Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session K48: Novel Superconducting Qubits & ArchitecturesFocus
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Sponsoring Units: GQI Chair: John Martinis, Google, Inc. Room: 349 |
Wednesday, March 16, 2016 8:00AM - 8:36AM |
K48.00001: The gatemon: a transmon with a voltage-variable superconductor-semiconductor junction Invited Speaker: Karl Petersson We have developed a superconducting transmon qubit with a semiconductor-based Josephson junction element.\footnote{T.W. Larsen \textit{et al.}, Phys. Rev. Lett. \textbf{115}, 127001 (2015).}$^{,}$\footnote{G. de Lange \textit{et al.}, Phys. Rev. Lett. \textbf{115}, 127002 (2015),} The junction is made from an InAs nanowire with \textit{in situ} molecular beam epitaxy-grown superconducting Al contacts. This gate-controlled transmon, or gatemon, allows simple tuning of the qubit transition frequency using a gate voltage to vary the density of carriers in the semiconductor region. In the first generations of devices we have measured coherence times up to $\sim$10 $\mu$s. These coherence times, combined with stable qubit operation, permit single qubit rotations with fidelities of $\sim$99.5~\% for all gates including voltage-controlled $Z$~rotations. Towards multi-qubit operation we have also implemented a two qubit voltage-controlled cPhase gate. In contrast to flux-tuned transmons, voltage-tunable gatemons may simplify the task of scaling to multi-qubit circuits and enable new means of control for many qubit architectures. [Preview Abstract] |
Wednesday, March 16, 2016 8:36AM - 8:48AM |
K48.00002: Progress toward coupled flux qubits with high connectivity and long coherence times Steven Weber, David Hover, Danna Rosenberg, Gabriel Samach, Jonilyn Yoder, Andrew Kerman, William Oliver The ability to engineer interactions between qubits is essential to all areas of quantum information science. The capability to tune qubit-qubit couplings \textit{in situ} is desirable for gate-based quantum computing and analog quantum simulation and necessary for quantum annealing. Consequently, tunable coupling has been the subject of several experimental efforts using both transmon qubits and flux qubits. Recently, our group has demonstrated robust and long-lived capacitively shunted (C-shunt) flux qubits. Here, we discuss our efforts to develop architectures for tunably coupling these qubits. In particular, we focus on optimizing the RF SQUID coupler to achieve high connectivity. This research was funded 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 No. FA8721-05-C-0002. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of ODNI, IARPA, or the US Government. [Preview Abstract] |
Wednesday, March 16, 2016 8:48AM - 9:00AM |
K48.00003: Three coupled qubits in a single superconducting quantum circuit Madhavi Chand, Suman Kundu, N. Nehra, Cosmic Raj, Tanay Roy, A. Ranadive, Meghan P. Patankar, R. Vijay We propose a new design for a 3-qubit system in the 3D circuit QED architecture. Our design exploits the geometrical symmetry of a single superconducting circuit with three degrees of freedom to generate three coupled qubits. However, only one of these is strongly coupled to the environment while the other two are protected from the Purcell effect. Nevertheless, all three qubits can be measured using the standard dispersive technique. \newline We will present preliminary data on this circuit showing evidence of three distinct qubits that retain the essential properties of a 3D transmon, namely insensitivity to charge noise, sufficient anharmonicity and good coherence times. We will also characterize the coupling of the three qubits to each other, to the environment and to a neighboring transmon qubit. Finally, we will compare our design to previous multi-qubit circuits and discuss possible applications in quantum computing and quantum simulations. [Preview Abstract] |
Wednesday, March 16, 2016 9:00AM - 9:12AM |
K48.00004: Analog approaches to quantum computation using highly-controllable superconducting qubits C. Neill, P. Roushan, R. Barends, B. Campbell, Y. Chen, Z. Chen, B. Chiaro, A. Dunsworth, A. Fowler, E. Jeffrey, J. Kelly, E. Lucero, A. Megrant, J. Mutus, M. Neeley, P. O'Malley, C. Quintana, D. Sank, J. Wenner, T. White, J. Martinis The first generation of quantum hardware that outperforms classical computers will likely be analog in nature. In an effort to realize such a platform, we have built a one-dimensional chain of 9 superconducting gmon qubits. This device provides individual time-dependent control over all nearest-neighbor couplings and local fields (X, Y, Z) in the multi-qubit Hamiltonian. In this talk, I will focus on open problems in non-equilibrium statistical mechanics where dynamical properties become impossible to compute for only a few 10s of qubits. In particular, I will review device performance and the scaling of analog errors with system size. By studying how errors scale during practical applications, we aim to predict if otherwise-intractable computations could be carried out with 30 to 40 qubits. [Preview Abstract] |
Wednesday, March 16, 2016 9:12AM - 9:24AM |
K48.00005: Concentric transmon qubit featuring fast tunability and site-selective Z coupling Martin Weides, Jochen Braumueller, Martin Sandberg, Michael Vissers, Andre Schneider, Steffen Schloer, Lukas Gruenhaupt, Hannes Rotzinger, Michael Marthaler, Alexander Lukashenko, Amadeus Dieter, Alexey Ustinov, David Pappas We present a planar qubit design based on a superconducting circuit that we call concentric transmon. While employing a simple fabrication process using Al evaporation and lift-off lithography, we observe qubit lifetimes and coherence times in the order of 10 $\mu$s. We systematically characterize loss channels such as incoherent dielectric loss, Purcell decay and radiative losses. The implementation of a gradiometric SQUID loop allows for a fast tuning of the qubit transition frequency and therefore for full tomographic control of the quantum circuit. The presented qubit design features a passive direct Z coupling between neighboring qubits, being a pending quest in the field of quantum simulation. [Preview Abstract] |
Wednesday, March 16, 2016 9:24AM - 9:36AM |
K48.00006: Blackbox quantization and numerical simulation of a concentric transmon superconducting qubit Alireza Najafi-Yazdi, Kevin Lalumiere, J. Braum\"uller, Martin Weides We present a blackbox quantization [1] and numerical study of a planar concentric transmon superconducting qubit. This architecture has been recently proposed and experimentally investigated by Braumüller et al [2]. The device involves a gradiometric SQUID loop for a fast tuning of the qubit transition frequency. This allows for full tomographic control of the quantum circuit. A fully automatized numerical package for quantization of superconducting qubits is developed and used for the study of the concentric transmon. A systematic characterization of loss channels such as Purcell decay and radiative losses are also studied. Numerical results are in close agreement with experimental data and suggest the platform to be a useful tool in the design of superconducting circuits. References: [1] Firat, S., DiVicenzo, D. W., David, P., Physical Review B, Vol. 90, No. 13, pp. 134-504, 2014. [2] J. Braumüller et al., arXiv:1509.08014 [Preview Abstract] |
Wednesday, March 16, 2016 9:36AM - 9:48AM |
K48.00007: Weakly-tunable transmon qubits in a multi-qubit architecture Jared Hertzberg, Nicholas Bronn, Antonio Corcoles, Markus Brink, George Keefe, Maika Takita, M. Hutchings, B. L. T. Plourde, Jay Gambetta, Jerry Chow Quantum error-correction employing a 2D lattice of qubits requires a strong coupling between adjacent qubits and consistently high gate fidelity among them. In such a system, all-microwave cross-resonance gates offer simplicity of setup and operation. [1] However, the relative frequencies of adjacent qubits must be carefully arranged in order to optimize gate rates and eliminate unwanted couplings. [2] We discuss the incorporation of weakly-flux-tunable transmon qubits into such an architecture. Using DC tuning through filtered flux-bias lines, we adjust qubit frequencies while minimizing the effects of flux noise on decoherence. [1] J.M. Chow et al, Nat Comm 5, 4015 (2014). [2] A.D. Corcoles et al, Nat Comm 6, 6979 (2015). [Preview Abstract] |
Wednesday, March 16, 2016 9:48AM - 10:24AM |
K48.00008: Semiconductor-inspired superconducting quantum computing Invited Speaker: Yun-Pil Shim Superconducting circuits offer tremendous design flexibility in the quantum regime culminating most recently in the demonstration of few qubit systems supposedly approaching the threshold for fault-tolerant quantum information processing. Competition in the solid-state comes from semiconductor qubits, where nature has bestowed some very useful properties which can be utilized for spin qubit based quantum computing. Here we present an architecture for superconducting quantum computing based on selective design principles deduced from spin-based systems [1]. We propose an encoded qubit approach realizable with state-of-the-art tunable Josephson junction qubits. Our results show that this design philosophy holds promise, enables microwave-free control, and offers a pathway to future qubit designs with new capabilities such as with higher fidelity or, perhaps, operation at higher temperature. The approach is especially suited to qubits based on variable super-semi junctions. [1] Yun-Pil Shim and Charles Tahan, arXiv:1507.07923 [Preview Abstract] |
Wednesday, March 16, 2016 10:24AM - 10:36AM |
K48.00009: Coupling a Transmon Qubit to a Superconducting Metamaterial Resonator Haozhi Wang, M. Hutchings, Sager Indrajeet, Francisco Rouxinol, Matthew LaHaye, B.L.T. Plourde, Bruno G. Taketani, Frank K. Wilhelm Arrays of lumped circuit elements can be used to form metamaterial resonant structures that exhibit significantly different mode structures compared to resonators made from conventional distributed transmission lines. In particular, it is possible to produce a high density of modes in the microwave regime where a superconducting qubit can be operated and coupled to the various modes. We will present our low-temperature measurements of such a superconducting metamaterial resonator coupled to a tunable transmon qubit. By tuning the magnetic flux biasing the qubit, we observe vacuum Rabi splittings in the modes that the qubit transition passes through. We will also discuss our measurements of an interaction between neighboring modes of the metamaterial system that is mediated by the qubit. Because of the dispersive coupling of the qubit to the various modes of the system, driving a microwave tone near one mode of the system can have a significant influence on the transmission through another mode, with a strong dependence on the bias point of the qubit. We will compare these measurements with a theoretical model of the system. [Preview Abstract] |
Wednesday, March 16, 2016 10:36AM - 10:48AM |
K48.00010: Coplanar waveguide flux qubit suitable for quantum annealing Chris Quintana, Yu Chen, D. Sank, D. Kafri, A. Megrant, T. C. White, A. Shabani, R. Barends, B. Campbell, Z. Chen, B. Chiaro, A. Dunsworth, A. Fowler, E. Jeffrey, J. Kelly, E. Lucero, J. Y. Mutus, M. Neeley, C. Neill, P. J. J. O'Malley, P. Roushan, A. Vainsencher, J. Wenner, J. M. Martinis We introduce the "fluxmon" flux qubit, designed with the goal of practical quantum annealing. The qubit's capacitance and linear inductance are provided by a coplanar waveguide on a low loss substrate, minimizing dielectric dissipation and in principle allowing for GHz-scale inter-qubit coupling in a highly connected tunable architecture. Utilizing a dispersive microwave readout scheme, we characterize single-qubit noise and dissipation, and present a simple tunable inter-qubit coupler. We discuss tradeoffs between coherence and coupling in a quantum annealing architecture. [Preview Abstract] |
Wednesday, March 16, 2016 10:48AM - 11:00AM |
K48.00011: Proposal for a cavity based superconducting qubit Andrei Vrajitoarea, Jens Koch, Andrew Houck Various technological challenges need to be resolved in order to demonstrate a working cQED network of superconducting qubits. For single Josephson junction devices important factors include improving coherence times and reducing fluctuations in junction critical current that ultimately lead to dephasing and unwanted frequency collisions. Superconducting microwave resonators show great potential for storing and manipulating quantum states and are known for their accurate reproducibility. We propose the direct addressability of a two level cavity state by dispersively coupling a fluxonium qubit to a coplanar lumped element resonator. We report preliminary experimental results that point towards an induced cavity anharmonicity due to the large dispersive shifts of the fluxonium system. [Preview Abstract] |
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