Fabrication Of Superconducting Quantum Devices And Researches On Extensible Packaging Scheme

Based on superconducting quantum bit(qubit)devices,superconducting quan-tum computing(SQC)has been attracting more and more attentions since it becomes one of the most feasible proposals for building a real universal quantum computer.Moreover,it also provides a stage for investigating frontier physical problems.SQC mainly turns out to follow a principle called circuit quantum electrodynamics(cQED)in the decades.Based on cQED,one can implement quantum non-demolition(QND)measurement which can protect quantum states from been interfered by broad noises.Furthermore,SQC has no hard physical defects preventing itself from been developing.On the way to build a real quantum computer,major researches on SQC have already been on the stage of error-correction.To summarize,superconducting quantum de-vices have dominant advantages such as flexible parameters,convenience for reading and controlling,easiness to scale up.As a key component,superconducting qubit plays an important role in quantum information processing.Long coherence time can accommodate more logic operations which are good for quantum information processing.To improve the coherence time,one can choose proper materials and optimize fabrication recipes.We proposed a suit-able microfabrication recipe based on present equipments and introduced the method for optimizing recipes.Finally we obtained a stable recipe for fabricating T-junction with 30-kV electron beam lithography.Superconducting coplanar waveguide provides a way for reading,controlling and coupling qubits.Its property can influence the results of quantum information process-ing.To reduce the microwave loss,we investigated the growth of TiN film.Based on reactive magnetron sputter,we performed systematic researches of the growth condi-tions including nitrogen gas flow,total gas pressure,substrate temperature and so on.AFM and XRD are utilized to characterize the film.Finally we successfully deposited TiN film with only(200)direction priority during film growth.Coplanar waveguides(CPW)patterned on such film exhibited very high quality factor.CNOT gate can generate entangled states between two qubits which is important in quantum information processing.We designed a four-qubit device and implemented cross resonance(CR)operation between two of the four qubits.CNOT gate can be realized by combining CR and certain single qubit operation,which paves the way for error-correction operation.Relying on 2D array of qubits with only nearest neighbor couplings,surface code is regarded as the most promising method to realize a fault-tolerant logic qubit.How-ever,thousands of qubits are needed to realize surface code based on present process fidelity.The increasing number of qubits is a challenge for packaging the chip with conventional wire bonding technique.To overcome the difficulty and weakness,we proposed a new kind of 3D architecture for packaging.We have successfully imple-mented two-qubit CR operation in this architecture,which indicates that this scheme can support quantum measurements and is suitable for qubit scalability.