Microwave Kinetic Inductance Detectors And Their Arrays For Weak Light Detection

In 2003,the low-temperature detector group in California Institute of Technology firstly proposed the microwave kinetic inductance detectors?MKIDs?,which are high-quality superconducting microwave resonators.They have shown great potential application in weak light detection for astronomy exploration.The working principle of the MKIDs is based on the effects of the photon-induced changes in the densities of the quasiparticles and Cooper pairs,which influence on the surface impedance of superconductors.Comparing with the other types of superconducting detectors,MKIDs have been developed a little late.With the development of fabrication technology and characteristic parameters optimization in recent years,the MKIDs have become one of the important single-photon detectors for the potential astronomy applications.Chaper 1 introduces the application of microwave kinetic inductance detectors and their arrays.MKIDs can be used in optical/X-ray detection,dark matter search,photon counting and antenna coupling.Many foreign groups have proved that MKIDs can be applied in the field of sub-millimeter astronomy.Next,we make an introduction of some famous astronomical detection projects,like BLAST-TNG,NIKA2,MUSIC,SuperSpec and so on.The study of MKIDs and their arrays are extremely important and necessary.In order to achieve wide application,we need to know more about their working principle.We learn the theory of low supercouductivity,microwave kinetic inductance detectors and microwave resonators in Chaper 2.This will lay the theoretical foundation for the furture research.In Chaper 3,we designed and simulated three types MKID resonators;the microstrip line resonators,coplanar waveguide resonators,and the lumped element resonators,respectively.Laid the sample foundation for our next work.To realize their measurements,we then built three sets of measuring circuit,in which the low-temperature parts located inside the cryo-free dilution refrigerator are common.The samples to be measured are placed on the Mixing Chamber plane,which is the minimum temperature plane?about 40mK?.The measuring circuit should include the low-temperature amplifiers,low-temperature attenuators and the low-temperature switches,etc.In addition,the microwave transmission characters of the devices are measured by the circuit with the vector network analyzer,and the noise characters are measured by one with the IQ mixer,which can also be utilized to implement the photon counting.Another work in Chaper 3 is the photon counting for the optical communication at near-infrared wavelengths?1550 nm?.So far,the superconducting nanowire single photon detectors?SNSPDs?and the superconducting edge transition sensors?TESs?have demonstrated good performance in single-photon detection.The SNSPDs can perform fast single-photon counting with a high detection efficiency.However,a single SNSPD element is not able to resolve the photon number and photon energy.TESs has low noise(NEP<10-19 W/Hz^1/2)and intrinsic photon-number and photon-energy resolving ability.However,TESs require on-chip SQUIDs for read-out,which brings complexity to the fabrication.MKIDs have intrinsic photon-number-resolving and energy-resolving.MKIDs are easy to fabricate and multiplex into large arrays.In previous studies,MKIDs only apply in the millimeter/sub-millimeter wave astronomy,but MKIDs have the ability of photon counting and single photon energy resolution.This is why we try to study the photon counting for the optical communication at near-infrared wavelengths.We hope they can be applied to light quantum information field in the furture.The samples we use are lumped resonators,made from titanium-nitride?TiN?film.The sizes of IDC fingers in each resonator are different.By studying devices with a variety of geometries,we have systematically investigated the dependence of photon counting performance on the absorber volume.It was found that the energy resolution increases with the decrease of the absorber volume.Using a TiN/Ti/TiN trilayer MKID,with the absorber volume of 0.40?m³ and also the narrowest inductor width of 1?m,we have demonstrated the photon counting at the wavelength of 1550 nm,and energy resolution as low as?E=0.22eV is obtained and up to 7-photon events can be resolved.It will have a positive meaning for MKIDs applying in quantum secure communications,1 linear optical quantum computing,and optical quantum metrology.By further improving the energy resolution and system detection efficiency,MKIDs may find important applications in quantum secure communications,linear optical quantum computing,and optical quantum metrology.Chaper 4 in this thesis is about the MKID arrays.For the astronomic application,the MKIDs are demanded to be multiplexed into a large array.We need to design lots of resonators within certain bandwidth.To this end,we need to solve the problem for distinguishing a single detector pixel from the other unperturbed MKID pixels.We demonstrate a cryogenic wafer mapper with light emitting diodes?LEDs?,which is easy to be implemented with low cost,low power dissipation,and no moving parts at cryogenic temperature.By powering one LED to illuminate,the resonance frequency and the quality factor of the irradiated resonator will change accordingly.As a consequence,the position of the resonance frequency is marked.In the preliminary experiment,we have adopted a 5mm round white LED,which can work in a low temperature.We also find many types of LEDs can work at extremely low temperatures??40 mK?,although the charge carriers are believed to be frozen at such low temperatures.However,the underlying physics of the LEDs at low temperature needs further study.From last experiment,the large deviations between the design frequency of each resonator and its actual measurement one were observed,with an irregular periodic variation.And these deviations make resonance frequency collide,i.e.,two or more resonance peaks with the overlapped frequency,which will reduce the yield of the MKID array.To solve such a problem,we proposed a so-called MKID trimming technology by the second photolithography.After this,each resonance peak is visible and the array yield increase.The efficiency of the trimming implies that,the same capacitor C and the same inductance L used in the design for all the resonators are imperfect.They are actually different.With the observed position of the resonance peaks,L_i???_l of each resonator can be calculated.Then,we can redesign all the resonance frequencies of the array,once the number of IDC fingers N_IDC,i^* is known.It is noted that,as the trimming only reduces the number of IDC fingers or shorten the length of the last IDC finger,i.e.,N_IDC,i^*<N_IDC,i,the new resonance frequency of each resonator must be larger than the old one.After trimming,we observed that the resonances are globally shifted up by about 20MHz,due to the number of IDC fingers are reduced for most resonators.Anyway,after trimming the uniformity of the frequency spacing is greatly improved and the array yield is significantly improved,from 84%to 97%.Our technique provides an easy-to-implement and effective tool to improve the yield and multiplexing density of large resonator arrays,which may find broad applications in photon detection and quantum computing.In Chaper 5,we try to analyze the physical mechanism of the resonance peak collision phenomenon?crosstalk?,observed in the above experiments.Phenomenologically,this effect may be related to the electromagnetically induced transparency?EIT?,which has been observed similarly in the coupled optical cavities.First,we analyzed the electromagnetically induced transparency of the coupled optical cavities in theory.Then,using the full quantum theory of single photon transport in real space,we calculate the transmission characteristics of the coupled microwave quarter-wave resonance cavities,typically the transmission spectra and phase shift spectra.Indeed,the EIT-like effects could be observed in our numerical simulations.Hopefully,the theoretical model developed here is useful to understand the further experimental observations,probably various nonlinear quantum coherence effects in the coupled resonators.