Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K33: Superconducting GatesFocus

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Sponsoring Units: DQI Chair: Alexandre Blais, Univ of Sherbrooke Room: LACC 408B 
Wednesday, March 7, 2018 8:00AM  8:36AM 
K33.00001: Scaling up a superconducting qubit lattice with parametric gates Invited Speaker: Blake Johnson Scaling up superconducting qubit systems presents a number of challenges in various domains including: control systems, fabrication, packaging, signal delivery, and software automation. I will report on initial efforts at Rigetti toward scaling up the 8Q platform toward larger, more connected lattices of qubits and how we address some of these challenges. In particular, I will examine the performance of parametric gates in these lattices, and touch on operational measures of crosstalk, such as dependence of simultaneous benchmarking on distance (in real space and frequency space) between qubit subsystems. 
Wednesday, March 7, 2018 8:36AM  9:12AM 
K33.00002: Deterministic teleportation of a quantum gate between two logical qubits Invited Speaker: Kevin Chou

Wednesday, March 7, 2018 9:12AM  9:24AM 
K33.00003: Entangling fixedfrequency transmon qubits with fast nonAbelian nonadiabatic geometric gates Daniel Egger, Marc Ganzhorn, Gian Salis, Panagiotis Barkoutsos, Ivano Tavernelli, Stefan Filipp Fixed frequency qubits and resonators are promising candidates to build a universal quantum computer because of their stability and long coherence times. However, the lack of energy tunability reduces controllability which may introduce an operational overhead. Additionally, twoqubit gates using microwave drives only are slow and impose conditions on the qubit frequencies. Our experimental results show how to use fast nonAbelian geometric phases to create entanglement between qubits. We entangle two fixedfrequency transmon qubits connected via a resonator by creating a lambda system where we simultaneously drive both transitions. Various two qubit states can be created by changing the amplitudes and phases of the two drives. The SWAP like nature of this geometric operation makes it well suited for variational quantum algorithms that compute molecular energies by exploring the part of Hilbert space with a fixed number of electrons. 
Wednesday, March 7, 2018 9:24AM  9:36AM 
K33.00004: Implementation and Applications of Two Qutrit Gates in Superconducting Transmon Qubits Machiel Blok, Vinay Ramasesh, James Colless, Kevin O'Brien, Thomas Schuster, Norman Yao, Irfan Siddiqi With recent improvements in stateselective quantum control and the coherent lifetimes of superconducting circuits, it has become feasible to encode quantum information in the higher excited states of a transmon qubit. A threelevel quantum system (qutrit) has an exponentially larger Hilbert space for a given number of elements and is the minimal system required to observe noncontextuality and the physics of scrambling. Here we describe the implementation of a gate between two transmon qutrits in a 2D planar architecture. The gate is constructed by incorporating the wellestablished crossresonance interaction into a multilevel decoupling sequence. In combination with single qutrit control, this gate allows for the implementation of a maximally scrambling operation which is a key component in a recently proposed proofofprinciple experiment to simulate the decoding of Hawking radiation to reconstruct a quantum state. 
Wednesday, March 7, 2018 9:36AM  9:48AM 
K33.00005: Allmicrowave CNOT gate between two transmon qubits Shavindra Premaratne, JenHao Yeh, Frederick Wellstood, Benjamin Palmer We have embedded two fixed frequency Al/AlO_{x}/Al transmon devices, with qubit transition frequencies at 6.07 GHz and 6.75 GHz, in a single 3D Al cavity with a fundamental mode at 7.60 GHz. Strong coupling between the cavity and the qubits results in an effective qubitqubit coupling of the form (σ_{1}^{+}σ_{2}^{} + σ_{1}^{}σ_{2}^{+}) with a coupling strength of 26 MHz resulting in a qubit resonance shift of 1 MHz depending on the state of the other qubit. Using an allmicrowave technique, we demonstrate the operation of an entangling CNOT gate between the two qubits, with a gate time of 900 ns. The final fidelity for the gate is approximately 90% which is verified by performing quantum state tomography on the two qubits. Improvements to the fidelity of the gate will be discussed. 
Wednesday, March 7, 2018 9:48AM  10:00AM 
K33.00006: Speeding up entangling gates for fixedfrequency superconducting qubits Xiuhao Deng, Sophia Economou, Edwin Barnes Superconducting transmon qubits have a weak nonlinearity which leads to spectral crowding in multiqubit circuits. This is one of the obstacles to fast and accurate entangling gates. Previously we introduced SWIPHT, an analytical protocol for designing fast, highfidelity twoqubit gates, and we showed that SWIPHT exhibits high performance in a particular regime of static system parameters. Here, we show that this regime can be greatly extended by overcoming coherent errors and leakage through the use of the DRAG protocol and pulse shaping, respectively. This enables a reduction of SWIPHT CNOT gate times down to the order of 10 ns while maintaining fidelities above the 99% level using simple pulse shapes. 
Wednesday, March 7, 2018 10:00AM  10:12AM 
K33.00007: Fast, highfidelity twoqubit entangling gates in superconducting multiqubit systems HsiangSheng Ku, Junling Long, Russell Lake, Xian Wu, Mustafa Bal, David Pappas Superconducting quantum circuit is a promising technology for building a faulttolerant quantum computer. However, challenges remain in the development of a twoqubit entangling gate with an ultrahigh fidelity and a short gate time compared to qubit relaxation and decoherence times. Especially for a largescale multiqubit system, the quality of the entangling gate suffers from the unintended excitations of the nearlydegenerate harmful transitions and the leakage outside the qubit computational subspace. Recently, the SWIPHT gate has been shown numerically to be a robust scheme for solving the above problems by incorporating the unwanted dynamics into the designs of the gate [1]. In this talk, we describe our designs of multiqubit systems, where the primitive is a coupled twoqubit device with one of the qubits being magneticflux tunable. We also present the experimental progress on demonstration of the SWIFT gate in the multiqubit systems. 
Wednesday, March 7, 2018 10:12AM  10:24AM 
K33.00008: Demonstration of Universal Parametric Entangling Gates on a MultiQubit Lattice Alexa Staley, Alexander Hudson, Chris Osborn, Nikolas Tezak, Guen Prawiroatmodjo, Michael Sheer, Nasser Alidoust, Eyob Sete, Nicolas Didier, Marcus da Silva, Blake Johnson, Sabrina Hong, Andrew Bestwick, Alexander Papageorge, Ben Bloom, Deanna Abrams, Shane Caldwell, Peter Karalekas, Prasahnt Sivarajah, Claire Thomas, Maxwell Block, Genya Crossman, Michael Selvanayagam, Matt Reagor, Chad Rigetti We show that parametric coupling techniques can be used to generate selective entangling interactions for multiqubit processors, and in such a way that is scalable. By inducing coherent population exchange between adjacent qubits under frequency modulation, we implement a universal gateset for a linear array of eight superconducting qubits. We establish the suitability of this technique by doing an error analysis on our twoqubit gate fidelity (via QPT), and by preparing an eightqubit register in all possible bitstring permutations and monitor the fidelity of a twoqubit gate across one pair of these qubits. These results thus offer a path to a scalable architecture with high selectivity and low crosstalk. 
Wednesday, March 7, 2018 10:24AM  10:36AM 
K33.00009: Controlled–Z gate for two transmon qubits coupled by semiconductor wire Zhenyi Qi, HongYi Xie, Javad Shabani, Vladimir Manucharyan, Alex Levchenko, Maxim Vavilov We propose a realization of controlled–Z (CZ) gate for two transmon qubits connected by an epitaxial semiconductor wire. This arrangement provides an electrical control of the interaction between the qubits by applying a voltage to a metallic gate near the wire. We calculate the gate fidelity and gate time for the CZ gate. We demonstrate that in the absence of decoherence, the CZ gate can be performed under 50ns with gate error below 10^{4}. We also evaluate the CZ gate for two gatemon qubits coupled by a semiconductor wire and for a system of two gatemon–like qubits formed by a single semiconductor Hjunction. 
Wednesday, March 7, 2018 10:36AM  10:48AM 
K33.00010: Controlling the arrow of time in circuit QED Andrew Keller, Nicole Yunger Halpern, Paul Dieterle, Michael Fang, Alp Sipahigil, Oskar Painter 
Wednesday, March 7, 2018 10:48AM  11:00AM 
K33.00011: Abstract Withdrawn By mapping between the quantum states of the simulator and the original system analog quantum simulation aims to synthesize the Hamiltonian of a certain quantum system of interest to mimick its time evolution. Herefore, the coupling scheme of neighboring qubits in the simulator determines the complexity and diversity of simulated system. In this presentation, we present two coupled concentric transmon qubits [1] featuring XXinteraction to allow for energy exchange and therefore entanglement of the qubit states. In addition, due to its nonvanishing geometric Inductance [2], concentric transmons are predicted to have additional ZZinteraction. Implemented in qubit chains, this allows for very interesting implementation of fermionic quantum state simulators. Spectroscopic and timedomain data of our coupled twoqubit circuit are discussed. 
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