Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session E33: Applications with NearTerm Superconducting Quantum DevicesFocus

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Sponsoring Units: DQI Chair: Rami Barends, Google Inc  Santa Barbara Room: LACC 408B 
Tuesday, March 6, 2018 8:00AM  8:36AM 
E33.00001: Applications of restricted nearterm superconducting qubit architectures: Using quantum control to reach quantum advantage Invited Speaker: Frank Wilhelm While universal quantum computers certainly will have to be fault tolerant, there is the alternative line of thinking to demonstrate quantum advantage on nearterm hardware, with limited number of gates, qubits, and connectivity. This can be achieved by careful codesign of hardware, algorithms, and controls. 
Tuesday, March 6, 2018 8:36AM  9:12AM 
E33.00002: Training a classifier with a superconducting quantum processor Invited Speaker: Antonio Corcoles Recent theoretical and experimental progress in quantum information suggests that there may be advantages in quantumassisted heuristic algorithms for nearterm devices, even at relatively shallow circuit depths. In the particular case of machine learning, in the light of increasing dataset sizes there is basis to hold the concern that traditional computational resources will become increasingly inefficient to growing challenges. In this talk, I will explore potential solutions to some of these problems by using quantum support to classical optimizers in solving classification problems. 
Tuesday, March 6, 2018 9:12AM  9:24AM 
E33.00003: Linear and Logarithmic Time Compositions of Quantum ManyBody Operators Michael Kaicher, Felix Motzoi, Frank Wilhelm We develop a generalized framework for constructing manybodyinteraction operations either in linear time or in logarithmic time with a linear number of ancilla qubits. Exact gate decompositions are given for Pauli strings, manycontrol Toffoli gates, number and parityconserving interactions, unitary coupled cluster operations, and sparse matrix generators. We provide a linear time protocol that works by creating a superposition of exponentially many different possible operator strings and then uses dynamical 
Tuesday, March 6, 2018 9:24AM  9:36AM 
E33.00004: Sampling and scrambling on a chain of superconducting qubits Michael Geller We study a circuit, the Josephson sampler, that embeds a real vector into an entangled state of n qubits, and optionally samples from it. We measure its fidelity and entanglement on the 16qubit ibmqx5 chip. To assess its expressiveness, we also measure its ability to generate Haar random unitaries and quantum chaos, as measured by PorterThomas statistics and outoftimeorder correlation functions. The circuit requires nearestneighbor CZ gates on a chain and is especially well suited for firstgeneration superconducting architectures. 
Tuesday, March 6, 2018 9:36AM  9:48AM 
E33.00005: Tensornetwork based variational approach to calculating ground state properties of interacting quantum systems with superconducting qubits Vinay Ramasesh, William Huggins, Kevin O'Brien, James Colless, Dar Dahlen, Machiel Blok, William Livingston, John Mark Kreikebaum, Vladimir Kremenetski, Birgitta Whaley, Irfan Siddiqi Variational quantumclassical hybrid algorithms have recently emerged as a promising application for nearterm quantum devices. In superconducting circuits, recent demonstrations of this algorithm with up to four qubits have probed the energy landscapes of simple molecules and spin chains. As these devices scale to increasingly larger numbers of qubits, the choice of ansatz for the variationallyoptimized wavefunction becomes more important. An ideal ansatz combines two desiderata: the ability to represent a large portion of the nqubit Hilbert space, specifically highlyentangled states; and a circuit depth which scales polynomially with the qubit number. Recently, classical methods based on tensor networks have become popular for compactly handling wavefunctions of interacting systems which possess a high degree of entanglement. Motivated by their successes, we apply tensor network ansatze to the variational quantum eigensolver in an experimental setting: an superconducting quantum processor comprising eight transmon qubits. Our approach is intended to study groundstate properties of interacting systems, e.g. spin chains. Here we detail the experimental protocol and present preliminary data. 
Tuesday, March 6, 2018 9:48AM  10:00AM 
E33.00006: Low Depth Quantum Simulation of Electronic Structure Ryan Babbush, Nathan Wiebe, Jarrod McClean, James McClain, Hartmut Neven, Garnet Chan The majority of quantum algorithms for solving the electronic structure problem encode the wavefunction using N Gaussian orbitals, leading to Hamiltonians with O(N^4) secondquantized terms. We avoid this overhead and extend methods to the condensed phase by utilizing a dual form of the plane wave basis which diagonalizes the potential operator, leading to a Hamiltonian representation with O(N^2) secondquantized terms. Using this representation we can implement single Trotter steps of the Hamiltonians with linear gate depth on a planar lattice. Properties of the basis allow us to deploy Trotter and Taylor series based simulations with respective circuit depths of O(N^{7/2}) and O(N^{8/3}) for fixed charge densities  both large asymptotic improvements over all prior results. Variational algorithms also require significantly fewer measurements to find the mean energy in this basis, ameliorating a primary challenge of that approach. We conclude with a proposal to simulate the uniform electron gas (jellium) using a low depth variational ansatz realizable on nearterm quantum devices. From these results we identify simulations of low density jellium as a promising first setting to explore quantum supremacy in electronic structure. 
Tuesday, March 6, 2018 10:00AM  10:12AM 
E33.00007: Quantum chemistry algorithms for efficient quantum computing Panagiotis Barkoutsos, Jerome Gonthier, Nikolaj Moll, Daniel Egger, Stefan Filipp, Ivano Tavernelli Quantum chemistry is definitely one of the most promising application areas of near term quantum computers. The exponentially large Hilbert space of molecular systems can be efficiently mapped into the spin configuration space of available quantum computers offering a unique opportunity for the solution of interesting electronic structure problems with unprecedented accuracy. To achieve this goal, new quantum algorithms need to be develop that are able to best exploit the potential of quantum speedup. While this effort should target the design of quantum algorithms for the future faulttolerant quantum hardware, there is pressing need to develop algorithms, which can be implemented in presentday nonfault tolerant quantum hardware with limited coherence time. In this talk, we will discuss (i) ways to derive efficient trial wavefunctions based on known quantum chemistry solutions (like e.g., MollerPlesset perturbation theory and Unitary Coupled Cluster), (ii) schemes to map states to available quantum computer architectures, and (iii) procedures to reduce the overall circuit depths in quantum chemistry calculations and experiments. These methods will be applied to a set of model systems (e.g., the Hubbard model) and molecules. 
Tuesday, March 6, 2018 10:12AM  10:24AM 
E33.00008: Adiabatic Quantum Chemistry Simulations with Superconducting Qubits Nikolaj Moll, Daniel Egger, Stefan Filipp, Andreas Fuhrer, Marc Ganzhorn, Peter Müller, Marco Roth, Gian Salis, Sebastian Schmidt Quantum technology is improving fast and quantum devices with more than 50 qubits appear feasible soon. The quest for systems which profit of exponential speedup and cannot be calculated on classical computers has recently triggered a lot of attention. Quantum chemistry is among the best candidates for exploiting such exponential speedup. Quantum chemistry Hamiltonians can be directly mapped on quantum devices based on superconducting qubits. However, the controlled realization of different types of interactions between qubits without compromising their coherence is essential. A coupling method between fixedfrequency transmon qubits can be achieved with the frequency modulation of an auxiliary capacitively coupled quantum bus. An adiabatic protocol for the hydrogen molecule can be implemented on such a coupled qubit system. We show that the electronic ground state of the molecule can be reached within the typical coherence time of a superconducting qubit. Hence, the quantum system of the hydrogen molecule can directly be mapped to the quantum system of a qubit device. 
Tuesday, March 6, 2018 10:24AM  10:36AM 
E33.00009: Spectral signatures of manybody localization of interacting photons Pedram Roushan, Charles Neill, Jirawat Tangpanitanon, Victor Bastidas, Anthony Megrant, Yu Chen, Rami Barends, Brooks Campbell, Zijun Chen, Ben Chiaro, Andrew Dunsworth, Evan Jeffrey, Julian Kelly, Erik Lucero, Josh Mutus, Matthew Neeley, Chris Quintana, Daniel Sank, Amit Vainsencher, James Wenner, Theodore White, Dimitris Angelakis, John Martinis Statistical mechanics is founded on the assumption that a system can reach thermal equilibrium, regardless of the starting state. Interactions between particles facilitate thermalization, but, can interacting systems always equilibrate regardless of parameter values? The energy spectrum of a system can answer this question and reveal the nature of the underlying phases. However, most experimental techniques only indirectly probe the manybody energy spectrum. Using a chain of nine superconducting qubits, we implement a novel technique for directly resolving the energy levels of interacting photons. We benchmark this method by capturing the intricate energy spectrum predicted for 2D electrons in a magnetic field, the Hofstadter butterfly. By increasing disorder, the spatial extent of energy eigenstates at the edge of the energy band shrink, suggesting the formation of a mobility edge. At strong disorder, the energy levels cease to repel one another and their statistics approaches a Poisson distribution the hallmark of transition from the thermal to the manybody localized phase. Our work introduces a new manybody spectroscopy technique to study quantum phases of matter. 
Tuesday, March 6, 2018 10:36AM  10:48AM 
E33.00010: Experimental implementation of error mitigation for shortdepth quantum circuits Abhinav Kandala, Kristan Temme, Antonio Mezzacapo, Antonio Corcoles, Maika Takita, Jerry Chow, Jay Gambetta Quantum simulation is believed to be one of the nearterm applications of early quantum computers. These simulations involve the preparation of a quantum state using a shortdepth quantum circuit and the measurement of expectation values of observables of interest. The accuracy of these expectation values is however affected by decoherence during state preparation. While the implementation of a fullyfault tolerant architecture is beyond the scope of nearterm hardware, a technique for mitigating such errors that requires no additional quantum resources was recently proposed [arXiv:1612.02058]. In this approach, the quantum state preparation is stretched in time, and the associated measurements of the expectation values are used to extrapolate to their noisefree values, thereby improving the fidelity of the chosen observable, without errorcorrecting the quantum state. We present our progress towards the experimental implementation of this technique. 
Tuesday, March 6, 2018 10:48AM  11:00AM 
E33.00011: Realization of a Quantum Random Generator Certified with the KochenSpecker Theorem Anatoly Kulikov, Markus Jerger, Anton Potocnik, Andreas Wallraff, Arkady Fedorov Random numbers are required for a variety of applications from secure communications to MonteCarlo simulation. Yet randomness is an asymptotic property and no output string generated by a physical device can be strictly proven to be random. I will present an experimental realization of a quantum random number generator (QRNG) with randomness certified by quantum contextuality and the KochenSpecker theorem. The certification is not performed in a deviceindependent way but through a rigorous theoretical proof of each outcome being value indefinite even in the presence of experimental imperfections. Our realization is based on cavity QED and transmon type qutrit. The coherent control and the singleshot quantum nondemolition readout enabled by the Josephson parametric amplifier has been recently used to demonstrate contextuality of the transmon based qutrit, the resource underlying the operation of the QNRG. We extend this technique to enable threelevel singleshot nondemolition readout required by the protocol and we generate 10 GBit of raw data with the bitrate of 50 kBit/s. The generated data passes the standard statistical test suites. Analysis of the data with tests related to the algorithmic randomness of a sequence provides evidence of incomputable nature of the QNRG. 
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