Experimental Study Towards Witnessing The Advantage Of Quantum Computing

Quantum computing is an exciting new computing paradigm based on quantum-mechanical phenomena,such as entanglement and superposition.A quantum system can carry information of a huge number of basis states,which can be operated by quantum gates simultaneously.Scientists have already designed quantum algorithms,such as Shor's and Grover's algorithms,which are supposed to solve certain problems much more quickly than any classical counterparts.However,based on the currently available fidelity values of the quantum gates,millions of physical qubits are required for building a practical quantum computer to run Shor's algorithm,which seems unrealistic within the next twenty years.Therefore scientists have designed a well-defined computational task in absence of the error correction scheme,which relies on the implementation of quantum random circuits to demonstrate quantum supremacy.This thesis covers what I have learned and thought during my graduate research and it is organized as follows.In chapter 1,we introduce the background of quantum computing and list the conditions that are necessary for constructing a quantum computer.Superconducting circuits based on Josephson junctions are a promising platform for realizing quantum computing,owing to their advantages in design,integration,and manipulation.In chapter 2,we introduce the basic knowledge of superconducting circuits,illustrating how they can be considered as qubits and how they interact with each other.In chapter 3,we show how to manipulate and couple qubits.We have successfully tuned the coupling strength between Gmon qubits and the central bus resonator.In chapter 4,we use quantum random circuits to demonstrate quantum advantage comparing to the classical method.We use up to 9 superconducting qubits to generate chaotic states and measure the output experimentally.With machine learning,we build a model to predict the random circuit output and then quantify the circuit fidelity using cross entropy,which yields errors less than 1%/cycle/qubit.Chapter 5 is the summary.