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Optics Express

Microwave-dressed spectroscopy of cesium Rydberg atoms under dual-frequency microwave fields

yang yue, Haoan Zhang, Shuli Miao, H. P. Liu

Published Jul 24, 2026• 0 citations
Publisher

Abstract

We present a spectroscopic study of cesium Rydberg atoms confined in a vapor cell and driven by dual microwave fields. The primary microwave field drives the 63D 5/2 -64P 3/2 transition at 2.758 GHz, generating an Autler-Townes-modulated heterodyne spectrum. A secondary microwave field, tuned near the 63D 5/2 -61F 7/2 transition at approximately 12.7 GHz, is applied to systematically investigate the effect of an additional resonant coupling channel on the Rydberg spectral response. By recording the optical spectra as functions of the strength and detuning of the secondary microwave field, we observe a field-dependent spectral shift, an optical background offset, and a redistribution of the microwave-to-optical conversion gain. Notably, we quantitatively characterize the conversion gain itself, which has not been the focus of previous Rydberg heterodyne studies. The dynamic spectral response associated with the 2.758 GHz transition remains discernible across the explored perturbation range, albeit with a gradual reduction in conversion gain as the perturbing field strength increases. The main experimental spectral features are well reproduced by wave-packet evolution calculations that incorporate both microwave couplings. These findings elucidate the role of resonant microwave perturbations in Rydberg EIT/AT spectroscopy and provide practical guidance for interpreting microwave-dressed atomic spectra in complex electromagnetic environments.

DOI
10.1364/oe.606090

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We present a spectroscopic study of cesium Rydberg atoms confined in a vapor cell and driven by dual microwave fields. The primary microwave field drives the 63D 5/2 -64P 3/2 transition at 2.758 GHz, generating an Autler-Townes-modulated heterodyne spectrum. A secondary microwave field, tuned near the 63D 5/2 -61F 7/2 transition at approximately 12.7 GHz, is applied to systematically investigate the effect of an additional resonant coupling channel on the Rydberg spectral response. By recording the optical spectra as functions of the strength and detuning of the secondary microwave field, we observe a field-dependent spectral shift, an optical background offset, and a redistribution of the microwave-to-optical conversion gain. Notably, we quantitatively characterize the conversion gain itself, which has not been the focus of previous Rydberg heterodyne studies. The dynamic spectral response associated with the 2.758 GHz transition remains discernible across the explored perturbation range, albeit with a gradual reduction in conversion gain as the perturbing field strength increases. The main experimental spectral features are well reproduced by wave-packet evolution calculations that incorporate both microwave couplings. These findings elucidate the role of resonant microwave perturbations in Rydberg EIT/AT spectroscopy and provide practical guidance for interpreting microwave-dressed atomic spectra in complex electromagnetic environments.
We show experimentally obtained frequency- and power-dependent optical response of a room-temperature cesium vapor cell used as a Rydberg microwave receiver based on electromagnetically induced transparency. An applied microwave field couples the 70S1/2{70S_{1/2}}70S1/2​ Rydberg state to the nearby 70P1/2{70P_{1/2}}70P1/2​, 70P3/2{70P_{3/2}}70P3/2​, 69P1/2{69P_{1/2}}69P1/2​, and 69P3/2{69P_{3/2}}69P3/2​ states, modifying the probe-transmission spectrum. Probe transmission is recorded over a 800 MHz range of coupling laser detunings. These EIT spectra are measured for RF frequencies from 9 to 13.5 GHz and over a 40 dB range of RF power. We analyze the RF induced splittings in the recorded EIT spectra. We observe both limiting cases, where the EIT peak separation is either dominated by the RF detuning or by the RF power. At higher powers we are also able to observe complex features due to coupling of multiple nearby Rydberg states. We further analyze the probe-transmission signal at zero coupling-laser detuning. Sigmoidal fits to the power-response curves are used to determine the midpoint power and the 10-90% transition interval as functions of RF frequency.
We examine spectral signatures of Rydberg atoms driven with near-resonant dual-tone radio-frequency (RF) fields in the regime of strong driving. We experimentally demonstrate and theoretically model a variety of nonlinear and multiphoton phenomena in the atomic Rydberg response that manifest in the EIT spectra. Our results echo previous studies of two-level atoms driven with bichromatic optical fields. In comparison to the optical studies, the RF-driven Rydberg system utilizes a more complex excitation pathway, and electromagnetic fields from two different spectral regimes: a two-photon optical excitation continuously creates highly excited Rydberg atoms, while RF fields drive resonant coupling between the Rydberg levels and generate strong mixing. Yet, our spectra reflect nearly identical effects of the dual-tone RF fields on the atomic Rydberg observables, showing detuning-dependent splittings and Rabi frequency dependent peak numbers and relative strengths, and avoided crossings at subharmonic resonances. We thus validate previous two-state models in this more complex physical system. In the context of Rydberg electrometry, we use these investigations to explore a technique where we tune a known RF field to observe spectra which give frequency and power of an unknown RF field using the complex dual-tone spectra.
We present an electromagnetically induced transparency and Aulter-Townes (EIT-AT) spectrum of a Rydberg three-level atom that is dressed with a microwave field in a room-temperature cesium cell. The EIT is a quantum coherent effect produced by the interaction of atoms with electromagnetic waves, which leads to the decrease of the absorption for a weak resonant probe laser. AT splitting refers to the phenomenon, that the absorption line splits when an electromagnetic field that is in resonance or near resonance acts on the transition of atoms. Rydberg atoms are extremely sensitive to an external electric field due to their large polarizabilities and microwave transition dipole moments, which can be used to measure the external field. In this work, a Rydberg three-level EIT is used to detect Rydberg atom and AT splitting induced by the microwave field. Cesium levels 6S1/2, 6P3/2 and 50S1/2 constitute a Rydberg three-level system, in which a weak probe laser locking to the transition from 6S1/2 to 6P3/2 couples ground-state transition and the strong coupling laser resonates on the Rydberg transition from 6P2/3 to 50S1/2. The two Rydberg levels 50S1/2 and 50P1/2 are coupled with the microwave field at a frequency of 30.852 GHz, leading to the AT splitting of EIT line and forming an EIT-AT spectrum, which is used to measure the electric field amplitude of microwave. In order to further study the EIT-AT splitting characteristics of the Rydberg levels, we carry out a series of measurements by changing the microwave field. The experimental results show a broadened EIT-AT signal for the weak field range and the four-peak spectrum for the strong field, which is attributed to the inhomogeneity of the microwave field. The microwave in cesium cell, emitted by a function generator, shows inhomogeneous behavior such that the atoms interacting with the laser field experience the different fields, leading to the line broadened and multi-peak EIT-AT spectra. For the microwave transition of nS1/2-nP1/2 in this paper, a pair of EIT-AT lines should be obtained for an electric field value. The broadening of the EIT-AT spectrum and the multi-peak structure here are due to the inhomogeneity of the microwave field measurement. We propose a method to increase the spatial resolution by reducing the length of cesium cell. The result in this work provides a method of measuring the field amplitude and monitoring the distribution of microwave electric field, meanwhile the spatial resolution of the measurements can be improved by reducing the size of the cell.
We present a two-photon microwave spectra of cesium Rydberg atoms in the room-temperature vapor cell. The three-level atom including a ground state 6S1/2 (F = 4), an excited state 6P3/2 (F′ = 5) and Rydberg state consists of Rydberg electromagnetically induced transparency (Rydberg-EIT), that is employed to detect the microwave two-photon spectra. The microwave field with frequency ν DD = 11.42865 GHz couples the transition of Rydberg energy level |68D5/2〉 → |69D5/2〉, measured two-photon spectra display a rich of information including the microwave ac Stark shifts and two-photon Autler-Townes (AT) splitting. In the strong microwave field, the two-photon spectroscopy shows the state mixture between |68D5/2〉 and |68D3/2〉 Stark lines. The microwave two-photon spectra of the |69S1/2〉 → |70S1/2〉 transition coupled with frequency ν SS = 11.73503 GHz are also presented. The Floquet theory is employed to simulate the two-photon microwave spectra, showing the good agreement with the measurements. The work suggests the new method that may be used to investigate the multi-photon field-atom interaction and as an atom-based technique for precision field measurements.
In this paper, we report an atomic oscillator in Ku band and its application for electric field (E-field) sensing with Cs Rydberg atoms in a room-temperature vapor cell. The oscillator is associated with the Cs Rydberg transition of 362D5/2– 372P3/2at 16.316 GHz which is generated with a two-laser double-resonance excitation. We characterized the energetics and the dipole moment of the Rydberg transition and used Electromagnetically Induced Transparency (EIT) and Autler-Townes (AT) effects for detecting continuous and amplitude/frequency modulated microwave E-fields. To enhance the oscillator’s response to weak signals, a superheterodyne technique was incorporated into the Rydberg oscillator system, which resulted in an improvement in the oscillator’s sensitivity by 100 times. Furthermore, our modeling shows that the Cs Rydberg atomic oscillator can be tuned to broad frequency ranges from MHz to THz for various RF applications.
Recently, Rydberg atoms have attracted increasing interests for applications as electric field sensors, RF spectrometers, and microwave receivers. In this paper, we present experimental studies of a cesium (Cs) Rydberg atomic microwave receiver and its temporal response characteristics to amplitude modulation (AM), frequency modulation (FM), and binary phase shift keying (BPSK) modulation. The receiver is associated with the Cs Rydberg transitions of n2D5/2 – (n+1)2P3/2 at various frequencies, which is generated by double-resonance laser excitations in a room temperature Cs vapor cell. We use the Electromagnetically Induced Transparency (EIT) and Autler-Townes (AT) effects to directly receive modulated microwave signals and recover the data encoded in the carriers. We demonstrated AM and FM digital data transmissions at data rates up to 1 Mbps and BPSK modulation and demodulation with a clock frequency of 250 kHz. Modulation depths up to 90% are experimentally observed and studied as a function of the modulation clock frequency. We also perform modeling to show that Cs atoms have accessible Rydberg transitions at frequencies covering the range from below GHz to THz for wideband microwave receiver applications across RF systems.