Abstract The amazing quantum effect of ‘entanglement’ was discovered in the 1935 thought experiment by Albert Einstein, Boris Podolsky and Nathan Rosen (‘EPR’)1. The ensuing research opened up fundamental questions and led to experiments that proved that quantum theory cannot be completed by local hidden variables2–4. Remarkably, EPR did not discuss how to create the entanglement in their thought experiment. Here I add this part. What is required in the original EPR thought experiment is a simple elastic particle collision, an unbalanced mass ratio of e.g. 1:3 and initial states that are position and momentum squeezed, respectively. In the limiting case of infinite squeeze factors, the measurement of the position or momentum of one particle allows an absolutely precise conclusion to be drawn about the value of the same quantity of the other particle. The EPR idea has never been tested in this way. I outline a way to do this.
Abstract The amazing quantum effect of ‘entanglement’ was discovered in the 1935 thought experiment by Albert Einstein, Boris Podolsky and Nathan Rosen (‘EPR’)1. The ensuing research opened up fundamental questions and led to experiments that proved that quantum theory cannot be completed by local hidden variables2–4. Remarkably, EPR did not discuss how to create the entanglement in their thought experiment. Here I add this part. What is required in the original EPR thought experiment is a simple elastic particle collision, an unbalanced mass ratio of e.g. 1:3 and initial states that are position and momentum squeezed, respectively. In the limiting case of infinite squeeze factors, the measurement of the position or momentum of one particle allows an absolutely precise conclusion to be drawn about the value of the same quantity of the other particle. The EPR idea has never been tested in this way. I outline a way to do this.
In 1935, Albert Einstein, Boris Podolsky, and Nathan Rosen ('EPR') reported on a thought experiment that they believed showed that quantum theory provided an incomplete description of reality. Today we know that quantum theory is a complete and correct description of Nature (in flat space-time). The EPR thought experiment is predicted by quantum theory and has since been experimentally confirmed. However, EPR experiments have no physical pictorial explanation, and are considered part of a "paradox". Here I resolve the "paradox". I show independently of any interpretation of quantum theory that EPR (thought) experiments are a direct and compelling consequence of the existence of true randomness and the conservation of energy. It becomes obvious why EPR (thought) experiments allow for the precise prediction of truly random measurement values. Local hidden variables are not motivated.
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.
By 1935, the Copenhagen interpretation had become the orthodoxy. Einstein needed to find a situation in which it is possible in principle to acquire knowledge of the state of a quantum system without disturbing it in any way. Working with two young theorists, Boris Podolsky and Nathan Rosen, Einstein devised an extraordinarily cunning challenge based on entangled particles. We can discover the state of one particle with certainty by making measurements on its entangled partner. All we have to assume is that the particles are local: any measurement we make on one in no way affects or disturbs the other. Through the work of David Bohm and John Bell, the challenge posed by EPR became accessible to experiment, and Bell devised a simple test for all locally realistic theories. All the experiments performed to date suggest that the standard quantum formalism is correct: in any realistic interpretation, quantum particles are non-local.
In 1935, Einstein, Podolsky, and Rosen (EPR) argued that (then new) quantum mechanics was incomplete. At the heart of EPR’s paradox was the strange non-local nature of an entangled state which allowed EPR to simultaneously assign local values for position and momentum of a particle. In 1964, John Bell proposed an inequality (Bell’s inequality) that must be satisfied by any local realistic theory. The experimental confirmation of quantum physics, i.e., the experimental test of Bell’s inequality, required a pair of particles in an entangled state. The experiments first performed in the early 1970s, followed by a series of experiments until now, have confirmed the violation of Bell’s inequality, strongly implying that local realistic descriptions of nature are not consistent with experimental observations. The early simplistic view of entanglement has now been significantly expanded to include mixed states and multiple particles. Moreover, theoretical and experimental studies on the nature of entanglement have led to quantum information science where entanglement is an essential resource. In this article, we briefly review the early experiments on Bell’s inequality and experimental attempts to close “loopholes” as well as some key experiments on quantum information.
The author describes several thought experiments that are important in modern physics, by which he mean the physical theory and practice that developed explosively from the late 19th century onwards. Some thought experiments provide the basis for rigorous arguments with clear conclusions; others seem to work simply by drawing attention to an important question that otherwise might not have been apparent. While the thought experiments to be discussed here are key turning points in the history of modern physical theory, in several cases their full implications remain to be plumbed. It is an extraordinary fact that most of the decisive thought experiments in 20th-century physics were born from the fertile imagination of one person, Albert Einstein. This forces to ponder the importance of individual creativity in the advancement of science. The Einstein-Podolsky-Rosen (EPR) thought experiment dominates investigations of the foundations of quantum mechanics and plays a defining role in quantum information theory.
Quantum entanglement, a fundamental concept in quantum theory, allows distant objects to establish unbreakable quantum links. This property makes entanglement an invaluable tool for quantum networks. Albert Einstein, Boris Podolsky, and Nathan Rosen devised a thought experiment to highlight the apparent absurdity of quantum entanglement, which seems to defy a fundamental law of the universe. Professor Thomas Vidick proposes that exploring the potential for particles to communicate across vast distances is an intriguing endeavor. However, the mathematical structure of the tensor product of two interacting quantum systems unequivocally indicates that, except for rare cases, the concept of “two separate particles” is misleading. The tensor product yields a unified whole, with the resulting parts occasionally differing from the original components due to experimental or conceptual mathematical decomposition.