Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session YY03: V: Focus Session: AMO Qubits and OptimizationFocus
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Sponsoring Units: DQI Chair: Hanyu Zhu, Rice University Room: Virtual Room 3 |
Wednesday, March 22, 2023 10:00AM - 10:36AM |
YY03.00001: Quantum Optimization with Rydberg Atom Arrays Invited Speaker: Hannes Pichler Programmable quantum systems based on Rydberg atom arrays are a promising platform for tests of quantum optimization algorithms with hundreds of qubits. In particular, the maximum independent set problem on so-called unit-disk graphs has a natrual realization in such systems. In this talk I discuss strategies to extend the classes of problems that can be efficiently encoded in Rydberg arrays by constructing explicit mappings from several generic optimization problems to maximum weighted independent set problems on unit-disk graphs, with at most a quadratic overhead in the number of qubits. This includes: maximum weighted independent set on graphs with arbitrary connectivity, quadratic unconstrained binary optimization problems with arbitrary connectivity, and integer factorization formulated as an optimization problem. This provides a blueprint for using Rydberg atom arrays to solve a wide range of combinatorial optimization problems with arbitrary connectivity, beyond the restrictions imposed by the hardware geometry. |
Wednesday, March 22, 2023 10:36AM - 10:48AM |
YY03.00002: Single-step multi-qubit operation via the Fermi scattering of a sole Rydberg electron Mohammadsadegh Khazali, Wolfgang Lechner The long-range many-body Rydberg interaction is vastly used in different quantum operations [1-9] including the direct operation of multi-qubit gates [10]. In this talk, I introduce a new type of interaction for multi-qubit operations that paves the way for a scalable Rydberg quantum simulator. Considering an optical lattice, the operation is performed by Rydberg electron's Fermi scattering from ground-state atoms in spin-dependent lattices [11]. Instead of relying on Rydberg pair potentials, the interaction is controlled by engineering the electron cloud of a sole Rydberg atom. The new scheme addresses the main bottleneck in Rydberg quantum simulation by suppressing the population of short-lived Rydberg states over multi-qubit operations. This scheme mitigates different competing infidelity criteria, eliminates unwanted cross-talks, and allows operations in dense atomic lattices. The restoring forces in the molecule type Ryd-Fermi potential preserve the trapping over a long interaction period. The features in the new scheme are of special interest for the implementation of quantum optimization and error correction algorithms [12].
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Wednesday, March 22, 2023 10:48AM - 11:00AM |
YY03.00003: Demonstration of three- and four-body interactions between trapped-ion spins Or Katz, Lei Feng, Andrew Risinger, Christopher Monroe, Marko Cetina Quantum processors use the native interactions between effective spins to simulate Hamiltonians or execute quantum gates. In most processors, the native interactions are pairwise, limiting the efficiency of controlling entanglement between many qubits. Here we experimentally demonstrate a new class of native interactions between trapped-ion qubits, extending conventional pairwise interactions to higher order. We realize three- and four-body spin interactions as examples, showing that high-order spin polynomials may serve as a new toolbox for quantum information applications. |
Wednesday, March 22, 2023 11:00AM - 11:12AM |
YY03.00004: Phonon induced pure dephasing in color centers from first principles Liang Tan, Jacopo Simoni, Vsevolod Ivanov, Thomas Schenkel Understanding dephasing mechanisms is the key to improving the performance of color centers for quantum information science applications. Phonon-induced processes, being intrinsic, cannot be removed by improving sample quality, and must be considered for all color centers. In this talk, we consider phonon-induced pure dephasing associated with the fluctuation of spin levels. Unlike the energy relaxation contribution, the pure dephasing contribution does not involve energy transfer. We compute these dephasing rates from density functional theory for nitrogen vacancy centers in diamond, obtaining good agreement with experiments, and showing that phonon-induced pure dephasing is a limiting contribution for clean samples at low temperatures. The largest contributions to the dephasing is attributed local phonon modes and local-continuum resonances associated with movement of the nearest- and second-nearest carbon neighbors of the vacancy. |
Wednesday, March 22, 2023 11:12AM - 11:24AM |
YY03.00005: Geometric optimization based on first-quantized Hamiltonian using imaginary-time evolution on a quantum computer Yu-ichiro Matsushita, Hirofumi Nishi, Taichi Kosugi Quantum computation has been thought of as a promising alternative to classical one due to its expressing power for encoding spatial grids of a wave function. Recently, a nonvariational approach for calculating the ground state in the many body problems has been presented, called the imaginary-time evolution (PITE) method. In this work, we propose a quantum algorithm employing the PITE technique for the geometry optimization of molecules based on the first quantization Hamiltonian. In the proposed framework, we treat the nuclei as classical point charges while the electrons treat as quantum mechanical particles and employ an exhaustive search from the geometric candidates. The encoding of nuclei as classical point charges is efficient because we alleviate to prepare huge qubits for expressing femtometer scale wave functions. We obtain a histogram that gives the global minimum of the energy surface from the repeated measurements of the output state generated by the PITE circuit. We hope that the proposed scheme could be helpful in realizing practical quantum computation for quantum chemistry. |
Wednesday, March 22, 2023 11:24AM - 11:36AM |
YY03.00006: A novel noisy intermediate-scale quantum computing algorithm for solving an n-vertex MaxCut problem with log(n) qubits. Marko Rancic As an error-corrected quantum computer is still far away the quantum computing community has dedicated much attention to developing algorithms for currently available Noisy Intermediate-Scale Quantum computers (NISQ). Thus far, within NISQ, optimization problems are one of the most commonly studied and are almost exclusively tackled with the Quantum Approximate Optimization Algorithm (QAOA). This algorithm is best known for computing graph partitions with a maximal separation of edges (MaxCut), but can easily calculate other problems related to graphs. Here, I present a novel quantum optimization algorithm which uses exponentially less qubits as compared to the QAOA while requiring a significantly reduced number of quantum operations to solve the MaxCut problem. Such an improved performance allowed me to partition graphs with 32 nodes on publicly available 5 qubit gate-based quantum computers without any preprocessing such as division of the graph into smaller subgraphs. This results represent a 40% increase in graph size as compared to state-of-art experiments on gate-based quantum computers such as Google Sycamore. The obtained lower bound is 54.9% on the solution for actual hardware benchmarks and 77.6% on ideal simulators of quantum computers. Furthermore, large-scale optimization problems represented by graphs of a 128 nodes are tackled with simulators of quantum computers, again without any pre-division into smaller subproblems and a lower solution bound of 67.9% is achieved. |
Wednesday, March 22, 2023 11:36AM - 11:48AM |
YY03.00007: Evaluating the efficiency of ground state preparation algorithms Aikaterini Gratsea, Chong Sun, Peter D Johnson In recent years, a lot of effort has been devoted to the development of different ground-state energy estimation (GSEE) algorithms for molecules and materials. To make GSEE methods practical, it is important to reduce their runtime which highly depends on the features of ground-state preparation (GSP) methods. Specifically, the magnitude of the ansatz overlap plays a crucial role in the performance of GSEE algorithms and the realization of a potential quantum advantage. In this work, we asked under which conditions a GSP method is acceptable over a reference method, such as the Hartree-Fock. We introduce the criteria under which a GSP method is acceptable for the purposes of ground state energy estimation. We consider different GSP methods ranging from heuristics to algorithms with provable performance guarantees. We perform numerical simulations to benchmark their performance on different problems and discuss the notion of “good” overlap. A GSP method needs to provide a better trade-off between the resource cost and the overlap provided to be accepted over the reference method. This work sets the ground to further explore the requirements to achieve quantum advantage in quantum chemistry. |
Wednesday, March 22, 2023 11:48AM - 12:00PM |
YY03.00008: Beyond the variational quantum eigensolver: Approximating solutions of 15 PDEs with a variational quantum algorithm in polynomial time Pete B Rigas Quantum algorithms have received much attention, not only for being able to potentially replicate computations that classical algorithms have provided, but also for being able to achieve such results with exponential speedup. To further build upon the ensemble of solution approximations to 8 PDEs that were obtained from an adaptation of a recent variational quantum algorithm (VQA) due to Lubasch et al in 2019, solution approximations for PDEs ranging from the Navier-Stokes to Hunter-Saxton equations were provided in the September 2022 posting, arXiv 2209.07714, in which it was demonstrated that the VQA is capable of simulating nonlinearities of several PDEs. Specifically, with modification to the budget and other parameters that are required by either stochastic, deterministic, gradient-based, or constrained, optimizers for approximating the ground state of a cost function, we illustrate that the VQA can produce solution approximations to several variants of PDEs exhibiting oscillatory wave behavior, including generalized Camassa-Holm, KdV-Burgers, non-homogeneous KdV, generalized KdV, KdV, super KdV, and Benney-Luke equations. From such a collection of a PDEs, solutions can either exhibit periodic peakon, cuspon, or combinations of such behaviors. Across the aforementioned list of 7 additional PDEs, in polynomial time as with previous analysis of VQA performance from the 8 PDEs characterized in arXiv 2209.07714, the VQA is able to obtain solution approximations with varying fidelity also in polynomial time, exhibiting similarities with the dynamics of quantum states for approximating Camassa-Holm solutions, with the total number of time steps of evolution varying from 500 to approximately 20,000. Across several initial conditions of the ansatz which correspond to the ZGR-QFT parameters that are reliant upon several iterations of computing Fourier coefficients required for initializing time-evolution, measurements extracted from cost functions for the KdV-Burgers, KdV, and generalized Camassa-Holm equations in particular exhibit good performance with the open-source Nevergrad optimizer provided by Facebook research. |
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