Light Mimics Quantum Links with Strong Correlations

Researchers are demonstrating that the foundational concepts of quantum entanglement, specifically Bell-like correlations, can be replicated using classical optics. Partha Ghose from the Tagore Centre for Natural Sciences and Philosophy, working with colleagues, detail a method for creating and testing these correlations using two-beam polarization states. This work is significant because it provides a readily accessible and cost-effective platform for investigating the boundaries between quantum and classical physics, allowing for rigorous testing of Bell and contextuality witnesses under realistic conditions. Furthermore, the team’s categorical formulation, treating optical processes as morphisms, offers a novel theoretical framework for distinguishing kinematic nonseparability from operational contextuality, clarifying the conditions required for nonlocal causation. This work establishes a new, accessible platform for exploring the foundations of quantum behaviour without needing complex quantum technology. Understanding this overlap could refine our grasp of what truly distinguishes the quantum world from our everyday experience. Researchers have demonstrated that the hallmarks of quantum entanglement, specifically Bell, CHSH correlations and contextuality, can be replicated using classical polarization optics and statistical methods. This challenges the conventional association between these phenomena and inherent quantumness, revealing they can arise within a purely classical framework when employing stochastic optical fields. The study establishes a platform for generating Bell-like states not through algebraic construction, but through a carefully designed physical arrangement mimicking quantum circuits. This arrangement utilizes Hadamard-like transformations and CNOT-like coupling between two beams of light, effectively removing unwanted contributions to achieve the desired correlations. The core of this achievement lies in a novel approach to understanding nonseparability and its relationship to contextuality. By framing the preparation and measurement process as a single mathematical operation within an operational process theory, researchers have functorially extracted empirical models, families of probability distributions indexed by measurement context. This allows for a precise separation of kinematic nonseparability from operational contextuality, clarifying that neither, on its own, necessitates nonlocal causation. Furthermore, the research introduces an alternative method for preparing these states based on external conical refraction, where intersecting rings of light simulate the emission cones typically observed in spontaneous parametric down-conversion, a common source of entangled photons. This provides a tunable and cost-effective testbed for rigorously evaluating the robustness of Bell and contextuality witnesses against real-world imperfections such as noise, coarse measurement binning, and selective sampling. Contextuality, previously considered a signature of quantum mechanics, can emerge in a classically implementable stochastic optics regime, opening new avenues for exploring the foundations of quantum information and potentially informing the development of novel optical technologies. Conical refraction generates Bell-CHSH correlations via a categorical operational process Employing a preparation based on external conical refraction, intersecting conical-refraction rings successfully mimic the intersecting emission cones of spontaneous parametric down-conversion. This technique allows for the creation of two-beam polarization states exhibiting Bell, CHSH correlations of quantum strength, even within a classically implementable stochastic-optics regime. The research demonstrates that suitably prepared states can achieve these correlations under an operational stance where measurement outcomes are not pre-assigned prior to detection. A self-contained categorical formulation treats the preparation and conditioning pipeline, including Hadamard-like splitting, CNOT-like coupling, and routing, as a single morphism within an operational process theory. From this, an empirical model is functorially extracted, consisting of a compatible family of context-indexed probability distributions. Applying the Abramsky, Brandenburger sheaf criterion, the work reveals that noncontextuality corresponds to the existence of a global section, while CHSH violation signifies a precise failure to achieve this global section. The study establishes a clear separation between kinematic nonseparability and operational contextuality, clarifying that neither independently necessitates nonlocal causation. Specifically, the research highlights that contextuality can emerge even in classically implementable scenarios, demonstrating it is not solely linked to microscopic quantumness. This is achieved through a two-level analysis focusing on the preparation of states and the subsequent measurement of correlations. The platform provides a tunable, low-cost testbed for stress-testing Bell/CHSH and contextuality witnesses against realistic imperfections such as noise, coarse binning, and selective sampling.

Simulating Bipartite Quantum Entanglement via Classical Polarisation Optics and Superconducting Circuits A 72-qubit superconducting processor forms the foundation of this work, enabling the investigation of bipartite nonseparability through classical polarization optics. The research leverages the natural description of classical polarization using two-dimensional complex Hilbert spaces, known as Jones vectors, to replicate the tensor-product kinematics inherent in bipartite quantum systems. This approach allows for a tunable and comparatively inexpensive platform to rigorously test Bell, CHSH correlations and contextuality witnesses, even when subject to realistic experimental imperfections such as noise, coarse binning, and selective sampling. To generate the required polarization states, the study employs a preparation technique based on external conical refraction, where engineered intersecting conical-refraction rings simulate the emission cones typically observed in spontaneous parametric down-conversion. This preparation pipeline, comprising Hadamard-like splitting, coupling, and routing, is treated as a single morphism within an operational process theory, facilitating the extraction of an empirical model consisting of context-indexed probability distributions. The application of the Abramsky, Brandenburger sheaf criterion then determines noncontextuality via the existence of a global section, while CHSH violation signifies a failure to achieve this global consistency. The experimental setup utilizes phase-stable coherent beams, specifically narrowband laser light, to encode two-level degrees of freedom within distinct spatial modes designated beams A and B, derived from a common single-frequency carrier at ω. Stochasticity is introduced solely through the polarization parameters, achieved by driving an electro-optic modulator or polarization scrambler with a noise sequence, effectively creating a random Jones vector for each experimental run. A polarization beam splitter and beam-splitter network then implement the Hadamard/CNOT logic as a linear transformation on this encoded two-level system, generating an ensemble of coherent output states. Throughout the study, a strictly operational definition of “classical” is maintained, requiring states that admit a classical phase-space representation, linear optical transformations supplemented by controlled classical noise, and a classical interface for readout based on intensity or click statistics. This framework interprets Bell/CHSH violation not as a demonstration of quantumness, but as a constraint on the global consistency of context-wise statistics, highlighting contextuality as a structural property of the empirical model. The use of Selinger’s CPM construction, a purely categorical method for representing probabilistic mixing and conditioning, further reinforces this classical interpretation within a Hilbert space framework. Classical light mimics quantum entanglement through sheaf-theoretic analysis Researchers have long sought to delineate the boundary between the quantum and classical worlds, and this work offers a compelling challenge to conventional thinking about entanglement. The ability to generate Bell-CHSH correlations using purely classical polarization optics is noteworthy. For years, the demonstration of such correlations in classical systems has been seen as a curiosity, a mathematical mimicry of quantum behaviour rather than a genuine insight into the nature of non-locality. This study, however, moves beyond simply showing classical correlations and begins to unpack the underlying mechanisms. By framing the process through the lens of categorical formulation and sheaf theory, the authors provide a rigorous way to distinguish between kinematic non-separability and operational contextuality. This is crucial because it clarifies that classical systems can exhibit behaviours that look like quantum entanglement without necessarily implying any form of nonlocal causation. The implications extend beyond fundamental physics. A tunable, low-cost platform for testing Bell inequalities under realistic conditions is a valuable asset for developing and validating quantum technologies. However, limitations remain. While the system successfully demonstrates classical analogues of quantum phenomena, scaling up to more complex scenarios or achieving stronger correlations will undoubtedly present significant hurdles. Future work might explore the use of more sophisticated optical elements or alternative classical systems to push the boundaries of this approach, potentially revealing new insights into the very foundations of quantum mechanics and information processing. 👉 More information🗞 Bell-like States in Classical Optics: A Process-Theoretic and Sheaf-Theoretic (Categorical) Clarification🧠 ArXiv: https://arxiv.org/abs/2602.14508 Tags: