  In previous implementations of adiabatic quantum algorithms using spin
systems, the average Hamiltonian method with Trotter's formula was
conventionally adopted to generate an effective instantaneous Hamiltonian that
simulates an adiabatic passage. However, this approach had issues with the
precision of the effective Hamiltonian and with the adiabaticity of the
evolution. In order to address these, we here propose and experimentally
demonstrate a novel scheme for adiabatic quantum computation by using the
intrinsic Hamiltonian of a realistic spin system to represent the problem
Hamiltonian while adiabatically driving the system by an extrinsic Hamiltonian
directly induced by electromagnetic pulses. In comparison to the conventional
method, we observed two advantages of our approach: improved ease of
implementation and higher fidelity. As a showcase example of our approach, we
experimentally factor 291311, which is larger than any other quantum
factorization known.
