I am a theoretical Physicist and carry out research in the area of Nonlinear Quantum Optics. I received my Ph.D. degree in Physics from Indian Institute of Technology Guwahati, Assam, India. I completed my post doc as a SERB-National Post-Doctoral Fellow (SERB-NPDF) in the Department of Physics at NIT Warangal. Currently, I am working as a UGC-DS Kothari Postdoctoral Fellow (UGC-DSK-PDF) in the Department of Physics, University of Allahabad.
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Welcome to Quantum Optics and Quantum Information (QOQI) Group
Self-healing of orbital angular momentum in bright twin light beams generated via four-wave mixing (J. A. Thachil , C. R. Patel, Onkar N. Verma , and Ashok Kumar, PHYSICAL REVIEW A 110, 053520 (2024)).
Abstract: The utilization of orthogonal modes of structured light, such as orbital angular momentum (OAM), in optical communication has led to an increased focus on the self-healing property of beams that contain OAM. In this paper, we theoretically and experimentally investigate the self-healing property in the twin Laguerre-Gaussian (LG) beams generated with a truncated input pump or probe having LG profiles in a four-wave mixing process in a double- configuration. We show that, along with the amplified probe, the newly generated conjugate beam also acquires the truncated profile and exhibits self-healing on propagation. The transverse spatial intensity is reconstructed, and the OAM associated with the topological charge of the beams is restored in the far field. The self-healing in the generated beams is also studied for different topological charges and different obstacle types. The experimental results are supported with a theoretical model based on the semiclassical approach. The results of the present paper hold promise for practical implementation in real-world applications such as quantum communication and information transfer with OAM modes, addressing critical challenges like losses due to obstructions.
All-optical generation of structured light beams via microwave-field-controlled electromagnetically induced transparency (Onkar N. Verma and Niti Kant, PHYSICAL REVIEW A 110, 013701 (2024)).
Abstract: We investigate theoretically a scheme for all-optical generation of structured light beams with and without a microwave field in an electromagnetically induced transparency (EIT) medium composed of rubidium atoms. In a conventional EIT system, two optical fields (namely, a strong control field and a weak probe field) drive two electric-dipole-allowed transitions of an atom to form a three-level system in a configuration. At EIT resonance, we found that a Laguerre-Gaussian (LG) control beam induces a radial modulation of probe’s absorption profile in such way that a Gaussian probe beam is reshaped into a hollow-Gaussian beam following the position-selective absorption. The transmitted probe beam has a doughnut-shaped intensity structure similar to that LG beam whereas the phase profile is still a spherical wave. Moreover, the presence of a microwave field between two ground states of three-level system leads to a closed-loop system, and probe response is modified with an additional term proportional to the amplitudes of Rabi frequencies of control and microwave fields, and relative phase of three fields. This term acts as driving field which is responsible for the generation of a vortex probe beam having a helical phase profile. We have further shown that the amplitude and helical phase of generated vortex beam can be manipulated by changing the relative phase of applied fields and temperature of the vapor cell. The present study may provide a useful tool for creation of structured light beams with and without orbital angular momentum.
Nonlinear frequency conversion of nondiffracting modes via nondegenerate four-wave mixing in atomic vapor (Onkar N. Verma and Niti Kant, Phys. Rev. A 109, 033515, 2024).
Abstract: We investigate the nonlinear frequency conversion of nondiffracting optical modes via a nondegenerate four-wave mixing (FWM) process in rubidium vapor. In this process, two strong control fields and a weak probe field mutually interact via a four-level double-Λ type atomic system to produce a low frequency weak Stokes field which is a phase conjugate to probe. We show that any arbitrary mode such as Airy, Bessel, Mathieu, and Weber beams encoded initially in the spatial envelope of the probe field are efficiently transferred to the FWM Stokes field by satisfying the phase-matching condition. Interestingly, we found that the transmitted intensity profiles of the Stokes beam are identical to that of the probe beam, while the phase profile is complementary. The phase conjugation property of output beams is revealed by interfering them with a copropagating plane wave. We further found the fidelity in terms of structural similarity between two transmitted modes of about 99%, which substantiates the high efficiency of the FWM process. The efficient transfer and frequency conversion of such diffraction-free beams may have potential applications in nonlinear optical and quantum technologies.
Efficient transfer of spatial intensity and phase information of arbitrary modes via four-wave mixing in an atomic vapor (PHYSICAL REVIEW A 106, 053713, 2022).
Abstract: We propose a scheme to transfer the spatial intensity as well as phase information encoded initially in the spatial profile of a weak probe field onto a newly generated Stokes field in a nonlinear process of four-wave mixing (FWM). The FWM process is explored in a gaseous medium consisting of atoms modeled as a three-level system in the configuration. We found that different orders of Hermite-Gaussian and Laguerre-Gaussian modes carried by a probe beam are effectively transferred to a Stokes beam. Interestingly, the transferred intensity of the Stokes beam is a clone of the probe beam, whereas the phase profile is conjugate to the probe. The phase distribution of the transmitted modes at the exit of the medium is explored by superimposing them on a copropagating plane wave. Moreover, the parametric amplification due to the nonlinear process of FWM prevents any information loss due to linear absorption and permits us to work at high optical depths. We found a structural similarity between transferred images of about 99%, which provides clear evidence for the successful transfer of information in the FWM process.
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