Apparatus and method of implementing a compact and tunable microwave resonator using NbN kinetic inductance

An apparatus for implementing a compact and tunable microwave resonator using niobium nitride (NbN) kinetic inductance, wherein the apparatus comprises:

• a direct current (DC) source, a superconducting coil, an attenuator, an oxygen-free copper cavity, a first-stage amplifier, a second-stage amplifier, a vector network analyzer and a control computer, wherein the oxygen-free copper cavity and the superconducting coil are at a low temperature of 30 mK and configured to carry a NbN resonator sample and provide a magnetic field, respectively;
• the attenuator and the first-stage amplifier are in a low-temperature environment of a dilution refrigerator, and the DC source, the second-stage amplifier, the vector network analyzer and the control computer are all in a room temperature environment;
• the DC source is used to provide a voltage needed by the superconducting coil to generate the magnetic field, the superconducting coil is used to provide an externally-applied magnetic field needed by the NbN resonator sample, the vector network analyzer is used to provide a microwave signal to the NbN resonator sample as a microwave input signal which is input through the attenuator into the NbN resonator sample to drive an inductor-capacitor (LC) resonance circuit, an input of the first-stage amplifier is connected to an output of the oxygen-free copper cavity so that the first-stage amplifier amplifies the output microwave signal at a low temperature, an input of the second-stage amplifier is connected to an output of the first-stage amplifier to receive the output signal of the first-stage amplifier for further amplification at a normal temperature, the vector network analyzer is used to measures a forward transmission coefficient S21 curve from an input port to an output port of the NbN resonator sample and observe a modulation effect of the magnetic field for the resonance frequency of the LC resonance circuit;
• the control computer is connected to the vector network analyzer and used to record data measured by the vector network analyzer.