Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L08: Superconducting Qubits: Materials, Fabrication and Coherence II |
Hide Abstracts |
Sponsoring Units: DQI Room: 104 |
Wednesday, March 4, 2020 8:00AM - 8:12AM |
L08.00001: PAMBE grown NbTiN-AlN-NbTiN Josephson junction heterostructures for superconducting quantum circuits Christopher Richardson, Austin Thomas, Ashish Alexander, Christopher Weddle, Alan Kramer, Matthew Olszta, Bruce Arey Plasma assisted molecular beam epitaxy (PAMBE) is used to grow niobium titanium nitride alloys (NbxTi1-xN) superconductors and wide bandgap nitride (AlN) trilayers directly on c-plane sapphire wafer. This combination of nitride materials provides sufficient degrees of freedom that synthesis of an epitaxial Josephson junction may be possible. Using a structure first approach to design optimization, the structural, surface topology, bonding, and interface characteristics will be described. Superconducting characteristics including microwave loss and work towards IV transport through Josephson junction devices will be discussed. |
Wednesday, March 4, 2020 8:12AM - 8:24AM |
L08.00002: Temperature Dependence of Relaxation-Time Fluctuations in Transmon Qubits Sudeep Dutta, Kungang Li, Rui Zhang, Dylan Poppert, Shahriar Keshvari, Christopher J Lobb, Frederick C Wellstood As the lifetime of superconducting qubits has increased, large temporal fuctuations in the relaxation time T1 of the excited state have been observed by different groups. We have measured such fluctuations in several Al/AlOx/Al transmons mounted in 3-D aluminum cavities. Our longest lived device showed T1 that varied from 100 to 300 μs at 20 mK. Comparing with shorter lived transmons, we find that the size of the fluctuations in T1 appears to scale with T1. Measurements of T1 versus temperature from 20 to 300 mK reveal that the fluctuations depend on temperature and support the idea that non-equilibrium quasiparticles are the dominant source of dissipation in these devices. |
Wednesday, March 4, 2020 8:24AM - 8:36AM |
L08.00003: Engineering Dynamical Sweet Spots to Protect Qubits from 1/f Noise Ziwen Huang, Andras Gyenis, Pranav Mundada, David I Schuster, Andrew Houck, Jens Koch Protecting superconducting qubits from low-frequency noise is important for advancing superconducting quantum computation. We present a protocol for engineering dynamical sweet spots protecting against 1/f noise, using a periodic drive. The position and strength of dynamical sweet spots can be obtained analytically in the framework of Floquet theory. For the example of fluxonium biased slightly away from half a flux quantum, we predict an improvement in pure-dephasing time from less than 1 μs to over 1 ms. Using the Floquet eigenstates as the computational basis, we show that high-fidelity single-qubit gates can be implemented at dynamical sweet spots. We further confirm that qubit readout can be performed by adiabatically mapping the qubit's Floquet states to the static qubit states, and subsequently employing standard measurement techniques. |
Wednesday, March 4, 2020 8:36AM - 8:48AM |
L08.00004: Investigating the mechanisms of charge-parity switching in offset-charge-sensitive transmons Spencer Diamond, Kyle Serniak, Max Hays, Valla Fatemi, Luigi Frunzio, Robert Schoelkopf, Gianluigi Catelani, Manuel Houzet, Leonid Glazman, Michel H. Devoret Charge-parity switches in superconducting qubits contribute to decoherence and limit qubit performance. In the past, such decoherence was exclusively attributed to pre-existing non-equilibrium quasiparticles tunneling across Josephson junctions and exchanging energy with the qubit. However, it was recently predicted that high-frequency photons can be efficiently absorbed at transmon Josephson junctions and cause charge-parity switches. This process requires no pre-existing quasiparticles, but in fact generates two quasiparticles and can likewise change the qubit state. These two types of charge-parity switches are distinguishable by their relative rates of qubit excitation and relaxation, which have been measured in single-junction offset-charge-sensitive transmons. The transition rates were found to be inconsistent with a thermal distribution of quasiparticles in the superconductor tunneling across the junction, but may be explained by photon-assisted tunneling events. Here, we will present experimental results demonstrating that adding flux-tunability to our device can further distinguish between these charge-parity switch-induced decoherence mechanisms. |
Wednesday, March 4, 2020 8:48AM - 9:00AM |
L08.00005: Effect of external high-energy radiation on coherence of superconducting qubits Antti Vepsalainen, Amir Karamlou, John Laurence Orrell, Akshunna S Dogra, Fransisca Vasconcelos, Ben Loer, Bethany Niedzielski, Alexander Melville, David K Kim, Mollie Schwartz, Jonilyn Yoder, Brent A VanDevender, Simon Gustavsson, William Oliver There is an anomalously high density of broken Cooper pairs in superconductors, which has been universally seen in experiments. It has been shown that external radiation can break Cooper pairs in superconducting circuits, causing elevated quasi-particle densities. The origin of the radiation has been a source of extensive research over several decades, but no conclusive answer has been found. It is known that thermal effects cause a finite quasi-particle density, but the observed densities are several orders of magnitudes higher than predicted by thermal equilibrium model. In superconducting devices infrared photons have shown to contribute to non-equilibrium quasi-particle densities through connected microwave lines. We propose that in addition to this effect, gamma-rays from radioactive decays in the environment are also a significant source of quasi-particle breaking radiation. We have measured the strength of the external radiation in our laboratory and demonstrated the effect of the high-energy radiation on qubit coherence using a Cu64 source with time-varying intensity. We show that proper shielding from gamma-rays is required for reaching high coherence times in transmon qubits. |
Wednesday, March 4, 2020 9:00AM - 9:12AM |
L08.00006: Synchrotron X-ray studies of superconducting qubit materials Ignace Jarrige, Anjali Premkumar, Conan R Weiland, Jack Berthold, Alexander Place, Ira Waluyo, Adrian Hunt, Andrew M. Kiss, Yong Chu, Valentina Bisogni, Jonathan Pelliciari, Abdul K Rumaiz, Mike Miller, Paula Russo, David I Schuster, Andrew Houck Despite dramatic improvements in the coherence times of superconducting qubits over the past decade, further progress is still needed to push quantum computers towards reality. Recent breakthroughs highlighted the paramount role played by the defect-prone native surface oxide layers in limiting the coherence of qubits. However, very little is known about the defects and their mechanism of coupling to the qubit degree of freedom, in part due to the lack of suitable probes for defects in thin amorphous layers. |
Wednesday, March 4, 2020 9:12AM - 9:24AM |
L08.00007: Highly uniform submicron junction arrays and applications to next generation photodetectors John Mark Kreikebaum, Kevin O'Brien, Baptiste Royer, Arne Grimsmo, Alexandre Blais, Irfan Siddiqi Josephson junctions are an ubiquitous circuit element in cQED experiments. In complex devices with many such junctions, such as state-of-the-art microwave photon detectors, precise control over each junction’s critical current is often required, and thus variations of the junction area and tunnel barrier thickness must be sufficiently minimized. Analyzing junction array resistance distributions from many wafers, we have identified several key processing variables to improve uniformity. Using this optimized recipe, we have fabricated and benchmarked a single microwave photon detector utilizing four identical transmons to mediate cross-Kerr coupling between a photon input waveguide and a readout resonator. Plans to increase detector performance by distributing the coupling over 1000’s of junctions will be discussed; a very challenging device to build without the uniformity improvements presented. |
Wednesday, March 4, 2020 9:24AM - 9:36AM |
L08.00008: Loss Characterization in Superconducting Resonators Alexander Melville, Greg Calusine, Wayne Woods, Kyle Serniak, Evan Golden, Arjan Sevi, Jonilyn Yoder, William Oliver Uniquely characterizing loss from two-level systems (TLS) in dielectric materials in coplanar waveguide resonators is challenging due to the nearly proportional scaling of the electric field participation in response to changes in geometry and anisotropic trench depth [1]. We tailor our resonator design and fabrication process to focus the participation into specific dielectric regions such that we can characterize the specific loss tangent of each dielectric [2]. In this talk, we characterize the change in overall quality factor and dielectric-specific loss tangent arising from specific changes to the fabrication process. |
Wednesday, March 4, 2020 9:36AM - 9:48AM |
L08.00009: Modeling geometric dependence of dielectric losses in superconducting coplanar-waveguide resonators Valtteri Lahtinen, Mikko Mottonen Superconducting coplanar-waveguide (CPW) resonators are essential devices in circuit quantum electrodynamics (cQED). Their performance is limited by dielectric losses in the substrate and in the thin lossy oxide layers on the material interfaces. Reliable modeling is required to aid in the design of low-loss CPW structures for cQED. We analyze the geometric dependence of the dielectric losses in CPW structures using finite-element modeling of the participation ratios of the lossy regions. Material and device specific parameters of these regions are generally not known accurately enough, introducing uncertainty in the simulations. To this end, we carry out simulations on a range of CPW geometries and parameters. Combining the simulations with measured two-level-system-limited Q factors of CPW resonators, we solve an inverse problem to find optimal model parameters producing these values. Utilizing this model and our geometric-dependence analysis, we predict high Q factors obtainable by optimizing the cross-sectional geometries of the measured CPW structures. Our results guide the fabrication of low-loss CPW resonators for cQED. |
Wednesday, March 4, 2020 9:48AM - 10:00AM |
L08.00010: Reducing dephasing for flux control of superconducting qubits Nicolas Didier Scaling up superconducting quantum processors with optimized performance requires sufficient flexibility in the choice of operating points for single and two qubit gates to maximize their fidelity and cope with imperfections. Flux control is an efficient technique to manipulate the parameters of tunable qubits, in particular to activate entangling gates. It however suffers from enhanced dephasing, induced by the ubiquitous 1/f flux noise at flux sensitive points of operation. We consider how flux pulses can protect a tunable qubit from slow flux noise for a range of frequencies in the tunability band. Preserving long coherence times during qubit interactions could furthermore alleviate the constraints on coupling strength and unlocks high fidelities for both single and two qubit gates in a scalable architecture based on static couplings. |
Wednesday, March 4, 2020 10:00AM - 10:12AM |
L08.00011: Characterizing noise for capacitively-shunted flux qubits Vinay Tripathi, Mostafa Khezri, Huo Chen, Daniel A Lidar Capacitively-shunted flux qubits (CSFQs), due to their high anharmonicity together with reduced persistent currents allow for relatively fast control pulses and long coherence times. This makes them a suitable candidate for both gate model quantum computing and quantum annealing. We report a joint theoretical-experimental study of 1/f noise in CSFQs using Macroscopic Resonance Tunneling (MRT). MRT has been used for flux qubits to characterize low-frequency flux noise using well stablished theoretical models. A detailed theoretical explanation of higher order MRT with correction of junction asymmetry is important for our understanding of noise in CSFQs. We carry out analyses of different theoretical models that account for relaxation and dephasing to explain experimental T1 and T2 results obtained from studies of CSFQs. |
Wednesday, March 4, 2020 10:12AM - 10:24AM |
L08.00012: Microwave loss of van der Waals dielectrics in the low-temperature, single-photon regime Joel Wang, Megan Yamoah, Qing Li, Charlotte Boettcher, Bharath Kannan, David K Kim, Jonilyn Yoder, Kenji Watanabe, Takashi Taniguchi, Terry Philip Orlando, Simon Gustavsson, Pablo Jarillo-Herrero, William Oliver Microwave dielectric loss – due to interaction between the electromagnetic field and spurious two-level-systems (TLS) – constitutes one of the main sources of decoherence in superconducting quantum circuits. Researches have shown the loss occurs in the bulk of dielectrics as well as of the many interfaces of circuit elements. |
Wednesday, March 4, 2020 10:24AM - 10:36AM |
L08.00013: Loss Mechanisms in Superconducting Quantum Transmission Line Metamaterials Tamin Tai, Jingnan Cai, Steven Anlage Superconducting quantum bits (qubits) coupled with resonators are widely utilized for applications in quantum computing. Efforts are under way to scale up the numbers of qubits, but there are many recurring issues of dielectric loss of substrate materials, two level systems, and quasi-particles loss, all leading to decoherence of superconducting qubits. In order to understand different loss mechanisms, our group is fabricating many high-quality aluminum half wavelength transmission line resonators by e-beam deposition and photo-lithography methods. Through the investigation of power dependence and temperature dependence of these transmission line resonators, and comparison with different theoretical models, the dominant loss mechanism in our half wavelength transmission line can be identified. This transmission line will later host many flux qubits to study the collective behavior of a quantum metamaterial system |
Wednesday, March 4, 2020 10:36AM - 10:48AM |
L08.00014: Over-100µs tunable planar transmons: epitaxial Josephson Junctions and design optimization* Anastasiya Pishchimova, Dmitriy Moskalev, Aleksei Matanin, Alina Dobronosova, Daria Ezenkova, Elizaveta Il'inichna Malevannaya, Ilya Besedin, Olga Sorokina, Lucia Almirovna Ganieva, Andronic Michael, Vladimir Vladimirovich Echeistov, Alexander Vyacheslavovich Zverev, Dmitriy Sergeevich Yakovlev, Ilya Rodionov Since superconducting qubits discovery over twenty years ago energy relaxation times has been improved by several orders. Josephson junctions, a crucial nonlinear component of superconducting qubits, are still fabricated from two aluminum polycrystalline electrodes with lossy amorphous aluminum oxide in between. Here we demonstrate our results in reducing two-level states (TLS) in amorphous oxides by means of Josephson Junctions optimization, thus reducing the participation of the lossy materials and interfaces. We carry out a comparative analysis of tunable X-mon qubit lifetimes based on various Josephson Junctions design types, demonstrating several times coherence improvement. From the other hand, we propose novel superconducting qubits fabrication technique based on Josephson junction epitaxial growth with inorganic masks. To experimentally test the proposed approaches we demonstrate tunable X-mon qubits with coherence over 100 microseconds. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700