arXiv subjects

S. P. Ram

Publications and source records attributed to S. P. Ram.

14 recordsLinked to original sources

arXiv2025

Spatio-temporal Monte Carlo modeling of loading and decay dynamics in an optical dipole trap

Here, we present our studies on intra-trap dynamics of an optical dipole trap (ODT) loaded from a Magneto-optical trap (MOT) of $^{87}$Rb atoms. A spatio-temporal Monte Carlo (MC) simulation approach has been employed in conjunction with the semi-classical theory based calculations for estimation of various intra-trap two-body loss parameters in the ODT. The temporal MC method based on estimated parameters from spatial MC, gives a close estimation of the experimentally observed atom-number evolution in ODT. We also find that, the decay rate of atoms in an ODT is dominated by momentum-transfer elastic collisions in the absence of MOT beams. However, in presence of MOT beams, the radiative escape process is the dominant two-body loss mechanism in the trap, which surpasses the fine-structure changing and hyperfine changing collisional losses by nearly an order of magnitude.

physics.atom-ph↗

arXiv2025

On damping of Rabi oscillations in two-photon Raman excitation in cold $^{87}$Rb atoms

Two-photon Raman excitation between the ground hyperfine states $|5 \ ^2S_{1/2}, F = 2\rangle$ and $|5 \ ^2S_{1/2}, F = 1\rangle$ of $^{87}$Rb atom has been experimentally studied. The Rabi coupling strengths of various transition involved have been calculated in presence of a weak magnetic field. A density matrix formalism has been developed to understand the experimentally observed damping of Rabi oscillations of population in a hyperfine state of $^{87}$Rb atom during interaction with the Raman laser beams. The observed damping of Rabi oscillations has been attributed to the dephasing during the light atom interaction.

physics.atom-ph↗

arXiv2024

Measurement of gravitational acceleration in a single laser operated atomic fountain

We present measurements on Earth's gravitational acceleration (g) using an in-house developed cold atom gravimeter (CAG) in an atomic fountain geometry. In the setup, the laser cooled $^{87}Rb$ atoms are launched vertically up in the fountain geometry and Doppler sensitive two-photon Raman pulse atom interferometry is applied to detect the gravitational acceleration experienced by the atoms. Using our gravimeter setup, we have measured the local value of 'g' in our laboratory with sensitivity of 621 $μ$Gal for integration time of 1350 s.

physics.atom-ph↗

arXiv2024

On trapping geometry for cold atoms in a radio-frequency (rf) dressed potential

We have investigated the atom trapping geometry for trapping of $^{87}{Rb}$ atoms in a radio-frequency (rf) dressed potential generated after superposing a strong linearly polarized rf-field on a static magnetic trap. For this, laser cooled atoms in a magneto-optical trap (MOT) in an ultra-high vacuum (UHV) chamber (pressure $\sim$ 1.5 $\times$ $10^{-10}$ Torr) were trapped in a quadrupole magnetic trap and evaporatively cooled before transferring them to the rf-dressed potential. The experimentally observed hollow shell type atom trapping geometry has been explained by theoretical modelling of the trapping potential.

physics.atom-ph↗

arXiv2022

A compact setup for loading magneto-optical trap in ultrahigh vacuum environment

We have developed a compact setup which enables loading a magneto-optical trap (MOT) in ultra-high vacuum (UHV) environment. Nearly $1 \times 10^{8}$ atoms of $^{87}Rb$ are trapped in the MOT at $\sim 2 \times 10^{-10}$ Torr base pressure in the chamber. After the MOT loading, we have successfully demonstrated working of quadrupole magnetic trap in this chamber with a lifetime of $\sim 8 $ s

physics.atom-ph↗

arXiv2021

Different atom trapping geometries with time averaged adiabatic potentials

In this article, we have theoretically studied the time averaged adiabatic potential (TAAP) scheme for realizing different atom trapping geometries. It is shown that by varying time orbiting potential (TOP) fields and radio frequency (rf) fields parameters, controlled manipulation of trapping potentials, and conversion from one trapping geometry to another, is possible. The proposed trapping geometries can be useful for studying various atom-optic phenomena such as Bose-Einstein condensation (BEC) in low dimensions, super-fluidity, tunnelling, atom interferometry, etc.

physics.atom-ph↗

arXiv2019

Observation of dual electromagnetically induced transparencies in cold $^{87}Rb$ atoms

We have observed two dual electromagnetically induced transparency (EIT) spectra in probe transmission through cold $^{87}Rb$ atoms trapped in a magneto-optical trap (MOT). These dual EIT peaks are generated in two different N-systems formed by probe, coupling and control beams interacting with different levels in $D_{2}$ line transitions of $^{87}Rb$ atom. The dependence of spectral features of two N-systems on driving beams (\textit{i.e.} coupling and control beams) strength and detuning has been investigated. The results show that the dual EIT spectral features in both the N-systems can be manipulated by varying the strength and detuning of both the driving beams. The two N-systems have been modelled theoretically using a density matrix formalism and results have shown a reasonable agreement with the experimental observations.

physics.atom-ph↗

arXiv2018

Coupling field dependent quantum interference effects in a $Λ$-system of $^{87}Rb$ atom

A $Λ$-system in $D_2$ line transition of the $^{87}Rb$ atom has been investigated for quantum interference effects for different configurations of coupling field. With a travelling wave coupling field (co-propagating with probe field), the probe beam shows the earlier known electromagnetically induced transparency (EIT) effect at the resonance. With a standing wave coupling field (which is co- and counter-propagating with probe beam), the probe EIT gets transformed into an electromagnetically induced absorption (EIA). A variation in coupling beam power has shown that, at high coupling power, EIA signals have much larger amplitude and slope than those of EIT signals with and without applied magnetic field. These EIA signals can be useful for tight laser frequency locking and optical switching.

physics.atom-ph↗

arXiv2018

Electromagnetically Induced Transparency in $Λ$-systems of $^{87}Rb$ atom in magnetic field

The electromagnetically induced transparency (EIT) observations in two $Λ$-systems of $^{87}Rb$ atom, $|5^{2}S_{1/2} F=1\rangle \rightarrow |5^{2}P_{3/2} F'=1\rangle \leftarrow |5^{2}S_{1/2} F=2\rangle$ and $|5^{2}S_{1/2} F=1\rangle \rightarrow |5^{2}P_{3/2} F'=2\rangle \leftarrow |5^{2}S_{1/2} F=2\rangle$, have been investigated in detail and the results are found consistent with our proposed theoretical models. The second $Λ$-system provides EIT signal with higher magnitude than the first system, both in absence and in presence of an applied magnetic field. The observed steeper slope of the EIT signal in presence of the magnetic field can enable one to achieve tight frequency locking of lasers using these EIT signals.

physics.atom-ph↗

arXiv2017

A study on evolution of a cold atom cloud in a time dependent radio frequency dressed potential

Using a Direct Simulation Monte Carlo technique, we have studied the time evolution of a cold atom cloud interacting with a time dependent radio frequency (rf) dressed state potential. Exposure of a cloud of $^{87}Rb$ atoms, trapped in a quadrupole magnetic trap, to a time dependent rf-field with increasing amplitude and decreasing frequency, shows a variation in the number of trapped atoms and the overall shape of the atom cloud. It is shown by simulations that, initially at lower rf-field strength, the rf-field results in ejection of atoms from the trap, leading to evaporative cooling of the atom cloud. Later, at higher rf-field strength, the atoms undergo the non-adiabatic Landau-Zener (LZ) transitions, which leads to their trapping in an rf-dressed state potential of toroidal shape. The results of simulations explain the experimentally observed results. The simulations can be useful to predict the atom cloud dynamics and trapping geometries with other forms of the potential.

physics.atom-ph↗

arXiv2017

A toroidal trap for cold $^{87}Rb$ atoms using an rf-dressed quadrupole trap

We demonstrate the trapping of cold $^{87}Rb$ atoms in a toroidal geometry using a radio frequency (rf) dressed quadrupole magnetic trap formed by superposing a strong rf-field on a quadrupole trap. This rf-dressed quadrupole trap has the minimum potential away from the quadrupole trap centre on a circular path which facilitates trapping in toroidal geometry. In these experiments, the laser cooled atoms were first trapped in a quadrupole trap, then cooled evaporatively using a weak rf-field, and finally trapped in an rf-dressed quadrupole trap. The radius of the toroid could be varied by varying the frequency of the dressing rf-field. It has also been demonstrated that a single rf source and an antenna can be used for the rf-evaporative cooling as well as for the rf-dressing of atoms. The atoms trapped in the toroidal trap may have applications in the realization of an atom gyroscope as well as in studying the quantum gases in low dimensions.

quant-ph↗

arXiv2016

Dependence of in-situ Bose condensate size on frequency of RF-field used for evaporative cooling

We report the results of in-situ characterization of $ ^{87}$Rb atom cloud in a quadrupole Ioffe configuration (QUIC) magnetic trap after radio frequency (RF) evaporative cooling of the trapped atom cloud. The in-situ absorption images of the atom cloud have shown clear bimodal optical density (OD) profiles which indicate the Bose-Einstein condensation (BEC) phase transition in the trapped gas. Also, we report the measured variation in the sizes of the condensate and thermal clouds with the final frequency in the frequency scan of the RF-field applied for evaporative cooling. The results are consistent with the theoretical understanding and predictions reported earlier.

physics.atom-ph↗

arXiv2014

Temperature and phase-space density of cold atom cloud in a quadrupole magnetic trap

We present studies on the modifications in temperature, number density and phase-space density when a laser cooled atom cloud from the optical molasses is trapped in a quadrupole magnetic trap. Theoretically it is shown that for a given temperature and size of the cloud from the molasses, the phase-space density in the magnetic trap first increases with magnetic field gradient and then decreases with it, after attaining a maximum value at an optimum value of magnetic field gradient. The experimentally measured variation in phase-space density in the magnetic trap with the magnetic field gradient has shown the similar trend. However, the experimentally measured values of number density and phase-space density are much lower than their theoretically predicted values. This is attributed to the higher experimentally observed temperature in the magnetic trap than the theoretically predicted temperature. Nevertheless, these studies can be useful to set a higher phase-space density in the trap by setting the optimum value of field gradient of the quadrupole magnetic trap.

physics.atom-ph↗

arXiv2006

Collective modes of a quasi two-dimensional Bose condensate in large gas parameter regime

We have theoretically studied the collective modes of a quasi two-dimensional (Q2D) Bose condensate in the large gas parameter regime by using a formalism which treats the interaction energy beyond the mean-field approximation. In the calculation we use the perturbative expansion for the interaction energy by incorporating the Lee, Huang and Yang (LHY) correction term. The results show that incorporation of this higher order term leads to detectable modifications in the mode frequencies.

cond-mat.other↗