Ferromagnetically Shifting the Power of Pausing

Izquierdo, Zoe Gonzalez; Grabbe, Shon; Hadfield, Stuart; Marshall, Jeffrey; Wang, Zhihui; Rieffel, Eleanor

doi:10.1103/physrevapplied.15.044013

Cited by 17 publications

(11 citation statements)

References 31 publications

(37 reference statements)

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“…This is consistent with the results of Ref. [41] which found experimentally for a certain set of problems requiring embedding (problem size more than 100 qubits), that an improvement in TTS was observed for pause times less than around 2µs.…”

Section: Condition For Advantage By Relaxationsupporting

confidence: 93%

Comparing relaxation mechanisms in quantum and classical transverse-field annealing

Albash,

Marshall

2020

Preprint

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Annealing schedule control provides new opportunities to better understand the manner and mechanisms by which putative quantum annealers operate. By appropriately modifying the annealing schedule to include a pause (keeping the Hamiltonian fixed) for a period of time, we show it is possible to more directly probe the dissipative dynamics of the system at intermediate points along the anneal and examine thermal relaxation rates, for example, by observing the re-population of the ground state after the minimum spectral gap. We provide a detailed comparison of experiments from a D-Wave device, simulations of the quantum adiabatic master equation and a classical analogue of quantum annealing, spin-vector Monte Carlo, and we observe qualitative agreement, showing that the characteristic increase in success probability when pausing is not a uniquely quantum phenomena. We find that the relaxation in our system is dominated by a single time-scale, which allows us to give a simple condition for when we can expect pausing to improve the time-to-solution, the relevant metric for classical optimization. In the system studied here, only for short pauses is there expected to be an improvement. Finally, we also explore in simulation the role of temperature whilst pausing as a means to better distinguish quantum and classical models of quantum annealers.

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Section: Condition For Advantage By Relaxationsupporting

confidence: 93%

Comparing relaxation mechanisms in quantum and classical transverse-field annealing

Albash,

Marshall

2020

Preprint

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“…Hardware upgrades and optimization of operational parameters like anneal times and ferromagnetic couplings are crucial for improving quantum annealing performance. Using sophisticating annealing schedules, as demonstrated in [6,7], are other ways to improve hardware performance that we did not consider in this report. Quantifying the performance of scheduling problems using these advanced annealing schedules would be a natural extension of this work.…”

Section: Discussionmentioning

confidence: 99%

“…In line with the typical practice for applied problems [7,17], we optimized the ferromagnetic couplings. For this optimization, we set the anneal time to 5, 1, and 20 µs for 2X, 2000Q, and Advantage, respectively.…”

Section: Methodsmentioning

confidence: 99%

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Inter-generational comparison of quantum annealers in solving hard scheduling problems

Pokharel¹,

Izquierdo²,

Aaron³

et al. 2021

Preprint

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We compare the performance of four quantum annealers, the D-Wave Two, 2X, 2000Q, and Advantage in solving an identical ensemble of a parametrized family of scheduling problems. These problems are NP-complete and, in fact, equivalent to vertex coloring problems. They are also practically motivated and closely connected to planning problems from artificial intelligence. We examine factors contributing to the performance differences while separating the contributions from hardware upgrades, support for shorter anneal times, and possible optimization of ferromagnetic couplings. While shorter anneal times can improve the time to solution (TTS) at any given problem size, the scaling of TTS with respect to the problem size worsens for shorter anneal times. In contrast, optimizing the ferromagnetic coupling improves both the absolute TTS and the scaling. There is a statistically significant improvement in performance between D-Wave Two and 2X and from all older generation annealers to Advantage, even when operated under identical anneal time and ferromagnetic couplings. However, the performance improvement from 2X to 2000Q requires the anneal time and ferromagnetic couplings to be optimized. Overall, owing to these inter-generational hardware improvements and optimizations, the scaling exponent reduces from 1.01 ± 0.01 on Two to 0.173 ± 0.009 on Advantage.

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“…Other advances have also been made to make annealing more practically useful, such as research showing that pausing the evolution just after the minimal gap during the annealing process makes the final overlap with the desired ground state orders of magnitude higher due to thermalization [17]. The time window for making this pause can also be regulated through the coupling strength between physical qubits representing a single logical one [18]. Though ASP, unlike annealing in general, does not take place at finite temperatures and requires the system to stay in the ground state during the evolution, annealing hardware is still useful for instantiating ASP as these additional restrictions are imposed.…”

Section: Introductionmentioning

confidence: 99%

Simulation of adiabatic quantum computing for molecular ground states

Kremenetski

Mejuto-Zaera

Cotton

et al. 2021

The Journal of Chemical Physics

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Quantum computation promises to provide substantial speedups in many practical applications with a particularly exciting one being the simulation of quantum many-body systems. Adiabatic state preparation (ASP) is one way that quantum computers could recreate and simulate the ground state of a physical system. In this paper we explore a novel approach for classically simulating the time dynamics of ASP with high accuracy, and with only modest computational resources via an adaptive sampling configuration interaction (ASCI) scheme for truncating the Hilbert space to only the most important determinants. We verify that this truncation introduces negligible error, and use this new approach to simulate ASP for sets of small molecular systems and Hubbard models. Further, we examine two approaches to speeding up ASP when performed on quantum hardware: (i) using the complete active space configuration interaction (CASCI) wavefunction instead of the Hartree-Fock initial state and (ii) a non-linear interpolation between initial and target Hamiltonians. We find that starting with a CASCI wavefunction with a limited active space yields substantial speedups for many of the systems examined while non-linear interpolation does not. Additionally, we observe interesting trends in the minimum gap location (based on the initial state) as well as how critical time can depend on certain molecular properties such as the number of valence electrons. Importantly, we find that the required state preparation times do not show an immediate exponential wall that would preclude an efficient run of ASP on actual hardware.

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Ferromagnetically Shifting the Power of Pausing

Cited by 17 publications

References 31 publications

Comparing relaxation mechanisms in quantum and classical transverse-field annealing

Comparing relaxation mechanisms in quantum and classical transverse-field annealing

Inter-generational comparison of quantum annealers in solving hard scheduling problems

Simulation of adiabatic quantum computing for molecular ground states

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