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Breaking through decades of testing, researchers support the case for quantum mechanics



  Cracking a Decade-Old Test, Bolster Case Researchers for Quantum Mechanics
Researchers created entangled pairs of photons and distributed two photons from each pair to two measuring stations in opposite directions. At each measuring station, a telescope received photons from a selected space source that is at least 11 light-years from Earth. Cosmic photon detection signals generate arbitrary bits to select a measurement setting for the Bell test without holes. In this experiment, the researchers closed the detection and localization doors and pressed the time limit to exclude local latent variable models up to 11 years before the experiment. Credit: Ming-Han Lee, USTC, Shanghai

In a new study, researchers demonstrate creative tactics to get rid of the gates that have long been confused with quantum mechanics tests. With their innovative method, researchers have been able to demonstrate quantum interactions between two particles more than 180 meters (590 feet) apart, while eliminating the possibility of shared events over the past 11 years affecting their interaction.


A report explaining these results will be presented at the Frontiers in Optics + Laser Science (FIO + LS) conference held September 15-19 in Washington, DC,

Quantum phenomena are being investigated for applications in computing, encryption, sensation and more, but the researchers still do not fully understand the physics behind them. New work could help advance quantum applications by improving quantum mechanics research techniques.

The Quantum Theory Test

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

The idea is that two parties, alias Alice and Bob, make measurements of particles that are spaced apart but interconnected by quantum. entanglement.

If the world were indeed governed solely by quantum mechanics, these distant particles would be governed by nonlocal correlation by quantum interactions, so that the measurement of the state of one particle affects the state of the other. However, some alternative theories suggest that particles appear to influence one another, but in reality they are related by other hidden variables following classical rather than quantum physics.

Researchers have conducted many experiments to test Bell's inequality. However, experiments may not always be perfect and there are some loopholes that could lead to misleading results. While most experiments strongly support the conclusion that quantum interactions exist, these loopholes still leave a remote possibility that researchers may inadvertently affect hidden variables, leaving room for doubt.

Closing the gates

In the new study, Lee and his colleagues demonstrate ways to close these gates and add to the evidence that quantum mechanics drives interactions between two particles.

"We implemented a Bell-free door test with the measurement settings determined by the remote space photons. In this way, we checked the completeness of quantum mechanics with high probability, "says Ming-Han Lee of China's University of Science and Technology, the lead author of the document.

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

Intricate photons travel through a single-mode optical fiber to measurement stations, ie where their polarization state is measured by a Pocells cell and photons are detected by superconducting single-photon nano-detectors

In designing their experiment seek to overcome three key problems: the idea that loss and noise make detection unreliable (the door opener), the idea that any communication that affects Alice and Bob's measurement choices makes measurement advantageous (the locality door) and the idea that choosing a measurement setting that is not "truly free and random" makes the result capable of being controlled for a hidden reason in the common past (the choice door).

To deal with the first problem, Lee and his colleagues demonstrate that the setup achieved a sufficiently low level of loss and noise by comparing measurements taken at the beginning and end of the photon journey. To address the latter, they constructed an experimental setup with space-like separation between events from the choice of measurement setup. To deal with the third, they base their choice on determining the measurement of cosmic photonic behavior from 11 years earlier, which offers great confidence that nothing in the shared past of particles – at least in the last 11 years – has created a hidden variable affecting on the result.

By combining theoretically calculated predictions with experimental results, the researchers were able to demonstrate quantum interactions between interconnected pairs of photons with a high degree of confidence and fidelity. In this way, their experiment provides strong evidence that quantum effects, not hidden variables, are behind the behavior of particles.


Unlocking and closing quantum entanglement "gates"


More information:
A Test of Local Realism in the Past with No Doors for Detection and Locality by Ming-Han Li et al. It will be presented on Monday, September 16, 2019, from 11:15 a.m. EDT in the Washington 4 Room of the Marriott Wardman Park Hotel in Washington, DC

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Breaking through decades of testing, researchers back the case for quantum mechanics (2019, August 22)
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