Universal Approach to Quantum Adiabaticity via Ancilla Cavity. (arXiv:1802.02285v1 [quant-ph])

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.

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