Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P26: Superconducting Circuits: New Qubit Components and Packaging 
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Sponsoring Units: DQI Chair: Sami Rosenblatt, IBM Thomas J. Watson Research Center Room: BCEC 160B 
Wednesday, March 6, 2019 2:30PM  2:42PM 
P26.00001: Scaling up package I/O for superconducting qubits Steven Weber, Danna Rosenberg, Jovi Miloshi, John Cummings, James Krieger, Sam Alterman, David Conway, Rabindra Das, Cyrus F. Hirjibehedin, David K Kim, Elizabeth Kowalski, Benjamin Lienhard, Alexander Melville, Bethany M. Niedzielski, John Rokosz, Wayne Woods, Jonilyn L Yoder, Andrew James Kerman, William D Oliver Device packages, which house qubit chips and make connections to control and readout wiring, are an essential component of any superconducting qubit architecture. In this presentation, we discuss our efforts to design packages with an increasing number of signal connections, for applications in quantum annealing and gatebased quantum computing. We present strategies for achieving highdensity wiring while avoiding package modes and reducing crosstalk. We characterize package performance using electromagnetic simulations, roomtemperature measurements, and cryogenic qubit measurements. 
Wednesday, March 6, 2019 2:42PM  2:54PM 
P26.00002: Simulation and Analysis of Packaging of Superconducting Qubits Benjamin Lienhard, Wayne Woods, Danna Rosenberg, Kevin P O'Brien, Greg Calusine, Steven J. Weber, Terry Philip Orlando, Simon Gustavsson, William D Oliver The superconducting qubit modality is a leading candidate today for the realization of a quantum information processor targeting first demonstrations of shallow depth quantum algorithms. The achievable circuit depth is limited in part by the lifetime of the constituent qubits. Although the lifetime of superconducting qubits has increased by several orders of magnitude over the last 15 years – largely due to improvements in design, materials, and fabrication methods – there is still need for further improvement. In this work, we present results from simulation and analysis of the materials and geometric effects related to qubit packaging and its impact on qubit lifetimes. 
Wednesday, March 6, 2019 2:54PM  3:06PM 
P26.00003: Engineering the environment of superconducting quantum processors with multilayer PCBs Kaidong Peng, Kevin O'Brien Precise and accurate coherent control of qubits is critical to the success of superconducting quantum computing. Microwave crosstalk is a ubiquitous problem for large scale superconducting quantum processors and poses a challenge to scaling up fewqubit coherent control results. Although crosstalk is classical, deterministic, and can be mitigated to some degree with electromagnetic nulling, the frequency dependence of crosstalk and significant calibration overhead for compensation schemes motivate hardware solutions. 3D integration techniques such as through silicon vias and bump bonds offer a solution at the cost of fabrication complexity. We propose and present initial experiments on a crosstalk mitigation scheme using commercial multilayer printed circuit boards (PCBs) to enable rapid turnaround and widespread adoption. 
Wednesday, March 6, 2019 3:06PM  3:18PM 
P26.00004: Qubit Dynamics in a Multimode Environment with a Superconducting Metamaterial Resonator Sagar Indrajeet, Haozhi Wang, Matthew D Hutchings, Matthew LaHaye, Bruno G. Taketani, Frank K Wilhelm, Britton L Plourde

Wednesday, March 6, 2019 3:18PM  3:30PM 
P26.00005: Kerr and crossKerrfree Josephson fourwave mixing device Shantanu O. Mundhada, Nicholas E. Frattini, Shruti Puri, Akshay Koottandavida, Shyam Shankar, Steven Girvin, Michel H. Devoret Parametrically pumped fourwave mixing is a key building block for many developments in the field of superconducting quantum information processing. However, undesired frequency shifts such as Kerr, crossKerr and Stark shifts, inherent with fourwave mixing, lead to difficulties in tuning up the desired parametric processes and, for certain applications, severely limit the fidelities of the resulting operations. In this talk, we explore a Josephson fourwave mixing device consisting of a SQUID transmon coupled to a halfflux biased SNAIL transmon, a.k.a. capacitively shunted flux qubit. When the two transmons have matching frequencies, an interference effect cancels the negative Kerr of the SQUID transmon with the positive Kerr of the SNAIL transmon while preserving parametric fourwave mixing capabilities. We present the design and experimental characterization of such a device. 
Wednesday, March 6, 2019 3:30PM  3:42PM 
P26.00006: Quickly tunable refrigerator for superconducting qubits Jan Goetz, Andras Gunyho, Matti Silveri, Hao Hsu, Gianluigi Catelani, Mikko Möttönen The emerging quantum technological devices call for fast and accurate initialization of functional quantum degrees of freedom to a lowentropy state. Here, we theoretically study a recently demonstrated quantumcircuit refrigerator [1] in the case of superconducting qubits. We find that for typical parameters, the refrigerator is suitable for quickly cooling both transmon and flux qubits close to their ground states. The maximum refrigeration rate of transmon qubits is roughly an order of magnitude stronger than that of resonators [2], providing additional flexibility in the design criteria. The on/off ratio of the refrigerator assumes values above 10^{4} with typical experimental parameters. Thus the refrigerator is a promising tool for quantum technology and for studies of open quantum systems. Finally, we present an experimental realization based on transmon qubits and coupled qubitresonator systems, which are the workhorses of quantum processors based on superconducting circuits. 
Wednesday, March 6, 2019 3:42PM  3:54PM 
P26.00007: Quickly Tunable Electromagnetic Environment for Superconducting Quantum Circuits Vasilii Sevriuk, Kuan Yen Tan, Matti Silveri, Shumpei Masuda, Jan Goetz, Matti Partanen, Dibyendu Hazra, Joonas Govenius, Russell Lake, Visa I Vesterinen, Leif Grönberg, Juha Hassel, Slawomir Simbierowicz, Marton Gunyho, Aarne Keränen, Jani Tuorila, Tapio AlaNissila, Hermann Grabert, Mikko Möttönen In the qubits operation it is of utmost importance to be able to quickly remove any unwanted excitations on demand for fast and accurate initialization. We recently introduced a device referred to as a quantumcircuit refrigerator (QCR) [1]. It is a standalone component that can readily be integrated into superconducting quantum electric devices, with negligible perturbation to the device operation. In our experiments, we demonstrate the ability to tune the dissipation of a superconducting resonator by orders of magnitude by the convenient application of a bias voltage on the QCR. The switching time of the tunable dissipation can be as low as a few nanoseconds. We also observe a tunable Lamb shift owing to the dissipation induced by the QCR. 
Wednesday, March 6, 2019 3:54PM  4:06PM 
P26.00008: Optimal Impedance Taper in the Presence of Nonlinear Voltage Reflections Robert Erickson, Mustafa Bal, David Pappas A signal introduced into a loadbearing transmission line will partially reflect back along the input line if an impedance mismatch exists at the injection interface. Placement of a tapered impedance transformer at the interface can reduce these reflections. [1] In earlier work we showed how to determine the optimal shape of a continuous lossless taper of wide frequency bandpass. [2] Our theory assumed impedance mismatch sufficiently small that large voltage reflections within the taper could be considered negligible. Here we extend our earlier theory, allowing for arbitrarily sized impedance mismatches and large voltage reflections, reporting results for a lossless taper. Our extended theory has important application to the design of tapered transformers for electronic devices with unavoidably large impedance mismatches, and can be leveraged to construct onchip Purcell filters used in the fast readout of superconducting transmon and Xmon qubits. 
Wednesday, March 6, 2019 4:06PM  4:18PM 
P26.00009: Verifying the radiative cooling of a superconducting resonator with a qubit spectrum analyzer Zhixin Wang, Mingrui Xu, Xu Han, Wei Fu, Hong X Tang, Shyam Shankar, Michel H. Devoret Cavity electrooptomechanical systems are among the leading candidates for transducing quantum signals between microwave and optical frequencies. In such a photon converter, highfidelity quantum state transfer is possible only if the electrical resonator is close to its quantum ground state in thermal equilibrium. However, the temperature dependence of the mechanical quality factor often may require the operation of the hybrid device at temperatures with nonnegligible thermal photon populations at microwave frequencies. To resolve this conflict, the electrical resonator at a higher temperature can predominantly be coupled to, and thus radiatively cooled by the blackbody radiation at a much lower temperature. In this talk, we will introduce an experiment in which a 10 GHz superconducting resonator anchored to the 1 K stage of a dilution refrigerator is overcoupled to a 20 mK environment anchored to the mixing chamber stage of the refrigerator. To verify this cooling mechanism, we use a transmon qubit as a quantum spectrum analyzer and measure the thermal noise coming from the resonator at 1 K through the photoninduced qubit dephasing. Preliminary results will be presented. 
Wednesday, March 6, 2019 4:18PM  4:30PM 
P26.00010: Fast flux control of 3D transmon qubits using a magnetic hose Stefan Oleschko, Oscar Gargiulo, Jordi PratCamps, Maximilian Zanner, Gerhard Kirchmair An important feature in analog quantum simulation experiments with superconducting qubits [1] is the possibility to change the frequency of SQUIDbased transmon qubits by applying magnetic flux. Implementing fast flux control on a transmon remains challenging in the 3D cavity architectures due to the presence of a massive metallic cavity. Here we introduce a new approach for fast flux control on 3D transmon qubits. We use a magnetic hose similar to the one proposed by C. Navau et al. [2] to guide a fast flux pulse from the outside to the inside of a microwave cavity. This hose enables us to locally circumvent any magnetic shielding effects such as the appearance of eddy currents in cavities made out of copper or the Meissner effect in superconducting cavities made out of aluminum. First experiments show that the transition frequency of a transmon can be tuned in less than 100 nanoseconds. Besides the high speed, the frequency shift is precise, without showing any ringing or hysteresis. Using a magnetic hose with an aluminum cavity preserves the benefits of a superconducting cavity, like providing magnetic field shielding and a high internal quality factor, along with the possibility to fasttune individual qubits. 
Wednesday, March 6, 2019 4:30PM  4:42PM 
P26.00011: Kinetic Inductance Microwave Resonators for Quantum Simulation of Nonequilibrium BoseHubbard Models Mattias Fitzpatrick, Alicia Kollar, Andrew Houck The field of circuitQED (cQED) provides a rich toolbox for doing both quantum computation and quantum simulation with superconducting circuits. Here we will discuss the use of kinetic inductance nonlinearities in microwave resonators as a new tool for quantum and classicalnonlinear simulation of BoseHubbard models. We explore the interplay between nonlinearities, dissipation, and disorder in largescale circuits consisting of cavity arrays or multimode cavities. In contrast to other quantum simulation platforms, the particles in cQED (photons) are inherently dissipative, allowing the study of BoseHubbard models from a drivendissipative and open system context. 
Wednesday, March 6, 2019 4:42PM  4:54PM 
P26.00012: Josephson Junctions with TwoDimensional van der Waals Tunnel Barrier KanHeng Lee, Srivatsan Chakram, Fauzia Mujid, Chibeom Park, Hui Gao, David Schuster, Jiwoong Park Better device structure and materials control have contributed to the performance improvement of the Al/AlO_{x}/Albased superconducting qubits, allowing the technology to initiate practical applications in quantum computing. However, one current limitation of such qubits is the use of amorphous alumina as the tunnel barrier, which is known to have defects that may compromise the qubit coherent time and performance stability. Here, we report novel Josephson Junctions with 2D van der Waals tunnel barriers made with stacked Nlayer MoS_{2} that has minimal number of defects. We first generate a MoS_{2} membrane with controlled layer number N by vacuum stacking monolayer MoS_{2} as the tunneling barrier, and then depositing Al superconductor on either side to form the Josephson junctions. We show that we can reliably fabricate large numbers of Josephson junction devices on a single chip, and they show critical supercurrent that can be directly tuned by changing the N. We also characterize the microwave properties of Al/MoS2/Al junctions in a bulk superconducting cavity. Our work offers a new, powerful platform for generating and studying novel qubits with diverse 2D materials, and thus may provide an additional route to further improve the qubit performance for advancing the quantum technology. 
Wednesday, March 6, 2019 4:54PM  5:06PM 
P26.00013: Observation of a broadband Lamb shift in a superconducting resonator Matti Silveri, Shumpei Masuda, Vasilii Sevriuk, Kuan Yen Tan, Eric Hyyppä, Matti Partanen, Jan Goetz, Russell Lake, Leif Grönberg, Mikko Möttönen The shift of energy levels owing to broadband electromagnetic vacuum fluctuations—the Lamb shift—has been pivotal in the development of quantum electrodynamics and in understanding atomic spectra. Currently, small energy shifts in engineered quantum systems are of paramount importance owing to the extreme precision requirements in applications such as quantum computing. However, without a tunable environment it is challenging to resolve the Lamb shift in its original broadband case. Consequently, the observations in other than atomic systems are limited to environments comprised of narrowband modes. Here, we experimentally observe in highquality superconducting resonators a Lamb shift of several megahertz, by externally tuning the coupling strength of an engineered broadband environment based on hybrid normalmetal–superconductor tunnel junctions. Our results may lead to improved control of dissipation in highquality engineered quantum systems such as superconducting qubits. 
Wednesday, March 6, 2019 5:06PM  5:18PM 
P26.00014: Quantum Dynamics of a fewphoton Microwave Parametric Oscillator Zhaoyou Wang, Marek Pechal, Amir SafaviNaeini We experimentally investigate quantum dynamics of a nonlinear superconducting RF resonator in the intermediate (n ~ 5) photon number regime. In particular, we study parametric processes induced by modulation of the resonator’s inductance to prepare nonclassical photon states, which may be useful in future continuousvariable quantum error correction schemes. The system can be described as a Kerr parametric oscillator (KPO) with linewidth significantly smaller than the single photon Kerr shift. We observe narrowing of the linewidth when approaching the parametric stability threshold as well as nonclassical signatures in the resonator state’s free evolution caused by the Kerr nonlinearity. To read out the quantum state of the resonator, we developed a tomography method which utilizes its nonlinear character to estimate the system’s density matrix from the power spectrum of the field emitted by it. 
Wednesday, March 6, 2019 5:18PM  5:30PM 
P26.00015: Packaging Largescale Superconducting Quantum Computer with Airbridge Hiroto Mukai, Keiichi Sakata, Devitt J Simon, Rui Wang, Yukito Nakajima, JawShen Tsai For superconducting circuits with quantum error correction, a twodimensional array of qubits is required. Recently it is challenged to build a practical largescale superconducting circuit with the array on a chip by using this threedimensional wiring technique to control the qubits, while maintaining high fidelity operations. In this talk, we present the novel arrangement of the array of qubits without nonmonolithic special technology of threedimensional wiring. In this architecture, standard twodimensional external lines are adopted and local crossovers of interqubit connections are required. The crossovers are realized by airbridge technology. We show this novel architecture and the result of quality factor of resonator with airbridge at center line. 
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