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 Q39: Superconducting Circuits and DevicesFocus
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Sponsoring Units: DMP Chair: Chris Ciccarino, Stanford University Room: Room 231 |
Wednesday, March 8, 2023 3:00PM - 3:36PM |
Q39.00001: Spin-split superconductivity in triple-hybrid materials Invited Speaker: Saulius Vaitiekenas Recently developed semiconducting InAs nanowires with epitaxial superconducting Al and ferromagnetic insulator EuS shells display induced superconductivity with a sizable Zeeman-like splitting at zero external magnetic field. The intricate interplay between spin-orbit coupling, magnetic domains, and superconducting phase coherence gives rise to unique ground states and corresponding electrical properties. In this talk, I will present some of the rich phenomenology emerging in these materials. |
Wednesday, March 8, 2023 3:36PM - 3:48PM |
Q39.00002: Characterization and braiding of Majorana bound states in planar topological Josephson tri-junctions Ellen Gulian, Laimei Nie, Varsha Subramanyan, Smitha Vishveshwara The extended S-I-S Josephson junction between p+ip superconductors is a promising platform for the realization and characterization of Majorana bound states (MBS). It has been shown that for a single junction geometry in the presence of an external magnetic field, MBS can be hosted at the cores of Josephson vortices. Here, we present analytical and numerical studies of MBS dynamics in a Josephson tri-junction system with three finite-sized p+ip superconducting islands. We begin by finding the locations of the MBS within the tri-junction and characterizing the current-phase relation. We also discuss and demonstrate possible braiding schemes within the system by adjusting both the applied magnetic field and the phase differences between the islands. Lastly, we relate our results to ongoing experimental efforts in S-TI-S tri-junction systems. |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q39.00003: Mott qubit and fractron in a Mott system Hyun-Tak Kim There is an instability for the Mott IMT(Insulator-to-Metal Transition) not accompanied with the structural phase transition, excitation (U at metal from Uc at insulator) of the Mott criterion nc from a doped Mott insulator; such as the instability at an effective mass of carrier, m*/m=1/[1-(U/Uc)2], in the Brinkman-Rice picture, where U is the on-site Coulomb energy between electrons and Uc is the critical Coulomb energy[1,2]. Due to the instability, near U/Uc=1, two phases of Mott insulator l0> and metal l1> are observed in a measurement region. They can be linearly combined like a superposition of Ψ=αl0>+βl1> and can also be entangled (coupled) as Ψ1Ψ2. In a Mott system, the metallic carrier charge is an fractional effective charge (fractron) coming from average of the measurement region. As an example, in VO2, the IMT oscillation as evidence of the fractron was observed[3] and the coupling was also measured[4]. Thus, we suggest a Mott qubit. [1]PRB 2(1970)4302. [2]Physica C 341-348(2000)259. [3]J.Appl.Phys.107(2010)023702. [4]Sci. Report.4(2014)4964. |
Wednesday, March 8, 2023 4:00PM - 4:12PM |
Q39.00004: Quantum Point Contacts in Cadmium Arsenide Thin Films Simon Munyan Quantum interferometry provides a means of encoding and reading information from qubits based on non-Abelian bound states. An essential component of quantum interferometers is a quantum point contact, which tunes the transmission of single quasiparticle states through a constriction. In addition to interferometry, quantum point contacts are useful for readout operations in flying qubit circuits and as spin filters in the quantum spin Hall state. We demonstrate operation of gate-defined quantum point contacts in the quantum Hall state of cadmium arsenide thin films tuned into different topological and trivial states by magnetic field. Both field and a top gate are used to control the global filling factor of the device, and thereby the number of edge channels flowing into the quantum point contact. A nano-sized split gate is used to form an electrostatic constriction and control the number of transmitted channels. With the global filling factor tuned to the n-type side, we observe integer steps in conductance as individual channels are selectively transmitted through the constriction. Tuning the filling factor through the zeroth Landau level to the p-type side, we observe fractional values of conductance through the constriction. We explain this result as a consequence of charge mixing between electron- and hole-like channels. Lastly, we present experiments of mesa-defined quantum point contacts in the topologically non-trivial state. |
Wednesday, March 8, 2023 4:12PM - 4:24PM |
Q39.00005: Van der Waals Reprogrammable Quantum Materials using Ultra-low Voltage E-beam Lithography Qingrui Cao, Dengyu Yang, Muqing Yu, Erin Akyuz, Ki-Tae Eom, Patrick R Irvin, Chang-Beom Eom, Benjamin M Hunt, Jeremy Levy Understanding quantum materials and developing quantum hardware are consistent goals and challenges for quantum information science. Among the materials, van der Waals (vdW) materials and reconfigurable complex oxides show great potential to support the route by providing plentiful properties. Here we demonstrate how reconfigurable quantum materials can be achieved by gating vdW stacks with complex-oxide heterostructures that are programmed by ultra-low voltage e-beam lithography (ULV-EBL) [1]. This technique for nanoscale gating of vdW materials has the potential for instantiating a wide range of 2D Fermi-Hubbard models, and for creating emergent properties such as novel magnetic and superconducting phases. Here we explore the Kagome lattice which is imprinted into LaAlO3/SrTiO3 (LAO/STO). The full device integrates the reprogrammable conductive LAO/STO layer with a vdW stack consisting of hexagonal boron nitride (hBN) encapsulated bilayer graphene (BLG), with a multi-layer graphene top electrode. Transport measurements reveal a non-trivial Landau fan diagram which is absent from the control device. The overall approach can be expanded to include other complex oxides, vdW materials other than graphene, transition metal dichalcogenides (TMD), and complex oxide membranes, such as LAO/KTO, WSe2, and LAO/STO membranes. The results obtained so far offer the promise of a reconfigurable method for creating novel electronic materials via analog quantum simulation. |
Wednesday, March 8, 2023 4:24PM - 4:36PM |
Q39.00006: Dimensionality-controlled electronic reconstruction in ruthenate heterostructures Ujjal Lamichhane, Rosty Martinez, Gilberto Fabbris, Yongseong Choi, Daniel Haskel, Valentina Bisogni, Mario F Borunda, Derek Meyers Heterostructuring as a means to create artificial analogues of bulk materials allows controlled engineering towards enhancing existing or generating emergent properties. We synthesized superlattices consisting of SrRuO3 interspaced with SrTiO3 as a potential platform to investigate unconventional superconductivity, as seen in Sr2RuO4. Synchrotron based x-ray absorption spectroscopy revealed charge redistribution as a function of SrTiO3 layer thickness. Density functional theory calculations support the experimental findings showing the electronic structure evolution as a function of confinement. This work reveals the importance of interlayer coupling to the electronic structure of layered ruthenate systems, with important implications for ruthenate-based unconventional superconductors. |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q39.00007: Superconducting routing platform for large-scale integration of spin qubits Candice THOMAS We will report on the fabrication, using 200 mm silicon wafer technologies, of a multi-layer routing platform designed for the hybridization and three-dimensional integration of spin qubit arrays and control electronics chips. This interposer electrically couples the qubits and the control circuits using front-side superconducting routing layers made from standard microelectronics materials such as TiN and Al0.995Cu0.005 as well as Nb and NbN superconductors. These layers are connected between them by W-based vias. Electrical characterizations of this platform routing layers will be detailed. Wafer-level parametric tests at 300 K validate the high yield of these technologies. Low temperature electrical measurements in cryostat identify the superconducting regimes of Al0.995Cu0.005, TiN, Nb and NbN in terms of temperature, magnetic field and current, highlighting the compatibility of these materials with the Si spin qubit operating conditions. Based on these results, radio frequency passive components have been designed and integrated on the interposer to form reflectometry circuits, providing read-out alternatives. Preliminary low temperature high frequency measurements performed on superconducting embedded resistors, capacitors and inductors will be presented. |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q39.00008: Observation of two-level systems with a giant dipole moment in superconducting granular aluminum films Maximilian Kristen, Jan Nicolas Voss, Micha Wildermuth, Jürgen Lisenfeld, Hannes Rotzinger, Alexey V Ustinov Thin films of disordered superconductors are currently extensively studied, for instance due to their applicability in modern quantum circuits or kinetic inductance detectors. While a variety of materials are possible, especially the ones with low microwave loss and a high degree of disorder are of interest for high impedance circuits. The disordered microscopic structure also favors the presence of intrinsic material defects, with some of them behaving as two-level systems (TLS). Found in dielectrics like surface oxides or tunnelling barriers, TLS are a major source of electromagnetic loss and limit the coherence of superconducting qubits. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q39.00009: Rapid characterization of superconducting microwave resonators using thePound-Drever-Hall technique John Pitten, Jim Phillips, Brandon Boiko, Josh Y Mutus, Corey Rae H McRae
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Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q39.00010: Modelling dielectric loss in superconducting resonators: Evidence for interacting atomic two-level systems at the Nb/oxide interface Noah Gorgichuk, Tobias Junginger, Rogério de Sousa While several experiments claim that two-level system (TLS) defects in amorphous surfaces/interfaces are responsible for energy relaxation in superconducting resonators and qubits, none can provide quantitative explanation of their data in terms of the conventional noninteracting TLS model. Here a model that interpolates between the interacting and noninteracting TLS loss tangent is proposed to perform numerical analysis of experimental data and extract information about TLS parameters and their distribution. As a proof of principle, the model is applied to TESLA cavities that contain only a single lossy material in their interior, the niobium/niobium oxide interface. |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q39.00011: Radiation effects on coplanar waveguide microwave resonators Nathan J Thobaben, Daria Kowsari, Kaiwen Zheng, Kater Murch, David S Wisbey, Denae Cherry, Kevin Goodman, Robert Cooper, Grant Osmon, Abigail Sohm We used superconducting microwave resonators to study the effect of radiation on devices used for quantum information. Niobium (Nb) and titanium nitride (TiN) coplanar waveguides (CPWs) were exposed to gamma radiation from a closed Cesium-137 (Cs137) source. We measured a change in internal quality factor and a change in resonance frequency when exposed to a gamma radiation source of about 3 microcuries. A shift of about 2000-4000 hertz was observed in the resonance frequency nitrogen passivated Nb samples. In the TiN samples, the shift was larger by two factors of 10. Shifts of 100,000 to 300,000 Hz were recorded. By better understanding the effects of radiation on quantum materials, mitigation methods can be further developed to increase the stability of quantum systems. It is important to understand the relationship between radiation on internal quality factor (Qi), since internal quality factor is a measure of how effective the resonator is at storing quantum states for computation. A decline in Qi factor was observed in most samples of NbN, and larger declines in TiN samples. The degradation in NbN Qi is more pronounced at lower power levels with the greatest shifts appearing in the TiN samples at low power. While Nb is still an important material for quantum information, even small amounts of radiation can make it less effective. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q39.00012: Theoretical investigation of magnetic losses in amorphous Ta2O5. Patrick G Pritchard, James M Rondinelli Experimental investigations have shown improved qubit coherence times (T1) when Ta superconducting coplanar waveguide (CPW) transmission lines are used for qubit readout instead of Nb transmission lines. The authors of these studies have suggested that this behavior is likely a result of a reduced number of loss channels in the amorphous Ta2O5 oxide layer as compared to the amorphous Nb2O5 oxide layer. A recent work has shown that d-channel magnetic defects in the amorphous Nb2O5 oxide layer of Nb CPW transmission lines are a potentially significant source of qubit decoherence. Owing to the increased spatial extent of Ta 5d orbitals compared to Nb 4d orbitals, we hypothesize that amorphous Ta2O5 will host fewer localized moments than amorphous Nb2O5. We confirm this hypothesis using spin-polarized density functional theory (DFT) calculations on magnetic moment formation in amorphous Ta2O5 and discuss the impact on magnetic losses. |
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