Measurement of the ground-state flux diagram of three coupled qubits as a first step towards the demonstration of adiabatic quantum computation

The ground-state susceptibility of a system consisting of three flux-qubits was measured in the complete three-dimensional flux space around the common degeneracy point of the qubits. The system's Hamiltonian could be completely reconstructed from measurements made far away from the common degeneracy point. The subsequent measurements made around this point show complete agreement with the theoretical predictions which follow from this Hamiltonian. The ground-state anti-crossings of the system could be read out directly from these measurements. This allows one to determine the ground-state flux diagram, which provides the solution for the non-polynomial optimization problem MAXCUT encoded in the Hamiltonian of the three-flux-qubit system. Our results show that adiabatic quantum computation can be demonstrated with this system provided that the minimal energy gap and/or the speed of the read-out is increased.