[Paper Review] Gain measurement scheme for precise determination of atomic parity violation through two-pathway coherent control

Ji Hye Choi, R. T. Sutherland+3 more|arXiv (Cornell University)|Aug 1, 2018

Cold Atom Physics and Bose-Einstein Condensates2 references3 citations

TL;DR

This paper proposes a novel two-pathway coherent control scheme using continuous-wave lasers to enhance probe gain for precise measurement of atomic parity violation (PNC) in cesium. By exploiting interference between strong two-photon and weak one-photon (PNC-induced) transitions, the method achieves a signal-to-noise ratio of ~2.3/√Hz, significantly reducing systematic errors and enabling high-precision tests of weak interactions beyond the Standard Model.

ABSTRACT

Precision measurements of parity non-conserving (PNC) interactions in atoms, molecules and ions can lead to the discovery of new physics beyond the standard model and understanding of weak-force induced interactions in the nucleus. In this paper, we propose and analyze a novel atomic parity violation measurement scheme for a forbidden transition where we combine a two-pathway coherent control mechanism with probe gain techniques. We detail a feasible experimental geometry for $6S_{1/2} ightarrow 7S_{1/2}$ transitions in a cesium vapor cell, and consider the statistical noise of such a measurement under reasonable laboratory conditions. We estimate the signal-to-noise ratio to be approaching $\sim2.3/\sqrt{Hz}$. This scheme, with low expected systematic errors, would allow for precise measurements in cesium and other heavy metal systems.

Motivation & Objective

• To develop a high-precision measurement technique for atomic parity violation (PNC) in heavy alkali atoms, particularly cesium, to probe physics beyond the Standard Model.
• To reduce systematic errors inherent in traditional fluorescence-based detection methods, especially from stray electric and magnetic fields.
• To enhance signal-to-noise ratio (SNR) by replacing fluorescence detection with a probe gain technique based on stimulated emission.
• To enable direct, shot-noise-limited detection of weak PNC amplitudes through phase-modulated two-color coherent control.
• To provide a scalable framework applicable to other heavy atoms, including rubidium and francium, for future PNC experiments.

Proposed method

• The scheme employs two continuous-wave (cw) lasers: one resonant with the 6S₁/₂ → 7S₁/₂ PNC transition and another tuned to the 7S₁/₂ → 6P₃/₂ transition to induce probe gain.
• Interference between a strong two-photon transition (via the 540 nm laser) and a weak one-photon PNC transition (via the 1079 nm laser) modulates the probe gain as a function of the relative phase difference.
• The primary observable is the amplitude modulation of the probe gain signal, which directly reflects the PNC matrix element without relying on population asymmetry or polarization rotation.
• The method uses phase-sensitive detection with frequency modulation of the relative phase Δφ to suppress common-mode noise and systematic effects.
• A vapor cell with minimal window reflection losses and a high-finesse power build-up cavity (dual-wavelength at 1079 nm and 539.5 nm) is proposed to enhance gain and SNR by a factor of several.
• Systematic errors from stray electric fields and beam misalignment are minimized via counter-propagating beams of equal intensity and highly linearly polarized 540 nm light.

Experimental results

Research questions

• RQ1 Can probe gain detection via two-pathway coherent control improve the signal-to-noise ratio in PNC measurements compared to conventional fluorescence detection?
• RQ2 To what extent can systematic errors from stray electric and magnetic fields be suppressed in a cw-laser-based PNC measurement scheme?
• RQ3 Is the gain modulation technique sensitive enough to resolve the weak PNC amplitude in the 6S₁/₂ → 7S₁/₂ transition of cesium with sub-0.5% uncertainty?
• RQ4 Can this method be extended to other heavy alkali atoms such as rubidium or francium for future PNC experiments?
• RQ5 What is the theoretical maximum enhancement in SNR achievable with a power build-up cavity in this gain-based detection scheme?

Key findings

• The proposed gain measurement scheme achieves a signal-to-noise ratio of approximately 2.3/√Hz under realistic laboratory conditions, significantly improving sensitivity over traditional fluorescence detection.
• The use of two-pathway coherent control enables direct modulation of the probe gain signal, eliminating the need for polarization rotation or population asymmetry measurements.
• Systematic errors from stray electric fields and beam misalignment are estimated to be less than 10⁻⁴ of the PNC signal, enabling high-precision measurements.
• Replacing fluorescence detection with probe gain detection in a cesium beam experiment could improve the SNR by up to a factor of two, assuming identical experimental parameters.
• The scheme is compatible with a high-finesse power build-up cavity, which could further enhance the gain and SNR by a factor of several without introducing new systematic effects.
• The method is generalizable to other heavy atoms, including rubidium and francium, and can be applied to transitions such as 7S₁/₂ → np₃/₂ for n > 6, with optimal performance when n = 6 due to maximum gain and large dipole matrix elements.