Improvement in Variational Quantum Algorithms by Measurement Simplification

After the discovery of Shor's algorithm and Grover's search algorithm, there has been many researches covering the concept of quantum advantage, which insists quantum computers will exhibit specific advantages over classical computers. Google named the advantage as "Quantum Supremacy"[1] and explains for specific problems, quantum computers can surpass classical computer in computation time and required memory capacity. However, complex quantum algorithms such as Shor's algorithm requires number of qubits and gate fidelity exponentially more than currently we have, and therefore investigating executable algorithms that show quantum advantage even with noisy and few qubits have been arised as an important question in the NISQ (Noisy Intermediate-Scale Quantum) era[2]. Among them, VQAs (Variational Quantum Algorithms)[3] have been remarked as efficient algorithms that can been executed in NISQ devices with low limitation. VQA is a hybrid quantum algorithm that utilizes classical optimizer and Variational Quantum Circuit (VQC), it first measures a state's probability after quantum circuit, and passes the result to classical optimizer.