From Measurement And Control To Quantum Simulation On Superconducting Qubits Chips

Quantum computing is considered a new generation of information processing technology.Utilizing the superposition and entanglement properties of quantum states,quantum computing has advantages that classical computing cannot match in dealing with certain problems.The basic unit that constitutes a quantum computing system is the quantum bit.In the past few decades,people have done a lot of research on a variety of physical systems(such as ion traps,quantum dots,nuclear spins,nitrogen vacancy color centers,cold atoms,etc.)that can be used to implement quantum computing.progress.In order to realize a practical quantum computing system,the scalability of qubits is particularly important.In this regard,superconducting quantum systems are considered to be one of the most promising candidate systems.In the superconducting quantum system,the preparation process of the qubit is similar to the semiconductor preparation process,and the parameters can be adjusted in a wide range,which gives great flexibility in the design of quantum chips.Over the past two decades,superconducting quantum computing has developed rapidly.Many domestic and foreign scientific research institutions and well-known technology and commercial companies have successively joined related research,achieving development from single qubits to dozens of qubits,which has been shown in specific algorithms.The quantum advantage over classical computing.Of course,there are still many problems to be solved on the road of superconducting qubit research,such as how to achieve better bit decoherence,more precise bit gate control,larger number of bits integrated,smaller crosstalk between bits,and more bits.Control ability and so on.This dissertation mainly introduces my research on qubit measurement and control and quantum simulation and related results obtained during my doctoral period.The first chapter of the thesis mainly introduces the development history of quantum computing,the basic theoretical knowledge of superconducting qubits,and the principles of related measurement and control.The second chapter mainly introduces a set of hardware and software systems for qubit measurement and control that I participated in during my Ph.D.period.In terms of hardware,he participated in the development of an electronic hardware system for multi-bit measurement and control.The system has the characteristics of short delay time,good integration,strong scalability,small size,and flexible use.Using FPGA,an on-chip algorithm was written to achieve fast signal demodulation and waveform output.After testing,the feedback delay is 178.4ns,which can be used for quantum feedback related research work.In terms of software,a set of multi-bit measurement and control software based on Python3 language has been developed.This software complies with multiple design principles and can better meet the various needs of quantum bit chip measurement and control.It has been used in multiple quantum simulation experiments.The third chapter mainly introduces some qubit measurement and control technologies,including: the characterization of each parameter of the qubit,the calibration of the undesirable experiment process,and some basic optimization work.Using the established hardware and software measurement and control system,a large number of superconducting bits,resonant cavities,Josephson parametric amplifiers and other samples were characterized,which supported the continuous optimization and improvement of the device preparation process and promoted the improvement of qubit decoherence.In addition,the suppression of qubit phase decoherence by three dynamic decoupling methods is also explored.The results show that the optimization method can make the phase decoherence time close to twice the energy relaxation time,which is close to the theoretical limit.The non-Hermitian system with parity time reversal symmetry has many novel properties and is an important subject of current research.Related research may be used for quantum precision measurement.The fourth chapter of this thesis describes my work to achieve PT symmetric phase transition observation in superconducting qubits using parametric modulation methods.First of all,it is experimentally verified that the method of parametric modulation can realize the controllable coupling between the bit and the readout cavity and adjust the energy level dissipation.Subsequently,the relevant parameters were changed,and the PT symmetry breaking phase transition was observed experimentally,and two methods were used to determine the position of the phase transition point.Finally,by adjusting the size of the dissipation,the relationship between the position of the EP point and the dissipation is shown.In the experiment,the measured experimental results are basically in line with theoretical expectations.The method of parametric modulation to adjust the dissipation to observe the EP point does not need to add additional hardware or redesign the device,which is conducive to being applied to multi-bit devices and exploring the various properties of the non-Hermitian system.The fifth chapter is about realizing the quantum simulation work of the gauge field of Z2 lattice in a one-dimensional 10-qubit system.I first calibrated the various parameters of the qubit,and calibrated and optimized some unsatisfactory factors.On this basis,considering multiple factors such as crosstalk and reading,the experimental work point is selected,and finally the evolution of the entire effective grid point specification Hamiltonian is realized.The non-local and local phenomena predicted by the theory have been observed experimentally,and the measured value of the gauge invariant operator is also consistent with the theoretical expected result.Finally,in Chapter 6,I summarized the work during my Ph.D.and looked forward to the future work of quantum computing measurement and control.