arXiv subjects

Kanhaiya Pandey

Publications and source records attributed to Kanhaiya Pandey.

At least 19 recordsLinked to original sources

arXiv2025

Efficient direct loading of the green MOT of Yb with low green laser power

We report the direct loading of Yb atoms in the magneto-optical trap (MOT) using the intercombination narrow optical transition 6s$^2$ $^1$S$_0$ $\rightarrow$ 6s6p $^3$P$_1$ at 556 nm (green), known as green MOT with limited power of green laser, 10 mW. Direct loading of the green MOT is achieved by superimposing the green laser beam, inside a hollow core of the laser beam driving the broad 6s$^2$ $^1$S$_0$ $\rightarrow$ 6s6p $^1$P$_1$, transition (blue) at 399 nm. We load up to 3$\times10^8$ in $1$ s. We characterize the green MOT loading with various experimental parameters such as magnetic field gradient, power of the green laser and blue MOT laser, and detuning of the green laser. We have also loaded the green MOT using center-shifted dual MOT configuration. In this configuration, the overlap region of the three counter-propagating blue laser beams is shifted towards Zeeman slower, where the magnetic field is non-zero. The atoms are first pre-cooled and partially trapped in blue MOT. These atoms enter the green MOT region and are trapped. In this method, we do not lose power (unlike in core-shell MOT) of the blue MOT laser because of masking the central portion. However, we load only 10$^7$ atoms, which has one order of magnitude fewer atoms than in the core-shell MOT.

physics.atom-ph↗

arXiv2025

EIT in V+ inverted $Ξ$ system using Rydberg state in thermal Rb atoms

Rydberg excitation using blue and IR transition is an advantageous path for quantum computation in alkali elements. Aiming to stabilize the IR laser for quantum computation, we study electromagnetically induced transparency (EIT) spectrum using Rydberg state in V+inverted $Ξ$ system (${5S_{1/2}}$ $\rightarrow$ ${5P_{3/2}}$ and ${5S_{1/2}}$ $\rightarrow$ ${6P_{1/2}}$ $\rightarrow$ ${r=69D_{3/2}}$) in Rb vapour cell at room temperature. The probe laser absorption at 780 nm is monitored in the presence of the two control lasers at 421 nm and 1003 nm. In comparison to the previously studied inverted $Ξ$ system, this system has a good signal-to-noise ratio even at room temperature with similar linewidth (around $10$~MHz). We also observe Autler-Towns splitting of the EIT due to the high power of probe and blue control lasers. For completeness and comparison, we also study the EIT in an inverted $Ξ$ system using $5S_{1/2}\rightarrow6P_{1/2}\rightarrow 69D_{3/2}$ transitions.

physics.atom-ph↗

arXiv2024

Role of spontaneously generated coherence (SGC) in laser cooling of atoms

The well-known sub-Doppler polarization gradient cooling in type-I transition ($F_e=F_g+1$) is caused by red-detuned lasers. On the other hand, in type-II transition ($F_e\le F_g$), sub-Doppler cooling takes place through blue-detuned lasers. This opposite behavior for the two types of transitions is due to SGC. In the absence of SGC, both types of transitions show blue-detuned cooling. In this work, we experimentally and theoretically demonstrate blue-detuned cooling for both types of transitions in $^{\textrm{87}}$Rb. For completeness, we compare the temperatures in various configurations.

physics.atom-ph↗

arXiv2024

Direct spectroscopy of Rubidium using a narrow-line transition at 420 nm

The 5S$\to$6P transition in Rubidium (Rb) at 420 nm offers the advantage of a narrower linewidth and diverse applications in quantum technologies. However, the direct spectroscopy at this transition is challenging due to its weak transition strength. In this paper, we have discussed the saturated absorption spectroscopy (SAS) of Rb using the narrow-line transition at 420 nm. We have studied the effect of the temperature of the Rb cell, pump power and the beam size on the SAS dip heights and their linewidths. Additionally, our study offers a comprehensive examination, encompassing all eight error signals of Rb for the 5S$\to$6P transition at 420 nm and 421 nm. These findings contribute valuable insights to the field of laser frequency stabilization of Rb at blue transition and can be useful in quantum technologies based on this transition.

physics.atom-ph↗

arXiv2024

Continuous loading of magneto-optical trap of Rb at narrow transition

We report continuous loading of $^{\textrm{87}}$Rb atoms in a magneto-optical trap (MOT) at narrow linewidth, 420 nm 5S$_{1/2}$, F$=2\rightarrow$ 6P$_{3/2}$, F$=3$ blue transition (blue MOT). Continuous loading of the blue MOT is achieved by superimposing the blue laser beam, inside a hollow core of infrared laser beam driving the broad 5S$_{1/2}$, F$=2\rightarrow$ 5P$_{3/2}$, F$=3$ transition at 780 nm. We typically load $\sim10^{8}$ atoms in the blue MOT in 2.5 seconds. We characterize the continuous loading of blue MOT with various parameters such as magnetic field gradient, detuning, power and diameter of blue MOT beam and diameter of the hollow core (spot) inside the IR MOT beam. We observe that the blue laser beam should overfill the spot of the IR laser beam. This is because the blue laser cools the atoms to a lower temperature even in the presence of the broad IR laser i.e. in the overlapped region and hence helps in loading. We also present the theoretical framework for cooling atoms in the presence of simultaneously two transitions to support the experimental result. This method of continuous loading of the blue MOT can be useful to produce a continuous atomic beam of cold Rb atoms.

physics.atom-ph↗

arXiv2022

Narrow-line cooling of $^{87}$Rb using 5S$_{1/2} \rightarrow$ 6P$_{3/2}$ open transition at 420 nm

Magneto-optical trap (MOT) at narrow (weak) transition offers lower temperature and hence is the key for production of high phase density atomic cloud and subsequently quantum degeneracy with high number of atoms for many elements. In this paper, we describe loading of $^{87}$Rb atoms in the MOT using a narrow open transition at 420 nm from the routinely implemented MOT using broad cyclic transition at 780 nm (IR). The total linewidth of the blue transition, 5S$_{1/2} \rightarrow $ 6P$_{3/2}$ is 1.4 MHz, which is around 4 times narrower than the standard 5S$_{1/2} \rightarrow$ 5P$_{3/2}$ cyclic transition. Using this narrow transition, we have trapped around $10^{8}$ atoms in the MOT with a typical temperature of around $54~μ$K. We have also studied the behavior of the blue MOT with various parameters such as hold time, detuning and power of trapping and repumper beams.

physics.atom-ph↗

arXiv2022

Homodyne detection of a two-photon resonance assisted by cooperative emission

Focusing on the transient regime, we explore atomic two-photon spectroscopy with self-aligned homodyne interferometry in a $Λ$-system with large optical depth. The two light sources at the origin of the interference are the single-photon transient transmission of the probe, and the slow light of the electromagnetically induced transparency. By switching off the probe laser abruptly (flash effect), the transient transmission signal is reinforced by cooperativity, showing enhanced sensitivity to the two-photon frequency detuning. If the probe laser is periodically switched on and off, the amplitude of the transmission signal varies and remains large even for high modulation frequency. This technique has potential applications in sensing, such as magnetometry and velocimetry, and in coherent population trapping clocks.

quant-ph↗

arXiv2021

Nature of interference between Autler-Townes peaks in multi-level system

In this work we present a theoretical frame work to identify the role and the nature of interference between Autler-Townes (AT) peaks (or dressed states) in generic multi-level system. The destructive interference between the AT peaks, gives rise to sharp transparency window known as electromagnetically induced transparency (EIT). In the three-level system, the two AT peaks interferes pair-wise with each other, almost similar to the two-slit interference. In the four-level system, the interference between the three AT peaks is also pair-wise analogous to three-slit interference but has a bit more complicated nature of interference. However, in many practical situations in atomic systems only the simple form of interference similar to three-level system dominates. In the three-level system, the nature of interference (i.e. constructive, destructive or zero/no interference) between the two AT peaks is purely determined by the natural decay rate of the states coupled by the control laser. However, in four-level system the nature of interference between the two extreme AT peaks can be tuned from constructive to destructive by tuning the power of the control laser.

physics.atom-ph↗

arXiv2021

Resolving closely spaced levels for Doppler mismatched double resonance

In this paper, we present experimental techniques to resolve the closely spaced hyperfine levels of a weak transition by eliminating the residual/partial two-photon Doppler broadening and cross-over resonances in a wavelength mismatched double resonance spectroscopy. The elimination of the partial Doppler broadening is based on velocity induced population oscillation (VIPO) and velocity selective saturation (VSS) effect followed by the subtraction of the broad background of the two-photon spectrum. Since the VIPO and VSS effect are the phenomena for near zero velocity group atoms, the subtraction gives rise to Doppler-free peaks and the closely spaced hyperfine levels of the $6\text{P}_{3/2}$ state in Rb are well resolved. The double resonance experiment is conducted on $5\text{S}_{1/2}\rightarrow5\text{P}_{3/2}$ strong transition (at 780~nm) and $5\text{S}_{1/2}\rightarrow6\text{P}_{3/2}$ weak transition (at 420~nm) at room temperature.

physics.atom-ph↗

arXiv2021

Hyperfine measurement of $6\text{P}_{1/2}$ state in $^{87}\text{Rb}$ using double resonance on blue and IR transition

In this paper, we present the spectroscopy of 6P$_{1/2}$ state in $^{87}$Rb using double resonance technique at $780~\text{nm}$ and $421~\text{nm}$. The double resonance technique is implemented using electromagnetically induced transparency (EIT) and optical pumping methods. Using these spectroscopy methods, we have measured the hyperfine splitting of 6P$_{1/2}$ state with precision of $<$400~kHz which agrees well with other spectroscopy methods such as electrical discharge and saturated absorption spectroscopy at $421~\text{nm}$.

physics.atom-ph↗

arXiv2020

Emergent photon pair propagation in circuit QED with superconducting processors

We propose a method to achieve photon pair propagation in an array of three-level superconducting circuits. Assuming experimentally accessible three-level artificial atoms with strong anharmonicity coupled via microwave transmission lines in both one and two dimensions we analyze the circuit Quantum Electrodynamics(QED) of the system. We explicitly show that for a suitable choice of the coupling ratio between different levels, the single photon propagation is suppressed and the propagation of photon pairs emerges. This propagation of photon pairs leads to the pair superfluid of polaritons associated to the system. We compute the complete phase diagram of the polariton quantum matter revealing the pair superfluid phase which is sandwiched between the vacuum and the Mott insulator state corresponding to the polariton density equal to two in the strong coupling regime.

quant-ph↗

arXiv2019

Laser interferometry based on atomic coherence

We demonstrate laser interferometry based on phase difference between the two arms of the interferometer. The experiments are done with a Cs atomic vapor cell at room temperature and use atomic coherence. The interference can be tuned from constructive to destructive by tuning the relative phase between the two arms. It is similar to the Michelson interferometer, but differs in the important aspect of allowing interference when the polarizations in the two arms are orthogonal. This would be a novel method for interfering two independent lasers, which even can allow interfering two independent lasers of completely different wavelengths---such as of UV and IR---and also possibly phase lock them.

physics.atom-ph↗

arXiv2018

Non-Abelian adiabatic geometric transformations in a cold Strontium gas

Topology, geometry, and gauge fields play key roles in quantum physics as exemplified by fundamental phenomena such as the Aharonov-Bohm effect, the integer quantum Hall effect, the spin Hall, and topological insulators. The concept of topological protection has also become a salient ingredient in many schemes for quantum information processing and fault-tolerant quantum computation. The physical properties of such systems crucially depend on the symmetry group of the underlying holonomy. We study here a laser-cooled gas of strontium atoms coupled to laser fields through a 4-level resonant tripod scheme. By cycling the relative phases of the tripod beams, we realize non-Abelian SU(2) geometrical transformations acting on the dark-states of the system and demonstrate their non-Abelian character. We also reveal how the gauge field imprinted on the atoms impact their internal state dynamics. It leads to a new thermometry method based on the interferometric displacement of atoms in the tripod beams.

quant-ph↗

arXiv2018

Single reference atomic based MW interferometry using EIT

Recently atomic based MW electrometry is experimentally demonstrated and interferometry has been proposed. The proposed interferometry bypasses the conventional, electrical circuit based MW interferometry in much superior fashion. However, this scheme requires three different references for characterizing the unknown MW field. In this work we theoretically study a scheme to develop an atomic based MW interferometry having only one referenced MW field. This scheme involves magnetic sublevels in the Rydberg states and hence will be suitable in even isotope of Yb or alkaline earth element where there is no complicacy due to absence of the hyperfine levels. Further, the wavelengths to excite the Rydberg states, are very close and hence cancels the Doppler shift more effectively which increases the amplitude sensitivity. We characterize this system for the phase and the amplitude of the unknown MW field w.r.t to the known field and compare it to the previously studied systems.

physics.atom-ph↗

arXiv2018

Study of CPO resonances on the intercombination line in $^{173}$Yb

We study coherent population oscillations (CPO) in an odd isotope of the two-electron atom Yb. The experiments are done using magnetic sublevels of the $ F_g = 5/2 \rightarrow F_e = 3/2 $ hyperfine transition in $^{173}$Yb of the $ {\rm {^1S_0} \rightarrow {^3P_1}} $ intercombination line. The experiments are done both with and without an appied magnetic field. In the absence of an applied field, the complicated sublevel structure along with the saturated fluorescence effect causes the linewidth to be larger than the 190 kHz natural linewidth of the transition. In the presence of a field (of magnitude 330 mG), a well-defined quantization axis is present which results in the formation of two M-type systems. The total fluorescence is then limited by spin coherence among the ground sublevels. In addition, the pump beam gets detuned from resonance which results in a reduced scattering rate from the $ {\rm ^3P_1} $ state. Both of these effects result in a reduction of the linewidth to a subnatural value of about 100 kHz.

physics.atom-ph↗

arXiv2017

Highly sensitive atomic based MW interferometry

We theoretically study a scheme to develop an atomic based MW interferometry using the Rydberg states in Rb. Unlike the traditional MW interferometry, this scheme is not based upon the electrical circuits, hence the sensitivity of the phase and the amplitude/strength of the MW field is not limited by the Nyquist thermal noise. Further this system has great advantage due to its very high bandwidth, ranging from radio frequency (RF), micro wave (MW) to terahertz regime. In addition, this is \textbf{orders of magnitude} more sensitive to field strength as compared to the prior demonstrations on the MW electrometry using the Rydberg atomic states. However previously studied atomic systems are only sensitive to the field strength but not to the phase and hence this scheme provides a great opportunity to characterize the MW completely including the propagation direction and the wavefront. This study opens up a new dimension in the Radar technology such as in synthetic aperture radar interferometry. The MW interferometry is based upon a six-level loopy ladder system involving the Rydberg states in which two sub-systems interfere constructively or destructively depending upon the phase between the MW electric fields closing the loop.

physics.atom-ph↗

arXiv2017

Micro-wave assisted transparency in a M-system

In this work we theoretically study a five level M-system whose two unpopulated ground states are coupled by a micro-wave (MW) field. The key feature which makes M-systems more efficient in comparison to closed loop $Λ$ systems is the absence of MW field induced population transfer even at high intensities of the later. We examine lineshape of probe absorption as a function of its detuning in the presence of both control and MW fields. The MW field facilitates the narrowing of the probe absorption lineshape in M-systems which is in contrast to closed loop $Λ$-systems. Hence this study opens up a new avenue for atom based phase dependent MW magnetometry.

physics.atom-ph↗

arXiv2015

Polarization-rotation resonances with subnatural widths using a control laser

We demonstrate extremely narrow resonances for polarization rotation in an atomic vapor. The resonances are created using a strong control laser on the same transition, which polarizes the atoms due to optical pumping among the magnetic sublevels. As the power in the control laser is increased, successively higher-order nested polarization rotation resonances are created, with progressively narrower linewidths. We study these resonances in the $D_2$ line of Rb in a room-temperature vapor cell, and demonstrate a width of $0.14 \, Γ$ for the third-order rotation. The explanation based on a simplified $Λ$V-type level structure is borne out by a density-matrix analysis of the system. The dispersive lineshape and subnatural width of the resonance lends itself naturally to applications such as laser locking to atomic transitions and precision measurements.

physics.atom-ph↗