Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K26: Superconducting Qubits: Noise and Decoherence I |
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Sponsoring Units: DQI Chair: David Pappas, National Institute of Standards and Technology Boulder Room: BCEC 160B |
Wednesday, March 6, 2019 8:00AM - 8:12AM |
K26.00001: Measuring charge and flux noise correlations with a superconducting qubit Bradley Christensen, Chris D Wilen, Alexander Opremcak, JJ Nelson, Francisco Schlenker, Lara Faoro, Lev B Ioffe, Britton L Plourde, Jonathan L DuBois, Robert F McDermott Superconducting qubits are a promising approach towards scalable quantum computing. Coherence times in state-of-the-art devices are now in excess of 100 us. While these times are impressive, achieving the necessary fidelities for suitably scalable surface code algorithms requires better coherence times, and as such, a better understanding of the microscopic origin of the fluctuators that gives rise to different noise sources (e.g., flux noise, charge noise, and dielectric noise). |
Wednesday, March 6, 2019 8:12AM - 8:24AM |
K26.00002: Piezoelectric loss in superconducting quantum circuits: Part 1 Taekwan Yoon, Yiwen Chu, Prashanta Kharel, Vijay Jain, William Renninger, Luigi Frunzio, Peter Rakich, Robert J Schoelkopf In recent studies, it has been shown that strong coupling between a superconducting qubit and phonons can be achieved. [1,2] These results imply that any unintended electro mechanical coupling in the system could lead to loss in superconducting circuit systems. In my talk, I will present a highly sensitive technique for measuring electromechanical coupling in a material at cryogenic temperatures and in the GHz regime. The measurement is based on RF driving of phonons through electromechanical coupling and optical readout through Brillouin scattering. I will present measurements done on an inversion symmetric material, the progress on relevant materials for superconducting circuits, and discuss its implications for qubit coherence times. |
Wednesday, March 6, 2019 8:24AM - 8:36AM |
K26.00003: Piezoelectric loss in superconducting quantum circuits: Part II Vijay Jain, Yiwen Chu, Taekwan Yoon, Luigi Frunzio, Robert J Schoelkopf
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Wednesday, March 6, 2019 8:36AM - 8:48AM |
K26.00004: Observation of Low Thermal Excited State Population of Transmon Qubit Yizhou Huang, Jen-Hao Yeh, Rui Zhang, Shavindra P Premaratne, Frederick C Wellstood, Benjamin Palmer We have measured the thermal excited-state population of a 3D Transmon qubit from 12 mK up to 150 mK. The Al/AlOx/Al qubit had a g-to-e transition frequency of 3.6 GHz, an e-to-f transition frequency of 3.4 GHz, and T1 of 17 microseconds. The device was mounted in a rectangular Al cavity with a transition frequency of 7.9 GHz and the cavity input line had custom-made attenuators ensuring that noise on the input line was well-filtered and thermalized[1]. The residual excited state population of the qubit was measured by measuring the response of the system when driving Rabi oscillations between the e and f states, with no initial preparation pulse applied to the qubit[2] for one of the pulse sequences. With the refrigerator at 12 mK, we found that the residual excited state population of the qubit in the e state was 0.17% with uncertainty of 0.02%, corresponding to a remarkably small effective qubit temperature of just 28 mK. For refrigerator temperatures T above 40 mK, the effective temperature Tn of the qubit was very close to T. |
Wednesday, March 6, 2019 8:48AM - 9:00AM |
K26.00005: An analysis method for two superconducting resonators with common defects Neda Forouzani, Bahman Sarabi, Omid Noroozian, Edward Wollack, Samuel H Moseley, Kevin Daniel Osborn
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Wednesday, March 6, 2019 9:00AM - 9:12AM |
K26.00006: Investigating superconducting qubit loss channels in a quantum acoustical device Bradley Moores, Lucas Sletten, K. W. Lehnert The loss channels that limit superconducting qubit coherence times are presently not well understood. Mounting evidence shows that qubits couple to dissipative two-level system baths in dielectrics. In contrast, a less explored loss channel is from phonon radiation that is intrinsic to the Josephson junction superconductor-insulator boundary. Most dielectrics have a vanishing piezoelectric effect in the bulk from inversion symmetry, but this is not the case at surfaces. Theory predicts that the loss rate from this piezoelectric effect can be comparable to the lifetimes of state-of-the-art transmon qubits. Here we investigate phonon radiation from Josephson junctions to put an upper bound on its limitations on the transmon's coherence time. |
Wednesday, March 6, 2019 9:12AM - 9:24AM |
K26.00007: Charge-parity dynamics in offset-charge-sensitive transmons: Part 1 Spencer Diamond, Kyle Serniak, Max Hays, Valla Fatemi, Gijs De Lange, Shyam Shankar, Luigi Frunzio, Robert J Schoelkopf, Leonid Glazman, Manuel Houzet, Michel H. Devoret Understanding and mitigating the effects of nonequilibrium quasiparticle excitations is an important step towards improving the performance of superconducting qubits. By designing transmon qubits in the offset-charge-sensitive regime, one can achieve direct dispersive detection of quasiparticle tunneling events. We utilize these devices to measure quasiparticle tunneling rates as a function of various experimental parameters such as RF filtering and qubit design. This talk will focus on experimental methods. |
Wednesday, March 6, 2019 9:24AM - 9:36AM |
K26.00008: Charge-parity dynamics in offset-charge-sensitive transmons: Part 2 Kyle Serniak, Spencer Diamond, Max Hays, Valla Fatemi, Gijs De Lange, Shyam Shankar, Luigi Frunzio, Robert J Schoelkopf, Leonid Glazman, Manuel Houzet, Michel H. Devoret Understanding and mitigating the effects of nonequilibrium quasiparticle excitations is an important step towards improving the performance of superconducting qubits. By designing transmon qubits in the offset-charge-sensitive regime, one can achieve direct dispersive detection of quasiparticle tunneling events. We utilize these devices to measure quasiparticle tunneling rates as a function of various experimental parameters such as RF filtering and qubit design. This talk will focus on experimental results. |
Wednesday, March 6, 2019 9:36AM - 9:48AM |
K26.00009: Non-equilibrium quasiparticles in superconducting circuits: photons vs. phonons Gianluigi Catelani, Denis M. Basko We study the effect of non-equilibrium quasiparticles on the operation of a superconducting device (a qubit or a resonator), including heating of the quasiparticles by the device operation. Focusing on the competition between heating via low-frequency photon absorption and cooling via photon and phonon emission, we obtain a remarkably simple non-thermal stationary solution of the kinetic equation for the quasiparticle distribution function. We estimate the influence of quasiparticles on relaxation and excitation rates for transmon qubits, and relate our findings to recent experiments. |
Wednesday, March 6, 2019 9:48AM - 10:00AM |
K26.00010: Superconducting quasiparticle traps for CPW resonators Ashish Alexander, Christopher Weddle, Christopher Richardson Excess quasiparticles limit the quality factor of the superconducting resonators by presenting an ohmic path for energy dissipation. It has been shown that normal metal in contact with the superconductor can act as a quasiparticle trap by confining quasiparticles away from the superconductor. Similarly, a small band gap superconductor in contact with a larger band gap superconductor can also act as a quasiparticle trap by confining quasiparticles away from the larger bandgap superconductor into the smaller one. |
Wednesday, March 6, 2019 10:00AM - 10:12AM |
K26.00011: Resolving the Location of Parasitic Defects in Superconducting Qubits Alexander Bilmes, Georg Weiss, Rami Barends, Julian Kelly, Anthony E Megrant, John M Martinis, Alexey V. Ustinov, Jürgen Lisenfeld
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Wednesday, March 6, 2019 10:12AM - 10:24AM |
K26.00012: Reducing dissipation for superconducting qubits Nasser Alidoust, Ani Nersisyan, Stefano Poletto, Riccardo Manenti, Russ Renzas, Eyob A Sete, Catvu Bui, Kim Vu, Tyler Whyland, Yuvraj Mohan, Sam Stanwyck, Jayss Marshall, Kamal Yadav, Andrew Bestwick, Matthew J Reagor Extending qubit lifetimes (T1, T2) remains a core challenge in developing large-scale quantum computers with superconductors. In this talk, we discuss a variety of substrate cleaning and subtractive patterning techniques responsible for increasing T1 for superconducting qubits. For these analyses, we have developed fabrication flows based on subtractively-patterned niobium that yield resonators with average internal quality factors of Qint ≈ 1×106 across several wafers and chips. We show options for integrating Josephson junctions into these process flows to make functional qubits with high coherence times. |
Wednesday, March 6, 2019 10:24AM - 10:36AM |
K26.00013: Spurious mode suppression using micromachined pillars in superconducting quantum devices Peter A Spring, Joseph Rahamim, Brian Vlastakis, Andrew D Patterson, Takahiro Tsunoda, Sophia Sosnina, Martina Esposito, Salha Jebari, Kitti Ratter, Giovanna Tancredi, Peter Leek As quantum circuits scale in size, the enclosures used to house them will contain spurious resonant electromagnetic modes detrimental to the circuits unless preventative steps are taken. A standard solution in microwave circuits is the use of through-chip vias. Here we present an alternative that moves the through-chip electrical connection off the substrate and to the enclosure, which suppresses substrate and enclosure modes simultaneously. We achieve this by placing a substrate in a rectangular cavity incorporating an array of micromachined pillars, such that the minimum mode frequency is set by the pillar spacing and not the enclosure dimensions. To accommodate the pillars the substrate is machined. We investigate the compatibility of both CNC and laser machining of holes in silicon with superconducting qubit fabrication. We present proof of principle experiments on enclosures incorporating pillars, and produce simulations with more complex arrangements of pillars in larger-scale devices. |
Wednesday, March 6, 2019 10:36AM - 10:48AM |
K26.00014: Phononic Losses in Superconducting Coplanar Waveguide Resonators on Piezoelectric Substrates Marco Scigliuzzo, Laure Bruhat, Andreas Bengtsson, Jonathan Burnett, Per Delsing In recent years there has been an increasing number of experiments involving superconducting qubits on piezoelectric substrates to investigate quantum acoustics. In this context Coplanar Waveguide (CPW) resonators provide a well established way for qubit manipulation and readout. However CPW resonators on piezoelectric substrates perform poorly, with two orders of magnitude lower internal quality factor (Q) compared with similar devices on low loss dielectrics. |
Wednesday, March 6, 2019 10:48AM - 11:00AM |
K26.00015: Tunable High-Q Photonic Bandgap Microwave Cavity Ankur Agrawal, Akash Dixit, David Schuster, Aaron Chou A woodpile structure made out of dielectric rods exhibits an omnidirectional photonic bandgap (PBG) which forbids the propagation of electromagnetic wave with energy within a certain range in all directions. We designed an electromagnetic cavity by creating a defect inside the crystal, such that its frequency lies within the forbidden bandgap. Very high Q-factors can be achieved since the light has no way to escape because of the bandgap and is only limited by the dielectric loss in the material. We predict the quality factor of such a cavity to be close to 108 near 10 GHz. The cavity frequency is tuned by sliding the rods in and out. One of the potential applications is in the axion dark matter search, which is currently limited by the use of low Q-factor copper cavities due to the presence of a strong magnetic field. We predict the Q-factor of a PBG cavity to increase in the presence of a large magnetic field due to the shift in the two-level system energies to a higher level. |
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