The shift of interest from general purpose quantum computers to adiabatic
quantum computing or quantum annealing calls for a broadly applicable and easy
to implement test to assess how quantum or adiabatic is a specific hardware.
Here we propose such a test based on an exactly solvable many body system --
the quantum Ising chain in transverse field -- and implement it on the D-Wave
machine. An ideal adiabatic quench of the quantum Ising chain should lead to an
ordered broken symmetry ground state with all spins aligned in the same
direction. An actual quench can be imperfect due to decoherence, noise, flaws
in the implemented Hamiltonian, or simply too fast to be adiabatic.
Imperfections result in topological defects: Spins change orientation, kinks
punctuating ordered sections of the chain. The number of such defects
quantifies the extent by which the quantum computer misses the ground state,
and is, therefore, imperfect.Comment: 8 pages, 7 figures, to appear in Scientific Reports, authors' list
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