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Classical optimisation of angles in QAOA for TSP gets stuck in local minima?

Quantum Computing Asked by ile2N on December 8, 2020

I have been trying to implement a QAOA for solving a traveling salesman problem (TSP) using qulacs and python. However, even for 3 cities, the implementation fails. Within QAOA, we try to minimise
$$
begin{equation}
F_p(gamma,beta) = langle gamma,beta | C | gamma,betarangle,
end{equation}
$$

where $C$ is the cost function of the TSP, and $|gamma,betarangle$ is a quantum state depending on these two angles. I had a closer look at my classical optimisation of the angles $beta, gamma$, for which I used the scipy.optimize.minimize function with the Nelder-Mead method. I realised that the resulting optimal angles are highly dependent on the initial angles. Additionally, I had a look at my cost function $C$. It seems like the optimisation got stuck in many local minima.

I have seen several implementations of a QAOA TSP using other software frameworks, and most of them also used scipy.optimize.minimize for the angles optimisation. Is getting stuck in local minima a known issue for QAOA TSP, or do I have to search for another error source? If the first, how can I overcome this issue?

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