Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session A28: Focus Session: Superconducting Qubits: Design & Tunable Coupling |
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Sponsoring Units: GQI Chair: Douglas McClure, IBM Room: 601 |
Monday, March 3, 2014 8:00AM - 8:36AM |
A28.00001: Noise spectroscopy and decoherence mitigation during free and driven evolution Invited Speaker: William Oliver Gate operations in a quantum information processor are generally realized by tailoring specific periods of free and driven evolution of a quantum system. Unwanted environmental noise, which may be distinct during these two periods, acts to decohere the system and increase the gate error rate. In this talk, we review our work on noise spectroscopy of superconducting qubits (persistent-current qubits, transmons) undergoing both free and driven evolution, and we present dynamical decoupling methods that can mitigate coherent errors in both cases. We discuss these results in the context of our present work and future directions. [Preview Abstract] |
Monday, March 3, 2014 8:36AM - 8:48AM |
A28.00002: Engineering Robust Superconducting Qubits Nate Earnest, Thomas Yu, Yao Lu, David Mckay, Jay Lawrence, Jens Koch, David Schuster The coherence times of superconducting qubits have advanced dramatically within the last few years. ~This has been primarily achieved by improving the microwave environment and reducing materials loss. ~Though the qubit parameters have changed significantly over the years, the qubit circuit has remained in the form of a LCJ circuit (flux,charge, and phase qubits). ~Recently, more sophisticated circuits, such as the 0-pi circuit proposed by Brooks et al.[1] offer the possibility of enhanced protection from dephasing and relaxation. In this talk, we will discuss the implementation of such circuits with realizable parameters, and present preliminary experimental results. [1] Brooks et al. PRA 87, 052306 (2013) [Preview Abstract] |
Monday, March 3, 2014 8:48AM - 9:00AM |
A28.00003: Systematic Design of Tuned Transmon Qubits David Abraham, Jay M. Gambetta, Jerry M. Chow, Srikanth Srinivasan, Matthias Steffen We demonstrate a systematic method for designing two-dimensional superconducting transmon qubits with highly controllable and reproducible properties, including anharmonicity, resonant frequency and the ratio Ej/Ec. The main source of variation in these qubit properties is shown to be due to spreads in the critical current of the Josephson junction connecting the transmon capacitor pads. This technique is illustrated in a series of qubits with a range of properties, culminating in a design which accurately meets the desired operating point for multiqubit operation, and in addition obtains coherence times 2x higher than previously obtained, using conventional materials and fabrication methods. [Preview Abstract] |
Monday, March 3, 2014 9:00AM - 9:12AM |
A28.00004: Coherence properties of a capacitively-shunt flux qubit Jeffrey Birenbaum, Adam Sears, Christopher Nugroho, Ted Gudmundsen, Paul Welander, Jonilyn Yoder, Archana Kamal, Simon Gustavsson, Jamie Kerman, William Oliver, John Clarke Coherence times for typical flux qubits have plateaued at $5-10 ~\mu$s for $T_1$ and $1-3 ~\mu$s for $T_{Ramsey}$. To achieve longer coherence times we study capacitively-shunted flux qubits using high-Q capacitors to individually shunt all four Josephson junctions (JJs). The additional shunt capacitance moves $90+\%$ of the qubit energy from the lossy capacitance of the JJs into the high-Q shunts while preserving an anharmonicity greater than $100\%$ and maintaining $f_{01} < f_{12}$. The band structure is also flattened providing moderately decreased sensitivity to flux noise. Using high-quality MBE aluminum [1] we fabricate a capacitively-shunted flux qubit inductively coupled to a lumped-element readout resonator. The qubit junctions are deposited via aluminum e-beam evaporation using a bridgeless mask. We characterize the influence of qubit design parameters such as capacitance and geometry on the coherence time of the device. \newline [1] Megrant, \textit{et al}. APL \textbf{100}, 113510 (2012) [Preview Abstract] |
Monday, March 3, 2014 9:12AM - 9:24AM |
A28.00005: Design and measurement of improved capacitively-shunted flux qubits Adam Sears, Jeffrey Birenbaum, David Hover, Theodore Gudmundsen, Andrew Kerman, Paul Welander, Jonilyn L. Yoder, Simon Gustavsson, Xiaoyue Jin, Archana Kamal, John Clarke, William Oliver The addition of a capacitive or inductive shunt across one of the junctions can alter the coherence properties of a classic flux or RF-SQUID qubit. We have studied the performance of capacitively shunted flux qubits fabricated with MBE aluminum[1], starting from a 2D coplanar waveguide geometry used in similar high-performance transmon qubits, and measured dispersively. We will detail the importance of design parameters that preserve the flux qubit's anharmonicity and discuss conclusions about materials quality based on calculations of the participation of junction, dielectric, and superconductor components. This research was funded in part by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA); and by the Assistant Secretary of Defense for Research \& Engineering under Air Force Contract number FA8721-05-C-0002. All statements of fact, opinion or conclusions contained herein are those of the authors and should not be construed as representing the official views or policies of IARPA, the ODNI, or the U.S. Government \\[4pt] [1] Megrant et al., APL 100, 113510 (2012). [Preview Abstract] |
Monday, March 3, 2014 9:24AM - 9:36AM |
A28.00006: Superconducting qubits with adjustable coupling, Part I: Architecture Yu Chen, C. Neill, P. Roushan, R. Barends, B. Campbell, B. Chiaro, Z. Chen, A. Dunsworth, I. Hoi, E. Jeffrey, J. Mutus, A. Megrant, P. O'Malley, C. Quintana, D. Sank, J. Wenner, T. White, J. Kelly, A.N. Cleland, J.M. Martinis Building a practical quantum computer requires a scalable architecture suitable for large numbers of qubits. A major challenge is to achieve on-demand qubit-qubit interaction, such that turning the coupling off allows isolated single-qubit operations and turning the coupling on allows multi-qubit operations. By combining the high coherence Xmon qubits with an adjustable inductance, we have developed a new qubit architecture called g-mon, which has a tunable qubit-qubit interaction from 10 MHz to -50 MHz. We achieved nanosecond control of the coupling from positive to negative through zero, allowing for a high on/off ratio exceeding 1000. With additional advantages such as high modularity and moderate-distance compatibility, the g-mon architecture provide a potential scalable approch for future quantum computers. [Preview Abstract] |
Monday, March 3, 2014 9:36AM - 9:48AM |
A28.00007: Superconducting qubits with adjustable coupling, Part II: Fast two-qubit gates Charles Neill, Yu Chen, Pedram Roushan, Rami Barends, Brooks Campbell, Zijun Chen, Ben Chiaro, Andrew Dunsworth, IoChun Hoi, Evan Jeffrey, Julian Kelly, Anthony Megrant, Josh Mutus, Peter O'Malley, Chris Quintana, Daniel Sank, Jim Wenner, Ted White, Andrew Cleland, John Martinis The g-mon architecture combines high coherence Xmon qubits with fast tunable coupling. In this work, we demonstrate the advantages of tunable coupling to high fidelity single and two-qubit gates. By suppressing the qubit-qubit interaction, we are able to achieve high-fidelity simultaneous single qubit operations without the need for substantial detuning. Turning on the qubit-qubit interaction allows for a fast two-qubit controlled Z with gate times less than 30 ns. By eliminating the frequency crowding issues associated with static coupling and achieving two-qubit gate times approaching that of single qubit operations, the g-mon architecture is a promising system for scalable quantum computation. [Preview Abstract] |
Monday, March 3, 2014 9:48AM - 10:00AM |
A28.00008: Superconducting qubits with adjustable coupling, Part III: Simulating topological properties of quantum systems Pedram Roushan, C. Neill, Y. Chen, M. Kolodrubetz, R. Barends, I. Hoi, E. Jeffrey, J.Y. Mutus, B. Campbell, Z. Chen, B. Chiaro, A. Dunsworth, J. Kelly, A. Megrant, P. O'Malley, C. Quintana, D. Sank, T. White, J. Wenner, A. Polkovnikov, A. Cleland, J. Martinis The g-mon architecture with its adjustable qubit-qubit coupling makes a promising candidate for building a quantum simulator. Here, we demonstrate the versatility of this system to simulate the topological properties of interacting Hamiltonians. So far, experimental studies of topological invariants in condensed matter systems have been limited to transport measurements. Recently, it was proposed [1] that the topological properties of Hamiltonians can be inferred from quantum dynamics. The Berry curvature, a quantity that reflects the geometrical properties of the eigenstates, can emerge as the non-adiabatic response to the rate of change of an external parameter. Using superconducting g-mon qubits, we measure the Berry curvature for various eigenstates of the Hamiltonian of the system. We will discuss the robustness of the measured Chern numbers, by showing their path independence in the parameter space. \\[4pt] [1] Gritsev and Polkovnikov, PNAS, 109, 6457 (2012). [Preview Abstract] |
Monday, March 3, 2014 10:00AM - 10:12AM |
A28.00009: Tunable coupling between two superconducting resonators F. Deppe, F. Wulschner, A. Baust, E. Hoffmann, E.P. Menzel, A. Marx, R. Gross, E. Solano, D. Zueco, J.-J. Garcia Ripoll During the last decade, tremendous progress has been made towards quantum computation and quantum simulation with superconducting circuits. In such architectures, the controlled exchange of information between two superconducting transmission line resonators via a tunable coupling is a useful tool. Here, we present experimental progress on such devices. Specifically, the coupling is mediated either by a superconducting flux qubit or by an RF~SQUID. Our results allow us to analyze the tunable coupling in frequency and time domain. We acknowledge support from: the DFG via SFB~631; the German excellence initiative via NIM; the EU projects \mbox{CCQED}, PROMISCE, SCALEQIT; Spanish MINECO FIS2009-12773-C02-01, FIS2011-25167, FIS2012-36673-C03-02; UPV/EHU UFI 11/55; Basque Government IT472-10. [Preview Abstract] |
Monday, March 3, 2014 10:12AM - 10:24AM |
A28.00010: Tunable-cavity QED with phase qubits Jed D. Whittaker, Fabio da Silva, Michael Shane Allman, Florent Lecocq, Katarina Cicak, Adam Sirois, John Teufel, Jose Aumentado, Raymond W. Simmonds We describe a tunable-cavity QED architecture with an rf SQUID phase qubit inductively coupled to a single-mode, resonant cavity with a tunable frequency that allows for both tunneling and dispersive measurements. Dispersive measurement is well characterized by a three-level model, strongly dependent on qubit anharmonicity, qubit-cavity coupling and detuning. The tunable cavity frequency provides dynamic control over the coupling strength and qubit-cavity detuning helping to minimize Purcell losses and cavity-induced dephasing during qubit operation. The maximum decay time $T_1 = 1.5\,\mu\rm{s}$ is limited by dielectric losses from a design geometry similar to planar transmon qubits. [Preview Abstract] |
Monday, March 3, 2014 10:24AM - 10:36AM |
A28.00011: A Simple, Rapid, and Accurate Method to Calculate Coupling in Coplanar Superconducting Qubit Circuits B. Chiaro, R. Barends, B. Campbell, Y. Chen, Z. Chen, A. Dunsworth, E. Jeffrey, J. Kelly, M. Mariantoni, A. Megrant, J. Mutus, C. Neill, P. O'Malley, C. Quintana, P. Roushan, D. Sank, A. Vainsencher, J. Wenner, T. White, A.N. Cleland, J.M. Martinis A critical design consideration for quantum circuits is the coupling between constituent elements. Both capacitive and inductive coupling can be accurately calculated through numerical simulations with commercial software. However, this approach can be slow and obscures the underlying physics, motivating the development of an analytic theory. The case of coupling between electrodes embedded in a groundplane is particularly interesting to the planar superconducting qubit community. As circuits in this field become more complex, notably in the UCSB multi-Xmon experiments, it is essential to understand the nature of electrode interactions and calculate them rapidly and accurately. I will show how to calculate electrode couplings with a simple integral method and compare its predictions with experimental data and Sonnet software simulations of coupling in planar circuits used for quantum computing. [Preview Abstract] |
Monday, March 3, 2014 10:36AM - 10:48AM |
A28.00012: Protected Josephson Rhombi Chains Matthew Bell, Josh Paramanandam, Lev Ioffe, Michael Gershenson We have studied the low-energy excitations in a minimalistic protected Josephson circuit which contains two basic elements (rhombi) characterized by the $\pi$ periodicity of the Josephson energy. The novel design of these elements, which reduces their sensitivity to the offset charge fluctuations, has been employed. We have observed that the lifetime $T_{1}$ of the first excited state of this quantum circuit in the protected regime is increased by up to $70\mu$s, a factor of $\sim$100 longer than that in the unprotected state. The decay quality factor $\omega_{01}T_{1}$ of this qubit exceeds $10^{6}$. Our results are in agreement with theoretical expectations; they demonstrate the feasibility of symmetry protection in rhombi-based qubits fabricated with existing technology. [Preview Abstract] |
Monday, March 3, 2014 10:48AM - 11:00AM |
A28.00013: Controlling discrete and continuous symmetries in ``superradian'' phase transitions Alexandre Baksic, Cristiano Ciuti The Dicke model describing the interaction of a single-mode boson field to an ensemble of two-level systems is an important paradigm in quantum optics. In particular, the physics of the ``superradiant phase transition'' is the subject of a vigorous research activity. Recently, we explored a model describing a collection of two-level systems, each one coupled to both quadratures of a boson mode [1]. We show that by tuning the two quadrature coupling constants it is possible to control the symmetries of the system, with the possibility of having a U(1)-symmetry even in presence of non-rotating wave (anti-resonant) coupling terms, which are relevant in the ultrastrong coupling regime. We determine the rich phase diagram of such model and show the appearance of Goldstone and amplitude modes. We also show an example of circuit QED configuration where those effects can be observed, by coupling both capacitively and inductively a Josephson junction artificial atom to a superconducting resonator.\\[4pt] [1] A. Baksic and C. Ciuti, arXiv:1310.3780 (2013). [Preview Abstract] |
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