arXiv subjects

Yong-Chao Tang

Publications and source records attributed to Yong-Chao Tang.

4 recordsLinked to original sources

arXiv2019

Engineering Nonlinear Response of Superconducting Niobium Microstrip Resonators via Aluminum Cladding

In this work, we find that Al cladding on Nb microstrip resonators is an efficient way to suppress nonlinear responses induced by local Joule heating, resulting in improved microwave power handling capability. This improvement is likely due to the proximity effect between the Al and the Nb layers. The proximity effect is found to be controllable by tuning the thickness of the Al layer. We show that improving the film quality is also helpful as it enhances the microwave critical current density, but it cannot eliminate the local heating.

cond-mat.supr-con↗

arXiv2018

Magnetic hysteresis of a superconducting microstrip resonator with a high edge barrier

We investigate the magnetic hysteresis of a superconducting microstrip resonator with a high edge barrier. We measure the magnetic hysteresis while either sweeping a magnetic field or tuning the edge barrier by high microwave current. We show that the magnetic hysteresis of such a device is qualitatively different from that of one without an edge barrier and can be understood based on the generalized critical-state model. In particular, we propose and demonstrate a simple and intuitive method that relies on a plot of the quality factor versus the resonance frequency for revealing the physical processes behind those hysteretic behaviors. Based on this, we find that the interplay between the Meisser current and vortex pinning is essential for understanding the magnetic hysteresis of such a device.

cond-mat.supr-con↗

arXiv2018

Magnetic Field Dependent Microwave Losses in Superconducting Niobium Microstrip Resonators

We describe an experimental protocol to characterize magnetic field dependent microwave losses in superconducting niobium microstrip resonators. Our approach provides a unified view that covers two well-known magnetic field dependent loss mechanisms: quasiparticle generation and vortex motion. We find that quasiparticle generation is the dominant loss mechanism for parallel magnetic fields. For perpendicular fields, the dominant loss mechanism is vortex motion or switches from quasiparticle generation to vortex motion, depending on cooling procedures. In particular, we introduce a plot of the quality factor versus the resonance frequency as a general method for identifying the dominant loss mechanism. We calculate the expected resonance frequency and the quality factor as a function of the magnetic field by modeling the complex resistivity. Key parameters characterizing microwave loss are estimated from comparisons of the observed and expected resonator properties. Based on these key parameters, we find a niobium resonator whose thickness is similar to its penetration depth is the best choice for X-band electron spin resonance applications. Finally, we detect partial release of the Meissner current at the vortex penetration field, suggesting that the interaction between vortices and the Meissner current near the edges is essential to understand the magnetic field dependence of the resonator properties.

cond-mat.supr-con↗

arXiv2016

2D implementation of quantum annealing algorisms for fourth order binary optimization problems

Quantum annealing may provide advantages over simulated annealing on solving some problems such as Kth order binary optimization problem. No feasible architecture exists to implement the high-order optimization problem (K > 2) on current quantum annealing hardware. We propose a two-dimensional quantum annealing architecture to solve the 4th order binary optimization problem by encoding four-qubit interactions within the coupled local fields acting on a set of physical qubits. All possible four-body coupling terms for an N-qubit system can be implemented through this architecture and are readily realizable with the existing superconducting circuit technologies. The overhead of the physical qubits is O(N4), which is the same as previously proposed architectures in four-dimensional space. The equivalence between the optimization problem Hamiltonian and the executable Hamiltonian is ensured by a gauge invariant subspace of the experimental system. A scheme to realize local gauge constraint by single ancillary qubit is proposed.

quant-ph↗