Fig. 1: Zitterbewegung in planar cavities.

a Schematic of the planar cavity structure resonantly excited at one point with the photons propagating away along the cavity. b Intensity of the photon field in the cavity when excited resonantly vs. x and y. The colour scale gives the intensity I relative to the peak intensity \(I_0\) in decibel units. The zero of the y-axis is defined as the point of peak intensity vs. y. c Angle and polarisation resolved photoluminescence spectrum showing the dispersion relation \(E\left( {k_y} \right)\) at a fixed \(k_x = 0\) for the case where the birefringent crystal principle axis \(y^\prime\) (\(\varphi = 90\)°, see Supplementary Section 1) is parallel to the direction y along which the polaritons are injected in the resonant excitation experiment. d As panel (c) but for the case where \(x^\prime\) is parallel to y (\(\varphi = 0\)°). In (c) and (d) the colour scale indicates the polarisation degree \(\left( {I_x - I_y} \right)/\left( {I_x + I_y} \right)\) with red indicating x polarisation and blue indicating y polarisation (\(I_x\) and \(I_y\) are the intensities in the x and y polarisations). Points with total intensity \(\left( {I_x + I_y} \right)\) less than 0.20 of the peak have been set to white since the polarisation degree is not well defined for low intensities. e The energy splitting between the TE and TM polarisations for the two values of φ. Points show the values extracted by fitting Lorentzian peaks to the data in panels (c, d). Dashed black curves are the fits described in the main text