Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session W27: Focus Session: Superconducting Qubits: Quantum Computing Architectures |
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Sponsoring Units: GQI Room: 329 |
Thursday, March 21, 2013 2:30PM - 3:06PM |
W27.00001: Overview of a Quantum Annealing Processor Invited Speaker: Mark W. Johnson Quantum Adiabatic Evolution algorithms have been proposed as a potentially powerful set of methods to solve computationally hard problems.\footnote{E. Farhi, \emph{et al.}, SCIENCE \textbf{292}, pp. 472-476, 20 April 2001} One example of this approach is to find the ground state configuration of an Ising spin system with a transverse field using quantum annealing (QA).\footnote{T. Kadowaki and H. Nishimori, Phys. Rev. E,\textbf{58}(5), pp. 5355-5363, (1998)} I will present an overview of the architecture and operation of the D-Wave One, an end-to-end computing platform that performs QA by slowly decreasing the transverse field of a programmable Ising spin system. After a brief review of quantum annealing, I will describe how superconducting flux qubits are used to construct the programmable Ising spins.\footnote{R. Harris, \emph{et al.}, Phys. Rev. B, \textbf{82}, 024511 (2010)} I will then discuss some recent experiments performed to determine whether or not the processor behaves as intended. Toward this end, it is particularly useful to be able to measure the spectrum of single and multiple coupled qubits as they progress through the annealing algorithm.\footnote{A. J. Berkley, \emph{et al.}, \texttt{arXiv:1210.6310v1}} Finally, since the primary measure of the efficacy of such a machine is how well it solves problems, I will conclude with a discussion of system performance and scaling. [Preview Abstract] |
Thursday, March 21, 2013 3:06PM - 3:42PM |
W27.00002: Realization of three-qubit quantum error correction with superconducting circuits Invited Speaker: Robert Schoelkopf |
Thursday, March 21, 2013 3:42PM - 3:54PM |
W27.00003: Cross-Talk in Superconducting Transmon Quantum Computing Architecture David Abraham, Jerry M. Chow, Antonio Corcoles, Mary Beth Rothwell, George Keefe, Jay Gambetta, Matthias Steffen Superconducting transmon quantum computing test structures often exhibit significant undesired cross-talk. For experiments with only a handful of qubits this cross-talk can be quantified and understood [1], and therefore corrected. As quantum computing circuits become more complex, and thereby contain increasing numbers of qubits and resonators, it becomes more vital that the inadvertent coupling between these elements is minimized. The task of accurately controlling each single qubit to the level of precision required throughout the realization of a quantum algorithm is difficult by itself, but coupled with the need of nulling out leakage signals from neighboring qubits or resonators would quickly become impossible. We discuss an approach to solve this critical problem.\\[4pt] [1] ``Characterization of addressability by simultaneous randomized benchmarking,'' Jay M. Gambetta, et al., arXiv:1204.6308 [quant-ph]. [Preview Abstract] |
Thursday, March 21, 2013 3:54PM - 4:06PM |
W27.00004: Implementation of a two-qubit Grover algorithm using superconducting qubits Matthias Steffen, Antonio Corcoles, Jerry Chow, Jay Gambetta, John Smolin, Matt Ware, Joel Strand, Britton Plourde High fidelity two-qubit gates have previously been demonstrated with fixed frequency superconducting qubits and employing the cross-resonance effect generating the qubit-qubit interaction in which qubit 1 is driven at the frequency of qubit 2. The drawback of previous implementations of the cross-resonance gate is the fact that single qubit gates on qubit 2 emerge when the qubits are multi-level systems instead of strictly two-level systems. As a result, two-qubit gates must be tuned up by careful timing or by explicitly applying single-qubit correction pulses. This is a cumbersome procedure and can add overall errors. Instead, we show a refocusing scheme which preserves the two-qubit interaction but eliminates the single-qubit gates. The total gate length is only increased by the duration of two single qubit pi-pulses which is a low overhead. When tuning up this composite pulse we show an implementation of a two-qubit Grover's algorithm without applying any correction pulses. The average success probability of the algorithm is consistent with fidelity metrics obtained by independent randomized bench-marking experiments (both single and two-qubit). [Preview Abstract] |
Thursday, March 21, 2013 4:06PM - 4:18PM |
W27.00005: Emulating a mesoscopic system using superconducting quantum circuits Yu Chen, R. Barends, J. Bochmann, B. Campbell, B. Chiaro, E. Jeffrey, J. Kelly, M. Mariantoni, A. Megrant, J. Mutus, C. Neill, P. O'Malley, S. Ohya, P. Roushan, D. Sank, A. Vainsencher, J. Wenner, T. White, A.N. Cleland, J.M. Martinis We demonstrate an emulation of a mesoscopic system using superconducting quantum circuits. Taking advantage of our ReZQu-architectured quantum processor, we controllably splitted a microwave photon and manipulated the splitted photons before they recombined for detection. In this way, we were able to simulate the weak localization effect in mesoscopic systems - a coherent backscattering process due to quantum interference. The influence of the phase coherence was investigated by tuning the coherence time of the quantum circuit, which in turn mimics the temperature effect on the weak localization process. At the end, we demonstrated an effect resembling universal conductance fluctuations, which arises from the frequency beating between different coherent backscattering processes. The universality of the observed fluctuation was shown as the independence of the fluctuation amplitude on detailed experimental conditions. [Preview Abstract] |
Thursday, March 21, 2013 4:18PM - 4:30PM |
W27.00006: Speed limits for quantum gates in multiqubit solid-state systems Sahel Ashhab, Pieter de Groot, Franco Nori We derive speed limits for various unitary quantum operations in multiqubit systems under typical experimental conditions, using parameters and constraints that are commonly encountered with superconducting qubits. In particular we focus on two- and three-qubit gates. We find that simple methods for implementing two-qubit gates generally provide the fastest possible implementations of these gates. We also find that the three-qubit Toffoli gate time varies greatly depending on the type of interactions and the system's geometry, taking only slightly longer than a two-qubit controlled-NOT (CNOT) gate for a triangle geometry. [Preview Abstract] |
Thursday, March 21, 2013 4:30PM - 4:42PM |
W27.00007: Designing entangling microwave gates between fixed frequency superconducting circuits coupled by resonators Seth Merkel, Jay Gambetta, John Smolin Many of the recent techniques for controlling superconducting quantum circuits are directly derived from the atomic theory of cavity QED, and the fixed frequency transmon provides a particularly close analogy to an ``artificial atom.'' However, even in this case new modelling techniques are required as we engineer parameter regimes that have been previously unexplored in atomic systems. In this talk we develop the Schrieffer-Wolff transformation as a means of adiabatically eliminating high-energy subspaces in order to derive effective entangling Hamiltonians. We can use this theory to explain many of the recent, experimentally demonstrated fixed frequency gates such as the cross-resonance gate and the two-photon 00 to 11 transition. In the case of the cross-resonance gate this more detailed model predicts spurious single qubit rotations, and their rates, which can then be removed through refocusing techniques. [Preview Abstract] |
Thursday, March 21, 2013 4:42PM - 4:54PM |
W27.00008: Hardware-efficient quantum memory protection Zaki Leghtas, Gerhard Kirchmair, Brian Vlastakis, Robert Schoelkopf, Michel Devoret, Mazyar Mirrahimi We propose a new method to autonomously correct for errors of a logical qubit induced by energy relaxation. This scheme encodes the logical qubit as a multi-component superposition of coherent states in a harmonic oscillator, more specifically a single cavity mode. The sequences of encoding, decoding and correction operations employ the non-linearity provided by a single physical qubit coupled to the cavity. We layout in detail how to implement these operations in a circuit QED architecture. This proposal directly addresses the task of building a hardware-efficient and technically realizable quantum memory. [Preview Abstract] |
Thursday, March 21, 2013 4:54PM - 5:06PM |
W27.00009: Engineered circuit QED with dense resonant modes Frank Wilhelm, Daniel Egger In circuit quantum electrodynamics even in the ultrastrong coupling regime, strong quasi-resonant interaction typically involves only one mode of the resonator as the mode spacing is comparable to the frequency of the mode. We are going to present an engineered hybrid transmission line consisting of a left-handed and a right-handed portion that has a low-frequency van-Hove singularity hence showing a dense mode spectrum at an experimentally accessible point. This gives rise to strong multi-mode coupling and can be utilized in multiple ways to create strongly correlated microwave photons. [Preview Abstract] |
Thursday, March 21, 2013 5:06PM - 5:18PM |
W27.00010: Observing the nonequilibrium dynamics of the quantum transverse-field Ising chain in circuit QED Oliver Viehmann, Jan von Delft, Florian Marquardt Circuit QED architectures of superconducting artificial atoms and microwave resonators are currently moving towards multi-atom, multi-resonator setups with drastically enhanced coherence times, making them increasingly attractive candidates for quantum simulations of interesting interacting quantum many-body systems. Here we propose and analyze a circuit QED design that implements the quantum transverse-field Ising chain coupled to a microwave resonator for readout. Our setup can be used to study quench dynamics, the propagation of localized excitations, and other nonequilibrium features, in a field theory exhibiting a quantum phase transition, and based on a design that is feasible with current technology and could easily be extended to break the integrability of the system. [Preview Abstract] |
Thursday, March 21, 2013 5:18PM - 5:30PM |
W27.00011: Strongly-coupled Josephson junction array for simulation of frustrated one-dimensional spin models Zhengwei Zhou, Lianghui Du, Xingxiang Zhou, Yongjian Han, Guangcan Guo We study the capacitance-coupled Josephson-junction array beyond the small-coupling limit. We find that, when the scale of the system is large, its Hamiltonian can be obtained without the small-coupling approximation and the system can be used to simulate strongly frustrated one-dimensional Ising spin problems. To engineer the system Hamiltonian for an ideal theoretical model, we apply a dynamical-decoupling technique to eliminate undesirable couplings in the system. Using a six-site junction array as an example, we numerically evaluate the system to show that it exhibits important characteristics of the frustrated spin model. [Preview Abstract] |
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