Is Einstein's interpretation of quantum entanglement true

Quantum theory: electron pairs with quantum long-distance relationships

Experiments with synchrotron radiation provide insights into the mysteries of quantum physics. This includes the quantum distance relationship, in which two objects are in a so-called entangled state.

Quantum mechanics puts our imagination to the test. Some even went too far for Albert Einstein. In 1935 he published an article together with Boris Podolsky and Nathan Rosen in which the authors came to the conclusion that - if quantum mechanics were correct and reality was independent of our observations, there must be quantum objects in spooky quantum long-distance relationships. And that just couldn't be.

In general, properties of quantum objects are often only determined after a measurement. The properties of two objects in a quantum distant relationship are linked in a mysterious way. Because if you examine a pair of two objects in a so-called entangled state by taking a measurement of a certain property on one of the two, the corresponding property is also immediately determined for the partner - even if they are at the other end of the universe should.

In the first few years after the publication of Einstein, Rosen and Podolsky, the work did not receive too much attention, as it appeared to many to be of a more philosophical nature. At that time there were no ideas for an experimental test of these fundamental assumptions about the structure of reality. It was only John Bell who put the problem, also known as the EPR paradox, on an experimentally verifiable basis in 1961. Bell's groundbreaking work makes it possible to differentiate between the existence of a locally realistic and a quantum mechanical world. In this context, realistic means that the measurements do not depend on an observer; Physicists speak of locality when distant events cannot directly influence one another. In his 2003 paper, Anthony J. Leggett went one step further by taking into account the nonlocality of reality. The only decisive factor for the measurable difference between the classical world and the quantum world is then the concept of reality. The fundamental question then is whether elements of reality - such as the characteristic properties of a common pair state - exist in reality independently of an observer or not.

Einstein was firmly convinced that this had to be independent of the observer. However, studies on the entanglement of the properties of the elements of our reality have proven the opposite. The components of a maximally entangled pair cannot even be assigned partially defined individual properties.

The proof of a long-distance quantum relationship

In the past few decades, experiments have proven the validity of the quantum mechanical interpretation of reality with increasing precision. However, following a suggestion by David Bohm, angular momentum properties were used instead of location and momentum properties. In contrast, Einstein, Podolsky's and Rosen's actual proposals for checking the concept of reality with regard to continuous variables such as location and momentum have not yet been experimentally checked. This obscurity about the entanglement of continuous variables lasted for nearly three quarters of a century.

Only in advanced experiments on diatomic molecules like N2 this vision became reality by means of synchrotron radiation. Here, researchers in a team led by working groups from the Fritz Haber Institute in Berlin, the University of Frankfurt and the California Institute of Technology in Pasadena (California) used synchrotron radiation to wrest two electrons from the innermost shells of the atoms. These electrons leave the atom in a quantum distance, the entanglement properties of which could be checked experimentally.

The result was a clear confirmation of quantum theory, but this time for the long ignored continuous variables position and momentum. Understanding these relationships is in many respects one of the foundations for the realization of future quantum computers, in which the laws of quantum theory are to be used in order to be able to carry out parallel calculations at the same time.