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We present an experimental investigation of two-photon interference using a continuous-wave laser. We demonstrate the violation of the CHSH inequality using the phase randomized weak coherent states from a continuous wave laser. Our…

Quantum Physics · Physics 2023-07-24 Moslem Mahdavifar , S. M. Hashemi Rafsanjani

Bell inequalities are a cornerstone of quantum physics. By carefully selecting measurement bases (typically polarization), their violation certifies quantum entanglement. Such measurements are disrupted by the presence of optical disorder…

Quantum Physics · Physics 2025-09-26 Baptiste Courme , Malo Joly , Adrian Makowski , Sylvain Gigan , Hugo Defienne

We report correlation measurements on two $^9$Be$^+$ ions that violate a chained Bell inequality obeyed by any local-realistic theory. The correlations can be modeled as derived from a mixture of a local-realistic probabilistic distribution…

Quantum Physics · Physics 2017-04-05 T. R. Tan , Y. Wan , S. Erickson , P. Bierhorst , D. Kienzler , S. Glancy , E. Knill , D. Leibfried , D. J. Wineland

The Clauser-Horne-Shimony-Holt (CHSH) inequality is a constraint that local theories must obey. Quantum Mechanics predicts a violation of this inequality in certain experimental settings. Treatments of this subject frequently make…

Quantum Physics · Physics 2015-05-21 Peter Bierhorst

We consider a subgroup of unitary transformations on a mode of light induced by a Mach-Zehnder Interferometer and an algebra of observables describing a photon-number detector proceeded by an interferometer. We explore the uncertainty…

Quantum Physics · Physics 2022-01-28 Madhura Ghosh Dastidar , Gniewomir Sarbicki

Spontaneous parametric down conversion (SPDC) has proven to be a robust and prominent method for creating non-classical light sources of entangled single-photon pairs. However, such sources suffer from low efficiency due to the inherent…

Optics · Physics 2025-08-27 Sky Semone , Matthew J. Brandsema , Christos Argyropoulos

The Bell inequality constrains the outcomes of measurements on pairs of distant entangled particles. The Bell contradiction states that the Bell inequality is inconsistent with the calculated outcomes of these quantum experiments. This…

Quantum Physics · Physics 2026-03-03 Kees van Hee , Kees van Berkel , Jan de Graaf

Interferometric phase estimation is an essential tool for precise measurements of quantities such as displacement, velocity and material properties. The lower bound on measurement uncertainty achievable with classical resources is set by…

Quantum Physics · Physics 2024-07-23 Shakib Daryanoosh , Geoff J. Pryde , Howard M. Wiseman , Sergei Slussarenko

Many quantum information protocols require a Bell-state measurement of entangled systems. Most optical Bell-state measurements utilize two-photon interference at a beam splitter. By creating polarization-entangled photons with spontaneous…

Quantum Physics · Physics 2009-11-07 S. P. Walborn , W. A. T. Nogueira , S. Pádua , C. H. Monken

The best upper bound for the violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality was first derived by Tsirelson. For increasing number of $\pm 1$ valued observables on both sites of the correlation experiment, Tsirelson obtained…

Quantum Physics · Physics 2009-11-13 Hoshang Heydari

The CHSH mod 3 Bell inequality is a natural testbed for higher-dimensional quantum nonlocality, yet its maximal quantum violation and self-testing properties have remained unresolved. We determine its exact maximal quantum value and show…

Optimization and Control · Mathematics 2026-04-07 Igor Klep , Nando Leijenhorst , Victor Magron

Bipartite Bell inequalities can be simultaneously violated by two different pairs of observers when weak measurements and signaling is employed. Here we experimentally demonstrate the violation of two simultaneous CHSH inequalities by…

Quantum Physics · Physics 2017-04-10 Matteo Schiavon , Luca Calderaro , Mirko Pittaluga , Giuseppe Vallone , Paolo Villoresi

We report the first experimental violation of Bell's inequality in the spatial domain using the Einstein--Podolsky--Rosen state. Two-photon states generated via optical spontaneous parametric downconversion are shown to be entangled in the…

Quantum Physics · Physics 2008-05-06 Timothy Yarnall , Ayman F. Abouraddy , Bahaa E. A. Saleh , Malvin C. Teich

The correlations between two qubits belonging to a three-qubit system can violate the Clauser-Horne-Shimony-Holt-Bell inequality beyond Cirel'son's bound [A. Cabello, Phys. Rev. Lett. 88, 060403 (2002)]. We experimentally demonstrate such a…

Quantum Physics · Physics 2007-05-23 Yu-Ao Chen , Tao Yang , An-Ning Zhang , Zhi Zhao , Adan Cabello , Jian-Wei Pan

We present an ultrabright polarization-entangled photon source that is optimally coupled into single-mode fibers (SMFs). This study theoretically and experimentally examines the characteristics of spontaneous parametric down-conversion…

Quantum Physics · Physics 2024-09-25 Kyungdeuk Park , Jungmo Lee , Dong-Gil Im , Dongkyu Kim , Yong Sup Ihn

We propose a new method for detecting entanglement of two qubits and discuss its relation with the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality. Without the need for full quantum tomography for the density matrix we can experimentally…

Quantum Physics · Physics 2007-05-23 Kai Chen , Ling-An Wu

Different variants of a Bell inequality, such as CHSH and CH, are known to be equivalent when evaluated on nonsignaling outcome probability distributions. However, in experimental setups, the outcome probability distributions are estimated…

Quantum Physics · Physics 2022-02-15 Marc-Olivier Renou , Denis Rosset , Anthony Martin , Nicolas Gisin

It is shown that the data of the Hensen et al. Bell test experiment exhibits anomalous postselection that can fully account for the apparent violation of the CHSH inequality. A simulation of a local realist model implementing similar…

Quantum Physics · Physics 2017-10-13 Donald A. Graft

Device independent protocols based on Bell nonlocality, such as quantum key distribution and randomness generation, must ensure no adversary can have prior knowledge of the measurement outcomes. This requires a measurement independence…

Quantum Physics · Physics 2020-12-08 Michael J. W. Hall , Cyril Branciard

The simplest device-independent quantum key distribution protocol is based on the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality and allows two users, Alice and Bob, to generate a secret key if they observe sufficiently strong…

Quantum Physics · Physics 2021-04-27 Erik Woodhead , Antonio Acín , Stefano Pironio