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We give bounds on the average fidelity achievable by any quantum state estimator, which is arguably the most prominently used figure of merit in quantum state tomography. Moreover, these bounds can be computed online---that is, while the…

Quantum Physics · Physics 2015-12-16 Richard Kueng , Christopher Ferrie

Because of the constraint that the estimators be bona fide physical states, any quantum state tomography scheme - including the widely used maximum likelihood estimation - yields estimators that may have a bias, although they are consistent…

Quantum Physics · Physics 2014-05-22 Jiangwei Shang , Hui Khoon Ng , Berthold-Georg Englert

Entanglement represents a pure quantum effect involving two or more particles. Spin systems are good candidates for studying this effect and its relation with other collective phenomena ruled by quantum mechanics. While the presence of…

Statistical Mechanics · Physics 2007-05-23 Andrea Fubini , Stephan Haas , Tommaso Roscilde , Valerio Tognetti , Paola Verrucchi

We propose to use neural networks to estimate the rates of coherent and incoherent processes in quantum systems from continuous measurement records. In particular, we adapt an image recognition algorithm to recognize the patterns in…

Quantum Physics · Physics 2017-11-15 Eliska Greplova , Christian Kraglund Andersen , Klaus Mølmer

Measurements with randomly chosen settings determine many important properties of quantum states without the need for a shared reference frame or calibration. They naturally emerge in the context of quantum communication and quantum…

Entanglement-enhanced quantum metrology explores the utilization of quantum entanglement to enhance measurement precision. When particles in a probe are prepared into a quantum entangled state, they collectively accumulate information about…

Quantum Physics · Physics 2024-08-20 Jiahao Huang , Min Zhuang , Chaohong Lee

Quantum computing systems need to be benchmarked in terms of practical tasks they would be expected to do. Here, we propose 3 "application-motivated" circuit classes for benchmarking: deep (relevant for state preparation in the variational…

Quantum Physics · Physics 2021-03-24 Daniel Mills , Seyon Sivarajah , Travis L. Scholten , Ross Duncan

We study the average case approximation of the Boolean mean by quantum algorithms. We prove general query lower bounds for classes of probability measures on the set of inputs. We pay special attention to two probabilities, where we show…

Quantum Physics · Physics 2007-05-23 A. Papageorgiou

Randomized benchmarking is a useful scheme for evaluation the average fidelity of a noisy quantum circuit. However, it is insensitive to the unitary error. Here, we propose a method of randomized benchmarking in which a unitary t-design is…

Quantum Physics · Physics 2017-12-13 Linxi Zhang , Chuanghua Zhu , Changxing Pei

Quantum compiling means fast, device-aware implementation of quantum algorithms (i.e., quantum circuits, in the quantum circuit model of computation). In this paper, we present a strategy for compiling IBM Q -aware, low-depth quantum…

Quantum Physics · Physics 2020-03-13 Davide Ferrari , Michele Amoretti

Quantum machine learning (QML) offers a promising avenue for advancing representation learning in complex signal domains. In this study, we investigate the use of parameterised quantum circuits (PQCs) for speech emotion recognition (SER) a…

Machine Learning · Computer Science 2025-06-26 Thejan Rajapakshe , Rajib Rana , Farina Riaz , Sara Khalifa , Björn W. Schuller

Quantum classifiers are trainable quantum circuits used as machine learning models. The first part of the circuit implements a quantum feature map that encodes classical inputs into quantum states, embedding the data in a high-dimensional…

Quantum Physics · Physics 2022-07-03 Seth Lloyd , Maria Schuld , Aroosa Ijaz , Josh Izaac , Nathan Killoran

Understanding the limiting capabilities of classical methods in simulating complex quantum systems is of paramount importance for quantum technologies. Although many advanced approaches have been proposed and recently used to challenge…

Quantum Physics · Physics 2025-02-05 I. A. Luchnikov , A. V. Berezutskii , A. K. Fedorov

We present an efficient algorithm for twirling a multi-qudit quantum state. The algorithm can be used for approximating the twirling operation in an ensemble of physical systems in which the systems cannot be individually accessed. It can…

Quantum Physics · Physics 2007-05-23 Geza Toth , Juan Jose Garcia-Ripoll

Quantum Machine Learning (QML) has emerged as a promising framework for exploring how quantum dynamics may enhance data processing tasks. Here we investigate Quantum Extreme Learning Machines (QELMs), a quantum analogue of classical Extreme…

Quantum Physics · Physics 2026-04-27 A. De Lorenzis , M. P. Casado , N. Lo Gullo , T. Lux , F. Plastina , A. Riera

It is shown that mean value of any observable with bounded spectrum can be uniquely determined from binary statistics of the measurement performed on {\it single} qubit ancilla coupled to a given system. The observable structure is fully…

Quantum Physics · Physics 2009-11-07 Pawel Horodecki

This thesis focuses on the experimental creation and detection of a variety of quantum correlations using nuclear magnetic resonance hardware. Quantum entanglement, being most common and counter-intuitive, is one of the main type considered…

Quantum Physics · Physics 2019-05-16 Amandeep Singh

In this paper we are discussing the question how a continuous quantum system can be simulated by mean field fluctuations of a finite number of qubits. On the kinematical side this leads to a convergence result which states that…

Quantum Physics · Physics 2016-01-20 Zoltan Kadar , Michael Keyl , Geza Toth , Zoltan Zimboras

Recent advancements in quantum computing (QC) and machine learning (ML) have garnered significant attention, leading to substantial efforts toward the development of quantum machine learning (QML) algorithms to address a variety of complex…

Quantum Physics · Physics 2024-12-18 Samuel Yen-Chi Chen

Notions of circuit complexity and cost play a key role in quantum computing and simulation where they capture the (weighted) minimal number of gates that is required to implement a unitary. Similar notions also become increasingly prominent…

Quantum Physics · Physics 2021-07-13 J. Eisert