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Three-Photon Rydberg EIT Lineshape Analysis in Rubidium

Jackson Lake

Published Jan 1, 2026• 0 citations
OpenAlex

Abstract

Electromagnetically Induced Transparency detection of high-lying Rydberg states in room-temperature rubidium vapor was investigated using a four state ladder-type excitation scheme with light provided by three External Cavity Diode Lasers (ECDLs) at 780 nm, 776 nm, and 1266 nm. This detection technique was studied by characterizing the lineshape parameters of the EIT transmission peak, specifically the height, width and area of the transparency window as functions of the dressing and coupling laser powers. With the goal of characterizing the linewidth of the transmission signal, a confocal etalon was built and implemented in the optical setup to perform frequency calibration of the EIT spectra. Our experimental results indicate that the EIT transmission peak exhibits a non-monotonic dependence on laser power as we observed that the signal initially increases in amplitude, reaches a maximum value and then decays gradually at higher powers. We also observed power broadening of the linewidth at low dressing powers with constant coupling power, and saturation of the broadening in the middle to high dressing power regime. The EIT linewidth was observed to be approximately constant with varying coupling power in the power regimes studied in this experiment.

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Electromagnetically Induced Transparency detection of high-lying Rydberg states in room-temperature rubidium vapor was investigated using a four state ladder-type excitation scheme with light provided by three External Cavity Diode Lasers (ECDLs) at 780 nm, 776 nm, and 1266 nm. This detection technique was studied by characterizing the lineshape parameters of the EIT transmission peak, specifically the height, width and area of the transparency window as functions of the dressing and coupling laser powers. With the goal of characterizing the linewidth of the transmission signal, a confocal etalon was built and implemented in the optical setup to perform frequency calibration of the EIT spectra. Our experimental results indicate that the EIT transmission peak exhibits a non-monotonic dependence on laser power as we observed that the signal initially increases in amplitude, reaches a maximum value and then decays gradually at higher powers. We also observed power broadening of the linewidth at low dressing powers with constant coupling power, and saturation of the broadening in the middle to high dressing power regime. The EIT linewidth was observed to be approximately constant with varying coupling power in the power regimes studied in this experiment.
Laser spectroscopy experiments are reported on rubidium atoms by using two or three external cavity diode lasers to study multiple resonance transitions in Λ- and V-type systems as well as on (Λ+V)-type system. Electromagnetically induced transparency (EIT) peaks having sub-natural line-widths are found on the Doppler broadened transmission backgrounds with velocity selective enhanced absorption dips. In the presence of a pump laser, probe spectrum shows enhancement of EIT signal by tuning the control laser frequency when the Λ- and V-type EIT signals are made to overlap. Theoretical analysis is carried out by solving the optical Bloch equations for five-level atomic model under Λ configuration. With the numerically simulated spectra, variation of EIT transmission peak with ground state decay rate and excited state spontaneous decay rate are investigated. Effect of pump Rabi frequency on the transmission peak is also shown.
We present nonlinear spectra of four-level ladder cesium atoms employing 6S 1/2 → 6P 3/2→ 7S 1/2 → 30P 3/2 scheme of a room temperature vapor cell. A coupling laser drives Rydberg transition, a dressing laser couples two intermediate levels, and a probe laser optically probes the nonlinear spectra via electromagnetically induced transparency (EIT). Nonlinear spectra are detected as a function of coupling laser frequency. The observed spectra exhibit an enhanced absorption (EA) signal at coupling laser resonance to Rydberg transition and enhanced transmission (ET) signals at detunings to the transition. We define the enhanced absorption (transmission) strength, H EA (H ET), and distance between two ET peaks, γ ET, to describe the spectral feature of the four-level atoms. The enhanced absorption signal H EA is found to have a maximum value when we vary the dressing laser Rabi frequency Ω d, corresponding Rabi frequency is defined as a separatrix point, Ω dSe . The values of Ω dSe and further η = Ω dSe /Ω c are found to depend on the probe and coupling Rabi frequency but not the atomic density. Based on Ω dSe , the spectra can be separated into two regimes, weak and strong dressing ranges, Ω d ≲ Ω dSe and Ω d ≳ Ω dSe , respectively. The spectroscopies display different features at these two regimes. A four-level theoretical model is developed that agrees well with the experimental results in terms of the probe-beam absorption behavior of Rabi frequency-dependent dressed states.
Spectroscopy of Rydberg states has become a popular platform for quantum sensing, with the most common readout scheme being two-photon electromagnetically induced transparency (EIT) using counterpropagating laser beams. In this scheme, the energy resolution of the Rydberg state is set by the spectral linewidth of the EIT feature. While selection criteria for the two-photon resonance can narrow the linewidth to the order of the Rydberg state decay rate for a single atom, the Doppler shift from thermal velocity of the atoms broadens the ensemble linewidth to the order of the decay rate of the intermediate state. Here, we derive an analytic expression for the Doppler residual line shape in the low-power limit and corroborate the results with experiment. For Rb, we find the full-width-at-half-maximum linewidth limit to be 1.84 MHz when scanning the coupling laser and measure an experimental linewidth of 2.04 MHz. These linewidths are around a factor of 2 narrower than previous theoretical estimates as well as previously reported measured linewidths. With this, we demonstrate the most precise two-photon energy resolution of a Rydberg state in thermal vapor to date. We then map out broadening mechanisms near this limit.
A high sensitivity spectroscopy of Rydberg atoms is presented by using electromagnetically induced transparency (EIT) in the 6S(1/2)-6P(3/2)-n D ladder-type system of cesium vapor cell at room temperature. The EIT spectra of 40 D Rydberg state are measured and the dependences of the EIT magnitude and linewidth on the coupling laser power are investigated in detail. The Rydberg EIT linewidth is measured to be about 5.6 MHz when the powers of probe and coupling lasers are 50 microW and 5.2 mW, respectively, and which is close to the natural linewidth of cesium atoms. The effect of double resonance optical pumping on EIT is also investigated. The fine structures of nD (n = 39-55) are measured and the experimental result is in agreement with quantum defect theory.
We investigate the effect of dressing the dark state in a ladder scheme of electromagnetically induced transparency (EIT) involving a Rydberg state by an optical field. We show that similarly to microwave dressing, the dressing by a laser field induces an Autler–Townes splitting of the EIT resonance which results in an absorption dip while scanning the frequency of the dressing laser. Experimental results show that the full width at half-maximum of the dressing-induced dip can become very narrow as the coupling laser power increases, while the probe transmission change Δ T P exhibits a non-monotonic trend. Numerical simulation using the Lindblad master equation attributes this evolution to a transition from the saturated to the linear regime of absorption. This laser dressing approach enables high-resolution, sub-Doppler measurements in room-temperature environments, providing a precise method for probing hyperfine structures in alkali metal atoms with enhanced clarity. Furthermore, we demonstrate frequency stabilization of a home-made 1064 nm laser to the dressing signal, achieving a stability of 1.5×10 −9 at τ ≈30s.
High-power, narrow-linewidth light sources in the visible and UV spectra are in growing demand, particularly as quantum information and sensing research proliferates. Vertical external-cavity surface-emitting lasers (VECSELs) with intra-cavity frequency conversion are emerging as an attractive platform to fill these needs. Using such a device, we demonstrate 3.5 MHz full-width half-maximum Rydberg-state spectroscopy via electromagnetically induced transparency (EIT). The laser's 690 mW of output power at a wavelength of 475 nm enables large Rabi frequencies and strong signal-to-noise ratio in shorter measurement times. In addition, we characterize the frequency stability of the VECSEL using the delayed self-heterodyne technique and direct comparison with a commercial external-cavity diode laser (ECDL). We measure the pre-doubled light's Lorentzian linewidth to be 2π × 5.3(2) kHz, and the total linewidth to be 2π × 23(2) kHz. These measurements provide evidence that intra-cavity frequency-doubled VECSELs can perform precision spectroscopy at and below the MHz level, and are a promising tool for contemporary, and future, quantum technologies.