Subhadeep De

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 of ≈22× performs close to the diffraction limit and resolves multi-ion clusters. Controlled ion loading and characterization of the trap are performed using 40Ca+. The experimentally determined quadrupole coefficient of the trap is ≈0.3, which is very close to the design value. The relative frequency shift along the spectroscopy beam due to excess micromotion is at the level of 3.5 × 10−18 for 40Ca+. 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.

We report a novel design of a digitally controlled oscillator (DCO), its operation and characteristics, whose performance is boosted with machine learning (ML) implementation. The DCO outputs 10-300MHz at the stability of rubidium atomic clocks, and the finest possible frequency tunability resolution is greatly enhanced to 10mHz with ML. The system described here is dual-channel and easily scalable to multi-channel, where the inter-channel output frequencies and phases are synchronized; however, they are tunable following end users’ control. The system shows inter-channel frequency and phase drifts of 1.3mHz and 3 mrad, respectively, over 24 hours of continuous operation and a phase noise < -140 dBc/Hz at 10 kHz. This makes it suitable for versatile time-sequenced precision RF measurements that simultaneously require multiple outputs with shot-to-shot redundancies. The system can be fully controlled from an in-built touch panel and also from a remote PC, therefore making it user-cum-time friendly.

We report the frequency stabilization of an external cavity diode laser (ECDL) to a reference molecular iodine (I₂) transition at 13,531.18 cm⁻¹ (739.03382 nm). Using the Modulation Transfer Spectroscopy (MTS) method for the highly sensitive detection of weak absorption signals, the Doppler-free absorption peaks of I₂ corresponding to the hot band transition R(78) (1–11) are resolved. The ECDL’s frequency is stabilized with respect to one of the lines lying within the reference absorption band. For this, the iodine vapor cell is heated to 450 °C and the corresponding circularly polarized pump and probe beam powers are maintained at 10 mW and 1 mW, respectively, to avoid power broadening. The short (100 ms) and long-term (50 h) linewidths of the frequency stabilized laser are measured to be 0.75(3) MHz and 0.5(2) MHz, respectively, whereas the natural linewidth of the specific I₂-transitions lie within a range of tens of MHz.

Time and frequency (T&F) measurement with unprecedented accuracy is the backbone for several sophisticated technologies, commensurate with the evolution of human civilisation in the 20th century in terms of communication, positioning, navigation, and precision timing. This necessity drove researchers in the early 1950s to build atomic clocks that have now evolved to a state-of-the-art level, operating at optical wavelengths as optical atomic clocks, which use cold and trapped samples of atomic/ionic species and various other sophisticated diagnostic test techniques. Such ultrahigh-precision accurate clocks have made it possible to probe fundamental aspects of science through incredibly sensitive measurements. On the other hand, they meet the T&F synchronisation standards for classical and emerging quantum technologies at the desired level of accuracy. Considering the impact of optical atomic clocks in the second quantum revolution (quantum 2.0), they have been identified as an indispensable critical technology in worldwide quantum missions, including in India. This article reviews the present international scenario regarding optical atomic clocks and their related technologies and draws a roadmap for their indigenisation over the next decade.

Instability of Fabry-Pérot cavity is investigated for different combinations of dimensions, materials, and support structures by using Finite Element Analysis. Salient results are presented and details will be expanded in the full paper.