A Study Of Thermal Escape And Macroscopic Quantum Tunneling In A Three-junction Flux Qubit

In recent years, with the rapid development of quantum communication and quantumcomputing, how to compute quantum in a real physical system has drawn much attention. For itsease of large-scale integration and scalability, solid quantum device has been considered as oneof the alternatives which are most likely to take the lead in computing quantum and among thosedevices, Josephson structure super-conductance quantum bits is the one with highest potentialand fastest growing. Adopting semiconductor integrated process, superconducting quantum bitsdeserve special attention for its advantages such as non-energy consumption and its ease of scale.This thesis focuses on thermal runaway in superconducting qubits and quantum tunnelingphenomena. The contents of this thesis include the following sections:Chapter one reviews the historical background and operation characteristics of quantumcomputing, the operating principles and the advantages of quantum computers; then introducesthe Josephson effects and some physical knowledge related with Josephson junction; mainlyillustrates three superconducting qubits that are widely used: superconducting phase qubits,superconducting flux qubit superconducting charge qubits, as well as several common couplingmodes; briefly introduces the important theoretical and experimental progress in recent years.Chapter two gives a detailed introduction in the classical physics of background conditionsand theoretical knowledge about thermal escape and quantum tunneling, based on which,displays the advantages of studying the classical thermal escape and quantum tunneling inJosephson junction; gives the important experimental achievements that has achieved in recentyears in the experimental research of Josephson junction.Employing the method of numerical simulation, the third chapter explores the process ofparticle thermal runaway in the three-junction flux qubit and the quantum tunneling; firstcalculates the thermal runaway rate and the quantum tunneling rate of the three-junction fluxqubit; obtains the variation regularity with temperature of instantaneous survival time at thecross-temperature of0.26K and also the distribution curve of switching flux with the variation ofmagnetic field and temperature; makes a quantitative comparison between distribution curve ofswitching flux and the distribution law of two-junction superconducting interferometer. Theresults show that the three-junction flux qubit in the thermal escape and quantum tunneling areobvious than that of two junction which demonstrates that the temperature is lower whenthree-junction flux qubit exhibiting the properties of quantum; three-junction flux qubit is moresensitive to flux variation than two junction and noisier than two junction’s. Those theoretical achievements are of great significance for people to utilize three-junction flux qubit and prolongits decoherence time.