Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session RR07: V: Superconducting Quantum Information: Materials & Design |
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Sponsoring Units: DQI Chair: Charles Guinn, Princeton University; Charlie Guinn Room: Virtual Room 7 |
Tuesday, March 21, 2023 11:30AM - 11:42AM |
RR07.00001: Observation of the Response of Tantalum Coplanar Waveguide Cavities to Cryogenic Cycle Hao Deng, Xiaohang Zhang, Make Ying, Fei Wang, Ran Gao, Chunqing Deng Tantalum (Ta) has demonstrated its capability as a high-quality, low-loss superconductor supporting high-coherence superconducting qubits. Locating key fabrication processes and understanding the dissipation mechanisms of Ta-based devices are critical for a wider range applications of this material in circuit quantum electrodynamics. In this work, we report our observation that the Ta coplanar waveguide (CPW) cavities respond to cryogenic cycles with boosted intrinsic quality factor (Qi). Typically, in the initial cryogenic measurement after the fabrication, the Ta CPW cavities show Qi in the 105 order of magnitude with a weak dependence on the measurement power. However, after warming up and in the following cryogenic test, the identical Ta CPW cavities demonstrate low/high-power Qi at a level of 106/107 with an expected power dependence. Moreover, the improved Qi becomes fixed thereafter. We confirm that the response of Ta CPW cavities to the cryogenic cycle is robust against the variance in deposition thickness, etching, and patterning, but is dependent on the deposition power. We conjecture that the effect is connected with the residual and the release of the strain in the Ta film. |
Tuesday, March 21, 2023 11:42AM - 11:54AM |
RR07.00002: Trimming the frequency of superconducting qubits on sapphire substrates by a mode-locked laser Yanjun Ma, Mo Chen, Jiesu Wang, Shiyao Wu, Kai Chang, Yirong Jin, Haifeng Yu As superconducting quantum processors build up in complexity, how to address the challenge of frequency crowding proves formidable. By utilizing continuous-wave lasers, the recently developed method of laser-annealing has been successfully exploited to realize frequency collision-free superconducting quantum processors synthesized on silicon substrates. Due to its very low microwave loss tangent and chemical inertness, sapphire provides an excellent substrate on which superconducting qubits with long coherence time can be fabricated. To confront the problem of frequency crowding for sapphire-based qubits, we developed a post-fabrication laser-annealing approach based on a Ti:sapphire mode-locked laser. The characterization of the annealed qubits at low temperatures demonstrated the preservation of high coherence after laser treatment. While the unannealed qubits showed about 3.5% variation in their resistances, the variation of the resistance of the annealed qubits was improved to be around 1%. This work demonstrates the effectiveness of employing the mode-locked laser to trim the frequency of sapphire-based superconducting qubits, and therefore paves the way to engineer the frequency collision-free lattice with > 100 qubits on such substrates. |
Tuesday, March 21, 2023 11:54AM - 12:06PM |
RR07.00003: Nitride-based superconducting microwave coplanar waveguide resonators with internal quality factors above one million for circuit quantum electrodynamics Paniz Foshat, Paul G Baity, Sergey Danilin, Valentino Seferai, Shima Poorgholam-khanjari, Oleg Mukhanov, Matthew D Hutchings, Robert Hadfield, Muhammad Imran, Martin P Weides, Kaveh Delfanazari Niobium nitride (NbN) is a promising candidate for applications in superconducting quantum technology because of its high critical magnetic field and relatively high critical temperature. In contrast, NbN-based devices are more susceptible to decoherence sources such as two-level system defects. The purpose of this experiment is to investigate superconducting microwave coplanar waveguide resonators based on NbN on a silicon substrate at millikelvin temperatures from a single photon number regime to high power regime in the presence of in-plane magnetic fields. |
Tuesday, March 21, 2023 12:06PM - 12:18PM |
RR07.00004: Demonstration of fluxonium qubits based on highly-disordered spinodal materials Ran Gao, Make Ying, Hantao Sun, Feng Wu, Hao Deng, Tian Xia, Jianjun Chen, Huijuan Zhan, Fei Wang, Hui-Hai Zhao, Chunqing Deng The reduced sensitivity to charge and flux noise of fluxonium qubits is mainly achieved by the inclusion of a high-impedance circuit element (i.e., large inductance and small capacitance). Such a circuit element, namely superinductor, is typically realized using either Josephson-junction arrays or disordered superconductor nanowires. Here we demonstrate that the highly-disordered spinodal superconducting material (Adv. Mater. 34, 202201268, 2022) is an alternative candidate for low-loss fluxonium qubits with improved process simplicity and robustness. In addition, the large tunability of such materials, e.g., chemical composition, meso/microscopic structures, and etc., provides new opportunities for the engineering and understanding of the decoherence of fluxonium qubits. |
Tuesday, March 21, 2023 12:18PM - 12:30PM |
RR07.00005: Bias dependence of Al/AlOx Josephson phase diffusion resistance Maxwell Wisne, Venkat Chandrasekhar, Hilal Cansizoglu, Cameron J Kopas, Josh Mutus We perform noise-optimized dc transport measurements on test qubit Josephson junctions in order to extract critical parameters that may affect transmon decoherence. We observe a large resistance at low bias (in the nominally zero resistance state) that increases with decreasing junction size. We analyze this low bias resistance as a function of the current bias, and describe our results in terms of phase diffusion with Josephson energy and charging energy extracted directly from the current-voltage measurements. We orient our findings in the context of what role dissipation and charge noise might play in a larger transmon structure. |
Tuesday, March 21, 2023 12:30PM - 12:42PM |
RR07.00006: Understanding the decoherence of fluxonium from an EJ-tunable device Feng Wu, Hantao Sun, Xizheng Ma, Zhijun Song, Tenghui Wang, Gengyan Zhang, Hui-Hai Zhao, Chunqing Deng The fluxonium qubit is known for high coherence when biased around its half flux quantum sweet spot. Here we report the intensive study of decoherence models of a fluxonium qubit with in situ tunability of its Josephson energy by varying the external fluxes. The dissipation of the fluxonium at the sweet spot ranging from 80 MHz to 2 GHz agrees with decoherence models including dielectric loss and 1/f flux noise with a crossover point. And the dephasing of the fluxonium also agrees with the model with a similar 1/f flux noise amplitude. This work further validates the decoherence models of fluxonium and paves the way for the optimization of the coherence time and high-fidelity operations. |
Tuesday, March 21, 2023 12:42PM - 12:54PM |
RR07.00007: Fast and Accurate Design of Readout Resonators for Flip-Chip-Integrated Multi-Qubit Superconducting Quantum Processors Hang-Xi Li, Sandoko Kosen, Marcus Rommel, Andreas Nylander, Lert Chayanun, Giovanna Tancredi, Kestutis Grigoras, Leif Grönberg, Liangyu Chen, Marco Caputo, Alexey Zadorozhko, Robert Rehammar, Joonas Govenius, Daryoush Shiri, Jonas Bylander Predicting the parameters of superconducting resonators is important for achieving high qubit readout fidelity and preventing substantial Purcell decay. We use analytic equations, derived from conformal mapping, and 2D cross-sectional EM simulation, to calculate the frequency and coupling quality factor of resonators within a flip-chip geometry. We achieve a good agreement between this method and the more resource-intensive 3D FEM simulation under different inter-chip distances, considering the effective length due to the resonator-qubit coupling structure. Our method dramatically reduces the simulation time required for a multi-qubit quantum processor chip. We measured the inter-chip distance after flip-chip bonding to infer the resonators' capacitance and inductance. We show that the calculated resonator frequencies deviate from the measured values by less than 2%. |
Tuesday, March 21, 2023 12:54PM - 1:06PM |
RR07.00008: Strong coupling of electron spin ensemble to the eigenmodes of a high-Q dielectric resonator Stefano Roccasecca, Zhuo Shen, HongWen Jiang We have fabricated a compact dielectric resonator set-up on a custom printed-circuit board, which contains a microwave loop antenna coupled to a high-Q cylindrical dielectric resonator. The antenna is designed to operate with a resonant frequency matching that of the dielectric resonator for strong field confinement. We also simulated the combined on-chip system using finite element analysis (HFSS) to visualize the magnetic field profiles and reflection coefficients as a function of frequency. While the internal quality factor is around 8000 for the resonator (at 4.6 GHz), it is deliberately over-coupled to the microwave fields to provide a fast detection bandwidth of about 50 MHz. The setup has been tested using a thin layer of 2,2-diphenyl-1-picrylhydrazyl (DPPH), a radical commonly used for electron spin resonance calibration. A strong electron spin resonance signal was detected from the microwave power reflection at both room temperatures and cryogenic temperatures. We have observed strong coupling of the resonant mode of the electron spin ensemble to different eigenmodes of the dielectric resonator at room temperature. The anti-crossing of the two modes shows a coupling energy of about 50 MHz. Such photon-spin coupling can potentially be useful, as it has been proposed that electron spin ensemble can be used as a medium for quantum memory. Results of the coupling study for different concentrations of the spin ensemble will be reported. |
Tuesday, March 21, 2023 1:06PM - 1:18PM |
RR07.00009: Microwave-enhanced electron spin polarization at millikelvin temperatures Boris V Yavkin, Patrice Bertet, Daniel Esteve, Emanuel Flurin, Denis Vion Electron paramagnetic resonance methods are widely used in many areas of research, however sometimes the sensitivity of standard tools is not enough to register the signal. To increase signal intensity, few polarization methods, among them are expensive low temperature/high field experiments, or reserved to special samples light-induced polarization and chemically-induced polarization are used. In the current project, we would like to present a modification of recently demonstrated radiative cooling of spins by Albanese et al [1]. In our project we propose to introduce efficient heat sink to reduce the spin temperature below the equilibrium field temperature. Briefly, in our planned experiments we will fabricate multimode planar superconducting resonator in a way that low-frequency resonator in RF domain will be in Purcell regime with electron spins below. High-frequency MW resonator will be effectively coupled to cold environment of dilution fridge. Photon conversion process between the RF-MW fields, which will reduce the field temperature of the RF mode, is present due to non-linear kinetic inductance of the superconducting material and will be modulated by microwave pumps. In turn, Purcell relaxation of the spins to the RF field will cool them well below fridge temperature. |
Tuesday, March 21, 2023 1:18PM - 1:30PM |
RR07.00010: Quantized conductance doubling in gate tunable hybrid superconducting-semiconducting quantum wire arrays Kaveh Delfanazari, Jiahui Li, YUSHENG XIONG, Peng Ma, Reuben Puddy, Ian Farrer, Sachio Komori, Jason Robinson, Llorenç Serra, David A Ritchie, Michael J Kelly, Hannah Joyce, Charles G Smith In gated hybrid superconductor-semiconductor junctions made from two-dimensional (2D) semiconducting electron gas systems, the electrostatic field effect produced by the split gate voltages enables the realisation of one-dimensional (1D) quantum wires (electron waveguides). In this work, we experimentally demonstrate large-scale on-chip integration of gate voltage tunable hybrid superconducting-semiconducting field-effect switch arrays on the InGaAs quantum wells platform. Each hybrid junction in the chip can be controlled and addressed through its corresponding source-drain as well as two global split gate contact pads that allow switching between their (super)conducting and insulating states. We systematically investigate the quantum transport, switching voltage (on/off) states, quantum yield, and reproducibility of quantized conductance in several field-effect devices at cryogenic temperatures. We observe quantized conductance doubling in gated field effect junctions with a single interface and study their behaviour as a function of temperature and magnetic fields. |
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