Using two old galactic nuclei called quasars, researchers have made a huge step forward towards confirming quantum entanglement – a concept that says that the properties of particles can be linked, no matter how far away they are in the universe.
If quantum entanglement is valid, then a few entangled particles can have billions of light years apart and actions that affect the properties of one particle will affect the properties of the other particle. Albert Einstein described this correlation between particles as "spooky action at distance." Last year, physicists from MIT, the University of Vienna and other institutions provided strong evidence for quantum entanglement, and now this same team of scientists has even gone further to confirm quantum entanglement.
Scientists who want to prove quantum entanglement must demonstrate that measured correlations between particles can not be explained by classical physics, according to a statement from MIT that describes the new work. In the 1960s, physicist John Bell calculated a theoretical limit, through which correlations between particles must have a quantum and no classical explanation. [Time Crystals to Tetraquarks: Quantum Physics in 2017]
But there are loopholes in this theoretical limit, in which observations of what appears to be correlated particles have a hidden, classic explanation, the MIT researchers said. One of these loopholes that scientists are trying to close is known as the mesh in the "freedom of choice" or the possibility that an unknown classical influence influences a measurement of a confused particle. With this mesh in the law, researchers observe a quantum correlation when there is none.
Last year, this team of scientists, using 600-year-old starlight, demonstrated that if the correlations they observed between particles could be explained by classical physics, this classic origin should originate from more than 600 years ago – before the light of the star ever seemed.
To close this gap further, these researchers have now used distant, old quasars – luminous, energetic galactic nuclei – to see if the correlation between particles can be explained by the classical mechanics of more than 600 years ago. In other words, they take the success of their study last year and scale it up to provide more evidence for quantum entanglement.
To do this, they chose to use two quasars that emitted light 7.8 billion years ago and 12.2 billion years ago. The researchers used the light from these two quasars to determine the angle at which a polarizer should be tilted, which measures the direction of the electric field of each photon.
They used telescopes that were on detectors to measure the wavelength of the interlaced photons (light particles) in the light of the quasars. If the light was redder than a reference wavelength – an equation used at a different wavelength than that studied – the polarizer tilted to measure the incoming photon. If the light was bluer than the reference wavelength, the polarizer would tilt to a different angle to measure the photon.
In the research carried out last year, researchers used small telescopes with which they could only measure light from stars at 600 light-years away, but by using larger, more powerful telescopes, the researchers have now managed to measure the light of much older , further removed quasars.
When studying entangled photons with these old quasars, the team found correlations in more than 30,000 pairs of photons. These correlations went far beyond the limit set by Bell, which shows that, if there were a classic explanation for the correlated particles, it would have to come from before these old quasars emitted light – many billions of years ago.
"If there is a conspiracy to simulate quantum mechanics with a mechanism that is actually classic, then that mechanism should have started working – somehow knowing exactly when, where and how this experiment would be done – at least 7 , 8 billion years ago, "said Alan Guth, a physicist at MIT and a co-author of the new work, in the statement. "That seems incredibly unbelievable, so we have very strong evidence that quantum mechanics is the right explanation."
So with these findings it is "unbelievable" that the measured correlations have a classic explanation, the researchers said. This is strong evidence that quantum mechanics has caused this correlation and that quantum entanglement is valid, they said.
"The earth is about 4.5 billion years old, so any alternative mechanism – different from quantum mechanics – that would have produced our results by abusing this loophole, should have existed long before even a planet Earth was, let alone an MIT, "David Kaiser, also a physicist at MIT and a co-author of the study, added in the statement. "So we have reduced all alternative explanations to very early in cosmic history."
Work was published August 20 in the journal Physical Review Letters.