arXiv subjects

Riddhi Chatterjee

Publications and source records attributed to Riddhi Chatterjee.

7 recordsLinked to original sources

arXiv2025

Quantum Speed Limit and Optimal Evolution Time in Driven-dissipative Systems

Quantum Speed Limit (QSL) is a lower bound on the evolution time $T_{\rm QSL}$ of a closed quantum system to evolve from one state to another, as shown by Mandelstam and Tamm. For a driving Hamiltonian enforcing the evolution, the time-energy uncertainty relations for the drive play the dominant role in setting the bound. On the other hand, dissipative systems can also suffer from drive-induced dissipation (DID). In this work, we ask how DID modifies the attainability of the QSL in open quantum systems and whether the time-energy uncertainty relation remains the dominating factor. For open quantum systems that suffer from DID, we report a finite optimal evolution time $T_{\rm DID} \; (> T_{\rm QSL})$ for constant-amplitude driving. We show that the competition between DID at short times and environmental dissipation at long times produces a non-monotonic dependence of fidelity on the evolution time. When the drive waveform is shaped using quantum optimal control (QOC), an intermediate attainable evolution time $T_{\rm QOC}$ provides the maximum fidelity. Our results therefore suggest that, in driven-dissipative systems, the conventional QSL lower bound should be complemented by a finite-time attainability window determined by dissipation, with $T_{\rm QSL} \le T_{\rm QOC} \le T_{\rm DID}$ for the cases studied here. Further, we show that the optimized control protocol is robust against detuning and variations in environmental parameters, enabling reliable quantum control in open systems and providing a practical route toward high-fidelity state transfer in two-level quantum systems.

quant-ph↗

arXiv2024

Accelerated first detection in discrete-time quantum walks using sharp restarts

Restart is a common strategy observed in nature that accelerates first-passage processes and has been extensively studied using classical random walks. In the quantum regime, restart in continuous-time quantum walks (CTQWs) has been shown to expedite the quantum hitting times. Here, we study how restarting monitored discrete-time quantum walks (DTQWs) affects the quantum hitting times. We show that the restarted DTQWs outperform classical random walks in target searches, benefiting from quantum ballistic propagation, a feature shared with their continuous-time counterparts. Moreover, the explicit coin degree of freedom in DTQWs allows them to surpass even CTQWs in target detection without sacrificing any quantum advantage. Additionally, knowledge of the target's parity or position relative to the origin can be leveraged to tailor DTQWs for even faster searches. Our study paves the way for more efficient use of DTQWs in quantum-walk-based search algorithms, simulations and modeling of quantum transport towards targeted sites in complex quantum networks.

quant-ph↗

arXiv2023

Rehabilitation Exercise Repetition Segmentation and Counting using Skeletal Body Joints

Physical exercise is an essential component of rehabilitation programs that improve quality of life and reduce mortality and re-hospitalization rates. In AI-driven virtual rehabilitation programs, patients complete their exercises independently at home, while AI algorithms analyze the exercise data to provide feedback to patients and report their progress to clinicians. To analyze exercise data, the first step is to segment it into consecutive repetitions. There has been a significant amount of research performed on segmenting and counting the repetitive activities of healthy individuals using raw video data, which raises concerns regarding privacy and is computationally intensive. Previous research on patients' rehabilitation exercise segmentation relied on data collected by multiple wearable sensors, which are difficult to use at home by rehabilitation patients. Compared to healthy individuals, segmenting and counting exercise repetitions in patients is more challenging because of the irregular repetition duration and the variation between repetitions. This paper presents a novel approach for segmenting and counting the repetitions of rehabilitation exercises performed by patients, based on their skeletal body joints. Skeletal body joints can be acquired through depth cameras or computer vision techniques applied to RGB videos of patients. Various sequential neural networks are designed to analyze the sequences of skeletal body joints and perform repetition segmentation and counting. Extensive experiments on three publicly available rehabilitation exercise datasets, KIMORE, UI-PRMD, and IntelliRehabDS, demonstrate the superiority of the proposed method compared to previous methods. The proposed method enables accurate exercise analysis while preserving privacy, facilitating the effective delivery of virtual rehabilitation programs.

cs.CV↗

arXiv2022

Bell's inequality violation by dynamical Casimir photons in a superconducting microwave circuit

We study the Bell's inequality violation by dynamical Casimir radiation with pseudospin measurement. We consider a circuit quantum electrodynamical set-up where a relativistically moving mirror is simulated by variable external magnetic flux in a SQUID terminating a superconducting-microwave waveguide. We analytically obtain expectation values of the Bell operator optimized with respect to channel orientations, in terms of the system parameters. We consider the effects of local noise in the microwave field modes, asymmetry between the field modes resulting from nonzero detuning, and signal loss. Our analysis provides ranges of the above experimental parameters for which Bell violation can be observed. We show that Bell violation can be observed in this set-up up to 40 mK temperature as well as up to 65 % signal loss.

quant-ph↗

arXiv2021

Violation of equivalence in an accelerating atom-mirror system in the generalized uncertainty principle framework

We study the spontaneous excitation of a two-level atom in the presence of a perfectly reflecting mirror, when the atom, or the mirror, is uniformly accelerating in the framework of the generalised uncertainty principle (GUP). The quantized scalar field obeys a modified dispersion relation leading to a GUP deformed Klein-Gordon equation. The solutions of this equation with suitable boundary conditions are obtained to calculate the spontaneous excitation probability of the atom for the two separate cases. We show that in the case when the mirror is accelerating, the GUP modulates the spatial oscillation of the excitation probability of the atom, thus breaking the symmetry between the excitation of an atom accelerating relative to a stationary mirror, and a stationary atom excited by an accelerating mirror. An explicit violation of the equivalence principle seems to be thus manifested. We further obtain an upper bound on the GUP parameter using standard values of the system parameters.

quant-ph↗

arXiv2020

Resonance interaction of two entangled atoms accelerating between two mirrors

We study the resonance interaction between two entangled identical atoms coupled to a quantized scalar field vacuum, and accelerating between two mirrors. We show how radiative processes of the two-atom entangled state can be manipulated by the atomic configuration undergoing noninertial motion. Incorporating the Heisenberg picture with symmetric operator ordering, the vacuum fluctuation and the self-reaction contributions are distinguished. We evaluate the resonance energy shift and the relaxation rate of energy of the two atom system from the self-reaction contribution in the Heisenberg equation of motion. We investigate the variation of these two quantities with relevant parameters such as atomic acceleration, interatomic distance and position with respect to the boundaries. We show that both the energy level shift and the relaxation rate can be controlled by tuning the above parameters.

quant-ph↗

arXiv2017

Preservation of quantum coherence under Lorentz boost for narrow uncertainty wave packets

We consider the effect of relativistic boosts on single particle Gaussian wave packets. The coherence of the wave function as measured by the boosted observer is studied as a function of the momentum and the boost parameter. Using various formulations of coherence it is shown that in general the coherence decays with the increase of the momentum of the state, as well as the boost applied to it. Employing a basis-independent formulation, we show however, that coherence may be preserved even for large boosts applied on narrow uncertainty wave packets. Our result is exemplified quantitatively for practically realizable neutron wave functions.

quant-ph↗