Dr RAGHAVAN K EASWARAN
@iitp.ac.in
Indian Institute of Technology, Patna
Scopus Publications
Scholar Citations
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Scopus Publications
Dixith Manchaiah, Rohit Kumar, Mobassir Ahmad, and Raghavan K. Easwaran
Optica Publishing Group
Here, we present a study on the dispersion features obtained in an electromagnetically induced transparency (EIT) experiment using a three-level cascade configuration in an 87Rb atomic vapor medium in the presence of Laguerre–Gaussian (LG) light as a coupling. A doublet transmission structure was obtained experimentally, and dispersion spectra were extracted using transmission spectra to study the probe light behavior. Dispersive regions that exhibit normal and anomalous nature were studied considering the polarization of various orientations as a coupling light. We established that normal dispersive region shows steep positive slopes, and anomalous dispersive region shows negative slopes, which can be controlled by polarization orientations. Owing to the change in the slopes of dispersion, normal and anomalous dispersive region is observed, and spectrum shows the effects of subluminal and superluminal propagation of probe light. This work, to the best of our knowledge, is novel in the study of dispersive region arising out of double-resonance EIT transmission spectra in the presence of LG light with the l=10 and p=0 mode as a coupling light with various polarization orientations. In the discussion, we establish that single parameter θ is sufficient for identifying the orientation and ellipticity of the polarization ellipse and also determine that the polarization of coupling light acts as a tuning parameter for changing the behavior of normal and anomalous dispersive region. Slow and fast light or superluminal propagation of probe light arise as a consequence of positive or negative group index, and fast light does not violate the principle of causality. Slow and fast light have future applications in high-speed quantum information and quantum communication using EIT-based protocol.
Rohit Kumar, Dixith Manchaiah, and Raghavan K Easwaran
IOP Publishing
Abstract In this manuscript, we have theoretically studied the four level closed loop atomic systems in the presence of two vector beams. A spatially dependent transparency for the probe vector beam is obtained based on the semiclassical model. We have explicitly shown that the number of petals formed for probe absorption depends on the value of orbital angular momentum (OAM) of the constituting beams. A detailed study for absorption and dispersion of right circularly polarized (RCP) and left circularly polarized (LCP) components of the probe beam is carried out and the importance of the polarization state of the beams on Higher Order Poincare Sphere (HOPS) is highlighted. An explicit effect of the interferometer phase of the vector beam which is geometric in nature, is shown for probe beam response. Three types of four level closed loop atomic system is studied with particular emphasis given for double Λ and Diamond atomic system. A dark state analysis of the atomic system is carried out which facilitate a physical understanding of the obtained results. Our study has explored the effects of inhomogeneity in both polarization and intensity for probe and coupling beam in a closed loop atomic system which is phase dependent.
S. Baral, Raghavan K. Easwaran, J. Jose, Aarthi Ganesan, and P. C. Deshmukh
MDPI AG
An atom confined in an optical dipole trap is a promising candidate for a qubit. Analyzing the temporal response of such trapped atoms enables us to estimate the speed at which quantum computers operate. The present work models an atom in an optical dipole trap formed using crossed laser beams and further examines the photoionization time delay from such confined atoms. We study noble gas atoms, such as Ne (Z = 10), Ar (Z = 18), Kr (Z = 36), and Xe (Z = 54). The atoms are considered to be confined in an optical dipole trap using X-ray Free Electron Lasers (XFEL). The present work shows that the photoionization time delay of the trapped atoms is different compared with that of the free atoms. This analysis alerts us that while talking about the speed of quantum computing, the temporal response of the atoms in the trapped environment must also be accounted for.
Rohit Kumar, Dixith Manchaiah, Aishi Barua, and Raghavan K. Easwaran
Springer Science and Business Media LLC
Dixith Manchaiah, Rohit Kumar, and Raghavan K Easwaran
IOP Publishing
Abstract We investigate both experimentally and theoretically the cascade electromagnetically induced transparency (EIT) in 5 S 1 / 2 − 5 P 3 / 2 − 5 D 5 / 2 configuration in 87Rb atomic vapor medium in the presence of vortex coupling Laguerre Gaussian (LG) light. We demonstrated Doppler free double resonance EIT structure in cascade configuration and observed transmission spectra for | H ⟩ − | H ⟩ and σ + − σ + polarized probe and coupling lights. We demonstrate that the double resonance structure can be identified by two photon transition probabilities and it is found to be F ′ ′ = 2 and F ′ ′ = 3 . By considering coupling LG light, several polarization combinations are taken into account, and their effects on amplifying and diminishing the EIT resonances are demonstrated experimentally. In order to understand the polarization effects of vortex coupling light on EIT spectrum in a degenerate multilevel atomic system, a theoretical model is developed by considering a simplified double hut level structure. Semi-classical density matrix analysis is used to understand the dynamics and also to establish the enhancement and reduction of EIT peak height with coupling light polarizations. The impact of two photon transition probabilities, polarization combinations and relative orientations of probe and coupling lights in degenerate multilevel atomic systems leads to modification of EIT resonances significantly. We establish quantitative agreement between our theory and experimental results.
Rohit Kumar, Dixith Manchaiah, and Raghavan K. Easwaran
Optica Publishing Group
In this work, we have theoretically studied the four-level atomic system for the measurement of a microwave (MW) field. We employed the electromagnetically induced transparency (EIT) technique for finding the MW field in the presence of a Laguerre–Gaussian (LG) beam as a coupling light. We have shown that, by the application of LG modes, narrower dips for the probe absorption spectrum can be generated, which can be easily identified and gives better resolution compared with the Gaussian mode. An exact location of dips in the probe absorption spectrum is found, and it is useful in the measurement of MW fields. We have estimated the FWHM of the probe absorption spectrum for Gaussian and LG coupling cases as 3.74 × 10 5 H z and 1.07 × 10 5 H z , respectively. Based on FWHM, we have found that minimum change in MW electric field in the order of 3.32 µ V c m − 1 will be detectable in the case of the LG mode as a coupling beam.
Dixith Manchaiah, Rohit Kumar, and Raghavan K. Easwaran
Springer Science and Business Media LLC
Vikas Singh Chauhan, Rohit Kumar, Dixith Manchaiah, and Raghavan K. Easwaran
The Optical Society
In the present work, a theoretical and experimental study to enhance electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) signals in an 85Rb atomic vapor medium at room temperature is conducted. Also, switching from EIT to EIA signal at a particular value of the magnetic field is observed. Further, by using circularly polarized coupling light, the dispersion profile of the linearly polarized probe signal is investigated theoretically and experimentally. The nine-level system of 85Rb D2 transition in a ladder-type configuration is fully solved by using the density matrix theory. The simulated results are found in good qualitative agreement with experimental observations. Hence, an experimental setup is developed for (1) achieving enhanced EIT and EIA signal, (2) switching from EIT to EIA, and (3) dispersion measurement. These observations have potential applications towards measurement of the group velocity of light, quantum memory, quantum information, and optical switching.
Vikas Singh Chauhan, Dixith Manchaiah, Praveen Kumar, Rohit Kumar, Sumit Bhushan, and Raghavan K. Easwaran
Elsevier BV
Abstract In this letter, we have measured the dispersive profile of the multi window Electromagnetically Induced Transparency(EIT) signals in Rubidium (Rb) atomic medium at room temperature. Weak probe laser light and strong coupling light in counter propagating direction are used to excite the atomic medium via ladder type configuration of 87Rb D2 line to obtain multiple EIT peaks. The uniqueness of our work is in the experimental setup which is used for the measurement of dispersion. We have used transmissive Spatial Light Modulator(SLM) in one arm of the Mach–Zehnder(M–Z) interferometer to obtain the desired phase shift between two interfering arms for the measurement of dispersive properties of multi window EIT in Rb vapor medium. One can easily obtain the phase shift without disturbing the alignment of the M-Z interferometer by using this setup.
Vikas Singh Chauhan, Dixith Manchaiah, Sumit Bhushan, Rohit Kumar, and Raghavan K. Easwaran
World Scientific Pub Co Pte Lt
In this paper, we present a theoretical proposal to realize Quantum Memory (QM) for storage of blue light pulses (420 nm) using Electromagnetically Induced Transparency (EIT). Three-level lambda-type EIT configuration system is solved in a fully quantum mechanical approach. Storing blue light has the potential application in the field of underwater quantum communication as it experiences less attenuation inside the sea water. Our model works by exciting the relevant transitions of [Formula: see text]Rb atoms using a three-level lambda-type configuration in a Two-Dimensional Magneto-Optical Trap (2D MOT) with an optical cavity inside it. We have estimated Optical Depth inside the cavity (ODc) of [Formula: see text], group velocity ([Formula: see text]) [Formula: see text][Formula: see text]ms[Formula: see text], Delay Bandwidth Product(DBP) of 23 and maximum storage efficiency as [Formula: see text] in our system.
Vikas Singh Chauhan, Sumit Bhushan, and Raghavan K. Easwaran
AIP Publishing
Vikas S Chauhan, Rohit Kumar, Dixith Manchaiah, Praveen Kumar, and Raghavan K Easwaran
IOP Publishing
Sumit Bhushan, Vikas Singh Chauhan, Dixith M, and Raghavan K. Easwaran
Elsevier BV
Abstract In this work, we experimentally study the effect of externally applied magnetic field on a ladder type EIT in a vapour cell consisting of 87Rb atoms. The introduction of magnetic field causes the Zeeman splitting of the hyperfine levels of 87Rb atoms and hence the number of available windows of transparency increases. We report the observation of nine such windows. Such multi window EIT systems are capable of storing pulses at the different frequencies, corresponding to these windows hence paving the way for realization of multi frequency quantum memories. Also, the total bandwidth of storage is 218.4 MHz which is two orders of magnitude higher than that typically obtained in single window EIT based storage systems. These systems have tremendous applications in the field of speedy transmission of data over a long distance quantum communication channel.
Sumit Bhushan, Vikas S. Chauhan, and Raghavan K. Easwaran
Informa UK Limited
ABSTRACT In this paper, we describe a theoretical design for the realization of a high capacity (bandwidth) atomic quantum memory based on wavelength division multiplexing and electromagnetically induced transparency in adjacently placed 87Rb vapour cells. Magnetic fields produced by Helmholtz coils are used to tailor the atomic energy levels in the vapour cells and hence storage of various probe signals of different wavelengths becomes possible. We give a detailed description of the proposed experimental setup. We have estimated a very high bandwidth of 50 MHz for our design with a delay bandwidth product of approximately 530. Our prototype design is for storing five different wavelength probe pulses which could be extended to larger values in principle.
Sumit Bhushan, Vikas S. Chauhan, and Raghavan K. Easwaran
Elsevier BV
Abstract Quantum communication with terahertz (THz) frequency signals has many advantages like reduced attenuation and scintillation effects in certain atmospheric conditions along with very high level of data security. In this work, we propose a scheme to realize Quantum Memory (QM) for efficient storage of terahertz (THz) frequency signals using Electromagnetically Induced Transparency (EIT) in an ultracold atomic medium of 87Rb Rydberg atoms prepared in a Two Dimensional Magneto Optical Trap (2D-MOT). The uniqueness of our scheme lies in the choice of the energy levels involved in the EIT process, all three of which have been chosen to be the Rydberg levels (enabling signal beam to be in THz) in a lambda type arrangement. This first of its kind proposal reveals that atomic media are a potential candidate for devising QMs which can store THz frequency signals. We have estimated that the Optical Depth (OD) in our scheme can reach a very high value of 690, very high maximum obtainable storage efficiency (η) of ∼99%, the group velocity ( v g ) can be as low as 5.07 × 103 m/s, and the Delay Bandwidth Product (DBP) can be as high as 9.5. All of these estimates emphasize the feasibility of our scheme as a QM device for efficient storage of THz pulses.
Gour M. Das, Anil B. Ringne, Venkata R. Dantham, Raghavan K. Easwaran, and Ranjit Laha
The Optical Society
Finite element method simulations have been carried out on the photonic nanojet (PNJ) mediated surface enhanced Raman scattering (SERS) technique for the first time, and this technique has been found to provide (i) better Raman scattering enhancement of single molecules and (ii) a long working distance between the microscopic objective lens and sample, as compared with the conventional SERS technique. A PNJ mediated surface enhanced fluorescence (SEF) technique has been proposed to enhance the fluorescence of single molecules using the combination of localized surface plasmons inside nanostructures and the PNJ of a dielectric microsphere (MS), and this technique is numerically proved to be efficient as compared with a conventional SEF technique. Moreover, the generation of a PNJ from single lollipop shaped microstructures and its applications in the above mentioned techniques have been reported.
Sumit Bhushan and Raghavan K. Easwaran
The Optical Society
In this paper, we propose a novel technique for slow light experiments using electromagnetically induced transparency using a two-dimensional magneto optical trap (2D-MOT). A compact 2D-MOT design efficient for quantum memory applications with adjustable optical depth (OD) is proposed. We estimated the OD for our 2D-MOT setup and found that light group velocities as low as 1.4 m/s can be attained. Our design for 2D-MOT allows precise control and optimization of the OD such that high storage efficiencies could also be achieved. With our design, it is possible to obtain a delay bandwidth product of 163, which is very high in comparison to previously obtained values.
Dipankar Nath, R Kollengode Easwaran, G. Rajalakshmi, and C. S. Unnikrishnan
American Physical Society (APS)
We report enhanced sub-Doppler cooling of the bosonic atoms of $^{39}$K facilitated by formation of dark states tuned for the Raman resonance in the $\\Lambda-$configuration near the D1 transition. Temperature of about 12 $\\mu$K is achieved in the two stage D2-D1 molasses and spans a very large parameter region where quantum interference persists robustly. We also present results on enhanced radiation heating with sub-natural linewidth (0.07$\\Gamma$) and signature Fano like profile of a coherently driven 3-level atomic system. The Optical Bloch Equations relevant for the three-level atom in bichromatic light field is solved with the method of continued fractions to show that cooling occurs only for a small velocity class of atoms, emphasizing the need for pre-cooling in D2 molasses stage.
Dipankar Nath, R Kollengode Easwaran, G Rajalakshmi, and C S Unnikrishnan
IOP Publishing
We report the rapid accelerated thermalisation of Potassium ( 39 K) atoms loaded in a magnetic trap, in the presence of a single dipole trap beam. More than an order of magnitude reduction in the thermalisation time, to less than a second, is observed with the focused off-resonant beam occupying only 0.01% of the volume of the magnetic trap. A new method for testing for thermalisation of relatively hot clouds is devised. The cold atoms are loaded from a Magneto- Optical Trap (MOT) of 39 K that has gone through a compressed MOT and sub- Doppler cooling stage. The atoms are prepared in the magnetically stretched |F = 2,mF = 2i state prior to loading into the hybrid trap. We also report a direct loading of 39K atoms, prepared in the state |F = 1i, into a single beam dipole trap.
Vandna Gokhroo, G Rajalakshmi, R Kollengode Easwaran, and C S Unnikrishnan
IOP Publishing
We report the sub-Doppler deep-cooled three-dimensional magneto-optical trap (3D MOT) of the fermionic 40K and bosonic 39K isotopes of potassium loaded by a very compact 2D+ MOT with a novel optical design feature. The set-up is meant for studies on the quantum dynamics of a few fermionic and bosonic atoms in an optical dipole trap near and well within quantum degeneracy. The loading rate and atom numbers achieved in the compact simple set-up are comparable to those in the previous set-ups with more elaborate vacuum design. We attained relatively low temperatures of 34 and 30 µK for 39K and 40K after the sub-Doppler cooling process.
R Kollengode Easwaran, L Longchambon, P-E Pottie, V Lorent, H Perrin, and B M Garraway
IOP Publishing
We study the spectroscopy of atoms dressed by a resonant radiofrequency (RF) field inside an inhomogeneous magnetic field and confined in the resulting adiabatic potential. The spectroscopic probe is a second, weak, RF field. The observed line shape is related to the temperature of the trapped cloud. We demonstrate evaporative cooling of the RF-dressed atoms by sweeping the frequency of the second RF field around the Rabi frequency of the dressing field.