Abstract Micromachined vapor cells have revolutionized chip-scale quantum sensors, including magnetometers and atomic clocks. In parallel, Rydberg-atom quantum sensing has emerged as a powerful platform for broadband, non-invasive and ultra-sensitive electrometry, enabling compact atom-based antenna elements for electromagnetic reception, often referred to as quantum antennas. Yet, to date, Rydberg sensing has largely been limited to glass-blown, cm-scale vapor cells. Here, we perform Rydberg spectroscopy and electrometry using a wafer-scale-fabricated Pyrex–Si–Pyrex cell with millimeter-scale dimensions. The Rydberg spectroscopic line is characterized with respect to critical parameters such as temperature, the frequency and amplitude of the applied radio frequency (RF) field, light intensity, and the spatial position of the interrogating beam. Our study reveals lineshapes directly influenced by a complex landscape of electrostatic fields with values up to approximately 0.6 V cm − 1 . By controlling key parameters, we were able to reduce the effect of these internal electric fields, and demonstrate the detection of RF fields assessed using the Autler–Townes splitting with a minimum detectable field of 20 μ V cm − 1 . Our results highlight the potential of micromachined vapor cells for subwavelength electromagnetic field measurements, with applications in communications, near-field RF imaging, and chip-scale quantum technologies.
Research of hot atomic vapor systems has a long history. Recently, much-improved technologies, such as lasers, microwaves and digital/analog control systems, have led to exciting progress in this reviving field. Due to its cryogenic-free and vacuum-free deployment potential, room-temperature and quantum-enabled sensing devices using gaseous atoms have become a popular research topic, and engineering such devices has received considerable attention. Proof-of-principle experiments have been performed demonstrating new ideas such as quantum-enhanced motion sensors, next-generation magnetometers, Rydberg enabled microwave sensors, etc. This thesis focuses on my work related to electromagnetic-field sensing using Rydberg atoms in vapor cells, where Rydberg atoms are excited and detected by electromagnetically induced transparency (EIT) spectroscopy. I first investigate the detection of strong magnetic fields (
sim 1~T) in the Paschen-Back regime. The diamagnetic (quadratic) response of the Rydberg levels makes the atoms sensitive to small fluctuations in field strength on a large background. By implementing an isotope-mixed cell, we demonstrate that accurate measurement, within a relative uncertainty of
pm0.12%. Many Rydberg-enabled radio frequency and microwave sensing applications require a capability of zeroing or intentional tuning of small DC electric fields inside the vapor cell. For this purpose, I explore an in-situ DC electric-field sensing and tuning method without using any bulk or thin film electrodes. I find that the photoelectric effect on the vapor cell walls (with invisible, atomic Rb aggregate layers covering the surfaces) can generate tuning fields up to 0.8~V/cm, with an inhomogeneity of about 2%. The spatial distribution of these fields can be directly monitored by quadratic Stark shifts of the Rydberg atoms. This work may inspire new approaches for DC-field control in miniaturized, metal-free atomic vapor-cell devices. Like many other quantum measurements on hot gaseous samples, short interaction time and other technical decoherence processes are the major factors which limit the precision and, in certain cases, the accuracy of the metrological results. In order to study these effects in the context of EIT, I performed an EIT experiment using a
Lambda-type quantum system consisting of the hyperfine ground states and the first excited electronic state of the Rb atoms contained in a buffer-gas-free thermal vapor cell without anti-relaxation coating. Technical line-broadening effects due to inhomogeneity of stray magnetic fields, laser frequency jitter, transverse beam intensity distribution, interaction time distribution, and atom-wall/impurity gas collisions are studied. Experimental results and numerical simulations are compared. These results provide crucial information and quantitative insights for vapor cell sensor design. The development of compact and multi-functional spectroscopy vapor cells is widely considered to be a critical engineering step towards manufacturing field-deployable sensors for real life applications. My R&D efforts towards fabrication of glass spectroscopy cells with integrated, highly-conductive silicon components are presented in the last part of my thesis. I explored various technical challenges and successfully developed a proof-of-principle prototype from scratch. The device allows the application of electric fields inside the cell for particle trapping and for tuning Rydberg transitions. Further, the highly-conductive silicon components enable microwave polarization filtering for microwave sensing applications, plasma-physics studies, etc. Preliminary experimental/technical data and simulations are presented. In summary, in my thesis I report on a comprehensive study of several spectroscopic and field sensing applications of Rydberg and ground-state atoms in vapor cells, as well as forays into novel methods to engineer vapor cells with embedded electrodes.
Rydberg atoms are highly excited atoms that have large sensitivities to external fields, lending these atoms extraordinary characteristics for fundamental high-precision spectroscopy as well as for electromagnetic-field sensing applications. Recent results on high-precision spectroscopy with cold Rydberg atoms in modulated optical lattices are presented. The discussed approach can serve as a platform for fundamental-physics studies, which include a model-insensitive measurement of the Rydberg constant and a search for wave-like dark matter. As an example for the utility of Rydberg atoms in field sensing applications, an experiment is presented in which the linear Stark effect of cold Rydberg atoms is employed to measure electric fields in cold ion clouds, demonstrating that Rydberg laser spectroscopy allows electrode-free, non-invasive plasma diagnostics.