Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F42: Applications of Noisy Intermediate Scale Quantum Computers IIIFocus
|
Hide Abstracts |
Sponsoring Units: DQI Chair: Kristan Temme Room: BCEC 210A |
Tuesday, March 5, 2019 11:15AM - 11:27AM |
F42.00001: Gate-efficient simulation of molecular eigenstates on a superconducting qubit quantum computer Marc Ganzhorn, Daniel Egger, Pauline Ollitrault, Panagiotis Barkoutsos, Gian Salis, Nikolaj Moll, Andreas Fuhrer, Peter Mueller, Marco Roth, Stefan Woerner, Ivano Tavernelli, Stefan Filipp A key requirement to perform simulations of large quantum systems on current quantum processors is the design of quantum algorithms with short circuit depth. To achieve this, it is essential to realize a gate set that is tailored to the problem at hand and which can be directly implemented in hardware [P. Barkoutsos et al., Phys. Rev. A 98, 022322 (2018)]. Here, we experimentally demonstrate that exchange-type gates are ideally suited for calculations in quantum chemistry [M. Ganzhorn et al., arXiv:1809.05057]. We determine the energy spectrum of molecular hydrogen using a variational quantum eigensolver algorithm based on exchange-type gates in combination with a method from computational chemistry to compute the excited states. We utilize a parametrically driven tunable coupler to realize exchange-type gates that are configurable in amplitude and phase on two fixed-frequency superconducting qubits. With gate fidelities around 95% we are able to compute the eigenstates within an accuracy of 50 mHartree on average, a limit set by the coherence time of the tunable coupler. |
Tuesday, March 5, 2019 11:27AM - 11:39AM |
F42.00002: Improved variational algorithms for optimization problems in a quantum computer Panagiotis Barkoutsos, Anton Robert, Giacomo Nannicini, Ivano Tavernelli, Stefan Woerner Recent advances in Noisy Intermediate-Scale Quantum (NISQ) computers allow us to solve combinatorial optimization problems encoded in Hamiltonians via hybrid quantum/classical variational algorithms. Current approaches minimize the expectation of the problem Hamiltonian for a parameterized trial state generated in the quantum circuit. The expectation is obtained by sampling the full outcome of an ensemble of measurements of the corresponding matrix element, while the trial wavefunction parameters are optimized classically. This procedure is fully justified for quantum mechanical observables (i.e. molecular energy). However, in the case of the simulation of classical optimization problems, which yield diagonal Hamiltonians, we argue that it is more natural to aggregate the samples using a different aggregation function than the expected value. In this talk, we present results of the aforementioned scheme for a plethora of interesting optimization problems where we demonstrate faster convergence towards more accurate solutions. |
Tuesday, March 5, 2019 11:39AM - 11:51AM |
F42.00003: Variational Approaches for Quantum Simulation Timothy Hsieh, Wen Wei Ho, Cheryne Jonay Many non-trivial quantum states, such as quantum critical points or topological phases, can potentially be realized in synthetic quantum systems, such as trapped ions or superconducting circuits. However, finding efficient and realizable approaches for such state preparation is challenging. I will show how a variant of the Quantum Approximate Optimization Algorithm (QAOA), originally introduced as a variational approach for solving classical optimization problems, serves as an efficient and general approach for realizing non-trivial quantum states. I will then show how long-range interactions, for example those in trapped ions systems, can further facilitate quantum state preparation. |
Tuesday, March 5, 2019 11:51AM - 12:27PM |
F42.00004: Quantum gate-model approaches to exact and approximate optimization Invited Speaker: Stuart Hadfield Many of the most challenging computational problems arising in practical applications are tackled by heuristic algorithms which have not been rigorously proven to outperform other approaches but rather have been empirically demonstrated to be effective. While quantum heuristics have been proposed since the early days of quantum computing, true empirical evaluation of the real-world performance of these algorithms is only becoming possible now as increasingly powerful quantum gate-model devices continue to come online. |
Tuesday, March 5, 2019 12:27PM - 12:39PM |
F42.00005: Characterizing quantum circuits by short-cutting quantum errors and a unitary-dissipative ''polar'' decomposition for quantum channels Arnaud Carignan-Dugas, Matthew Alexander, Joseph Emerson The richness of quantum dynamics allows for a plethora of noise models which, given only a partial knowledge of a device's components can result in widely different conclusions regarding the quality of larger circuits. In fact, the sole formulation of an assessment regarding the overall operational performance is demanding in that it typically requires invoking a broad range of quantum dynamical scenarios. In this work, we pave the way between partially characterized elementary operations and circuits thereof. Our paving stone consists of a simplified picture of quantum processes that we refer to as the leading Kraus (LK) approximation. This incomplete dynamical representation closely prescribes the evolution of celebrated characterization figures of merit, namely the average gate fidelity, which captures the overlap between an implemented operations and their targets, and the unitarity, which captures the level of coherence in the noise. Moreover, the transparency in the LK parametrization allows the derivation of a quantum unitary-dissipative (polar) factorization for quantum channels. |
Tuesday, March 5, 2019 12:39PM - 12:51PM |
F42.00006: Quantum Feedback Protocol for Approximating Single-Body Green's Functions at Finite Temperature Jeffrey Cohn, Khadijeh Najafi, James Freericks, Barbara Jones We present a quantum feedback algorithm that aims to approximate single-body Green's functions at finite temperature. Extracting a single particle Green's function from a quantum computer is a well known process, but if one is interested in thermal properties the challenges and resources necessary for full Gibbs state preparation are generally too expensive for these machines in the near future. Here, we examine how sampling from more easily preparable states can yield precise approximations to single-particle Green's functions at finite temperature. We also show, through a feedback mechanism, that one can test for convergence and extract the effective temperature of the system being simulated. Further, we compare the trade-offs of different approaches to make these techniques applicable on near term devises. We draw on the ideas of the Eigenstate Thermalization Hypothesis as well as specific properties of Green's functions and use a family of 1-D Fermi-Hubbard models as our test case. |
Tuesday, March 5, 2019 12:51PM - 1:03PM |
F42.00007: WITHDRAWN ABSTRACT
|
Tuesday, March 5, 2019 1:03PM - 1:15PM |
F42.00008: Quantum simulation and Time-Dependent Density Functional Theory James Whitfield, James Brown, Jun Yang Time evolution of quantum systems is of interest in physics, in chemistry, and, more recently, in computer science. One route to numerically propagating quantum systems is time dependent density functional theory. The application of TDDFT to a particular system's time evolution is predicated on V-representablility which we've analyzed in previous work. Here we consider the application of quantum simulation to the problem of characterizing time-dependent Kohn-Sham potentials. We consider both the V-representability of some simple 1D examples numerically and their implementation using quantum computation. The measurement of the one-body electronic probability density on quantum hardware given various qubit encodings is also discussed. |
Tuesday, March 5, 2019 1:15PM - 1:27PM |
F42.00009: Digital quantum simulation of a two-dimensional electron gas pierced by a strong magnetic field Michael Kaicher, Simon Balthasar Jäger, Frank K Wilhelm, Ryan Babbush, Pierre-Luc Dallaire-Demers A two dimensional electron gas, confined to a finite disk geometry and pierced by a strong transversal magnetic field at zero temperature describes the physical setting of the fractional quantum Hall effect. We give an ab-initio roadmap on how this system may be simulated on a quantum processor. We show how the approximate ground state could be extracted through a hybrid quantum-classical variational algorithm and how to extract ground state properties. This heuristic method can be extended to incorporate more physical effects, such as impurity models, to ultimately test theoretical models against experimental data beyond the limits of classical computational power. |
Tuesday, March 5, 2019 1:27PM - 1:39PM |
F42.00010: Linear Depth Circuit Unitary Coupled Cluster Wavefunctions for Quantum Computation William Huggins, Joonho Lee, Martin Head-Gordon, Birgitta K Whaley Motivated by the rapid development of quantum computing hardware we introduce a new unitary coupled cluster wavefunction ansatz for quantum chemistry which we call k-UpCCGSD. k-UpCCGSD employs k products of the exponential of a sparse generalized doubles excitation operator, together with generalized single excitation operators, resulting in a wavefunction which can be approximated by a linear-depth circuit. We compare its performance with that of the generalized unitary coupled cluster ansatz employing the full generalized singles and doubles excitation operators (UCCGSD), as well as with the standard ansatz containing only excitations between occupied and virtual orbitals (UCCSD). We find that k-UpCCGSD offers an appealing tradeoff between accuracy and cost, and dramatically outperforms the standard UCCSD, particularly for the calculation of low-lying excited states. |
Tuesday, March 5, 2019 1:39PM - 1:51PM |
F42.00011: Quantum digital simulation of three toy models using IBM quantum hardware. Pedro Cruz, Ronan Gautier, Gonçalo Catarina, Joaquin Fernandez-Rossier Using the phase estimation algorithm it is possible, in principle, to obtain the eigenstates of a large family of many-body Hamiltonians. In this talk we will present the results of our attempts to implement phase estimation algorithms to obtain the eigenvalues of 3 simple model Hamiltonians, using IBM quantum hardware. For that matter, we have considered a two level system, a two site Ising model with longitudinal magnetic field, and a two site Hubbar model at half filling. We have made use of both the phase estimationa and iterative phase estimation algorithms. We have explored to which point the unwanted hardware noise compromises the accuracy of the algorithm. In the case of the Hubbard model, for which a Troterization procedure is required, we study the optimal number of Trotter steps. Our results illustrate the limits of the phase estimation approach for quantum digital simulation in state of the art hardware. |
Tuesday, March 5, 2019 1:51PM - 2:03PM |
F42.00012: Implementing the Variational Quantum Eigensolver with native 2-qubit interaction and error mitigation Takahiro Tsunoda, Andrew D Patterson, Xiao Yuan, Suguru Endo, Joseph Rahamim, Peter A Spring, Martina Esposito, Salha Jebari, Kitti Ratter, Sophia Sosnina, Giovanna Tancredi, Brian Vlastakis, Simon Benjamin, Peter Leek The variational quantum eigensolver (VQE) is an algorithm that may provide near-term applications of small-scale quantum computers, in quantum chemistry and optimisation problems. In order for the VQE to provide accurate solutions to problems on real devices, methods have been proposed recently to mitigate the errors caused by imperfect gates. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700