Pulse based Variational Quantum Optimal Control for hybrid quantum computing

Abstract

This work studies pulse based variational quantum algorithms (VQAs), which are designed to determine the ground state of a quantum mechanical system by combining classical and quantum hardware. In contrast to more standard gate based methods, pulse based methods aim to directly optimize the laser pulses interacting with the qubits, instead of using some parametrized gate based circuit. Using the mathematical formalism of optimal control, these laser pulses are optimized. This method has been used in quantum computing to optimize pulses for quantum gate implementations, but has only recently been proposed for full optimization in VQAs. Pulse based methods have several advantages over gate based methods such as faster state preparation, simpler implementation and more freedom in moving through the state space. Based on these ideas, we present the development of a novel adjoint based variational method. This method can be tailored towards and applied in neutral atom quantum computers. This method of pulse based variational quantum optimal control is able to approximate molecular ground states of simple molecules up to chemical accuracy and is able to compete with the gate based variational quantum eigensolver in terms of total number of quantum evaluations. The total evolution time $T$ and the form of the control Hamiltonian $H_c$ are important factors in the convergence behavior to the ground state energy, both having influence on the quantum speed limit and the controllability of the system.

15 pages, 16 figures

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• PANSATZ: Pulse-based Ansatz for Variational Quantum Algorithms
• Probabilistic Interpolation of Quantum Rotation Angles
• Recapture Probability for anti-trapped Rydberg states in optical tweezers
• Qubit fidelity under stochastic Schrödinger equations driven by colored noise
• Fidelity-Enhanced Variational Quantum Optimal Control
• Parameterization and optimizability of pulse-level VQEs
• Framework for Learning and Control in the Classical and Quantum Domains
• BBQ-mIS: a parallel quantum algorithm for graph coloring problems
• Pulse family optimization for parametrized quantum gates using spectral clustering
• Hybrid Quantum Singular Spectrum Decomposition for Time Series Analysis
• Tackling the Challenges of Adding Pulse-level Support to a Heterogeneous HPCQC Software Stack: MQSS Pulse
• Consensus-based qubit configuration optimization for variational algorithms on neutral atom quantum systems
• A Robust Strontium Tweezer Apparatus for Quantum Computing
• Pulse engineering via projection of response functions