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Parameterized quantum circuits used as variational ans\"atze are emerging as promising tools to tackle complex problems ranging from quantum chemistry to combinatorial optimization. These variational quantum circuits can suffer from the…

Quantum Physics · Physics 2023-12-14 Valentin Heyraud , Zejian Li , Kaelan Donatella , Alexandre Le Boité , Cristiano Ciuti

Barren plateaus are a notorious problem in the optimization of variational quantum algorithms and pose a critical obstacle in the quest for more efficient quantum machine learning algorithms. Many potential reasons for barren plateaus have…

Quantum Physics · Physics 2022-05-02 Ankit Kulshrestha , Ilya Safro

Quantum kernel methods promise enhanced expressivity for learning structured data, but their usefulness has been limited by kernel concentration and barren plateaus. Both effects are mathematically equivalent and suppress trainability. We…

Barren plateau landscapes correspond to gradients that vanish exponentially in the number of qubits. Such landscapes have been demonstrated for variational quantum algorithms and quantum neural networks with either deep circuits or global…

Quantum Physics · Physics 2021-10-06 Andrew Arrasmith , M. Cerezo , Piotr Czarnik , Lukasz Cincio , Patrick J. Coles

Sequential minimum optimization is a machine-learning global search training algorithm. It is applicable when the functional dependence of the cost function on a tunable parameter given the other parameters can be cheaply determined. This…

Quantum Physics · Physics 2023-03-03 Wojciech Roga , Takafumi Ono , Masahiro Takeoka

Quantum operations on pure states can be fully represented by unitary matrices. Variational quantum circuits, also known as quantum neural networks, embed data and trainable parameters into gate-based operations and optimize the parameters…

Quantum Physics · Physics 2026-04-09 Basil Kyriacou , Mo Kordzanganeh , Maniraman Periyasamy , Alexey Melnikov

Training deep quantum neural networks (QNNs) for image classification is notoriously difficult due to vanishing gradients (barren plateaus) and limited nonlinearity in purely unitary circuits. We propose a novel gradient-free…

Quantum Physics · Physics 2025-05-09 Yichen Xie

Model-independent estimation of the properties of quantum states is a central challenge in quantum technologies, as experimental imperfections, drifts, and imprecise models of the actual quantum dynamics inevitably hinder accurate…

Linear optical quantum circuits with photon number resolving (PNR) detectors are used for both Gaussian Boson Sampling (GBS) and for the preparation of non-Gaussian states such as Gottesman-Kitaev-Preskill (GKP), cat and NOON states. They…

Quantum Physics · Physics 2023-08-30 Robbe De Prins , Yuan Yao , Anuj Apte , Filippo M. Miatto

The evolution of quantum light through linear optical devices can be described by the scattering matrix $S$ of the system. For linear optical systems with $m$ possible modes, the evolution of $n$ input photons is given by a unitary matrix…

Quantum Physics · Physics 2025-01-17 Juan Carlos Garcia-Escartin , Vicent Gimeno , Julio José Moyano-Fernández

The image classification machine learning model was trained with the intention to predict the category of the input image. While multiple state-of-the-art ensemble model methodologies are openly available, this paper evaluates the…

Machine Learning · Computer Science 2020-10-19 W. H. Huang

Diffractive neural networks hold great promise for applications requiring intensive computational processing. Considerable attention has focused on diffractive networks for either spatially coherent or spatially incoherent illumination.…

Optics · Physics 2025-03-25 Matan Kleiner , Lior Michaeli , Tomer Michaeli

The barren plateau phenomenon is one of the main obstacles to implementing variational quantum algorithms in the current generation of quantum processors. Here, we introduce a method capable of avoiding the barren plateau phenomenon in the…

Optical phenomena always display some degree of partial coherence between their respective degrees of freedom. Partial coherence is of particular interest in multimodal systems, where classical and quantum correlations between spatial,…

Optics · Physics 2024-11-14 Charles Roques-Carmes , Shanhui Fan , David Miller

Physically motivated quantum algorithms for specific near-term quantum hardware will likely be the next frontier in quantum information science. Here, we show how many of the features of neural networks for machine learning can naturally be…

Quantum Physics · Physics 2018-09-21 Gregory R. Steinbrecher , Jonathan P. Olson , Dirk Englund , Jacques Carolan

Variational quantum algorithms are expected to demonstrate the advantage of quantum computing on near-term noisy quantum computers. However, training such variational quantum algorithms suffers from gradient vanishing as the size of the…

Quantum Physics · Physics 2021-11-29 Anbang Wu , Gushu Li , Yufei Ding , Yuan Xie

Quantum neural networks (QNNs) leverage quantum entanglement and superposition to enable large-scale parallel linear computation, offering a potential solution to the scalability limits of classical deep learning. However, their practical…

Quantum Physics · Physics 2025-08-05 Pei-Kun Yang

Nonclassical states of light are fundamental in various applications, spanning quantum computation to enhanced sensing. Fast free electrons, which emit light into photonic structures through the mechanism of spontaneous emission, represent…

Quantum Physics · Physics 2025-07-08 Valerio Di Giulio , Rudolf Haindl , Claus Ropers

Entanglement between large numbers of quantum modes is the quintessential resource for future technologies such as the quantum internet. Conventionally the generation of multimode entanglement in optics requires complex layouts of…

Quantum photonic neural networks are variational photonic circuits that can be trained to implement high-fidelity quantum operations. However, work-to-date has assumed idealized components, including a perfect $\pi$ Kerr nonlinearity. Here,…

Quantum Physics · Physics 2023-01-31 Jacob Ewaniuk , Jacques Carolan , Bhavin J. Shastri , Nir Rotenberg