Disorder effects in NbTiN superconducting resonators

Disordered superconducting materials like NbTiN possess a high kinetic inductance fraction and an adjustable critical temperature, making them a good choice for low-temperature detectors. Their energy gap(D), critical temperature(T_(c)),and quasiparticle density of states(QDOS) distribution, however, deviate from the classical BCS theory due to the disorder effects. The Usadel equation, which takes account of elastic scattering, non-elastic scattering, and electro–phonon coupling,can be applied to explain and describe these deviations. This paper presents numerical simulations of the disorder effects based on the Usadel equation to investigate their effects on the △, Tc, QDOS distribution, and complex conductivity of the NbTiN film. Furthermore, NbTiN superconducting resonators with coplanar waveguide(CPW) structures are fabricated and characterized at different temperatures to validate our numerical simulations. The pair-breaking parameter α and the critical temperature in the pure state T_(c)^(P) of our NbTiN film are determined from the experimental results and numerical simulations. This study has significant implications for the development of low-temperature detectors made of disordered superconducting materials.

Tunable superconducting resonators via on-chip control of local magnetic field

Superconducting microwave resonators play a pivotal role in superconducting quantum circuits.The ability to finetune their resonant frequencies provides enhanced control and flexibility.Here,we introduce a frequency-tunable superconducting coplanar waveguide resonator.By applying electrical currents through specifically designed ground wires,we achieve the generation and control of a localized magnetic field on the central line of the resonator,enabling continuous tuning of its resonant frequency.We demonstrate a frequency tuning range of 54.85 MHz in a 6.21-GHz resonator.This integrated and tunable resonator holds great potential as a dynamically tunable filter and as a key component of communication buses and memory elements in superconducting quantum computing.

Mechanical Analysis and Measurements of a Multicomponent NbTi/Cu Superconducting Magnets Structure for the Fully Superconducting Electron Cyclotron Resonance Ion Source

A fully superconducting electron cyclotron resonance （ECR） ion source （SECRAL ID is currently being built in the Institute of Modern Physics, Chinese Academy of Sciences. Its key components are three superconducting solenoids （Nb-Ti/Cu） and six superconducting sextupoles （Nb-Ti/Cu）. Different from the conventional supercon- ducting ECR magnetic structure, the SEC17AL Ⅱ includes three superconducting solenoid coils＇ that are located inside the superconducting sextupoles. The SECRAL Ⅱ can significantly reduce the interaction forces between the sextupole and the solenoids, and the magnets can also be more compact in size. For this multi-component SECRAL Ⅱ generating its self field of -8 T and being often exposed to the high self field, the mechanical analysis has become the main issue to keep their stress at 〈200 MPa on coils. The analytical and experimental results in mechanics are presented in the SECRAL Ⅱ structure. To improve the accuracy and efficiency of analysis, according to the composite rule of micromechanics, the equivalent uniform windings are used to simulate the epoxy-impregnated Nb-Ti/Cu coils. In addition, using low temperature strain gauges and a wireless fast strain acquisition system, a fundamental experiment on the based on our analysis, the stresses and deformations optimized. strains developments of a sextupole is reported. Finally, for its assembly of each SECRAL Ⅱ coil will be further

Controllably Coupling Superconducting Charge and Flux Qubits by Using Nanomechanical Resonator

We propose an effective mechanism to couple superconducting charge and flux qubits by using a quantized nanomechanical resonator. The coupling between the charge and flux qubits can be controlled by the external flux of the charge qubit. Under the strong coupling limR, an iSWAP gate can be generated by this scheme. The experimental feasibility in our scheme is also presented.

Multiplexing Read-Out of Charge Qubits by a Superconducting Resonator

Wavelength division multiplexing （WDM） is widely used in modern optics and electronics. For future quantum computers, the integration of readout is also vitally important. Here we incorporate an idea of WDM to demon- strate multiplexing readout of charge qubits by using a single integrated on-chip superconducting microwave resonator. Two distant qubits formed by two graphene double quantum dots （DQDs） are simultaneously readout by an interconnected superconducting resonator. This readout device is found to have 2 MHz bandwidth and 1.1 x 10-4 e/x/-H-z charge sensitivity. Different frequency gate-modulations, which are used selectively to change the impedance of the qubits, are applied to different DQDs, which results in separated sidebands in the spectrum. These sidebands enable a multiplexing readout for the multi-qubits circuit. This architecture can largely reduce the amount of detectors and can improve the prospect for scaling-up of semiconductor qubits.

Compact NbN resonators with high kinetic inductance

We design and fabricateλ/2 coplanar waveguide NbN resonators,the thickness and length of which are only several nanometers and hundred microns,respectively.The quality factor of such compact resonators can reach up to 7.5×10~4 at single photon power level at 30 m K with the resonance frequency around 6.835 GHz.In order to tune the resonant frequency,the resonator is terminated to the ground with a dc-SQUID.By tuning the magnetic flux in the dc-SQUID,the effective inductance of the dc-SQUID is varied,which leads to the change in the resonant frequency of the resonator.The tunability range is more than 30 MHz and the quality factor is about 3×10~3.These compact and tunable NbN resonators have potential applications in the quantum information processing,such as in the precision measurement,coupling and/or reading out the quantum states of qubits.

A Triplet Resonance in Superconducting Fe_(1.03)Se_(0.4_Te_(0.6)

From heavy fermion compounds and cuprates to iron pnictides and chalcogenides, a spin resonance at hΩ0 ∝ kBTc is a staple of nearly magnetic superconductors. Possible explanations include a two-particle bound state or loss of magnon damping in the superconducting state. While both scenarios suggest a central role for magnetic fluctuations,distinguishing them is important to identify the right theoretical framework to understand these types of unconventional superconductors. Using an inelastic neutron scattering technique,we show that the spin resonance in the optimally doped Fe1.03 Se0.4 Te0.6 superconductor splits into three peaks in a high magnetic field,a signature of a two-particle S = 1 triplet bound state.

A preliminary study of the feasibility of using superconducting quarter-wave resonators for accelerating high intensity proton beams

The superconducting （SC） cavities currently used for the acceleration of protons at a low velocity range are based on half-wave resonators. Due to the rising demand on high current, the issue of beam loading and space-charge problems has arisen. Qualities of low cost and high accelerating efficiency are required for SC cavities, which are properly fitted by using SC quarter-wave resonators （QWR）. We propose a concept of using QWRs with frequency 162.5 MHz to accelerate high current proton beams. The main factor limiting SC QWRs being applied to high current proton beams is vertical beam steering, which is dominantly caused by the magnetic field on axis. In this paper, we intend to analyze steering and eliminate it to verify the qualification of using QWRs to accelerate high intensity proton beams.

Electromagnetic design and optimization of a superconducting quarter wave resonator

Superconducting （SC） cavities currently used for the acceleration of protons at a low velocity range are based on half wave resonators. Due to the rising demand on high current, the issue of beam loading and space charge problems has arisen. Qualities of low cost and high accelerating efficiency are required for SC cavities, which are properly fitted by using an SC quarter wave resonator （QWR）, We propose a concept of using QWRs with frequency 162.5 MHz to accelerate high current proton beams. The electromagnetic design and optimization of the prototype have been finished at Peking University. An analytical model derived by the transmission line theory is used to predict an optimal combination of the geometrical parameters, with which the calculation by Microwave Studio shows a good agreement. The thermal analysis to identify the temperature rise of the demountable bottom plate under various levels of thermal contact also has been done, and the maximum increment is less than 0.5 K even though the contact state is poor.