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đPapers:

- Quantum Lego: Building Quantum Error Correction Codes from Tensor Networks
- Classification of (2+1)D invertible fermionic topological phases with symmetry
- Deep recurrent networks predicting the gap evolution in adiabatic quantum computing
- Variational Quantum Algorithm for Schmidt Decomposition
- A Quantum-Inspired Classical Solver for Boolean k-Satisfiability Problems
- Multi-angle Quantum Approximate Optimization Algorithm
- A loop Quantum Approximate Optimization Algorithm with Hamiltonian updating
- A QUBO Formulation for Minimum Loss Spanning Tree Reconfiguration Problems in Electric Power Networks
- Active Learning for the Optimal Design of Multinomial Classification in Physics
- Phase diagram of quantum generalized Potts-Hopfield neural networks
- On Circuit-based Hybrid Quantum Neural Networks for Remote Sensing Imagery Classification
- Quantum variational PDE solver with machine learning
- Fundamental Machine Learning Routines as Quantum Algorithms on a Superconducting Quantum Computer

## Quantum Lego: Building Quantum Error Correction Codes from Tensor Networks

ChunJun Cao,Brad LackeySep 20 2021Â quant-phcond-mat.str-elhep-thÂ arXiv:2109.08158v1

We introduce a flexible and graphically intuitive framework that constructs complex quantum error correction codes from simple codes or states, generalizing code concatenation. More specifically, we represent the complex code constructions as tensor networks built from the tensors of simple codes or states in a modular fashion. Using a set of local moves known as operator pushing, one can derive properties of the more complex codes, such as transversal non-Clifford gates, by tracing the flow of operators in the network. The framework endows a network geometry to any code it builds and is valid for constructing stabilizer codes as well as non-stabilizer codes over qubits and qudits. For a contractible tensor network, the sequence of contractions also constructs a decoding/encoding circuit. To highlight the framework’s range of capabilities and to provide a tutorial, we lay out some examples where we glue together simple stabilizer codes to construct non-trivial codes. These examples include the toric code and its variants, a holographic code with transversal non-Clifford operators, a 3d stabilizer code, and other stabilizer codes with interesting properties. Surprisingly, we find that the surface code is equivalent to the 2d Bacon-Shor code after “dualizing” its tensor network encoding map.

## Classification of (2+1)D invertible fermionic topological phases with symmetry

Maissam Barkeshli,Yu-An Chen,Po-Shen Hsin,Naren ManjunathSep 24 2021Â cond-mat.str-elhep-thmath-phmath.MPquant-phÂ arXiv:2109.11039v1

We provide a classification of invertible topological phases of interacting fermions with symmetry in two spatial dimensions for general fermionic symmetry groupsÂ GfGfÂ and general values of the chiral central chargeÂ câcâ. HereÂ GfGfÂ is a central extension of a bosonic symmetry groupÂ GbGbÂ by fermion parity,Â (â1)F(â1)F, specified by a second cohomology classÂ [Ď2]âH2(Gb,Z2)[Ď2]âH2(Gb,Z2). Our approach proceeds by gauging fermion parity and classifying the resultingÂ GbGbÂ symmetry-enriched topological orders while keeping track of certain additional data and constraints. We perform this analysis through two perspectives, usingÂ GG-crossed braided tensor categories and Spin(2câ)1(2câ)1Â Chern-Simons theory coupled to a backgroundÂ GGÂ gauge field. These results give a way to characterize and classify invertible fermionic topological phases in terms of a concrete set of data and consistency equations, which is more physically transparent and computationally simpler than the more abstract methods using cobordism theory and spectral sequences. Our results also generalize and provide a different approach to the recent classification of fermionic symmetry-protected topological phases by Wang and Gu, which have chiral central chargeÂ câ=0câ=0. We show how the 10-fold way classification of topological insulators and superconductors fits into our scheme, along with general non-perturbative constraints due to certain choices ofÂ câcâÂ andÂ GfGf. Mathematically, our results also suggest an explicit general parameterization of deformation classes of (2+1)D invertible topological quantum field theories withÂ GfGfÂ symmetry.

## Deep recurrent networks predicting the gap evolution in adiabatic quantum computing

Naeimeh Mohseni,Carlos Navarrete-Benlloch,Tim Byrnes,Florian MarquardtSep 20 2021Â quant-phÂ arXiv:2109.08492v1

One of the main challenges in quantum physics is predicting efficiently the dynamics of observables in many-body problems out of equilibrium. A particular example occurs in adiabatic quantum computing, where finding the structure of the instantaneous gap of the Hamiltonian is crucial in order to optimize the speed of the computation. Inspired by this challenge, in this work we explore the potential of deep learning for discovering a mapping from the parameters that fully identify a problem Hamiltonian to the full evolution of the gap during an adiabatic sweep applying different network architectures. Through this example, we find that a limiting factor for the learnability of the dynamics is the size of the input, that is, how the number of parameters needed to identify the Hamiltonian scales with the system size. We demonstrate that a long short-term memory network succeeds in predicting the gap when the parameter space scales linearly with system size. Remarkably, we show that once this architecture is combined with a convolutional neural network to deal with the spatial structure of the model, the gap evolution can even be predicted for system sizes larger than the ones seen by the neural network during training. This provides a significant speedup in comparison with the existing exact and approximate algorithms in calculating the gap.

## Variational Quantum Algorithm for Schmidt Decomposition

Ranyiliu Chen,Benchi Zhao,Xin WangSep 23 2021Â quant-phÂ arXiv:2109.10785v1

Entanglement plays a crucial role in quantum physics and is the key resource in quantum information processing. In entanglement theory, Schmidt decomposition is a powerful tool to analyze the fundamental properties and structure of quantum entanglement. This work introduces a hybrid quantum-classical algorithm for Schmidt decomposition of bipartite pure states on near-term quantum devices. First, we show that the Schmidt decomposition task could be accomplished by maximizing a cost function utilizing bi-local quantum neural networks. Based on this, we propose a variational quantum algorithm for Schmidt decomposition (named VQASD) of which the cost function evaluation notably requires only one estimate of expectation with no extra copies of the input state. In this sense, VQASD outperforms existent approaches in resource cost and hardware efficiency. Second, by further exploring VQASD, we introduce a variational quantum algorithm to estimate the logarithm negativity, which can be applied to efficiently quantify entanglement of bipartite pure states. Third, we experimentally implement our algorithm on Quantum Leaf using the IoP CAS superconducting quantum processor. Both experimental implementations and numerical simulations exhibit the validity and practicality of our methods for analyzing and quantifying entanglement on near-term quantum devices.

## A Quantum-Inspired Classical Solver for Boolean k-Satisfiability Problems

S. Andrew Lanham,Brian R. La CourSep 22 2021Â quant-phÂ arXiv:2109.10291v1

In this paper we detail a classical algorithmic approach to the k-satisfiability (k-SAT) problem that is inspired by the quantum amplitude amplification algorithm. This work falls under the emerging field of quantum-inspired classical algorithms. To propose our modification, we adopt an existing problem model for k-SAT known as Universal SAT (UniSAT), which casts the Boolean satisfiability problem as a non-convex global optimization over a real-valued space. The quantum-inspired modification to UniSAT is to apply a conditioning operation to the objective function that has the effect of “amplifying” the function value at points corresponding to optimal solutions. We describe the algorithm for achieving this amplification, termed “AmplifySAT,” which follows a familiar two-step process of applying an oracle-like operation followed by a reflection about the average. We then discuss opportunities for meaningfully leveraging this processing in a classical digital or analog computing setting, attempting to identify the strengths and limitations of AmplifySAT in the context of existing non-convex optimization strategies like simulated annealing and gradient descent.

## Multi-angle Quantum Approximate Optimization Algorithm

Rebekah Herrman,Phillip C. Lotshaw,James Ostrowski,Travis S. Humble,George SiopsisSep 24 2021Â quant-phÂ arXiv:2109.11455v1

The quantum approximate optimization algorithm (QAOA) generates an approximate solution to combinatorial optimization problems using a variational ansatz circuit defined by parameterized layers of quantum evolution. In theory, the approximation improves with increasing ansatz depth but gate noise and circuit complexity undermine performance in practice. Here, we introduce a multi-angle ansatz for QAOA that reduces circuit depth and improves the approximation ratio by increasing the number of classical parameters. Even though the number of parameters increases, our results indicate that good parameters can be found in polynomial time. This new ansatz gives a 33\% increase in the approximation ratio for an infinite family of MaxCut instances over QAOA. The optimal performance is lower bounded by the conventional ansatz, and we present empirical results for graphs on eight vertices that one layer of the multi-angle anstaz is comparable to three layers of the traditional ansatz on MaxCut problems. Similarly, multi-angle QAOA yields a higher approximation ratio than QAOA at the same depth on a collection of MaxCut instances on fifty and one-hundred vertex graphs. Many of the optimized parameters are found to be zero, so their associated gates can be removed from the circuit, further decreasing the circuit depth. These results indicate that multi-angle QAOA requires shallower circuits to solve problems than QAOA, making it more viable for near-term intermediate-scale quantum devices.

## A loop Quantum Approximate Optimization Algorithm with Hamiltonian updating

Fang-Gang DuanSep 24 2021Â quant-phÂ arXiv:2109.11350v1

Designing noisy-resilience quantum algorithms is indispensable for practical applications on Noisy Intermediate-Scale Quantum~(NISQ) devices. Here we propose a quantum approximate optimization algorithm~(QAOA) with a very shallow circuit, called loop-QAOA, to avoid issues of noises at intermediate depths, while still can be able to exploit the power of quantum computing. The key point is to use outputs of shallow-circuit QAOA as a bias to update the problem Hamiltonian that encodes the solution as the ground state. By iterating a loop between updating the problem Hamiltonian and optimizing the parameterized quantum circuit, the loop-QAOA can gradually transform the problem Hamiltonian to one easy for solving. We demonstrate the loop-QAOA on Max-Cut problems both with and without noises. Compared with the conventional QAOA whose performance will decrease due to noises, the performance of the loop-QAOA can still get better with an increase in the number of loops. The insight of exploiting outputs from shallow circuits as bias may be applied for other quantum algorithms.

## A QUBO Formulation for Minimum Loss Spanning Tree Reconfiguration Problems in Electric Power Networks

Filipe F. C. Silva,Pedro M. S. Carvalho,Luis A. F. M. Ferreira,Yasser OmarSep 21 2021Â quant-phcs.ETmath.OCÂ arXiv:2109.09659v1

We introduce a novel quadratic unconstrained binary optimization (QUBO) formulation for a classical problem in electrical engineering — the optimal reconfiguration of distribution grids. For a given graph representing the grid infrastructure and known nodal loads, the problem consists in finding the spanning tree that minimizes the total link ohmic losses. A set of constraints is initially defined to impose topologically valid solutions. These constraints are then converted to a QUBO model as penalty terms. The electrical losses terms are finally added to the model as the objective function to minimize. In order to maximize the performance of solution searching with classical solvers, with hybrid quantum-classical solvers and with quantum annealers, our QUBO formulation has the goal of being very efficient in terms of variables usage. A standard 33-node test network is used as an illustrative example of our general formulation. Model metrics for this example are presented and discussed.

## Active Learning for the Optimal Design of Multinomial Classification in Physics

Yongcheng Ding,JosĂŠ D. MartĂn-Guerrero,Yujing Song,Rafael Magdalena-Benedito,Xi ChenSep 20 2021Â quant-phÂ arXiv:2109.08612v1

Optimal design for model training is a critical topic in machine learning. Active Learning aims at obtaining improved models by querying samples with maximum uncertainty according to the estimation model for artificially labeling; this has the additional advantage of achieving successful performances with a reduced number of labeled samples. We analyze its capability as an assistant for the design of experiments, extracting maximum information for learning with the minimal cost in fidelity loss, or reducing total operation costs of labeling in the laboratory. We present two typical applications as quantum information retrieval in qutrits and phase boundary prediction in many-body physics. For an equivalent multinomial classification problem, we achieve the correct rate of 99% with less than 2% samples labeled. We reckon that active-learning-inspired physics experiments will remarkably save budget without loss of accuracy.

## Phase diagram of quantum generalized Potts-Hopfield neural networks

Eliana Fiorelli,Igor Lesanovsky,Markus MĂźllerSep 22 2021Â quant-phcond-mat.dis-nnÂ arXiv:2109.10140v1

We introduce and analyze an open quantum generalization of the q-state Potts-Hopfield neural network, which is an associative memory model based on multi-level classical spins. The dynamics of this many-body system is formulated in terms of a Markovian master equation of Lindblad type, which allows to incorporate both probabilistic classical and coherent quantum processes on an equal footing. By employing a mean field description we investigate how classical fluctuations due to temperature and quantum fluctuations effectuated by coherent spin rotations affect the ability of the network to retrieve stored memory patterns. We construct the corresponding phase diagram, which in the low temperature regime displays pattern retrieval in analogy to the classical Potts-Hopfield neural network. When increasing quantum fluctuations, however, a limit cycle phase emerges, which has no classical counterpart. This shows that quantum effects can qualitatively alter the structure of the stationary state manifold with respect to the classical model, and potentially allow one to encode and retrieve novel types of patterns.

## On Circuit-based Hybrid Quantum Neural Networks for Remote Sensing Imagery Classification

Alessandro Sebastianelli,Daniela A. Zaidenberg,Dario Spiller,Bertrand Le Saux,Silvia Liberata UlloSep 21 2021Â eess.IVcs.CVcs.ETquant-phÂ arXiv:2109.09484v1

This article aims to investigate how circuit-based hybrid Quantum Convolutional Neural Networks (QCNNs) can be successfully employed as image classifiers in the context of remote sensing. The hybrid QCNNs enrich the classical architecture of CNNs by introducing a quantum layer within a standard neural network. The novel QCNN proposed in this work is applied to the Land Use and Land Cover (LULC) classification, chosen as an Earth Observation (EO) use case, and tested on the EuroSAT dataset used as reference benchmark. The results of the multiclass classification prove the effectiveness of the presented approach, by demonstrating that the QCNN performances are higher than the classical counterparts. Moreover, investigation of various quantum circuits shows that the ones exploiting quantum entanglement achieve the best classification scores. This study underlines the potentialities of applying quantum computing to an EO case study and provides the theoretical and experimental background for futures investigations.

## Quantum variational PDE solver with machine learning

Jaewoo Joo,Hyungil MoonSep 21 2021Â quant-phÂ arXiv:2109.09216v1

To solve nonlinear partial differential equations (PDEs) is one of the most common but important tasks in not only basic sciences but also many practical industries. We here propose a quantum variational (QuVa) PDE solver with the aid of machine learning (ML) schemes to synergise two emerging technologies in mathematically hard problems. The core quantum processing in this solver is to calculate efficiently the expectation value of specially designed quantum operators. For a large quantum system, we only obtain data from measurements of few control qubits to avoid the exponential cost in the measurements of the whole quantum system and optimise a pathway to find possible solution sets of the desired PDEs using ML techniques. As an example, a few different types of the second-order DEs are examined with randomly chosen samples and a regression method is implemented to chase the best candidates of solution functions with another trial samples. We demonstrated that a three-qubit system successfully follows the pattern of analytical solutions of three different DEs with high fidelity since the variational solutions are given by a necessary condition to obtain the exact solution of the DEs. Thus, we believe that final solution candidate sets are efficiently extracted from the QuVa PDE solver with the support of ML techniques and this algorithm could be beneficial to search for the solutions of complex mathematical problems as well as to find good ansatzs for eigenstates in large quantum systems (e.g., for quantum chemistry).

## Fundamental Machine Learning Routines as Quantum Algorithms on a Superconducting Quantum Computer

Sristy Sangskriti,Protik Nag,Summit HaqueSep 21 2021Â quant-phÂ arXiv:2109.09522v1

The Harrow-Hassidim-Lloyd algorithm is intended for solving the system of linear equations on quantum devices. The exponential advantage of the algorithm comes with four caveats. We present a numerical study of the performance of the algorithm when these caveats are not perfectly matched. We observe that, between diagonal and non-diagonal matrices, the algorithm performs with higher success probability for the diagonal matrices. At the same time, it fails to perform well on lower or higher density sparse Hermitian matrices. Again, Quantum Support Vector Machine algorithm is a promising algorithm for classification problem. We have found out that it works better with binary classification problem than multi-label classification problem. And there are many opportunities left for improving the performance.

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