The status and prospects of the Q & A experiment with some applications

TL;DR

This paper discusses the development and upgrades of the Q & A experiment aimed at measuring QED birefringence and detecting pseudoscalar-photon interactions, highlighting technical improvements and expected sensitivity improvements.

Contribution

The paper presents a significant upgrade to the Q & A experiment, including a longer interferometer and enhanced magnetic and optical components, to improve measurement sensitivity of QED effects.

Findings

Successful measurement of Cotton-Mouton effects of gases

Upgrade to 7 m interferometer with higher finesse

Projected 28% measurement of QED birefringence in 50 days

Abstract

Motivated to measure the QED birefringence and to detect pseudoscalar-photon interaction, we started to build up the Q & A experiment (QED [Quantum Electrodynamics] and Axion experiment) in 1994. In this talk, we first review our 3.5 m Fabry-Perot interferometer together with our results of measuring Cotton-Mouton effects of gases. We are uprading our interferometer to 7 m armlength with a new 1.8 m 2.3 T permanent magnet capable of rotation up to 13 cycles per second. We will use 532 nm Nd:YAG laser as light source with cavity finesse around 100,000, and aim at 10 nrad/Hz^{1/2} optical sensitivity. With all these achieved and the upgrading of vacuum, QED birefringence would be measured to 28% in about 50 days. Along the way, we should be able to improve on the dichroism detection significantly.