Fig. 4: Magnetospectroscopy of the singlet-triplet qubit.

a Dispersive shift χ as a function of the magnetic field B at an angle of α = 130° and detuning ε. The white dashed line is a fit of the effective two-electron Hamiltonian (Eq. (12)) to the data. b Extracted tunnel rate 2t/2π (black), qubit-photon coupling g₀/2π (blue) and qubit linewidth γ/2π (purple). The bare resonator frequency is indicated by the dashed black line. Shaded areas indicate the errorbars which originate from the uncertainty of the gate lever arm, which was independently measured. c Two-electron energy level diagrams at various magnetic fields with the corresponding field strength indicated in a and b by the given symbols. For clarity a constant offset of 10, 20, and 30 GHz was added to the energy levels at 300, 410 and 600 mT. Given the input power P_in = −128 dBm, the average photon number is n < 0.8 in these experiments (see methods).