Eugene Polzik's recent article on the ability of physicists to "entangle" large numbers of atoms for long periods of time (Physics World September pp33–37) illustrates how new technology has revolutionized quantum measurement and information. It is now possible, for example, to demonstrate experimentally key paradoxes of quantum mechanics. These include the famous Einstein–Podolsky–Rosen (EPR) paradox that if the position and momenta of two distant particles are correlated, then knowing the position or momentum of one particle immediately reveals the position and momentum of the other–without any physical measurement having to be made.
Eugene Polzik's recent article on the ability of physicists to "entangle" large numbers of atoms for long periods of time (Physics World September pp33–37) illustrates how new technology has revolutionized quantum measurement and information. It is now possible, for example, to demonstrate experimentally key paradoxes of quantum mechanics. These include the famous Einstein–Podolsky–Rosen (EPR) paradox that if the position and momenta of two distant particles are correlated, then knowing the position or momentum of one particle immediately reveals the position and momentum of the other–without any physical measurement having to be made.
In 1935, Albert Einstein, Boris Podolsky and Nathan Rosen (EPR) published a thought experiment that is entirely correct, has been demonstrated in real experiments, and is now the most famous in quantum physics. Their pioneering work described, for the first time, quantum correlations and can be regarded as a very early glimpse into today's 'deep' quantum technologies, by which I mean those that enhance functionality by making use of quantum correlations. However, their work also contains a paradox that Erwin Schroedinger had already recognised as such in 1935 and which has since been cemented by the so-called Bell experiments. Here, I am now able to pinpoint the origin of the paradox within the chain of reasoning, which ultimately resolves the paradox.
Quantum physics is now one hundred years old, and this description of physical phenomena, which has transformed our vision of the world, has never been found at fault, which is exceptional for a scientific theory. Its predictions have always been verified by experiment with impressive accuracy. The basic concepts of quantum physics such as probability amplitudes and linear superpositions of states, which seem so strange to our intuition when encountered for the first time, remain fundamental. However, during the last few decades an important evolution has occurred. The spectacular progress made in observational techniques and methods of manipulating atoms now makes it possible to perform experiments so delicate that they were once considered as only “thought experiments” by the founders of quantum mechanics. The existence of “nonseparable” quantum correlations, which forms the basis of the Einstein–Podolsky–Rosen “paradox” and which violates the famous Bell inequalities, has been confirmed experimentally with high precision. “Entangled” states of two systems which manifest such quantum correlations are now better understood and even used in practical applications such as quantum cryptography. The entanglement of a measuring device with its environment reveals an interesting new pathway to better understanding of the measurement process. In parallel with these conceptual advances, our everyday world is being invaded by devices which function on the basis of quantum phenomena. The laser sources used to read compact disks, in ophthalmology, and in optical telecommunications are based on light amplification by atomic systems with population inversion. Nuclear magnetic resonance is widely used in hospitals to obtain ever more detailed images of the organs of the human body.
Quantum entanglement was once a subject of intense philosophical debate and regarded as a puzzling theoretical anomaly. However, it has now been empirically validated and is widely recognized as a fundamental feature of quantum mechanics. This review traces its development in chronological order, beginning with the Einstein–Podolsky–Rosen (EPR) paradox, which raised profound questions about the completeness of quantum theory, and John Stewart Bell’s subsequent theorem, which established a measurable framework to verify entanglement’s non-local nature. The discussion then turns to contemporary experimental and applied domains where entanglement serves as a critical resource. Notable examples include quantum teleportation, entanglement-enhanced metrology, quantum radar, and emerging quantum energy devices such as quantum batteries. The transition from theoretical dispute to practical application underscores how entanglement now enables tangible technologies—ranging from ultra-secure communication networks to highly precise sensors. Furthermore, potential interdisciplinary applications in fields such as quantum biology are also explored, suggesting new pathways for innovation. This review aims to bridge foundational concepts with current technological advances, illustrating the continuing impact of quantum entanglement on both scientific understanding and real-world engineering.
In this paper, the new mathematical correlation of two quantum systems that were initially allowed to interact and then separated is being formulated and analyzed. These correlations are illustrated by many examples and are also connected with fractals at a certain level. The main idea of the paper arises from the EPR paradox, the paradox of Einstein, Podolsky, and Rosen that occurs when the measurement of a physical observable performed on one system has an immediate effect on the other separate system being entangled with it. That is a physical phenomenon, especially when the particles are separated by a large distance. In this paper, we define distant correlations as the advanced method for the exact interpretation of strong connection and influence among those particles even when they are widely separated. On the given topological space (X,τ), we define a notion of τ-metric such that the set X is a τ-metric space and we prove some properties of these spaces. By using this new proposed model, we nullify the contradiction that appears in the EPR paradox. An illustrative example involving fractals is given. This innovative mathematical approach to this physical phenomenon may be attractive for future research in the field of quantum physics.
Entanglement lies at the heart of quantum mechanics, and has sparked fierce debate between physicists over the years. The phenomenon, whereby two particles become inextricably linked without actually interacting with each other, certainly goes against intuition. For instance, two photons can be created in an experiment such that if one is polarized in the vertical direction, the other is always polarized horizontally. By measuring the polarization state of one entangled photon, we therefore immediately know the state of the other – no matter how far apart the photons are.
The famous EPR paradox shows that if we describe quantum particles in the usual way -- by their wave functions -- then we get the following seeming contradiction. If we entangle the states of the two particles, then move them far away from each other, and measure the state of the first particle, then the state of the second particle immediately changes -- which contradicts to special relativity, according to which such immediate-action-at-a-distance is not possible. It is known that, from the physical viewpoint, this is not a real paradox: if we measure any property of the second particle, the results will not change whether we perform the measurement on the first particle or not. What the above argument shows is that the usual wave function description of a quantum state does not always adequately describe the corresponding physics. In this paper, we propose a new, more physically adequate description of a quantum state, a description in which there is no EPR paradox: measurements performed at the first particle does not change the state of the remote second one.