arXiv subjects

Sushanta Barman

Publications and source records attributed to Sushanta Barman.

4 recordsLinked to original sources

arXiv2026

Magnetically assisted spin-resolved electron diffraction: Coherent control of spin population and spatial filtering

Electron diffraction from nanogratings provides a platform for free-electron interferometry, yet controlled manipulation of electron spin in such geometries remains largely unexplored. In particular, the role of the self-generated magnetic field arising from electron motion and the feasibility of coherent spin control without disrupting diffraction coherence have not been quantitatively investigated. In this article, a self-consistent Maxwell-Pauli framework is developed to study spin-resolved electron diffraction from nanogratings in the presence of magnetic fields. The model incorporates geometric confinement, image-charge interactions, self-generated magnetostatic fields, and externally applied magnetic fields. Numerical simulations show that the intrinsic magnetic self-field produced by the electron probability current is several orders of magnitude too weak to induce measurable spin mixing, demonstrating that nanogratings act as spin-conserving beam splitters under field-free conditions. When a uniform magnetic field is applied upstream of the nanograting, coherent Larmor precession enables controlled spin rotation without modifying the diffraction geometry or degrading coherence. The magnetic field required for a $\pi$ spin rotation scales inversely with the interaction length and electron de Broglie wavelength $\lambda_{dB}$. Furthermore, a downstream nonuniform magnetic field applied after the nanograting imparts a spatially varying Zeeman phase, producing opposite transverse momentum shifts for the two spin components. The spin-dependent transverse dynamics is analyzed using Husimi Q-function phase-space maps, which visualize spin-dependent population redistribution and momentum separation. The proposed approach enables tunable spatial separation of spin-resolved free electron beams and establishes an all-magnetic route for coherent spin rotation, control, and interferometry.

quant-ph↗

arXiv2024

Electrically controlled focusing of de Broglie matter waves by Fresnel zone plate

The evolution from classical to quantum matter wave optics has been influenced by transformative optical devices. Fresnel zone plates (FZP), initially designed for light manipulation, have now found expanded applications in matter waves. In this study, focusing of helium atoms by an electrically biased FZP is investigated numerically. The $n$th opaque zone of the FZP is subject to electrostatic biasing using three ways: (i) $V_n=V_1$, where $V_1$ is the biasing voltage applied to the central zone, (ii) $V_n=V_1 \sqrt{n}$, and (iii) $V_n = V_1 \sin (k_E n)$, with $k_E$ being the radial modulation factor. The effect of biasing the FZP on the transmission coefficient ($T_c$), focal length ($f$), size of the focused wave packet ($\sigma_F$), transverse intensity profile, and focusing efficiency ($\eta$) is investigated. The study reveals that the electrical biasing of the FZP modulates the diffractive focusing of neutral atoms by altering the atom-surface interaction with induced polarization potential. It is observed that biasing with $V_n=V_1$ induces multi-focusing of the FZP, reducing wave packet transmission and focusing efficiency. Biasing with $V_n=V_1 \sqrt{n}$ significantly enhances the transmission coefficient by $23.7\%$, increases the focal length $f$ by $103\%$, and improves the focusing efficiency from $10\%$ to $20.17\%$, indicating enhanced focusing performance. Biasing with $V_n=V_1 \sin(k_E n)$ offers increased controllability in focusing matter waves through the parameters $k_E$ and $V_1$. In this case, a highly intense focused wave packet with a better efficiency of $20.3\%$ is observed compared to the other cases. The findings will be helpful in various emerging applications of atom optics, such as improving the performance of helium microscopes, enabling control in cold atom trapping on atom chips, and high-precision atom lithography for quantum electronic devices.

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arXiv2023

Near-field diffraction of protons by a nanostructured metallic grating under external electric field: Asymmetry and sidebands in Talbot self-imaging

Self-imaging in near-field diffraction is a practical application of coherent manipulation of matter waves in Talbot interferometry. In this work, near-field diffraction of protons by a nanostructured metallic grating under the influence of (a) uniform, (b) spatially modulated, and (c) temporally modulated electric fields are investigated. Time-domain simulations of two-dimensional Gaussian wave packets for protons are performed by solving the time-dependent Schrödinger's equation using the generalized finite difference time domain (GFDTD-Q) method for quantum systems. Effects of strength ($E_0$) and orientation ($θ$) of the uniform electric field on the diffraction properties, such as fringe pattern, intensity of the peaks, fringe shift, and visibility, are investigated. The results show that the Talbot fringes shift significantly in the transverse direction even for a small change in the applied electric field ($ΔE_0$ $=0.1$ V/m) and its orientation ($Δθ$ $=0.1^o$). The potential barriers arising from a spatially modulated electric field are observed to cause significant distortions in the Talbot patterns when the modulation length ($λ'$) is equal to the de Broglie wavelength ($λ_{dB}$). Sidebands are observed in the Talbot pattern due to the efficient transfer of energy from the oscillating field to the wave packet when the frequency of oscillation ($ω$) is of the order of $ω_0$ ($=2π/T_0$), where $T_0$ is the interaction time. This study will be helpful in uniform electric field-controlled precision metrology, developing a highly sensitive electric field sensor based on Talbot interference, and precisely aligning the matter wave optical setup. Furthermore, the sidebands in the Talbot fringe can be used as a precise tool as momentum splitter in matter wave interferometry.

quant-ph↗

arXiv2020

Time evolution of charged particle wave functions in optical crystal: The coherent Kapitza-Dirac effect for plasma-based proton beams

The stationary eigenstates and eigenvalues for the ponderomotive potential of an optical crystal confined in a one-dimensional infinite square well are numerically obtained. The initial states of the incoming particles taken as Gaussian, are expanded in the basis of the stationary eigenstates of the ponderomotive potential, to obtain the subsequent time evolution of the wave function of the particle during the interaction with the optical crystal. From the results of the time evolution of the probability density, it is observed that the particles get localized at equidistant positions in the transverse direction, which results in the diffraction pattern. The temporal evolution of the diffraction pattern is analyzed. As an application, the diffraction of proton beams is studied, where the experimental parameters are optimized to observe the diffraction pattern for a microwave plasma-based proton beam system. The observations are important for design of proton based matter-wave interferometers.

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