Experimental observation of optical rotation generated in vacuum by a magnetic field

TL;DR

The experimental observation of a light polarization rotation in vacuum in the presence of a transverse magnetic field is reported, and the relevance of this result in terms of the existence of aLight, neutral, spin-zero particle is discussed.

Abstract

We report the experimental observation of a light polarization rotation in vacuum in the presence of a transverse magnetic field. Assuming that data distribution is Gaussian, the average measured rotation is (3.9+/-0.5)e-12 rad/pass, at 5 T with 44000 passes through a 1m long magnet, with lambda = 1064 nm. The relevance of this result in terms of the existence of a light, neutral, spin-zero particle is discussed.

Figures (4)

• Figure 1: Schematic layout of the PVLAS experimental apparatus. P1 and P2 crossed polarizing prisms, M1 and M2 Fabry-Perot cavity mirrors, QWP quarter-wave plate, SOM ellipticity modulator, RGA residual gas analyzer.
• Figure 2: Typical Fourier amplitude spectra from vacuum rotation data ($P\sim10^{-8}$ mbar) with and without magnetic field. Both spectra were taken with the magnet rotating. Arrows and numbers below the curves indicate the expected position of sidebands with frequency shifts that are integer multiples of $\nu_{m}$; the relevant signal peaks correspond to frequency shifts of $\pm 2\nu_{m}$.
• Figure 3: Polar plot showing the distribution of rotation data in vacuum with $B=5$ T and (a) the QWP in the $90^{\circ}$ position, and (b) the QWP in the $0^{\circ}$ position. Each data point corresponds to a single 100 s record. The statistical uncertainties from the fit procedure are small ($\sim10^{-12}$ rad/pass) and are omitted for clarity. Solid lines represent the resulting average vectors and the dotted line the physical axis.
• Figure 4: Polar plot showing the weighted averages of the vectors shown in Figure 3. Angles are measured in degrees and amplitudes in rad/pass. The dotted line at $15.1^{\circ}$ shows the direction of the physical axis. The vectors $0$ and $90$ represent the average rotations for two orientations of the QWP, with ellipses at their tips giving the $3\sigma$ uncertainty regions. The vectors $\Delta$ and $\Sigma$ are the half-difference and half-sum of the average vectors, respectively.