Tetramer association spectra at different ellipticities obtained by modulating the ellipticity of the microwave field. The solid lines show the fitted line shape, and the dashed lines mark the extracted binding energies. The line shapes are shifted and broadened by the linewidth of the tetramer states and other technical broadening effects ( Methods ). The Rabi frequency of the microwave field is =2 x 29(1) MHz and detuning = 2 x 9.5 MHz. The peak-to-peak modulation amplitude is 1 degree and the modulation time is 100 ms, except for the lowest ellipticity for which we use an amplitude of 0.5 degree and a modulation time of 400 ms. The error bars represent the standard error of the mean of four repetitions.
