Abstract
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.
Highlights
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
Adiabatic quantum computing1–3–an alternative to the quantum Turing machine paradigm–is at its core very simple and very quantum: Evolve a system from the ground state of an “easy” Hamiltonian H0 to the ground state of H1 that encodes the solution to the problem of interest by varying the parameter s from 0 to 1 in
We put forth a simple test based on the behavior of the exactly solvable quantum Ising chain in transverse field and deploy it on the D-Wave chip
Summary
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 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. 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, imperfect. There are several papers that, with varying degrees of success, model the behavior of D-Wave[5] We applaud such efforts, but aim at a rather different goal–a general TAC
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