arXiv subjects

Shah Fahad

Publications and source records attributed to Shah Fahad.

7 recordsLinked to original sources

arXiv2026

Nonreciprocal Control of the Goos--H\"{a}nchen Shift via the Barnett Effect in Cavity Magnomechanics

We propose a theoretical scheme for realizing a tunable nonreciprocal Goos-H\"{a}nchen shift (GHS) in a hybrid cavity magnomechanical system. The setup consists of a rotating yttrium iron garnet sphere embedded in a microwave cavity, with magnetic-dipole and magnetostrictive interactions mediating magnon-photon and magnon-phonon couplings, respectively. Owing to the Barnett effect, the magnon frequency acquires a rotation-induced shift whose sign can be reversed by changing the direction of the bias magnetic field. We show that the output probe spectrum exhibits a Fano resonance, while the associated GHS responds asymmetrically to opposite field directions, providing a controllable mechanism for nonreciprocal beam shifts. The magnon-photon and magnon-phonon interactions are found to affect the GHS in opposite ways, while the cavity length offers an additional degree of tunability. These results provide a route toward magnetically reconfigurable microwave photonic devices and sensitive detection of Barnett-induced effective fields.

cond-mat.other↗

arXiv2026

Goos-Hänchen Shift in $\mathcal{PT}$-Symmetric and Passive Cavity Optomechanical Systems

We theoretically investigate the control of the Goos-Hänchen shift (GHS) of a reflected weak probe field in both parity-time ($\mathcal{PT}$)-symmetric and conventional optomechanical systems. The proposed scheme consists of a single optomechanical platform where a passive optical cavity is coupled to an active mechanical resonator, in contrast to standard passive-passive configurations. Analysis of the eigenfrequency spectrum reveals the emergence of an exceptional point under balanced gain-loss conditions at a tunable effective optomechanical coupling strength. Using the transfer-matrix method combined with stationary-phase analysis, we examine the GHS across broken and unbroken $\mathcal{PT}$ phases and compare it with that in the conventional system. The lateral shift exhibits strong phase dependence: it is markedly enhanced in the unbroken regime relative to both the broken phase and the passive configuration. We further show that the GHS can be actively tuned through the cavity detuning and the intracavity medium length. These results provide a controlled means for manipulating beam shifts in optomechanical systems and suggest pathways toward tunable photonic components and precision optical sensing.

physics.optics↗

arXiv2026

Coherent Control of the Goos-Hänchen Shift in Polariton Optomechanics

We propose a theoretical scheme for controlling the Goos-Hänchen shift (GHS) of a reflected probe field in a polariton optomechanical system. The system comprises an optical mode, a molecular vibrational mode, and $N$ excitonic modes, where excitons couple to molecular vibrations via conditional displacement interactions and to photons through electric dipole interactions. We show that the effective exciton-vibration coupling provides a powerful mechanism for coherent GHS control: in its absence, the system exhibits a pronounced GHS at resonance, while activating it strongly suppresses the shift. The effective cavity detuning and the cavity length serve as additional tunable parameters for GHS manipulation. Furthermore, increasing the collective exciton-optical coupling enhances the GHS. Our results establish a framework for probing the GHS in polariton optomechanical systems and offer new avenues for designing optical devices that exploit beam-displacement phenomena.

physics.optics↗

arXiv2025

$\mathcal{PT}$-assisted control of Goos-Hänchen shift in cavity magnomechanics

We propose a scheme to manipulate the Goos-Hänchen shift (GHS) of a reflected probe field in a non-Hermitian cavity magnomechanical system. The platform consists of a yttrium-iron-garnet sphere coupled to a microwave cavity, where a strong microwave drive pumps the magnon mode and a weak field probes the cavity. The traveling field's interaction with the magnon induces gain, yielding non-Hermitian dynamics. When the traveling field is oriented at $π/2$ relative to the cavity's $x$-axis, the system realizes $\mathcal{PT}$ symmetry; eigenvalue analysis reveals a third-order exceptional point ($\mathrm{EP}_3$) at a tunable effective magnon-photon coupling. Under balanced gain-loss and finite effective magnomechanical coupling, we demonstrate coherent control of the GHS by steering the system across the $\mathcal{PT}$-symmetric transition and through $\mathrm{EP}_3$ via the effective magnon-photon coupling, enabling pronounced enhancement or suppression of the lateral shift. Furthermore, we show that without effective magnomechanical coupling, the system exhibits a second-order exceptional point ($\mathrm{EP}_2$) with a distinct GHS phase transition. This phase transition vanishes when the effective magnomechanical coupling exceeds a parametric threshold, where strong absorption at resonance suppresses the GHS. We also identify the intracavity length as an additional control parameter for precise shift tuning. Notably, the $\mathcal{PT}$-symmetric configuration yields substantially larger GHS than its Hermitian counterpart. These results advance non-Hermitian magnomechanics and open a route to GHS-based microwave components for quantum switching and precision sensing.

physics.optics↗

arXiv2025

Photonic spin Hall effect in $\mathcal{PT}$-symmetric non-Hermitian cavity magnomechanics

Non-Hermitian cavity magnomechanics (CMM), which incorporates the magnon-photon and magnon-phonon interactions simultaneously, enables rich physical phenomena, including exceptional-point-enhanced sensing, and offers pathways toward topological transitions and nonreciprocal quantum transformation. These interactions exert a pivotal influence on the optical response of a weak probe field and pave the way for novel applications in quantum technologies. In this work, we consider a yttrium-iron-garnet (YIG) sphere coupled to a microwave cavity. The magnon mode of the YIG sphere is directly excited through microwave field coupling, whereas the cavity mode is probed via a weak-field interrogation scheme. The direct interaction of a traveling field with the magnon mode induces gain in the system, thereby establishing non-Hermitian dynamics. The parity-time (PT)-symmetric behavior of a hybrid non-Hermitian CMM is designed and investigated. Eigenvalue spectrum analysis demonstrates that a third-order exceptional point (EP_3) emerges under tunable effective magnon-photon coupling when the traveling field is oriented at an angle of π/2 relative to the cavity's x-axis. The photonic spin Hall effect (PSHE) in a reflected probe field is subsequently examined in such a system. Under balanced gain and loss conditions and in the presence of effective magnon-phonon coupling, tunable effective magnon-photon coupling enables coherent control of the PSHE across the broken PT-symmetric phase, at the EP_3, and in the PT-symmetric phase. Investigation reveals that the PSHE can be significantly enhanced or suppressed via effective magnon-photon coupling. The influence of intracavity length on the PSHE is further explored, providing an additional parameter for fine-tuning the transverse shift. These findings establish a direct correspondence between the PSHE and the underlying non-Hermitian eigenvalue spectrum.

physics.optics↗

arXiv2024

$\mathcal{PT}$-Symmetry induced Bi-Stability in Non-Hermitian Cavity Magnomechanics

We study the steady-state non-Hermitian magnomechanical system driven by a transverse magnetic field directly interacting with YIG sphere and excites cavity magnons and photons. To make the system non-Hermitian, we use a traveling field directly interacting with magnons generating gain to the system. We start by illustrating PT-configuration of the system, which contains two PT broken region around exceptional point and PT protected region along the axis of exceptional point. Late, we discover that the numbers of cavity photons and magnons show bistable behavior depending upon the PT configuration, which becomes more significant as the values of the magnon-photon coupling and traveling field strength increases. We illustrate that steady-state photon only shows bistable behavior when the system in in lossy PT broken configuration, means strength of traveling field is less than the magnon-photon coupling. Otherwise, it will just contain a single stable state because of bistability suppression with gain in the system, which is unlike with any other investigation in this direction. Further, a larger magnon-photon coupling increases photon intensity and decreases magnon intensity, because of photon and magnon energy exchange, leading to enhanced photon bistablity and decreased magnon bistability. However, in case of increasing strength of traveling field, both photon as well as magnon bistability is appeared to be decreasing. We also study the steady-state effective potential of the system and illustrate the occurrence of bistability with nonlinear interactions between contour trajectories, which similarly depends on the PT broken configuration of the system.

quant-ph↗

arXiv2020

An Advanced Two-Stage Grid Connected PV System: A Fractional-Order Controller

A fractional-order (FO) based controller for a grid-connected PV system is presented in this paper. A single phase two-stage grid-connected photovoltaic generator (PVG) is used to test the performance of the FO controller. The main objectives of the proposed controller are: (1) To regulate the output voltage of PVG at a point where the maximum power is drawn. (2) Constant DC-link voltage control. (3) Power factor control (PFC) at the inverter output with low total harmonic distortion (THD). To solve the first problem, a non-linear control method known as fractional-order back-stepping control (FOBSC) is used to regulate the output voltage of PVG. A maximum power point tracking (MPPT) technique known as perturb and observe (P & O) is used to generate a reference voltage which is suitable for tracking the maximum power generation of PVG. The generated reference is used to regulate the output voltage of PVG using FOBSC. The DC-link voltage fluctuation issue is tackled using FO based PI controller. The last objective is achieved using FOBSC to obtain maximum power factor of the grid. Lyapunov candidate function is used to verify the stability of the system. To test the performance of the proposed controller, it is compared to conventionally known Integer-order (IO) controller. Results have shown a significant improvement in THD and efficiency of the system. The proposed controller offers 0.94%, 1.43% and 1.86% lower THD in comparison with IO controller at 100%, 80% and 70% of the power generation capacity of PVG, respectively. The overall efficiency of the system for 100%, 80%, and 70% of the dynamic powers of the system is noticed to be better in case of FO controller.

eess.SY↗