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In quantum physics, multiparticle systems are described by quantum states acting on tensor products of Hilbert spaces. This product structure leads to the distinction between product states and entangled states; moreover, one can quantify…

Quantum Physics · Physics 2026-03-06 Lisa T. Weinbrenner , Albert Rico , Kenneth Goodenough , Xiao-Dong Yu , Otfried Gühne

We introduce a geometric framework for studying Bell nonlocality in Hilbert space, where, for a given quantum state, nonlocality is quantified by the distance between the state and the set of local states. This approach applies to any Bell…

Quantum tomography is an important tool for obtaining information about the quantum state from experimental data. In this study, we conduct a comparative analysis of various quantum tomography protocols, including protocols based on highly…

Quantum Physics · Physics 2022-01-11 Yu. I. Bogdanov , B. I. Bantysh , N. A. Bogdanova , K. B. Koksharov , V. F. Lukichev

We develop a comprehensive axiomatic framework for quantum-inspired distance metrics on projective Hilbert spaces, providing a unified foundation that organizes and generalizes existing measures in quantum information theory. Starting from…

Quantum Physics · Physics 2026-03-03 Maryam Bagherian

We describe a quantum state tomography scheme which is applicable to a system described in a Hilbert space of arbitrary finite dimensionality and is constructed from sequences of two measurements. The scheme consists of measuring the…

Quantum Physics · Physics 2015-06-04 Amir Kalev , Pier A. Mello

It is well established that unpolarized light is invariant with respect to any SU(2) polarization transformation. This requirement fully characterizes the set of density matrices representing unpolarized states. We introduce the degree of…

Quantum Physics · Physics 2007-05-23 A. B. Klimov , L. L. Sanchez-Soto , E. C. Yustas , J. Soderholm , G. Bjork

Quantum metrology enhances measurement precision by utilising the properties of quantum physics. In interferometry, this is typically achieved by evolving highly-entangled quantum states before performing single-shot measurements to reveal…

Quantum Physics · Physics 2023-01-11 Kawthar Al Rasbi , Almut Beige , Lewis A. Clark

Quantum coherence marks a deviation from classical physics, and has been studied as a resource for metrology and quantum computation. Finding reliable and effective methods for assessing its presence is then highly desirable. Coherence…

Measures are introduced to quantify the degree of superposition in mixed states with respect to orthogonal decompositions of the Hilbert space of a quantum system. These superposition measures can be regarded as analogues to entanglement…

Quantum Physics · Physics 2007-05-23 Johan Aberg

Quantum teleportation is one of the essential primitives of quantum communication. We suggest that any quantum teleportation scheme can be characterized by its efficiency, i.e. how often it succeeds to teleport, its fidelity, i.e. how well…

Quantum Physics · Physics 2015-06-26 Dik Bouwmeester , Jian-Wei Pan , Harald Weinfurter , Anton Zeilinger

Establishing a notion of the quantum state that applies consistently across space and time could be a crucial step toward formulating a relativistic quantum theory. We give an operational meaning to multipartite quantum states over…

Quantum Physics · Physics 2026-04-14 Seok Hyung Lie , Hyukjoon Kwon

We propose a measure of entanglement that can be computed for any pure state of an $M$-qubit system. The entanglement measure has the form of a distance that we derive from an adapted application of the Fubini-Study metric. This measure is…

The study of quantum correlations in High-dimensional bipartite systems is crucial for the development of quantum computing. We propose relative entropy as a distance measure of correlations may be measured by means of the distance from the…

Quantum Physics · Physics 2016-04-12 M. Mahdian , M. B. Arjmandi

We study measures of quantum information when the space spanned by the set of accessible observables is not closed under products, i.e., we consider systems where an observer may be able to measure the expectation values of two operators,…

High Energy Physics - Theory · Physics 2018-08-15 Sudip Ghosh , Suvrat Raju

Recently, trace distance measure of coherence has been proposed for characterizing the coherence of a given quantum state. However, it seems difficult to estimate the optimal incoherent state for high dimensional states. An explicit…

Quantum Physics · Physics 2016-10-25 Zhen Wang , Yan-Ling Wang , Zhi-Xi Wang

We experimentally demonstrate in NMR a quantum interferometric multi-meter for extracting certain properties of unknown quantum states without resource to quantum tomography. It can perform direct state determinations,…

Quantum Physics · Physics 2007-05-23 Jiangfeng Du , Ping Zou , Daniel K. L. Oi , Xinhua Peng , L. C. Kwek , C. H. Oh , Artur Ekert

Quantum state tomography is an important tool for quantum communication, computation, metrology, and simulation. Efficient quantum state tomography on a high dimensional quantum system is still a challenging problem. Here, we propose a…

Quantum Physics · Physics 2019-08-07 Ruifeng Liu , Junling Long , Pei Zhang , Russell E. Lake , Hong Gao , David P. Pappas , Fuli Li

Mutually unbiased bases (MUBs) play a key role in many protocols in quantum science, such as quantum key distribution. However, defining MUBs for arbitrary high-dimensional systems is theoretically difficult, and measurements in such bases…

Quantum Physics · Physics 2013-04-03 D. Giovannini , J. Romero , J. Leach , A. Dudley , A. Forbes , M. J. Padgett

Quantum metrology studies the use of entanglement and other quantum resources to improve precision measurement. An interferometer using N independent particles to measure a parameter X can achieve at best the "standard quantum limit" (SQL)…

Quantum Physics · Physics 2012-03-06 M. Napolitano , M. Koschorreck , B. Dubost , N. Behbood , R. J. Sewell , M. W. Mitchell

Hilbert space combines the properties of two fundamentally different types of mathematical spaces: vector space and metric space. While the vector-space aspects of Hilbert space, such as formation of linear combinations of state vectors,…

Quantum Physics · Physics 2015-05-27 I. D'Amico , J. P. Coe , V. V. Franca , K. Capelle