Breaking down a decades-old test, researchers support the case of quantum mechanics

In a new study, researchers demonstrate a creative tactic to get rid of the flaws that have long confused quantum mechanical testing. Thanks to their innovative method, researchers have been able to demonstrate quantum interactions between two particles spaced more than 180 meters apart, while eliminating the possibility that events shared over the last 11 years have affected their interaction.

A paper explaining these results will be presented at the FIO + LS conference (Frontiers in Optics + Laser Science), held September 15-19 in Washington, D.C., U.S.A.

Quantum phenomena are explored for applications in computing, encryption, detection, etc., but researchers do not yet fully understand the physics that underlies them. The new work could help advance quantum applications by improving verification techniques of quantum mechanics.

A test for quantum theories

Physicists have long struggled with different ideas about the forces that govern our world. While theories of quantum mechanics have gradually moved beyond classical mechanics, many aspects of quantum mechanics remain mysterious. In the 1960s, physicist John Bell proposed a way to test quantum mechanics, known as Bell's inequality.

The idea is that two parts, nicknamed Alice and Bob, make measurements on particles distant from each other but connected one to the other by a quantum entanglement.

If the world were indeed governed solely by quantum mechanics, these distant particles would be governed by a nonlocal correlation by quantum interactions, so that the measure of the state of a particle affects the quantum mechanics. state of the other. However, some alternative theories suggest that particles only seem to affect each other, but that they are actually linked by other hidden variables in classical physics rather than quantum physics.

Researchers have conducted many experiments to test Bell's inequality. However, experiences can not always be perfect, and there are loopholes that can lead to misleading results. Although most experiments have strongly supported the conclusion that quantum interactions exist, these flaws still leave a distant possibility that researchers may inadvertently affect hidden variables, leaving the doubt behind.

Closing gaps

In the new study, Li and his colleagues showed ways to fill these gaps and added to the evidence that quantum mechanics governs interactions between the two particles.

"We performed a bell-free Bell test with measurement parameters determined by distant cosmic photons, thus verifying the completeness of quantum mechanics with a high probability of confidence," said Ming-Han Li, of University of Science and Technology of China. is the main author on the paper.

Their experimental setup consists of three main components: a device that periodically sends entangled photon pairs and two stations that measure photons. These stations are Alice and Bob, in the jargon of Bell's inequality. The first measuring station is 93 meters (305 feet) from the photon pair source and the second station is 90 meters (295 feet) in the opposite direction.

The entangled photons travel through a monomode optical fiber to the measuring stations, where their polarization state is measured with a Pockels cell and the photons are detected by superconducting single photon detectors.

In designing their experience, the researchers sought to overcome three key problems: the idea that loss and noise make detection unreliable (loophole), the idea that any communication affecting the measurement choices of the time. Alice and Bob makes the measure unfathomable (loophole of locality). and the idea that a measurement adjustment choice that is not "truly free and random" allows the result to be controlled by a hidden cause of the common past (loophole in freedom of choice).

To solve the first problem, Li and his colleagues demonstrated that their configuration made it possible to obtain a sufficiently low level of loss and noise by comparing the measurements made at the beginning and at the end of the photon path. To answer the second question, they constructed the experimental setup with a separation similar to the space between the measurement parameter choices. To answer the third question, they based their measurement choices on the behavior of cosmic photons from 11 years ago, suggesting that nothing in the common past of particles – for at least 11 years – n & rsquo; Created a hidden variable affecting the result.

By combining theoretically calculated predictions with experimental results, the researchers were able to demonstrate quantum interactions between entangled photon pairs with a high degree of confidence and fidelity. Their experience thus provides strong evidence that quantum effects, rather than hidden variables, are at the origin of particle behavior.