Cavity-based chiral polarimetry: parity nonconserving optical rotation in Cs, Dy, and HgH

Abstract

The measurement of single-pass chiral optical rotation and circular dichroism are the most widely used methods for chirality sensing, and are of fundamental importance to many fields in physics, chemistry and biology. The optical rotation method is also one of two successful methods for the measurement of atomic parity nonconservation (PNC), for low-energy tests of the electroweak sector of the standard model. However, PNC optical rotation signals are typically very weak, having been measured only in the most favourable cases of Tl, Bi, and Pb, and their measurement is limited by larger time-dependent backgrounds (such as spurious birefringence) and by imperfect and slow subtraction procedures. Using a novel bowtie cavity with an intracavity Faraday Effect, we have demonstrated three important improvements: (a) the enhancement of the chiral optical rotation angle by the number of the cavity passes (typically ≈1000); (b) the suppression of birefringent backgrounds; and (c) the ability to reverse the sign of the chiral optical rotation signal rapidly, allowing the isolation of the PNC signals from backgrounds. We discuss how these cavity-based improvements may allow the extension of the measurement of PNC optical rotation to atomic and molecular systems that would otherwise be inaccessible, for example to Cs and Dy atoms in magneto-optical traps, and to HgH molecules in jet expansions. For these cases, we show that potentially large PNC signals are possible, and we discuss the potential measurement of nuclear-spin-independent, nuclear-spin-dependent, and isotope-dependent PNC effects.