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We report on a stringent test of the non-classicality of the motion of a massive quantum particle, which propagates on a discrete lattice. Measuring temporal correlations of the position of single atoms performing a quantum walk, we observe…

Quantum Physics · Physics 2015-02-11 Carsten Robens , Wolfgang Alt , Dieter Meschede , Clive Emary , Andrea Alberti

We propose an experimental programme to test Leggett--Garg-type temporal correlations in single-neuron dynamics. The goal is to distinguish between diffusive (Wiener/cable-equation) models and non-diffusive persistent stochastic models…

Quantum Physics · Physics 2026-05-13 Partha Ghose

The Leggett-Garg inequality (LGI) distinguishes nonmacrorealistic channels from macrorealistic ones by constraining the experimental outcomes of the underlying system. In this work, we propose a class of channels which, initially, cannot…

The notion of macrorealism was introduced by Leggett and Garg in an attempt to capture our intuitive conception of the macroscopic world, which seems difficult to reconcile with our knowledge of quantum physics. By now, numerous…

Quantum Physics · Physics 2024-01-10 David Schmid

We derive a set of Leggett-Garg inequalities (temporal Bell's inequalities) for the moment generating function of charge transferred through a conductor. Violation of these inequalities demonstrates the absence of a macroscopic-real…

Mesoscale and Nanoscale Physics · Physics 2012-09-10 Clive Emary

In a recent paper, Chatterjee et al. [Phys. Rev. Lett 135, 220202 (2025)] analyze and experimentally implement a specific unitary evolution of a simple quantum system. The authors refer to this type of dynamics as a "superposition of…

Quantum Physics · Physics 2026-01-27 Antoni Wójcik , Jan Wójcik

We assess non-Markovianity of a quantum open-system dynamics through the violation of temporal bell-like inequalities in a controllable Nuclear Magnetic Resonance system. We investigate experimentally the connections between the violation…

We highlight the existence of a joint probability distribution as the common underpinning assumption behind Bell-type, contextuality, and Leggett-Garg-type tests. We then present a procedure to translate contextual scenarios into temporal…

Quantum Physics · Physics 2016-10-13 M. Markiewicz , P. Kurzynski , J. Thompson , S. -Y. Lee , A. Soeda , T. Paterek , D. Kaszlikowski

Generalised quantum measurements with two outcomes are fully characterised by two real parameters, dubbed as sharpness parameter and biasedness parameter and they can be linked with different aspects of the experimental setup. It is known…

Quantum Physics · Physics 2018-04-04 Debarshi Das , Shiladitya Mal , Dipankar Home

The possibility of observing violations of temporal Bell inequalities, originally proposed by Leggett as a mean of testing the quantum mechanical delocalization of suitably chosen macroscopic bodies, is discussed by taking into account the…

Quantum Physics · Physics 2009-10-31 Tommaso Calarco , Marcello Cini , Roberto Onofrio

Macroscopic realism is the name for a class of modifications to quantum theory that allow macroscopic objects to be described in a measurement-independent manner, while largely preserving a fully quantum mechanical description of the…

Generalised dichotomic quantum measurements are fully characterised by two real parameters, dubbed as sharpness parameter and biasedness parameter. The trade-off between the degree of joint measurability, sharpness and biasedness of…

Quantum Physics · Physics 2020-03-17 Debarshi Das , Arindam Gayen , Ranit Das , Shiladitya Mal

Test of {macroscopic realism} (MR) is key to understanding the foundation of quantum mechanics. Due to the existence of the {non-invasive measurability} loophole and other interpretation loopholes, however, such test remains an open…

Quantum Physics · Physics 2024-01-17 Ping Wang , Chong Chen , Hao Liao , Vadim V. Vorobyov , Joerg Wrachtrup , and Ren-Bao Liu

In their comment[1] on our Letter [arXiv:0907.0767], Leggett and Garg claim that they have introduced in their original paper (LG1) a dependence on measurement times. They also claim that Eqs.(HMDR1) and (LG2a) can therefore not be linked…

Quantum Physics · Physics 2011-05-31 Karl Hess , Kristel Michielsen , Hans De Raedt

In this paper, we study the two-time Leggett-Garg (LG) inequalities of a quantum optical model that appears in the Josephson-junction quantum bit (qubit) interacting with an external magnetic flux. This model is a natural extension of an…

Quantum Physics · Physics 2026-01-19 Hiroo Azuma

Violations of classicality can be probed through measurements performed on a system at different times, as proposed by Leggett and Garg. Specifically, violations of Leggett-Garg inequalities suggest the presence of quantum effects in…

High Energy Physics - Phenomenology · Physics 2026-01-23 Murshed Alam , Vedran Brdar , Dibya S. Chattopadhyay

Macroscopic realism (MR) specifies that where a system can be found in one of two macroscopically distinguishable states (a cat being dead or alive), the system is always predetermined to be in one or other of the two states (prior to…

Quantum Physics · Physics 2018-04-25 M D Reid

Quantum theory provides rules governing much of the microscopic world, and among its counter-intuitive consequences are correlations that exceed the bounds from local, classical theories. In two-level quantum systems - qubits - unitary…

In this, partly pedagogical review, I attempt to give a self-contained overview of the basis of (non-relativistic) QM measurement theory expressed in density matrix formalism. The focus is on applications to the theory of weak measurement,…

Quantum Physics · Physics 2013-05-27 Bengt E. Y. Svensson

In 1862, George Boole derived an inequality for variables, now known as Boolean variables, that in his opinion represents a demarcation line between possible and impossible experience. This inequality forms an important milestone in the…

Quantum Physics · Physics 2016-08-29 Karl Hess , Hans De Raedt , Kristel Michielsen