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Quantum Information and Measurement (QIM)

Identification of the Cirel'son bound using uncertainty limited joint measurement of photon polarization

Kengo Matsuyama, Holger Friedrich Hofmann, M. Iinuma

Published Jan 1, 2021• 0 citations
Publisher

Abstract

Joint measurements of complementary polarizations are performed on entangled photon pairs, clarifying the relation between measurement uncertainties and quantum non-locality. Extremely low probabilities indicate that the non-local correlations are close to the Cirel'son bound.
DOI
10.1364/qim.2021.w2a.5

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Abstract Bell’s inequalities are defined by sums of correlations involving non-commuting observables in each of the two systems. Violations of Bell’s inequalities are only possible because the precision of any joint measurement of these observables will be limited by quantum mechanical uncertainty relations. In this paper we explore the relation between the local measurement uncertainties and the magnitude of the correlations by preparing polarization entangled photon pairs and performing joint measurements of non-commuting polarization components at different uncertainty trade-offs. The change in measurement visibility reveals the existence of a non-trivial balance between the measurement uncertainties where the probabilities of a specific pair of measurement outcomes approaches zero because of the particular combination of enhancement and suppression of the experimentally observed correlations. The occurrence of these high-contrast results shows that the quantum correlations between the photons are close to their maximal value, confirming that the Cirel’son bound of Bell’s inequality violations is defined by the minimal uncertainties that limit the precision of joint measurements.
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Quantum correlations, like entanglement, represent the characteristic trait of quantum mechanics and pose essential issues and challenges to the interpretation of this pillar of modern physics. Although quantum correlations are largely acknowledged as a major resource to achieve quantum advantage in many tasks of quantum technologies, their full quantitative description and the axiomatic basis underlying them are still under investigation. Previous works have suggested that the origin of nonlocal correlations is grounded in principles capturing (from outside the quantum formalism) the essence of quantum uncertainty. In particular, the recently introduced principle of relativistic independence has given rise to a new bound intertwining local and nonlocal correlations. Here, we test such a bound by realizing together sequential and joint weak measurements on entangled photon pairs, allowing us to simultaneously quantify both local and nonlocal correlations by measuring incompatible observables on the same quantum system without collapsing its state, a task typically forbidden in the traditional (projective) quantum measurement framework. Our results demonstrate the existence of a fundamental limit on the extent of quantum correlations, shedding light on the profound role of uncertainty in both enabling and balancing them. Published by the American Physical Society 2024
Probing the polarization response of an object with the well-acknowledged technique of optical polarimetry enables determination of the specimen's inner properties. Prominent examples include the measurement of the chirality of proteins and molecules [1] or the induced anisotropy of disease-affected cells and tissues [2]. Aiming for better signal-to-noise ratio, lower photon flux of the probing beam and non-local diagnostics, polarimetric approaches employing the quantum nature of light and entanglement are currently rapidly developing [3]–[6]. In the present work we study the experimental feasibility of the non-local identification of different polarizing samples by performing only few coincidence measurements [6] without necessity for full density matrix reconstruction of the quantum state.