arXiv subjects

Ajay Wasan

Publications and source records attributed to Ajay Wasan.

12 recordsLinked to original sources

arXiv2026

Finite-blockade dynamics of a three-qubit ccz gate in neutral-atom arrays

We present a theoretical study of finite-blockade dynamics in a symmetric three-neutral-atom system, providing a framework for understanding high-fidelity multiqubit quantum operations. The transition from the finite- to the strong-blockade regime is systematically investigated to examine the effects of finite Rydberg blockade. Using a single Gaussian laser pulse, we analyze the complete gate dynamics while explicitly accounting for population leakage into non-computational Rydberg states. By exploiting the permutation symmetry of the system, we construct a symmetry-adapted Hamiltonian that reduces the computational complexity while preserving the exact dynamics. This enables a systematic investigation of the interplay among the Rabi frequency, laser detuning, and Rydberg blockade strength, leading to the identification of optimal operating regimes with high fidelity, fast gate operation, and suppressed leakage. We further quantify the dominant error mechanisms, including phase errors, population leakage, and finite Rydberg-state lifetimes, and evaluate their impact on the gate fidelity. Our results demonstrate experimentally accessible high-fidelity gate operation and provide practical guidelines for multi-qubit quantum computing.

quant-ph↗

arXiv2025

Segmentation-Aware Generative Reinforcement Network (GRN) for Tissue Layer Segmentation in 3-D Ultrasound Images for Chronic Low-back Pain (cLBP) Assessment

We introduce a novel segmentation-aware joint training framework called generative reinforcement network (GRN) that integrates segmentation loss feedback to optimize both image generation and segmentation performance in a single stage. An image enhancement technique called segmentation-guided enhancement (SGE) is also developed, where the generator produces images tailored specifically for the segmentation model. Two variants of GRN were also developed, including GRN for sample-efficient learning (GRN-SEL) and GRN for semi-supervised learning (GRN-SSL). GRN's performance was evaluated using a dataset of 69 fully annotated 3D ultrasound scans from 29 subjects. The annotations included six anatomical structures: dermis, superficial fat, superficial fascial membrane (SFM), deep fat, deep fascial membrane (DFM), and muscle. Our results show that GRN-SEL with SGE reduces labeling efforts by up to 70% while achieving a 1.98% improvement in the Dice Similarity Coefficient (DSC) compared to models trained on fully labeled datasets. GRN-SEL alone reduces labeling efforts by 60%, GRN-SSL with SGE decreases labeling requirements by 70%, and GRN-SSL alone by 60%, all while maintaining performance comparable to fully supervised models. These findings suggest the effectiveness of the GRN framework in optimizing segmentation performance with significantly less labeled data, offering a scalable and efficient solution for ultrasound image analysis and reducing the burdens associated with data annotation.

cs.CV↗

arXiv2024

ShaNQar: Simulator of Network Quantique

The nature-inspired field of quantum communication has witnessed exciting developments over the past few years with countries all over the world working hard to scale their experimental quantum networks to larger sizes and increased coverage. Evidently, quantum network simulators are the need of the hour as they provide a framework for tuning hardware parameters, optimizing control protocols, and testing configurations of large and complex quantum networks before their deployment in the real world. In this work, we present ShaNQar (Simulator of Network Quantique): a modular and customizable photonic quantum network simulator. It comprises models of components such as photons, lasers, neutral density filters, sources of entangled photon pairs, communication channels, mirrors, waveplates, beam splitters, single photon detectors, and nodes which incorporate a diverse set of tunable parameters for variability and versatility. It enables adaptive timing control and synchronization with virtually no simulation time resolution limit and features a 'plug and play' design for faster coding and efficient execution. We successfully simulated previous real-life experimental setups for Quantum Key Distribution (QKD) and quantum teleportation, thereby, demonstrating the reliability and accuracy of ShaNQar.

quant-ph↗

arXiv2016

Wavelength mismatch effect in electromagnetically induced absorption

We present a theoretical investigation of the phenomenon of electromagnetically induced absorption (EIA) in a 4-level system consisting of vee and ladder subsystems. The four levels are coupled using one weak probe field, and two strong control fields. We consider an experimental realization using energy levels of Rb. This necessitates dealing with different conditions of wavelength mismatch---near-perfect match where all three wavelengths are approximately equal; partial mismatch where the wavelength of one control field is less than the other fields; and complete mismatch where all three wavelengths are unequal. We present probe absorption profiles with Doppler averaging at room temperature to account for experiments in a room temperature Rb vapor cell. Our analysis shows that EIA resonances can be studied using Rydberg states excited with diode lasers.

physics.atom-ph↗

arXiv2015

Optical properties of an inhomogeneously broadened multilevel V-system in the weak and strong probe regimes

We present a theoretical model, using density matrix approach, to study the effect of weak as well as strong probe field on the optical properties of an inhomogeneously broadened multilevel V-system of the $^{87}$Rb D2 line. We consider the case of stationary as well as moving atoms and perform thermal averaging at room temperature. The presence of multiple excited states results in asymmetric absorption and dispersion profiles. In the weak probe regime, we observe the partial transparency window due to the constructive interference occurs between transition pathways at the line center. In a room temperature vapour, we obtain an increased linewidth of the transparency window and steep positive dispersion. For a strong probe regime, the transparency window with normal dispersion switches to enhanced absorption with anomalous dispersion at the line center. Here, we show how the electromagnetically induced transparency (EIT) depends on the polarizations of the applied fields. We also discuss the transient behaviour of our system which agrees well with the corresponding absorption and dispersion profiles. This study may help to understand optical switching and controllability of group velocity.

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↗

arXiv2005

High-resolution hyperfine spectroscopy of excited states using electromagnetically-induced transparency

We use the phenomenon of electromagnetically-induced transparency in a three-level atomic system for hyperfine spectroscopy of upper states that are not directly coupled to the ground state. The three levels form a ladder system: the probe laser couples the ground state to the lower excited state, while the control laser couples the two upper states. As the frequency of the control laser is scanned, the probe absorption shows transparency peaks whenever the control laser is resonant with a hyperfine level of the upper state. As an illustration of the technique, we measure hyperfine structure in the $7S_{1/2}$ states of $^{85}$Rb and $^{87}$Rb, and obtain an improvement of more than an order of magnitude over previous values.

physics.optics↗

arXiv2002

Laser cooling and trapping of Yb from a thermal source

We have successfully loaded a magneto-optic trap for Yb atoms from a thermal source without the use of a Zeeman slower. The source is placed close to the trapping region so that it provides a large flux of atoms that can be cooled and captured. The atoms are cooled on the ${^1S_0} \leftrightarrow {^1P_1}$ transition at 398.8 nm. We have loaded all seven stable isotopes of Yb into the trap. For the most abundant isotope ($^{174}$Yb), we load more than $10^7$ atoms into the trap within 1 s. For the rarest isotope ($^{168}$Yb) with a natural abundance of only 0.13%, we still load about $4 \times 10^5$ atoms into the trap. We find that the trap population is maximized near a detuning of $-1.5Γ$ and field gradient of 75 G/cm.

physics.atom-ph↗

arXiv2002

Observation of sub-natural linewidths for cold atoms in a magneto-optic trap

We have studied the absorption of a weak probe beam through cold rubidium atoms in a magneto-optic trap. The absorption spectrum shows two peaks with the smaller peak having linewidth as small as 28% of the natural linewidth. The modification happens because the laser beams used for trapping also drive the atoms coherently between the ground and excited states. This creates ``dressed'' states whose energies are shifted depending on the strength of the drive. Linewidth narrowing occurs due to quantum coherence between the dressed states. The separation of the states increases with laser intensity and detuning, as expected from this model.

physics.atom-ph↗

arXiv2002

High-accuracy wavemeter based on a stabilized diode laser

We have built a high-accuracy wavelength meter for tunable lasers using a scanning Michelson interferometer and a reference laser of known wavelength. The reference laser is a frequency stabilized diode laser locked to an atomic transition in Rb. The wavemeter has a statistical error per measurement of 5 parts in $10^7$ which can be reduced considerably by averaging. Using a second stabilized diode laser, we have verified that systematic errors are below 4 parts in $10^8$.

physics.ins-det↗

arXiv2002

Loading of a Rb magneto-optic trap from a getter source

We study the properties of a Rb magneto-optic trap loaded from a commercial getter source which provides a large flux of atoms for the trap along with the capability of rapid turn-off necessary for obtaining long trap lifetimes. We have studied the trap loading at two different values of background pressure to determine the cross-section for Rb--N$_2$ collisions to be 3.5(4)x10^{-14} cm^2 and that for Rb--Rb collisions to be of order 3x10^{-13} cm^2. At a background pressure of 1.3x10^{-9} torr, we load more than 10^8 atoms into the trap with a time constant of 3.3 s. The 1/e lifetime of trapped atoms is 13 s limited only by background collisions.

physics.atom-ph↗

arXiv2002

Sub-natural linewidth in room-temperature Rb vapor using a control laser

We demonstrate two ways of obtaining sub-natural linewidth for probe absorption through room-temperature Rb vapor. Both techniques use a control laser that drives the transition from a different ground state. The coherent drive splits the excited state into two dressed states (Autler-Townes doublet), which have asymmetric linewidths when the control laser is detuned from resonance. In the first technique, the laser has a large detuning of 1.18 GHz to reduce the linewidth to 5.1 MHz from the Doppler width of 560 MHz. In the second technique, we use a counter-propagating pump beam to eliminate the first-order Doppler effect. The unperturbed probe linewidth is about 13 MHz, which is reduced below 3 MHz (0.5 Γ) at a detuning of 11.5 MHz.

physics.atom-ph↗