Efficient population transfer via non-ergodic extended states in quantum spin glass

Understand

We analyze a new computational role of coherent multi-qubit quantum tunneling that gives rise to bands of non-ergodic extended (NEE) quantum states each formed by a superposition of a large number of computational states (deep local minima of the energy landscape) with similar energies.

• NEE provide a mechanism for population transfer (PT) between computational states and therefore can serve as a new quantum subroutine for quantum search, quantum parallel tempering and reverse annealing optimization algorithms.
• We study PT in a quantum n-spin system subject to a transverse field where the energy function $E(z)$ encodes a classical optimization problem over the set of spin configurations $z$.
• Given an initial spin configuration with low energy, PT protocol searches for other bitstrings at energies within a narrow window around the initial one.