Researches On Superconducting Microwave Resonators For Quantum Information Processing

In recent years,the quantum information processing has become one of the most hot fields in information science and physics.Among them,the researches on realizing quantum information processing with solid-state systems,typically including the superconducting electronics circuits,has been paid much attention.Based on the laboratory micromachining process platform and microwave measurement system,this paper systematically studied the superconducting microwave resonator,the core device of superconducting quantum information processing,from material optimization,device design,preparation process development to test analysis.The main research contents include:First,to develop the practical single-photon detector with photon-number/energy resolution for the implementation of optical quantum communication,we develop a double-layer photoresist lift-off process without etching to fabricat the granular aluminium（gr Al）films,with them the lumped element superconducting resonators have being made.The test results show that the kinetic inductance ratio of gr Al resonators reach^{gr Al}～56%.This ratio is much higher than that of the Al resonators(^Al～1%)with the same thickness and structure.Therefore,it can be used to develop the desired high-quality microwave kinetic inductance single-photon detector.To systematically understand the physical mechanism of single-photon detection by using the superconducting resonator,we performed series of experimental studies on the optical impulse response characteristics of the superconducting microwave resonator.Typically,for a half-wavelength coplanar waveguide（CPW）superconducting resonator,an equivalent circuit model with variable inductance have been introduced to simulate the time-domain response of light pulse irradiations.It is shown that,under the irradiation of light pulse,the law of the kinetic inductance of device changing with the time can be explained well by the quasi-particle generation-recombination processes.By using the quasi-particle Gaussian distribution model,the diffusion constant of the quasi-particle on the resonator surface was estimated successfully.More importantly,we have verified experimentally,for the first time,by measuring the response of light at different positions of the resonator,the intensity of the optical impulse response in the half-wavelength CPW resonator is proportional to the square of the current distributed on the surface of the resonator.These works provide a reliable theoretical and experimental basis to better understand the physical mechanism of single-photon detection of a superconducting resonators,and thus are useful to design and fabricate the superconducting single-photon detectors with the higher qualities.Finally,aiming at the practical demand of weakly perturbing readouts of the solid-state qubits in the solid-state quantum computing chip,we have designed an on-chip integrated circuit,wherein the superconducting quarter wavelength CPW resonator is set to realize weakly perturbing readout of a superconducting qubit working in the large detuning regime.Experimentally,we have design and fabricated the quarter-wavelength CPW resonators on sapphire substrates.The low temperature measurement results showed,the quality factor of the resonator reaches 10⁵ orders of the magnitude under the low microwave driving power,which corresponds to the case wherein only one photon was excited in the resonator,and the fractional frequency noise level of the resonator is very low.Therefore,the generated quarter-wave superconducting resonator with the demonstrated qulity can preliminarily meet the requirement for the weakly perturbing readouts of the qubits.