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Journal of Chemical Biological and Physical Sciences

New Experiment for Bell’s Inequalities for Photons Using Different Polarization Angles

Published May 6, 2024• 1 citation
Publisher

Abstract

In quantum mechanics, quantum entanglement is a physical phenomenon in which quantum particles (such as photons, electrons...) are connected to each other despite the large distances between them.This phenomenon occurs when a pair or group of particles is created in such a way that the quantum state of a particular particle cannot be described independently of other particles, even if there is a large distance between these particles.This research dealt with a computerized theoretical study of John Bell's theory to verify quantum entanglement, which was later tested by the French scientist Alain Aspect on photons of light, and the polarization angles of light were (0.45, 22.5, 67.5)This experiment was conducted and the results were recorded from the virtual interactive quantum entanglement laboratory (VIQEL), which is highly efficient in simulating the equations of quantum mechanics and probability functions, where we obtained accurate results by increasing the number of photonic pairs involved in the experiment and then the results were compared with the results of previous research by other scientists to prove that the main variable, which is the angle of polarization, does not affect the result when its value changes, but its effect lies in the difference in angles in the experiment, which in turn enhances From the theory of quantum entanglement.

DOI
10.24214/jcbps.c.14.2.11117

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In quantum mechanics, quantum entanglement is a physical phenomenon in which quantum particles (such as photons, electrons...) are connected to each other despite the large distances between them.This phenomenon occurs when a pair or group of particles is created in such a way that the quantum state of a particular particle cannot be described independently of other particles, even if there is a large distance between these particles.This research dealt with a computerized theoretical study of John Bell's theory to verify quantum entanglement, which was later tested by the French scientist Alain Aspect on photons of light, and the polarization angles of light were (0.45, 22.5, 67.5)This experiment was conducted and the results were recorded from the virtual interactive quantum entanglement laboratory (VIQEL), which is highly efficient in simulating the equations of quantum mechanics and probability functions, where we obtained accurate results by increasing the number of photonic pairs involved in the experiment and then the results were compared with the results of previous research by other scientists to prove that the main variable, which is the angle of polarization, does not affect the result when its value changes, but its effect lies in the difference in angles in the experiment, which in turn enhances From the theory of quantum entanglement.
John Bell’s theorem of 1964 states that local elements of physical reality, existing independent of measurement, are inconsistent with the predictions of quantum mechanics (Bell, J. S. (1964), Physics (College. Park. Md). Specifically, correlations between measurement results from distant entangled systems would be smaller than predicted by quantum physics. This is expressed in Bell’s inequalities. Employing modifications of Bell’s inequalities, many experiments have been performed that convincingly support the quantum predictions. Yet, all experiments rely on assumptions, which provide loopholes for a local realist explanation of the measurement. Here we report an experiment with polarization-entangled photons that simultaneously closes the most significant of these loopholes. We use a highly efficient source of entangled photons, distributed these over a distance of 58.5 meters, and implemented rapid random setting generation and high-efficiency detection to observe a violation of a Bell inequality with high statistical significance. The merely statistical probability of our results to occur under local realism is less than 3.74×10-31, corresponding to an 11.5 standard deviation effect.
Quantum entanglement is an essential principle in quantum mechanics, illustrating the relationship between two or more spatially separated particles.This correlation has been experimentally proven through various techniques, including the entangled photon experiment. Furthermore, the breach of Bell's inequality has confirmed that entanglement represents a genuine physical occurrence, which cannot be accounted for by local hidden variables, thus highlighting the peculiar characteristics of quantum mechanics. This article aims to introduce quantum entanglement and Bell's inequality, and to discuss the experiments conducted by Alain Aspect, John Clauser, and Anton Zeilinger, which paved the way for the development of quantum information science. Additionally, this paper will explore the potential applications of quantum technology in communication, cryptography, and computing, which rely on the exceptional properties of entanglement.
We will describe a simple setup experiment that allows students to create polarization-entangled photons pairs. These photon pairs are in an entangled state first described in the famous 1935 article in Phys.Rev by Einstein-Podolsky-Rosen, often called E.P.R. state. Photons pairs at 810 nm are produced in two nonlinear crystals by spontaneous parametric downconversion of photons at 405 nm emitted by a violet laser diode. The polarization state of the photons pairs is easily tunable with a half-wave plate and a Babinet compensator on the laser diode beam. After having adjusted the polarization-entangled state of the photon pairs, our students can perform a test of Bell’s inequalities. They will find the amazing value for the Bell parameter between 2.3 and 2.6, depending on the quality of the adjustments of the state of polarization. The experiments described can be done in 4 or 5 hours. What is the importance of creating an entangled photons experiment for our engineering students? First of all, entanglement concept is clearly one of the most strikingly nonclassical features of quantum theory and it is playing an increasing role in present-day physics. But in this paper, we will emphasise the experimental point of view. We will try to explain why we believe that for our students this lab experiment is a unique opportunity to deal with established concepts and experimental techniques on polarization, non linear effects, phase matching, photon counting avalanche photodiodes, counting statistics, coincidences detectors. Let us recall that the first convincing experimental violations of Bell’s inequalities were performed by Alain Aspect and Philippe Grangier with pairs of entangled photons at the Institut d’Optique between 1976 and 1982. Twenty five years later, due to recent advances in laser diode technology, new techniques for generation of photon pairs and avalanche photodiodes, this experiment is now part of the experimental lab courses for our students.
It is well known that Bell’s inequality may be violated for special quantum states, e.g., an entangled state for a pair of particles. The entangled state is generalized here into a polyentangled state. Specifically, instead of only two possible states for each individual particle of the pair, several states are possible in an entangled way. An experimental realization for the polyentangled state is presented. It is the state for a pair of atoms in their Zeeman sublevels, in which the atoms are produced from dissociation of a homonuclear (I = 1/2) paradimer that is initially in a J = even rotational state of the singlet electron state. The three possible angular momentum components (M2 = 0,±1) in a specific direction can be determined because the different Zeeman sublevels can be selectively excited by polarized lasers, and then subsequently detected by photoionization. Because of the high detection efficiency (>90%) and fast responsivity (<10 ns) for these processes, the two main loopholes in previous LHV experiments using optical photons can be blocked.
Experimental tests of Bell's inequality allow to distinguish quantum mechanics from local hidden variable theories. Such tests are performed by measuring correlations of two entangled particles (e.g. polarization of photons or spins of atoms). In order to constitute conclusive evidence, two conditions have to be satisfied. First, strict separation of the measurement events in the sense of special relativity is required ("locality loophole"). Second, almost all entangled pairs have to be detected (for particles in a maximally entangled state the required detector efficiency is 82.8%), which is hard to achieve experimentally ("detection loophole"). By using the recently demonstrated entanglement between single trapped atoms and single photons it becomes possible to entangle two atoms at a large distance via entanglement swapping. Combining the high detection efficiency achieved with atoms with the space-like separation of the atomic state detection events, both loopholes can be closed within the same experiment. In this paper we present estimations based on current experimental achievements which show that such an experiment is feasible in future.
Experimental tests of Bell's inequality allow to distinguish quantum mechanics from local hidden variable theories. Such tests are performed by measuring correlations of two entangled particles (e.g. polarization of photons or spins of atoms). In order to constitute conclusive evidence, two conditions have to be satisfied. First, strict separation of the measurement events in the sense of special relativity is required ("locality loophole"). Second, almost all entangled pairs have to be detected (for particles in a maximally entangled state the required detector efficiency is 82.8%), which is hard to achieve experimentally ("detection loophole"). By using the recently demonstrated entanglement between single trapped atoms and single photons it becomes possible to entangle two atoms at a large distance via entanglement swapping. Combining the high detection efficiency achieved with atoms with the space-like separation of the atomic state detection events, both loopholes can be closed within the same experiment. In this paper we present estimations based on current experimental achievements which show that such an experiment is feasible in future.