RF E-field Sensing Using Rydberg Atom-Based Microwave Electrometry
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ORIGINAL PAPER
RF E-field Sensing Using Rydberg Atom-Based Microwave Electrometry Monika1,2, H. S. Rawat1,2 and S. K. Dubey1,2* 1
Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
2
CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012, India Received: 24 August 2020 / Accepted: 10 October 2020 Ó Metrology Society of India 2020
Abstract: In this work, a microwave field is sensed by rubidium atoms instead of a conventional antenna like dipole or horn antenna. Microwave field is projected onto a glass cell containing Rb vapors which act as an antenna in this case. A four-level ladder atomic system is considered for analytical solution, and E-field measurement is reported by utilizing quantum phenomena like electromagnetically induced transparency and Autler–Townes splitting. It has been shown that atoms can also sense weak microwave field with this approach. The amplitude measurement of microwave E-field is changed to frequency measurement, and E-field is evaluated by monitoring the frequency difference between two EIT peaks. Measurement results are reported for variable input microwave power at frequency 15.09 GHz varying from 12.5 lW to 4 mW generated from synthesized signal generator. Moreover, the effect on the EIT resonance due to the distance variation of the source antenna is also discussed. The microwave frequency is detuned from the resonant frequency, and results are reported in this work. Keywords: Electromagnetically induced transparency; Autler–Townes splitting; Rydberg atoms; Microwave electrometry 1. Introduction From the past two decades, the science of measurements is continuously working toward realization of all parameters traceable to either SI units or any physical constant. The measurement techniques of various physical quantities by utilizing the atoms and molecules showed promising results. Atom-based standards have the advantage of selfcalibration due to the invariance of atomic parameters. The length, time and magnetometry standards have already exploited atom-based metrology for absolute measurements of physical quantities [1–3]. Till date, microwave metrology relies on physical antennae to detect the microwave fields which have indirect and complex traceability. The RF and microwaves have a broad range of applications in our everyday life ranging from the field of communication, defence, healthcare, and many more [4]. The rise in the sophisticated technology in microwaves raises the need for highly accurate and precise measurements of electric field. The probes/antennae, currently
under use throughout the world for microwave E-field sensing, have many limitations, e.g., the sensitivity of the probe is governed by the dipole length; it needs to be calibrated; and the metal in the probe perturbs the field being measured [5]. Recently, a new approach has been demonstrated that utilizes the sensitivity of high-lying Rydberg states to RF field in RF electrometry [6–8]. In this approach, the RF field causes the splitting in electromagneti
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