A Fidelity Susceptibility Approach to Quantum Annealing of NP-hard   problems
  The computational complexity conjecture of NP $\nsubseteq$ BQP implies that there should be an exponentially small energy gap for Quantum Annealing (QA) of NP-hard problems. We aim to verify how this computation originated gapless point could be understood based on physics, using the quantum Monte Carlo method. As a result, we found a phase transition detectable only by the divergence of fidelity susceptibility. The exponentially small gapless points of each instance are all located in the phase found in this study, which suggests that this phase transition is the physical cause of the failure of QA for NP-hard problems. 
Jun Takahashi and Koji Hukushima
quant-ph cond-mat.dis-nn cond-mat.stat-mech