Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session A33: Scaling Superconducting CircuitsFocus

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Sponsoring Units: DQI Chair: Andrew Houck, Princeton University Room: LACC 408B 
Monday, March 5, 2018 8:00AM  8:36AM 
A33.00001: Engineering superconducting qubit arrays for Quantum Supremacy Invited Speaker: Julian Kelly Using qubits to perform a classically intractable computation is a key milestone in quantum computing, and is known as “Quantum Supremacy”. I will outline our experiment to achieve this where moderatedepth pseudorandom circuits are programmed to entangle an array of qubits, and the sampled output distribution is benchmarked against a classical simulation. A system larger than 50 qubits with low errors can no longer be checked, as the exponentially scaling Hilbert space becomes too large for stateoftheart supercomputers. I will describe our experimental progress towards building and operating a sufficiently large 2D array of nearestneighbor coupled Xmon transmon qubits with fidelities needed for “Quantum Supremacy.” 
Monday, March 5, 2018 8:36AM  9:12AM 
A33.00002: Microwave Engineering Challenges in Scaling Superconducting Qubits Invited Speaker: Damon Russell

Monday, March 5, 2018 9:12AM  9:24AM 
A33.00003: Frequency precision in fixedfrequency transmon qubits, and implications for scalable faulttolerant quantum computing circuits. Jared Hertzberg, Sami Rosenblatt, Jose Chavez, Nicholas Bronn, Hanhee Paik, Martin Sandberg, Easwar Magesan, John Smolin, Markus Brink, Jerry Chow

Monday, March 5, 2018 9:24AM  9:36AM 
A33.00004: Random access quantum information processing in multimode cavities 1 Ravi Naik, Srivatsan Chakram, Akash Dixit, Nelson Leung, Yao Lu, Nathan Earnest, Carolyn Zhang, Peter Groszkowski, David McKay, Jens Koch, David Schuster Multimode cavities are a promising resource for quantum information and simulation, due to their large Hilbert space, restricted set of decoherence channels, and large singlephoton lifetimes. We describe the design of a novel seamless superconducting multimode cavity with a tailored mode spectrum and singlephoton lifetimes on the order of a millisecond. Universal quantum control of the modes of the cavity is performed using a superconducting transmon circuit, realizing a random access quantum information processor [1] in a 3D architecture. We construct quantum gates using sideband transitions with the transmon and characterize their fidelities. 
Monday, March 5, 2018 9:36AM  9:48AM 
A33.00005: Random access quantum information processing in multimode cavities 2 Srivatsan Chakram, R. K. Naik, Nelson Leung, Yao Lu, Akash Dixit, Nathan Earnest, Peter Groszkowski, David McKay, Jens Koch, David Schuster A multimode superconducting cavity coupled to a single superconducting transmon circuit can be used to realize quantum information processors in which quantum logic gates between arbitrary pairs of cavity modes can be performed with equal ease using sideband transitions with the transmon [1]. Such random access processors allow efficient pulse sequences for realizing different families of multimode entangled states of arbitrary cavity modes, as well as threemode gates such as the Toffoli and controlledSWAP. We discuss methods for creating Dicke, GHZ and Cluster states, and interferometric methods for characterizing their entanglement using multimode quantum gates [2].\\ 
Monday, March 5, 2018 9:48AM  10:00AM 
A33.00006: Multilayer Microwave Integrated Quantum Circuits Lev Krayzman, Chan U Lei, Teresa Brecht, Christopher Axline, Yiwen Chu, Luke Burkhart, Luigi Frunzio, Robert Schoelkopf Superconducting circuits are a promising candidate for a quantum computing architecture. However, in order to construct a universal faulttolerant quantum computer, the number of circuit elements used needs to be much greater than what is currently attained. Simply scaling up current technologies faces several challenges. For planarlayout circuits, increasing the number of elements presents increased crosstalk as well as difficulties with providing connectivity to inner elements. In this talk, we discuss an architecture for scaling up circuits while avoiding these challenges via the 3D layout of circuits. For example, lithographicallyproduced superconducting micromachined cavities provide isolation between the different parts of the circuit, and can additionally be harnessed as highQ resonators for storage. The added benefits of massproducibility and lithographic precision provided by the design help it avoid additional difficulties likely to arise in attempting to create larger circuits. This talk will expound on our vision and provide updates with some recent results. 
Monday, March 5, 2018 10:00AM  10:12AM 
A33.00007: Scaling of variational quantum eigensolver performance in a superconducting quantum processor Kevin O'Brien, James Colless, Vinay Ramasesh, Dar Dahlen, William Livingston, John Mark Kreikebaum, Machiel Blok, Wibe de Jong, Jonathan Carter, Irfan Siddiqi The calculation of molecular energies and dynamics from firstprinciples is a classically intractable problem due to the exponential scaling in computational cost with both the number of atoms and the basis set size. Variational quantumclassical hybrid algorithms offer a promising route towards solving currently intractable molecular structure problems in nearterm quantum processors. We experimentally quantify the scaling of convergence, speed, and accuracy of a hybrid quantumclassical variational simulation of chemical energies using a gatebased superconducting quantum processor with up to 8 qubits. 
Monday, March 5, 2018 10:12AM  10:24AM 
A33.00008: Hardware Considerations for Highconnectivity Quantum Annealers Steven Weber, Gabriel Samach, Danna Rosenberg, Jonilyn Yoder, David Kim, Andrew Kerman, William Oliver Quantum annealing is an optimization technique which could potentially make use of quantum tunneling to enhance performance. Existing quantum annealers implement pairwise interactions between qubits, with each qubit coupling to up to six others on a “Chimera” connectivity graph. This hardware graph can be used to embed complex optimization problems, but with significant overhead in energy scale and problem size. Here, we investigate an approach to designing quantum annealers with a higher degree of hardware connectivity. In particular, we discuss coupler chains and parallel couplers, the basic building blocks of a proposed coupler tree architecture. 
Monday, March 5, 2018 10:24AM  10:36AM 
A33.00009: A Variable Coupling Network for Superconducting Qubits Sudeep Dutta, Cody Ballard, James Carbin, Valerie Yoshioka, Kristen Voigt, Christopher Lobb, Frederick Wellstood We use a tunable resonator to vary the coupling between two fixedfrequency transmon qubits (4.6 and 5.0 GHz) mounted in a single 3D superconducting cavity. The effective qubitqubit coupling is provided by a thinfilm lumped element resonator containing two singlejunction SQUID loops, which is fabricated on the same chip as the qubits. An external flux, applied to the loops by an inductive drive coil, modulates the resonance frequency of the coupling circuit by nearly 1 GHz. The resonator capacitively couples to each transmon with a strength g ~ 50 MHz. When the resonator frequency is tuned from 4.6 to 4.2 GHz, the qubitqubit coupling decreases by an order of magnitude, providing an effective switch between the devices. 
Monday, March 5, 2018 10:36AM  10:48AM 
A33.00010: The LargeScale Quantum Socket: Mitigating Coherent Leakage Thomas McConkey, Jérémy Béjanin, Carolyn Earnest, Corey Rae McRae, Zachary Pagel, John Rinehart, Matteo Mariantoni The race for larger number of operational physical qubits is growing. Current targets are in the realm of 50 qubits, though in the near future will be breaching the hundreds. To achieve such numbers, while maintaining operations with low error rates, extensible architectures with compatible packaging must be employed. To this end, we present the largescale quantum socket. A package and chip of such size would normally lead to unwanted modes that will interfere with qubit operations, which we analyze in the context of qubit coherent leakage. To prevent these errors, we have developed two methods by which such box modes are detuned from operational frequencies. These methods are analyzed through electromagnetic field simulations confirming that the resonance frequency of the modes can be significantly increased through the optimal placement of installed threedimensional wires, far higher than standard qubit frequencies. Finally, we show experimental results towards the implementation of a largescale quantum socket. 
Monday, March 5, 2018 10:48AM  11:00AM 
A33.00011: Extensible highperformance twoqubit gate. Fei Yan, Youngkyu Sung, Terry Orlando, Simon Gustavsson, William Oliver We explore alternative twoqubit gate schemes based on different flavors of qubits and/or couplers. With specific combination, we expect high performance in the context of surface code architecture. Limitations and infidelities are also discussed. 
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