arXiv subjects

Subhadeep De

Publications and source records attributed to Subhadeep De.

3 recordsLinked to original sources

arXiv2026

Endcap-Type Paul Trap for Precision Spectroscopy and Studies of Controlled Interactions

We present the design and fabrication of an endcap-type Paul trap. The trap is designed for studies with Ca$^{+}$ and Yb$^{+}$. The design, fabrication process, and characterization are presented in detail with a focus on trapping a single compensated ion at the rf node. A custom-built imaging system of $NA = 0.14$ and magnification $\approx 22 \times$ performs close to diffraction-limit and resolves multi-ion clusters. Controlled ion loading and characterization of the trap are performed using $^{40}$Ca$^{+}$. The experimentally determined quadrupole coefficient of the trap is $\approx 0.3$, which is very close to the design value. The relative frequency shift along the spectroscopy beam due to excess micromotion (EMM) is at the level of $3.5\times 10^{-18}$ for $^{40}$Ca$^{+}$. Applications of this trap encompass single-ion-based optical frequency standards, tests of fundamental physics, the study of mesoscopic Coulomb clusters, and the controlled interaction of a single ion with co-trapped atoms.

physics.atom-ph↗

arXiv2025

Frequency drift corrected ultra-stable laser through phase-coherent fiber producing a quantum channel

Phase coherent fibers (PCF) are essential to distribute nearly monochromatic photons, ultra-stable in their frequency and phases, which have demanding requirements for state-of-the-art networked experiments, quantum as well as very high-speed communications. We report the development of a novel system that produces PCF links, also actively corrects the unavoidable slow frequency drift of the source laser. The PCF follows white phase noise limited $\sigma_o \times \tau^{-1}$ stability behavior having $\sigma_o$ values $1.9(2) \times 10^{-16}$ and $2.6(1) \times 10^{-16}$ for a 3.3 km field-deployed and 71 km spool fibers, respectively, with up to 47.5 dB suppression of the phase noise compared to a normal fiber. Additionally, the system is featured to correct the source laser's 33.8 mHz/s frequency drift to as low as $\simeq 0.05$ mHz/s. Therefore, this all-in-one solution producing a quantum link can potentially enhance the effectiveness of the twin field quantum key distribution (TF-QKD) by nearly a 73-fold reduction of the QBER that arises from using unstabilized fiber links, as well as relaxes the laser frequency drift correction constraints by severalfold.

quant-ph↗

arXiv2014

Optimally focused cold atom systems obtained using density-density correlations

Resonant absorption imaging is a common technique for detecting the two-dimensional column density of ultracold atom systems. In many cases, the system's thickness along the imaging direction greatly exceeds the imaging system's depth of field, making the identification of the optimally focused configuration difficult. Here we describe a systematic technique for bringing Bose-Einstein condensates (BEC) and other cold-atom systems into an optimal focus even when the ratio of the thickness to the depth of field is large: a factor of 8 in this demonstration with a BEC. This technique relies on defocus-induced artifacts in the Fourier-transformed density-density correlation function (the power spectral density, PSD). The spatial frequency at which these artifacts first appear in the PSD is maximized on focus; the focusing process therefore both identifies and maximizes the range of spatial frequencies over which the PSD is uncontaminated by finite-thickness effects.

physics.atom-ph↗