Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P42: Quantum Annealing: Architectures |
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Sponsoring Units: DQI Chair: Richard Harris Room: BCEC 210A |
Wednesday, March 6, 2019 2:30PM - 2:42PM |
P42.00001: A proposed superconducting circuit quantum annealer with fully programmable all-to-all coupling Peter McMahon, Tatsuhiro Onodera, Edwin Ng A grand challenge for quantum annealing is the development of annealing hardware that allows fully programmable all-to-all connectivity between logical qubits, with the lowest possible overhead in physical resources. The LHZ [1] scheme achieves fully programmable all-to-all connectivity with a planar architecture that is amenable to implementation with superconducting circuits [2], but does so at a cost of O(N2) physical qubits to realize N logical qubits. We propose a novel architecture for a superconducting circuit quantum annealer that requires only N physical qubits to realize N logical qubits, and present analytical and numerical evidence that fully connected and programmable quantum annealers with N=1000 logical qubits can be constructed with technology that requires only modest improvements over what currently exists. |
Wednesday, March 6, 2019 2:42PM - 2:54PM |
P42.00002: Coherent oscillations in the annealing of a flux qubit Mostafa Khezri, Huo Chen, Humberto Munoz Bauza, Daniel A Lidar Annealing of a single qubit under certain schedules can reveal characteristics related to the coherence of a 2-level system in the form of oscillations in the success probability vs anneal time. |
Wednesday, March 6, 2019 2:54PM - 3:06PM |
P42.00003: Modeling Coherent Oscillations in the Ground State Probability of Annealed Qubits Humberto Munoz-Bauza, Huo Chen, Mostafa Khezri, Daniel A Lidar The ground state amplitude of an annealed qubit oscillates as a function of the anneal time away from the adiabatic limit. We propose and characterize classes of anneal schedules that exhibit experimentally accessible oscillations as signatures of quantum coherence of a qubit, presenting both time-dependent perturbation theoretic analysis and open system results. |
Wednesday, March 6, 2019 3:06PM - 3:18PM |
P42.00004: Coupling annealing-capable high-coherence flux qubits Steven Disseler, James I. Basham, Jeffrey Grover, Sergey Novikov, David Ferguson, Zachary A Stegen, Alexander Marakov, David K Kim, Alexander Melville, Bethany M Niedzielski, Jonilyn L Yoder, Robert Hinkey, Daniel A Lidar, Kenneth M. Zick Despite progress in quantum annealing algorithms and hardware development, key questions remain regarding the role of quantum coherence, entanglement, etc., on key figures of merit needed for real world applications. In this talk we will discuss results of small scale annealing experiments with high-coherence superconducting flux qubits as a part of the Quantum Enhanced Optimization program, which seeks to understand and address these issues. Using systems of two and three fully-connected qubits, we demonstrate controllable, scalable couplings between the Z-like fields of individual qubits. We will discuss the impact of coupling on the coherence of the system as it relates to both multi-qubit measurement fidelity as well as the potential importance as a source of error during computation. |
Wednesday, March 6, 2019 3:18PM - 3:30PM |
P42.00005: Development of a Scalable Annealing Machine Dedicated to Integer Factoring Hanpei Koike, Kentaro Imafuku, Shiro Kawabata Commercial annealing machines such as D-Wave and Fujitsu necessarily features general-purpose programmability to cover as wide area of combinatorial optimization problems and thus to obtain as much markets as possible. On the contrary, research annealing machines can enjoy freedom to specialize in a specific problem and to investigate the optimal calculation method to maximum extent. We call this approach Application Specific Annealing Circuit (ASAC). We chose integer factoring as the first target application in our ASAC research. Integer factoring is accomplished by reverse-directional calculation of a digital multiplier circuit by expressing the logic circuit as an energy function and by finding the minimum energy state using annealing method. We have developed a scalable classical ASAC machine using commercial electronic components as a proof of concept. We call our experimental machine AIST Analog Annealer (AAA). We are going to introduce this machine in our presentation. |
Wednesday, March 6, 2019 3:30PM - 3:42PM |
P42.00006: Fluxonium Qubit Systems for Coherent Quantum Annealing Maxim Vavilov, Zhenyi Qi, Mark Dykman, Vladimir Manucharyan Fluxonium systems are perfect candidates for coherent quantum annealing. Individual fluxonium qubits have: (i) substantially long coherence time in excess 5 μs away from sweet spot and 100 μs at the half-flux sweet spot[1], (ii) strong X-X qubit coupling, which can be made to exceed the qubit transition energy[2], and (iii) two low-energy states, well separated from higher-energy states. These characteristics are expected enable long-coherence annealing protocols, whilekeeping the system in the computational subspace. A potential resource for quantum speed up is multiqubit tunneling in hard optimization problems [3]. In this talk, we describe the multiqubit tunneling in the system of strongly coupled fluxonium qubits during annealing. We discuss the effect of flux noise and dielectric losses on the multiqubit tunneling events. |
Wednesday, March 6, 2019 3:42PM - 3:54PM |
P42.00007: Flux qubit readout at the degeneracy point Marius Schöndorf, Adrian Lupascu, Frank K Wilhelm
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Wednesday, March 6, 2019 3:54PM - 4:06PM |
P42.00008: High coherence annealing, Part 1: fast, high-fidelity readout James Basham, Jeffrey Grover, Steven Disseler, Sergey Novikov, David Ferguson, Zachary A Stegen, Alexander Marakov, Robert Hinkey, Moe S Khalil, David K Kim, Alexander Melville, Bethany M Niedzielski, Jonilyn L Yoder, Anthony J Przybysz, Daniel A Lidar, Kenneth M. Zick Recently developed capacitively-shunted flux qubits offer a promising path toward building a high-coherence quantum annealer. These qubits take advantage of lower persistent currents to achieve lower noise sensitivity. As such, readout of their state at the end of the anneal operation presents unique challenges. We report experimental results of a persistent current readout scheme that provides fast readout while isolating the qubit from the resonator during the anneal. |
Wednesday, March 6, 2019 4:06PM - 4:18PM |
P42.00009: High coherence annealing, Part 2: fast annealing experiments Jeffrey Grover, James I. Basham, Steven Disseler, Sergey Novikov, David Ferguson, Zachary A Stegen, Alexander Marakov, David K Kim, Alexander Melville, Bethany M Niedzielski, Jonilyn L Yoder, Robert Hinkey, Moe S Khalil, Daniel A Lidar, Kenneth M. Zick Recently developed capacitively-shunted flux qubits offer a promising path toward building a high-coherence quantum annealer. These qubits take advantage of lower persistent currents to achieve lower noise sensitivity. Using the fast readout scheme and device discussed in Part 1, Part 2 presents single-qubit annealing experiments performed using RF bias lines. We study the behavior of the qubit transition width by changing the annealing time, and we use excited state readout to determine other parameters of the system. This setup also allows for programming highly nonlinear annealing schedules to probe quantum coherence. |
Wednesday, March 6, 2019 4:18PM - 4:30PM |
P42.00010: High-order and long-range connectivity for embedding problems in quantum annealing with superconducting flux qubits Denis Melanson, Antonio Martinez, Muhammet Ali Yurtalan, Yongchao Tang, David K Kim, Alexander Melville, Bethany M Niedzielski, Jonilyn L Yoder, Sergey Novikov, Evgeny Mozgunov, Daniel A Lidar, Adrian Lupascu A high degree of connectivity between qubits is believed to be important in quantum annealing. An approach for implementing high connectivity in superconducting flux qubit annealers was proposed in which the qubits are connected via chains of rf-SQUID couplers. We report an application of this concept in building problem-specific annealing architectures with high-order connectivity. We analyzed the coupling strength between qubits and the coupler network induced qubit decoherence for application-oriented architectures, using both simplified spin models and full quantum circuit models. We designed devices with capacitively shunted flux qubits coupled by coupler trees. We discuss experimental prospects and the relevance for large scale annealing. |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P42.00011: Multi-body flux-qubit couplers for quantum annealing Gioele Consani, Paul A. Warburton, Nedeen Al Sharif Despite the enormous progress achieved in the field of quantum annealing over the last decade, the demonstration of a computational advantage over classical methods remains elusive. One possible solution is to provide quantum annealers with qualitatively new features, such as higher-order terms in the driver and/or problem Hamiltonians and error-suppression. These capabilities both rely on the physical implementation of multi-body interactions. While interactions between pairs of flux qubits can be achieved rather easily, multi-body interactions require more sophisticated constructions. Some of these use ancillary qubits, while others are based on coupling loops with carefully-engineered flux non-linearities. Here we present a comparative analysis of a few such proposed implementations and propose a quantitative way to compare their performances, with specific focus on their possibility to generate the correct quantum energy spectrum during the annealing process. |
Wednesday, March 6, 2019 4:42PM - 4:54PM |
P42.00012: Parity measurement via ancillary RF-SQUIDs for superconducting flux qubit quantum annealers Antonio Martinez, Denis Melanson, Daniel Tennant, Yongchao Tang, Sergey Novikov, Steven Disseler, James Basham, Jeffrey Grover, Alexander Marakov, Zachary A Stegen, Adrian Lupascu Next generation quantum annealing (QA) will likely rely on error suppression codes. Proposals for error suppression in QA often use energy penalties [Quantum Inf. Process. 16: 89 (2017)] or parity measurements [Phys.Rev.A 95, 032317 (2017)]. We propose a device to do parity measurements in quantum annealers based on flux qubits. This device consists of two RF-SQUIDs coupled to the measured qubits. We simulate the quantum measurement process, including realistic implementation effects. We consider generalizations of this approach to higher-order parity measurements. We also present a different approach based on symmetrical coupling of a flux readout device, designed to measure parity information. Prospects for experimental demonstration are discussed. |
Wednesday, March 6, 2019 4:54PM - 5:06PM |
P42.00013: Quantum annealing with mediated interactions: from a perturbative to a ultrastrong mediated coupling. Manuel Pino Garcia, Juan Jose Garcia-Ripoll We present a study of a quantum annealer where bosons mediate the Ising-type interactions between qubits. We compare the efficiency of ground state preparation for direct and mediated couplings, for which Ising and spin-boson Hamiltonian are employed respectively. This comparison is done numerically for a small frustrated antiferromagnet, with a careful choice of the optimal adiabatic passage that reveals the features of the boson-mediated interactions. Those features can be explained by taking into account what we called excited solutions: states with the same spin correlations as the ground-state but with a larger bosonic occupancy. For similar frequencies of the bosons and qubits, the performance of quantum annealing depends on how excited solutions interchange population with local spin errors. We report an enhancement of quantum annealing thanks to this interchange under certain circumstances. |
Wednesday, March 6, 2019 5:06PM - 5:18PM |
P42.00014: Schrieffer-Wolff Methods for Interacting Superconducting Qubits Rudolph J Magyar, David Ferguson There are many possible methods for implementing a low-energy Pauli decomposition of a quantum circuit Hamiltonian as a continuous function of qubit and coupler control fields. Effective low energy models are helpful designs tools to optimize performance in device applications where quantum effects are important. In this talk, we report a method based on the Bravyi et al Schrieffer-Wolff transformation [1] that provides a Pauli decomposition with the following desirable properties: (i) the effective Hamiltonian remains block diagonal so that the computational subspace is completely decoupled from the non-computational states, (ii) the adiabatic connection terms generated by the time dependence of the computational subspace are block off-diagonal and thus do not generate any terms within the computational subspace, and (iii) the computational subspace has a non-trivial holonomy over the control parameter manifold. We report application of these methods to tunable flux qubits comparing results to more explicit models and experimental measurements. |
Wednesday, March 6, 2019 5:18PM - 5:30PM |
P42.00015: Superconducting Quantum Annealing Architecture with LC Resonators Akiyoshi Tomonaga, Hiroto Mukai, Jaw-Shen Tsai We report on the architecture and experimental results of superconducting quantum annealer with LC resonator. In the architecture, qubit and a LC resonator are connected via a Josephson junction to realize deep strong-coupling. Such arrangement of deep strongly coupled circuit QED system is resulted with an extremely long novel quantum system. With the exceedingly gigantic compound qubit, we can realize a unique network of fully coupled large number of spins. For the actual fabrication of the system, we can conveniently separate the fabrication processes of qubit itself and resonator network. Where qubits can be fabricated by the standard Al angled evaporation, the resonator network can be fabricated by the standard Nb superconducting multilayer integration technology. |
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