[Paper Review] Paschen-Back effect and Rydberg-state diamagnetism in vapor-cell electromagnetically induced transparency

Lu Ma, David Anderson+1 more|arXiv (Cornell University)|Feb 18, 2017

Quantum optics and atomic interactions23 references25 citations

TL;DR

This study demonstrates Rydberg electromagnetically induced transparency (EIT) in a 0.7 T magnetic field using a rubidium vapor cell, where all levels—ground, intermediate, and Rydberg—are in the hyperfine Paschen-Back regime. By exploiting isotope-specific magnetic shifts in 85Rb and 87Rb, the authors achieve a magnetic field measurement with ±0.12% relative uncertainty, while observing unexpectedly large Rydberg-state dephasing rates (~50 MHz) attributed to ionization effects.

ABSTRACT

We report on rubidium vapor-cell Rydberg electromagnetically induced transparency (EIT) in a 0.7~T magnetic field where all involved levels are in the hyperfine Paschen-Back regime, and the Rydberg state exhibits a strong diamagnetic interaction with the magnetic field. Signals from both $^{85}\mathrm{Rb}$ and $^{87}\mathrm{Rb}$ are present in the EIT spectra. This feature of isotope-mixed Rb cells allows us to measure the field strength to within a $\pm 0.12$\% relative uncertainty. The measured spectra are in excellent agreement with the results of a Monte Carlo calculation and indicate unexpectedly large Rydberg-level dephasing rates. Line shifts and broadenings due to small inhomogeneities of the magnetic field are included in the model.

Motivation & Objective

• To investigate Rydberg-EIT in strong magnetic fields where all atomic levels are in the hyperfine Paschen-Back regime.
• To exploit differential magnetic shifts between 85Rb and 87Rb isotopes for high-accuracy magnetic field measurement.
• To probe the role of diamagnetic interactions in enhancing sensitivity to field variations.
• To identify and quantify unexpected Rydberg-state dephasing rates in vapor-cell EIT.

Proposed method

• Utilizes a 0.7 T magnetic field generated by NdFeB permanent magnets, with field inhomogeneity mapped via finite-element analysis.
• Employs a dual-channel optical setup: one for Rydberg-EIT and one for saturation spectroscopy to stabilize the probe laser.
• Leverages isotope-mixed Rb vapor to measure field strength via relative frequency separations between 85Rb and 87Rb EIT lines.
• Performs Monte Carlo simulations including Zeeman and diamagnetic terms, field inhomogeneity, and line-pulling effects to model spectral lineshapes.
• Uses frequency-stabilized EIT probe laser locked to a 5S1/2 → 5P3/2 transition to access the |33S1/2, mj=1/2⟩ Rydberg state.
• Measures EIT transmission via lock-in detection at 33 kHz, with laser frequency scanning linearized using a Fabry-Perot cavity.

Experimental results

Research questions

• RQ1 Can Rydberg-EIT in a vapor cell be reliably implemented in a 0.7 T magnetic field where all levels are in the Paschen-Back regime?
• RQ2 How do differential magnetic shifts between 85Rb and 87Rb isotopes enable high-accuracy magnetic field determination?
• RQ3 What is the origin and magnitude of the unexpectedly large Rydberg-state dephasing rate observed in the experiment?
• RQ4 To what extent do magnetic field inhomogeneities and line-pulling effects distort the EIT spectra in this regime?
• RQ5 Can the diamagnetic enhancement of the Rydberg state’s differential magnetic moment be exploited for high-sensitivity field sensing?

Key findings

• The magnetic field strength was measured as 0.6960 T with a relative uncertainty of ±0.12%, based on isotope-differential line shifts.
• The experimental EIT spectra show excellent agreement with Monte Carlo simulations that include field inhomogeneity and line-pulling effects.
• An unexpectedly high Rydberg-state dephasing rate of 2π × 50 MHz (±10 MHz uncertainty) was required to fit the data, suggesting significant decoherence from ionization.
• The diamagnetic contribution to the differential magnetic dipole moment accounts for ~70% of the total, enhancing sensitivity to field changes.
• The spectra exhibit line-pulling of ~10 MHz due to field inhomogeneity, but the frequency ratio used for field calibration remains unaffected.
• The method shows promise for high-precision differential and absolute measurements of strong magnetic fields, especially at higher principal quantum numbers.