Universal Approach to Quantum Adiabaticity via Ancilla Cavity.

A central challenge in the successful implementation of adiabatic quantum algorithms is to maintain the quantum adiabaticity during the entire evolution. However, the energy gap between the ground and the excited states of interacting many-body systems often decreases quickly with the number of qubits, and the quantum adiabaticity can be severely impaired. Despite numerous previous efforts, a practical method to preserve the quantum adiabaticity has yet to be developed. Here we present a universal approach to enhancing the quantum adiabaticity via cavity or circuit QED. By coupling an adiabatic quantum computer to an ancilla cavity, the coupled system can exhibit a bistable regime with bifurcation points, where the time evolution becomes very slow. Utilizing these generic nonlinear features, we show that the energy gap of the adiabatic quantum computer can be positioned between the bifurcation points, which results in strongly-enhanced quantum adiabaticity. We then apply this method to a quantum two-level system, an Exact Cover problem, and a transverse field Ising model. In contrast to previous works, this approach does not require the spectral knowledge of the quantum system or the construction of unphysical interactions and can be applied to a vast variety of adiabatic quantum processes.