Fig. 3: Hamiltonian engineering of exchange interaction.
From: Quantum logic with spin qubits crossing the surface code threshold
a, Frequency detuning of each qubit conditional on the state of the other qubit as a function of barrier pulse amplitude. The horizontal axis shows the real voltage applied to gate B. b, Exchange strength as a function of barrier pulse amplitude. The data are extracted directly from a. c, \({T}_{2}^{\ast }\) of each qubit conditional on the state of the other qubit as a function of barrier pulse amplitude (same colour code as in a). Each data point is averaged for about 8 min. By fitting the \({T}_{2}^{\ast }\) values to a quasistatic noise model (solid lines, see Methods), the low-frequency amplitudes of the fluctuations are estimated as \(\delta {f}_{{{\rm{Q}}}_{1}}=11\,{\rm{k}}{\rm{H}}{\rm{z}}\), \(\delta {f}_{{{\rm{Q}}}_{2}}=24\,{\rm{k}}{\rm{H}}{\rm{z}}\) and δvB = 0.4 mV. d, Shape of the barrier pulse, designed to achieve a high-fidelity CZ gate. e, The cosine-shaped J envelope seen by the qubits during the pulse shown in d.
