K and NOvA, as well as upcoming experiments such as DUNE and P2O. Our findings indicate that the difference in the cost function between normal and inverted mass orderings during neutrino propagation in matter is sensitive to these experiments, with the appropriate choice of NSI parameters and the best-fit $CP$-violation phase values.

hep-ph↗

Quantum Thermodynamics of Open Quantum Systems: Nature of Thermal Fluctuations

We investigate the thermodynamic behavior of open quantum systems through the Hamiltonian of Mean Force, focusing on two models: a two-qubit system interacting with a thermal bath and a Jaynes-Cummings Model without the rotating wave approximation. By analyzing both weak and strong coupling regimes, we uncover the impact of environmental interactions on quantum thermodynamic quantities, including specific heat capacity, internal energy, and entropy. Further, the ergotropy and entropy production are computed. We also explore the energy-temperature uncertainty relation, which sets an upper bound on the signal-to-noise ratio.

quant-ph↗

Probing the quantum speed limit and entanglement in flavor oscillations of neutrino-antineutrino system in curved spacetime

We consider a spinning primordial black hole (PBH) described by the Kerr metric in Kerr-Schild polar coordinates. We derive an analytical expression for the four-vector gravitational potential in the underlying Hermitian Dirac Hamiltonian using these coordinates. This gravitational potential introduces an axial vector term in the Dirac equation in curved spacetime. We find that the magnitudes of the temporal and spatial components of the four-vector gravitational potential are significantly affected by the angle of the position vector of the spinor with respect to the spin axis of the PBH, its radial distance from the PBH, and the strength of the specific angular momentum of the PBH. These potentials modify the effective mass matrix of the neutrino-antineutrino system and significantly affect the transition probabilities during the flavor oscillation of the neutrino-antineutrino system. We then use the transition probability to investigate the quantum speed limit time bound ratio for the two-flavor oscillation of the neutrino-antineutrino system in curved spacetime. This helps us estimate how quickly the initial neutrino flavor state evolves over time under the influence of the gravitational field. Finally, we discuss quantum correlations such as entanglement entropy during the two-flavor oscillation of the neutrino-antineutrino system near a spinning PBH.

gr-qc↗

Probing $CP$ violation and mass ordering in neutrino oscillations in matter through quantum speed limits

The quantum speed limits (QSLs) set fundamental lower bounds on the time required for a quantum system to evolve from a given initial state to a final state. In this work, we investigate $CP$ violation and the mass ordering problem of neutrino oscillations in matter using the QSL time as a key analytical tool. We examine the QSL time for the unitary evolution of two- and three-flavor neutrino states, both in vacuum and in the presence of matter. Two-flavor neutrino oscillations are used as a precursor to their three-flavor counterparts. We further compute the QSL time for neutrino state evolution and entanglement in terms of neutrino survival and oscillation probabilities, which are experimentally measurable quantities in neutrino experiments. A difference in the QSL time between the normal and inverted mass ordering scenarios, for neutrino state evolution as well as for entanglement, under the effect of a $CP$ violation phase is observed. Our results are illustrated using the length scales and energies of ongoing long-baseline accelerator neutrino experiments such as T2K, NOvA, and the upcoming DUNE experiment. Notably, three-flavor neutrino oscillations in constant matter density exhibit faster state evolution across all these neutrino experiments in the normal mass ordering scenario. Additionally, we observe fast entanglement suppression in DUNE assuming a normal mass ordering.

hep-ph↗

Strong coupling non-Markovian quantum thermodynamics of a finite-bath system

The focus is on understanding the quantum thermodynamics of strongly coupled non-Markovian quantum systems. To this end, a non-trivial, non-Markovian model of a central spin surrounded by a spin bath is taken up, and its exact evolution is derived for arbitrary system-bath couplings. The fundamental quantum thermodynamic quantities, such as system and bath internal energies, work, heat, entropy production, and ergotropy, are calculated using the dynamics and original system (bath) Hamiltonian. An explicit expression for the work, a mismatch between the system and bath internal energies, is derived. The thermodynamic entropy of the system at thermal equilibrium is studied using the Hamiltonian of mean force in the strong coupling regime. The role of a canonical Hamiltonian in calculating the above thermodynamic quantities, a recently developed technique, is also investigated. Further, an interesting observation relevant to the spin bath acting as a charger is made in a scenario where the central spin is envisaged as a quantum battery.

quant-ph↗

Quantum Thermal Analogs of Electric Circuits: A Universal Approach

In this work, we develop a panoramic schematic of quantum thermal analogs of electric circuits in the steady state regime. We establish the foundations of said premise by defining the analogs of Kirchhoff's laws for heat currents and temperature gradients, as well as a quantum thermal step transformer. Using this, we develop two novel quantum thermal circuits, viz., quantum thermal super Wheatstone bridge and quantum thermal adder circuit, paving the way for the corresponding integrated circuits. We further show that our approach encompasses various circuits like thermal diode, transistor, and Wheatstone bridge. This sheds new light on the present architecture of quantum device engineering.

quant-ph↗

Two and three-state quantum heat engines with stochastic resetting

Quantum heat engines have undergone extensive studies over the last two decades. Simultaneously, the studies of the applications of stochastic resetting in various fields are on the rise. We explore the effect of stochastic resetting on the dynamics of a two-level and a three-level quantum heat engine. The extracted work is shown to increase with the resetting rate. The effective efficiency that takes into account the work done due to resetting remains constant. However, if the work done due to resetting is ignored, then the system can incorrectly imply a different behaviour, including the false inference that it is not working as an engine at all. The efficient power is observed to increase beyond that obtained in the absence of resetting, and is shown to be higher for a three-level engine.

cond-mat.stat-mech↗

Non-classicality of two-qubit quantum collision model: non-Markovian effects

We investigate a two-qubit quantum system in contact with an environment modeled by a microscopic collision model with added ancilla-ancilla collisions in the non-Markovian regime. Two schemes of the two-qubit collision model with carried-forward correlations are introduced. In one scheme, a single stream of ancillae interacts with only one of the qubits of the two-qubit system; in the other, both the qubits interact with two independent sequences of ancillae, which could be at the same or different temperatures. The system's non-Markovian evolution is examined using the trace distance measure, and the non-classicality of the system is studied using the Wigner function, non-classical volume, and concurrence. Also, interesting steady-state behavior is observed when both the independent ancillae are kept at the same temperature.

quant-ph↗

Non-Markovianity in Discrete-Time Open Quantum Random Walk on Arbitrary Graphs

In this work, we present a new model of the Discrete-Time Open Quantum Walk (DTOQW) applicable to an arbitrary graph, thereby going beyond the case of quantum walks on regular graphs. We study the impact of noise in the dynamics of quantum walk by applying Kraus operators of different dimensions which are constructed using the Weyl operators. The DTOQW employs these Kraus operators as its coin operators. The walker dynamics are studied under the impact of non-Markovian amplitude damping, dephasing and depolarizing noise channels. We also implement the walk on various graphs, including path graphs, cycle graphs, star graphs, complete graphs, complete bipartite graphs, etc. We gauge the dynamics by computing coherence and fidelity at different time steps, taking into account the influence of noise. Furthermore, we compute the probability distribution at different time steps for the above noises, which represents the availability of the quantum walker at different vertices of the graph.

quant-ph↗

Realizing Negative Quantum States with the IBM Quantum Hardware

This study explores robust entangled states described using the framework of discrete Wigner functions. Notably, these states are known to outperform the Bell state in measures of entanglement in the presence of non-Markovian noise. Our study focuses on methods for preparing these states using quantum circuits that can be implemented on superconducting hardware and testing the efficacy of these methods on IBM's quantum device. We present quantum circuits for state preparation and validate them through tomographic reconstruction on the IBM \emph{ibm\_brisbane} device. We propose a teleportation scheme that leverages these entangled states as a resource. We believe that these entangled states have the potential to be used in place of the traditional Bell state in scenarios where non-Markovian errors are prevalent.

quant-ph↗

Finite and Asymptotic Key Analysis for CubeSat-Based BB84 QKD with Elliptical Beam Approximation

Satellite and CubeSat-based quantum key distribution (QKD) presents a promising solution for secure long-distance communication by transmitting quantum keys through free space, with CubeSats offering a compact, cost-effective, and scalable platform for deployment. This study investigates the performance of statistical techniques used to compute the finite-block and single-pass secret key lengths (SKL) for weak coherent pulse (WCP)-based efficient BB84 and standard decoy-state BB84 protocols in CubeSat-based systems. An asymptotic key rate analysis is also conducted for both protocols, providing deeper insights into their theoretical performance within the CubeSat context. The channel transmittance is modeled using an elliptical beam approximation, and the key rate performance is evaluated under varying weather conditions for the downlink scenario. The results demonstrate that the efficient BB84 protocol consistently outperforms the standard version across different atmospheric conditions. Furthermore, the probability distribution of key rates (PDR) for both implementations is analyzed, offering a comprehensive evaluation of their practical effectiveness in CubeSat-based QKD applications.

quant-ph↗

Husimi phase distribution in non-Gaussian operations

The Husimi phase distribution, an experimentally measurable quantity, is investigated for single-mode and two-mode squeezed vacuum states. The analysis highlights that non-Gaussian operations, i.e., photon subtraction (PS), photon addition (PA) and photon catalysis (PC), are effective tools for localizing phase distribution and enhancing phase robustness in the presence of noise, while PC enhances phase sensitivity but leads to greater delocalization. The work highlights the perspective that combined effects of squeezing, beam splitter transmittance, and environmental interactions must be carefully considered when quantum state engineering protocols are designed and phase properties provide a valuable insight into this endeavour.

quant-ph↗

Exploring the Non-Markovian Dynamics in Depolarizing Maps

The non-Markovian depolarizing channel is explored from the perspective of understanding its non-Markovian behavior as well as the occurrence of singularities. The study brings together the various ways to identify and quantify non-Markovianity. This includes dynamical techniques such as quantum information backflow witness, Breuer-Laine-Piilo, Rivas-Huelga-Plenio and Hall- Cresser-Li-Andersson measures. In addition, geometrical visualization of non-Markovian effects is presented using the variation in the volume of accessible states during dynamical evolution. Further, a trajectory-based visualization of the dynamical map within the parameter space is presented. The trajectories traced during evolution demonstrate the loss of CP divisibility and the emergence of non-Markovianity under systematic variations of the system parameters. The effects of increasing system dimensions and qubit numbers on singularity and non-Markovianity are presented, with an extension of characterization techniques to higher-dimensional systems.

quant-ph↗

Quantum speed limit and nonclassicality in open quantum system models using the Wigner function

The quantum speed limit and the Wigner function of open system models are studied. To this end, we use the phase covariant and a two-qubit model interacting with a squeezed thermal bath via position-dependent coupling. The dependence of the coupling on the position of the qubits allows for the study of the dynamics in the collective regime, which is conducive to speeding up the evolution. An interesting interplay is observed between non-Markovian behavior, quantumness, and the quantum speed limit. The presence of quantum correlations is seen to speed up the evolution.

quant-ph↗

Dynamics of Quantum Coherence and Non-Classical Correlations in Open Quantum System Coupled to a Squeezed Thermal Bath

We investigate the intricate dynamics of quantum coherence and non-classical correlations in a two-qubit open quantum system coupled to a squeezed thermal reservoir. By exploring the correlations between spatially separated qubits, we unravel the complex interplay between quantum correlations and decoherence induced by the reservoir. Our findings demonstrate that non-classical correlations such as quantum consonance, quantum discord, local quantum uncertainty, and quantum Fisher information are highly sensitive to the collective regime. These insights identify key parameters for optimizing quantum metrology and parameter estimation in systems exposed to environmental interactions. Furthermore, we quantify these quantum correlations in the context of practical applications such as quantum teleportation, using the two metrics viz. maximal teleportation fidelity and fidelity deviation. This work bridges theoretical advancements with real-world applications, offering a comprehensive framework for leveraging quantum resources under the influence of environmental decoherence.

quant-ph↗

Quantum Correlations in Neutrino and Neutral Meson Oscillations

We discuss the impact of ideas of open quantum systems and quantum information to various facets of neutrino and neutral meson oscillations. These oscillations are characterized by a number of quantum correlations, both spatial as well as temporal. For neutrinos, the correlations are shown to be simple functions of the product of neutrino survival and oscillation probabilities. The quantum correlations in the neutral mesons are seen to be non-trivially different from their stable counterparts.

hep-ph↗