Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
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
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Wednesday, March 7, 2018 9:12AM - 9:24AM |
K33.00003: Entangling fixed-frequency transmon qubits with fast non-Abelian non-adiabatic 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, two-qubit gates using microwave drives only are slow and impose conditions on the qubit frequencies. Our experimental results show how to use fast non-Abelian geometric phases to create entanglement between qubits. We entangle two fixed-frequency 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 state-selective 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 three-level quantum system (qutrit) has an exponentially larger Hilbert space for a given number of elements and is the minimal system required to observe non-contextuality 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 well-established cross-resonance interaction into a multi-level 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 proof-of-principle experiment to simulate the decoding of Hawking radiation to reconstruct a quantum state. |
Wednesday, March 7, 2018 9:36AM - 9:48AM |
K33.00005: All-microwave CNOT gate between two transmon qubits Shavindra Premaratne, Jen-Hao Yeh, Frederick Wellstood, Benjamin Palmer We have embedded two fixed frequency Al/AlOx/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 qubit-qubit coupling of the form (σ1+σ2- + σ1-σ2+) 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 all-microwave 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 fixed-frequency superconducting qubits Xiuhao Deng, Sophia Economou, Edwin Barnes Superconducting transmon qubits have a weak nonlinearity which leads to spectral crowding in multi-qubit circuits. This is one of the obstacles to fast and accurate entangling gates. Previously we introduced SWIPHT, an analytical protocol for designing fast, high-fidelity two-qubit 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, high-fidelity two-qubit entangling gates in superconducting multiqubit systems Hsiang-Sheng Ku, Junling Long, Russell Lake, Xian Wu, Mustafa Bal, David Pappas Superconducting quantum circuit is a promising technology for building a fault-tolerant quantum computer. However, challenges remain in the development of a two-qubit entangling gate with an ultra-high fidelity and a short gate time compared to qubit relaxation and decoherence times. Especially for a large-scale multiqubit system, the quality of the entangling gate suffers from the unintended excitations of the nearly-degenerate 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 two-qubit device with one of the qubits being magnetic-flux 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 Multi-Qubit 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 multi-qubit 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 two-qubit gate fidelity (via QPT), and by preparing an eight-qubit register in all possible bitstring permutations and monitor the fidelity of a two-qubit 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, Hong-Yi 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 H-junction. |
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 The unitary time evolution of a quantum system implies that flipping the overall sign of a Hamiltonian is equivalent to reversing time. Time reversal operations have utility in, for example, measuring out-of-time-ordered correlators (OTOCs), which have been considered theoretically to quantify information scrambling and identify many-body localized phases. Following a proposal by Zhu, Hafezi, and Grover [Phys. Rev. A 94, 062329 (2016)], we present the design and preliminary measurements of a planar superconducting circuit where the sign of an effective Hamiltonian of bus-coupled qubits is controlled by the state of an ancilla qubit. We discuss some of the practical challenges of this approach and the implications for OTOC measurements. |
Wednesday, March 7, 2018 10:48AM - 11:00AM |
K33.00011: Abstract Withdrawn |
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