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Quantum Information Processing

Enhancing quantum approximate optimization with CNN-CVaR integration

Pengnian Cai, Kang Shen, Tao Yang, Yuanming Hu, Bin Lv, Liuhuan Fan, Zeyu Liu, Qi Hu, Shixian Chen, Yunlai Zhu, Zuheng Wu, Yuehua Dai, Fei Yang, Jun Wang, Zuyu Xu

Published Jan 24, 2025• 5 citations
Publisher

Abstract

Abstract The Quantum Approximate Optimization Algorithm (QAOA) represents a promising approach for tackling combinatorial optimization challenges on near-term quantum devices. Central to QAOA optimization is the minimization of the expectation of the problem Hamiltonian for parameterized trial quantum states, which motivates the exploration of advanced optimization techniques. In this study, we propose a novel combinatorial optimization strategy, CNN-CVaR-QAOA, which integrates a Convolutional Neural Network (CNN) with Conditional Value at Risk (CVaR) to optimize QAOA circuits. By replacing the traditional loss function with CVaR and leveraging CNN for variational quantum parameter optimization, we demonstrate the superior efficacy of CNN-CVaR-QAOA through experimental validation on Erdos-Renyi random graphs. Our results show enhanced approximation ratios across various graph configurations. Furthermore, we investigate the influence of the CVaR parameter ($\alpha$) on algorithm performance, revealing that lower $\alpha$ values lead to smoother objective functions and improved approximation ratios. CNN-CVaR-QAOA offers significant advantages in optimizing QAOA parameters, particularly in the context of small-scale quantum devices, highlighting its potential to enhance QAOA optimization efforts across diverse optimization domains.

DOI
10.1007/s11128-025-04655-3

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Abstract The Quantum Approximate Optimization Algorithm (QAOA) represents a promising approach for tackling combinatorial optimization challenges on near-term quantum devices. Central to QAOA optimization is the minimization of the expectation of the problem Hamiltonian for parameterized trial quantum states, which motivates the exploration of advanced optimization techniques. In this study, we propose a novel combinatorial optimization strategy, CNN-CVaR-QAOA, which integrates a Convolutional Neural Network (CNN) with Conditional Value at Risk (CVaR) to optimize QAOA circuits. By replacing the traditional loss function with CVaR and leveraging CNN for variational quantum parameter optimization, we demonstrate the superior efficacy of CNN-CVaR-QAOA through experimental validation on Erdos-Renyi random graphs. Our results show enhanced approximation ratios across various graph configurations. Furthermore, we investigate the influence of the CVaR parameter (α\alphaα) on algorithm performance, revealing that lower α\alphaα values lead to smoother objective functions and improved approximation ratios. CNN-CVaR-QAOA offers significant advantages in optimizing QAOA parameters, particularly in the context of small-scale quantum devices, highlighting its potential to enhance QAOA optimization efforts across diverse optimization domains.
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Abstract The Quantum approximate optimization algorithm (QAOA) is a quantum-classical hybrid algorithm aiming to produce approximate solutions for combinatorial optimization problems. In the QAOA, the quantum part prepares a quantum parameterized state that encodes the solution, where the parameters are optimized by a classical optimizer. However, it is difficult to find optimal parameters when the quantum circuit becomes deeper. Hence, there is numerous active research on the performance and the optimization cost of QAOA. In this work, we build a convolutional neural network to predict parameters of depth p + 1 QAOA instance by the parameters from the depth p QAOA counterpart. We propose two strategies based on this model. First, we recurrently apply the model to generate a set of initial values for a certain depth QAOA. It successfully initiates depth 10 QAOA instances, whereas each model is only trained with the parameters from depths less than 6. Second, the model is applied repetitively until the maximum expected value is reached. An average approximation ratio of 0.9759 for Max-Cut over 264 Erdős–Rényi graphs is obtained, while the optimizer is only adopted for generating the first input of the model.
Abstract Quantum computing has recently emerged as a promising approach to solve complex combinatorial optimization problems beyond the reach of classical algorithms. This study explores the integration of machine learning techniques with the Quantum Approximate Optimization Algorithm (QAOA) to improve its effectiveness in graph-based optimization tasks, with a particular focus on the Max-Cut problem. We propose a hybrid framework that utilizes a neural network to dynamically adjust QAOA parameters, leveraging historical data to enhance performance. We conduct a comparative analysis between the machine learning-augmented QAOA and a traditional QAOA implementation. Through extensive simulations on random graphs with up to 2000 nodes, the machine learning-enhanced QAOA demonstrates superior performance, reducing training loss significantly and achieving a final loss of approximately 3.112 x 10-33 compared to 2.34 x 10-15 for the standard QAOA. Statistical analysis reveals a moderate negative correlation between training epochs and loss, highlighting the benefits of continued training while acknowledging other influencing factors. This research highlights the potential of combining quantum algorithms with machine learning to solve real-world optimization problems, offering promising applications in fields such as logistics, finance, and network design.
Hybrid quantum/classical variational algorithms can be implemented on noisy intermediate-scale quantum computers and can be used to find solutions for combinatorial optimization problems. Approaches discussed in the literature minimize the expectation of the problem Hamiltonian for a parameterized trial quantum state. The expectation is estimated as the sample mean of a set of measurement outcomes, while the parameters of the trial state are optimized classically. This procedure is fully justified for quantum mechanical observables such as molecular energies. In the case of classical optimization problems, which yield diagonal Hamiltonians, we argue that aggregating the samples in a different way than the expected value is more natural. In this paper we propose the Conditional Value-at-Risk as an aggregation function. We empirically show -- using classical simulation as well as quantum hardware -- that this leads to faster convergence to better solutions for all combinatorial optimization problems tested in our study. We also provide analytical results to explain the observed difference in performance between different variational algorithms.
The quantum approximate optimization algorithm (QAOA) has numerous promising applications in solving the combinatorial optimization problems on near-term Noisy Intermediate Scalable Quantum (NISQ) devices. QAOA has a quantum-classical hybrid structure. Its quantum part consists of a parameterized alternating operator ansatz, and its classical part comprises an optimization algorithm, which optimizes the parameters to maximize the expectation value of the problem Hamiltonian. This expectation value depends highly on the parameters, this implies that a set of good parameters leads to an accurate solution. However, at large circuit depth of QAOA, it is difficult to achieve global optimization due to the multiple occurrences of local minima or maxima. In this paper, we propose a parameters fixing strategy which gives high approximation ratio on average, even at large circuit depths, by initializing QAOA with the optimal parameters obtained from the previous depths. We test our strategy on the Max-cut problem of certain classes of graphs such as the 3-regular graphs and the Erdös-Rényi graphs.
Abstract The quantum approximate optimization algorithm (QAOA) is a leading iterative variational quantum algorithm for heuristically solving combinatorial optimization problems. A large portion of the computational effort in QAOA is spent by the optimization steps, which require many executions of the quantum circuit. Therefore, there is active research focusing on finding better initial circuit parameters, which would reduce the number of required iterations and hence the overall execution time. While existing methods for parameter initialization have shown great success, they often offer a single set of parameters for all problem instances. We propose a practical method that uses a simple, fully connected neural network that leverages previous executions of QAOA to find better initialization parameters tailored to a new given problem instance. We benchmark state-of-the-art initialization methods for solving the MaxCut problem of Erdős-Rényi graphs using QAOA and show that our method is consistently the fastest to converge while also yielding the best final result. Furthermore, the parameters predicted by the neural network are shown to match very well with the fully optimized parameters, to the extent that no iterative steps are required, thereby effectively realizing an iteration-free QAOA scheme.