arXiv subjects

Souvik Agasti

Publications and source records attributed to Souvik Agasti.

14 recordsLinked to original sources

arXiv2026

Dark-Mode Control of Contrasting Entanglement and Bell Nonlocality between Mechanical Oscillators

This study presents a detailed proposal for an optomechanical system consisting of two mechanical oscillators coupled to a common cavity, aimed at generating pure and entangled two-mode squeezed mechanical steady states. We found that the violation of Bell's measurement may not occur where the entanglement is maximum; rather, nonlocality can be observed for lower entangled states. A central result is that optomechanical coupling imperfections can enhance mechanical entanglement while simultaneously suppressing Bell nonlocality by reducing the purity of the mechanical state. To mitigate this trade-off, we introduce phase-dependent phonon hopping between the mechanical oscillators and show that Bell nonlocality can be selectively enhanced in specific dark-mode configurations, even when the overall entanglement is reduced. We trace this contrasting behaviorto changes in state purity associated with the imbalance of the Bogoliubov-mode occupations. Compatible with existing microwave cavity optomechanical platforms, the proposed architecture provides an experimentally accessible route for controlling nonlocal quantum correlations in multimode mechanical systems. Our proposed scheme serves as an attractive platform for the deployment of continuous-variable teleportation and high-fidelity quantum communication.

quant-ph↗

arXiv2026

Bell Nonlocality Test on Two-Mode Squeezed Output Generated in Double-Cavity Optomechanical

We explore here how to generate a two-mode squeezed output using reservoir engineering in a double-cavity optomechanical system coupled to a common mechanical resonator. Such hybrid platforms are experimentally accessible in electro-optomechanical interfaces and are relevant for high-fidelity state transfer, quantum communication, and metrological applications. By examining violations of the CHSH Bell inequality, we demonstrate that maximal squeezing does not necessarily imply nonlocality; instead, nonlocal correlations can emerge in states with lower squeezing. Furthermore, by analyzing the CHSH inequality across different cavity finesse values, we find that the parameter region supporting nonlocality can broaden even as the squeezing region shrinks. Across all regimes considered, our results emphasize the crucial influence of the mixedness of the state in determining the relationship between squeezing and nonlocality.

quant-ph↗

arXiv2025

All non-locally Realized Continuous Variable Bipartite Gaussian States are Entangled

We investigate the connection between entanglement and non-locality between continuous-variable bipartite Gaussian states. The investigation initiates with formulating non-locality by using the phase-space Wigner representation of Bell's function. Furthermore, our analysis shows entanglement to be necessary for nonlocality, but not sufficient for it; however, nonlocality is sufficient to ensure entanglement.

quant-ph↗

arXiv2024

Thermalization Dynamics of Entanglement and non-Locality of Filtered Two-Mode Squeezed States

We explore how entanglement and non-locality evolve between specific spectral components of two-mode squeezed states in thermal environments. These spectral components are extracted from output modes using filters that are frequently utilized in optomechanical systems. We consider two distinct thermalization scenarios: one occurring in the vacuum state prior to entering the nonlinear crystal for squeezing, and another after the generation of the two-mode squeezed vacuum but before passing through filters and detectors. Entanglement and non-locality generally remain at their peak when identical filters are applied throughout. In the first scenario, higher initial squeezing levels cause the dissipation of entanglement to begin slower, then accelerate over time, while the dissipation rate of non-locality moreover stays consistent. In the second scenario, greater squeezing results in a more rapid loss of both entanglement and non-locality. We identify the evolution of specific boundaries for entanglement and non-locality and the conditions for their optimization. Finally, for all the cases, increasing the thermal population of the environment enhances the rate of dissipation, whereas stronger interaction slows dissipation in a normalized dimensionless time scale

quant-ph↗

arXiv2024

Synthetic magnetism enhanced mechanical squeezing in Brillouin optomechanical system

We propose a scheme to generate large amount of mechanical squeezing, far beyond the $\rm{3dB}$ limit, which is based on synthetic magnetism in optomechanical system that hosts a Backward Stimulated Brillouin Scattering (BSBS) process. Our benchmark system consists of an acoustic mode coupled to two optical modes through the BSBS process, and a Duffing mechanical oscillator that couples to the same optical modes through the standard optomechanical radiation pressure. The synthetic magnetism comes from the modulation of the mechanical coupling between the acoustic and the mechanical mode. When there is no synthetic magnetism, a given amount of mechanical squeezing is generated in the system. This squeezing is mainly dependent on the BSBS process, and it is fragile against thermal noise. By switching on the synthetic magnetism, the degree of the generated squeezing is greatly enhanced and goes far beyond the limit of the $\rm{3dB}$. This large magnetism induced squeezing persists even when there is no BSBS process in the system. Moreover, this generated squeezing is robust enough against thermal noise in comparison to the one induced when the synthetic magnetism is off. Furthermore, both the mechanical variance squeezing and effective phonon number exhibit series of peaks and dips depending on the phase modulation of the mechanical coupling. This oscillatory feature is reminiscent of a sudden death and revival of squeezing phenomenon, which can be used to maintain a desired magnitude of squeezing by tuning this phase. Our proposal provides a path toward a flexible scheme that generates large amount of squeezing, far beyond the $\rm{3dB}$ limit. Such a generated squeezed states can be used for quantum applications including quantum information processing, quantum sensing and metrology, and quantum computing.

quant-ph↗

arXiv2024

Entanglement, Squeezing and non-Locality in Filtered Two-Mode Squeezed Mixed States

We investigate the entanglement and non-locality between specific spectral components of continuous variable two-mode squeezed mixed states, identifying their limits. These spectral components are selected from output modes using filters commonly employed in optomechanical systems. Both entanglement and non-locality reach their peak when the filters are identical. However, increasing the degree of input squeezing while applying non-identical filters disrupts both entanglement and non-locality, leading to a bell-shaped pattern. Additionally, we provide precise boundaries for entanglement and non-locality. Furthermore, we also evaluate the squeezing of two-mode hybrid quadrature as a measure of entanglement, thereby demonstrating how it remains analogous to logarithmic negativity. Combined with the filter, the population of two-mode squeezed thermal light influences the angle of a maximally squeezed hybrid quadrature.

quant-ph↗

arXiv2024

Simulation of Matrix Product States to Unveil the Initial State Dependency of non-Gaussian Dynamics of Kerr Nonlinearity

We simulate a free dissipative and coherent-driven Kerr nonlinear system using a time-evolving block decimation (TEBD) algorithm, to study the impact of the initial state on the exact quantum dynamics of the system. The superposition of two coherent branches results in non-classical time dynamics. The Wigner state representation confirms that the system ends up saturating to two different branches, through evolving different trajectories, resulting in de-Gaussification throughout evolution. Furthermore, we also see that the time evolution suffers a residual effect of the initial state.

quant-ph↗

arXiv2023

Bistability-assisted Mechanical Squeezing and Entanglement

We propose a scheme to squeeze mechanical motion and to entangle optical field with mechanical motion in an optomechanical system containing a parametric amplification. The scheme is based on optical bistability which emerges in the system for a strong enough driving field. By considering the steady state's lower branch of the bistability, the system shows weak entanglement and almost no mechanical squeezing. When the steady state is on the upper branch of the bistable shape, both squeezing and entanglement are greatly enhanced. Specifically, the entanglement shows three degrees of magnitude enhancement. However, this giant entanglement is fragile against decoherence and thermal fluctuation. Regarding the mechanical squeezing, it reaches the standard quantum limit (SQL) in the upper branch of the bistability. Our proposal provides a way to improve quantum effects in optomechanical systems by taking advantage of nonlinearities. This scheme can be realized in similar systems such as superconducting microwave, and hybrid optomechanical systems.

quant-ph↗

arXiv2023

Simulation of Kerr Nonlinearity: Revealing Initial State Dependency

We simulate coherent driven free dissipative Kerr nonlinear system numerically using time evolving block decimation (TEBD) algorithm and time propagation on the Heisenberg equation of motion using Eulers method to study how the numerical results are analogous to classical bistability. The system evolves through different trajectories to stabilize different branches for different external drives and initial conditions. The Wigner state reprentation confirms the system to suffer a residual effect of initial state throughout the non-classical dynamical evolution and the steady state of the system. Furthermore, we also see the numerically simulated spectral density remains significantly different from analytical counterparts when initial states do not lie to the same branch of the final state.

quant-ph↗

arXiv2023

Back-Action Evading Measurement in Gravitational Wave Detectors to Overcome Standard Quantum Limit, Using Negative Radiation Pressure

Aiming at application for gravitational wave (GW) detection, we propose a novel scheme how to obtain quantum back action evading measurements performed on an opto-mechanical cavity, by introducing a negative radiation pressure coupling between the cavity field and the end mirror. The scheme consists of introducing a double cavity with end mirrors interlocked by a pivot and moving in opposite directions. The measurement is performed by sending a two-mode squeezed vacuum to both cavities and detecting the output through the heterodyne detection. Compared to the previously proposed hybrid negative mass spin-optomechanical system in Phys. Rev. Lett. 121, 031101 (2018), we see that our scheme is capable to suppress back action noise by nearly two orders of magnitude more in the lower frequency region. Overall, the setup has been able to squeeze the output noise below the standard quantum limit, with more efficiency. In addition, the scheme has also proven to be beneficial for reducing thermal noise by a significant amount. We confirm our result by a numerical analysis and compared it with the previous proposal Phys. Rev. Lett. 121, 031101 (2018).

quant-ph↗

arXiv2021

Entanglement Limits in Hybrid Spin-Mechanical Systems

We investigate how to generate continuous-variable entanglement between distant optomechanical and spin systems, by transferring input two-mode squeezed vacuum state to the system. Such a setup has been proposed for backaction evading gravitational-wave measurement, squeezing the output noise below the standard quantum limit. We find that the spin cavity entanglement saturates to a particular value when no mechanics are involved even though the entanglement of the input beam increases steadily, and drops down when the mechanical oscillator interacts with the cavity. Our study also reveals that the spin optical readout rate enables the robustness of the spin-cavity entanglement with input squeezing whereas the optomechanical coupling strength disables it. The entanglement reaches its maximum when the effective resonance frequency and bandwidth of the cavity match the spin system. Determining collective quadrature fluctuations, our analysis also shows that even though the entanglement between spin and cavity, and cavity and mechanics is significantly present; it is still impossible to obtain entanglement between spin and mechanical oscillator.

quant-ph↗

arXiv2020

Spectral Index of OAM-Carrying Ultrafast Localized Pulses

We investigate the spectral degree of freedom of OAM-carrying localized waves, and its influence on their transverse intensity distribution. In particular, we focus our attention on two different families of spectra, namely exponentially decaying spectra, which are very tightly connected to fundamental X-waves, and Bessel-modulated spectra. For each class we show how it is possible, by suitable manipulating their spectrum, to structure their transverse intensity distribution, thus creating a radial structure similar to that of Laguerre-Gaussian beams. To complete our analysis, we investigate the impact of the two spectral functions on linear and angular momentum of such localized waves.

physics.optics↗

arXiv2017

Nonlinear quantum Langevin equations for bosonic modes in solid-state systems

Based on the experimental evidence that impurities contribute to the dissipation properties of solid-state open quantum systems, we provide here a description in terms of nonlinear quantum Langevin equations of the role played by two-level systems in the dynamics of a bosonic degree of freedom. Our starting point is represented by the description of the system/environment coupling in terms of coupling to two separate reservoirs, modelling the interaction with external bosonic modes and two level systems, respectively. Furthermore, we show how this model represents a specific example of a class of open quantum systems that can be described by nonlinear quantum Langevin equations. Our analysis offers a potential explanation of the parametric effects recently observed in circuit-QED cavity optomechanics experiments.

quant-ph↗

arXiv2017

Structural and Optical Properties of Pulse Laser Deposited Ag_2O Thin Films

We deposited Ag_2O films in PLD system on glass substrate for a fixed partial oxygen gas pressure (70 mili Torr) with the variation of laser energy from 75 to 215 mJ/Pulse. The XRD patterns confirm that the films have well crystallinity and deposited as hexagonal lattice and the crystalline size increases from 26.38 nm to 27.27 nm. The FESEM images show that the particle size of the films increases from 34.84 nm to 65.83 nm. The composition of the films is analyzed from EDX spectra which show that the percentage of oxygen increases from 41.03% to 48.38% with the increment of laser energy. From the optical characterization, it is observed that the optical band gap appears in the visible optical range in an increasing order from 0.87 to 0.98 eV with the increment of laser energy. Our analysis concludes that the Ag_2O thin films, deposited with these parameters, can be considered as a good absorbent layer for solar photovoltaic application.

physics.chem-ph↗