Open-System Quantum Annealing in Mean-Field Models with Exponential Degeneracy

Real-life quantum computers are inevitably affected by intrinsic noise resulting in dissipative nonunitary dynamics realized by these devices. We consider an open-system quantum annealing algorithm optimized for such a realistic analog quantum device which takes advantage of noise-induced thermaliza...

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Bibliographic Details
Published in:Physical review. X 2016-05, Vol.6 (2), p.021028, Article 021028
Main Authors: Kechedzhi, Kostyantyn, Smelyanskiy, Vadim N.
Format: Article
Language:English
Subjects:
Algorithms
Analog computers
Error correction
Hardware
Ising model
Metastable state
Noise
Optimization
Phase transitions
Potential barriers
Quantum computers
Quantum computing
Quantum tunnelling
Simulated annealing
Simulation
Spin glasses
Temperature dependence
Temperature effects
Thermalization (energy absorption)
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Summary:Real-life quantum computers are inevitably affected by intrinsic noise resulting in dissipative nonunitary dynamics realized by these devices. We consider an open-system quantum annealing algorithm optimized for such a realistic analog quantum device which takes advantage of noise-induced thermalization and relies on incoherent quantum tunneling at finite temperature. We theoretically analyze the performance of this algorithm considering a p -spin model that allows for a mean-field quasiclassical solution and, at the same time, demonstrates the first-order phase transition and exponential degeneracy of states, typical characteristics of spin glasses. We demonstrate that finite-temperature effects introduced by the noise are particularly important for the dynamics in the presence of the exponential degeneracy of metastable states. We determine the optimal regime of the open-system quantum annealing algorithm for this model and find that it can outperform simulated annealing in a range of parameters. Large-scale multiqubit quantum tunneling is instrumental for the quantum speedup in this model, which is possible because of the unusual nonmonotonous temperature dependence of the quantum-tunneling action in this model, where the most efficient transition rate corresponds to zero temperature. This model calculation is the first analytically tractable example where open-system quantum annealing algorithm outperforms simulated annealing, which can, in principle, be realized using an analog quantum computer.
ISSN:2160-3308
2160-3308
DOI:10.1103/PhysRevX.6.021028