This could be a really huge breakthrough for quantum entanglement physics. Thanks to a recent practical experiment to test their theories, scientists think they just built the first dark matter detector. There’s more to our universe than anyone knows. A whole lot more. Physicists are stumped that a full 85 percent of everything can’t be seen, felt, or even detected. For instance, gravity theories don’t work at all unless there is whole lot more stuff out there than we know about and can throw on a scale.
Lab breakthrough twists time
The key to the whole thing involves the theory of quantum “entanglement.” What makes this experiment such a special breakthrough is that two scientists collaborating together told Werner Heisenberg to take his uncertainty principle and go fly a kite with it.
In the simple version, Heisenberg says you can know either the position or momentum of a particular particle, but not both, and also that the act of measuring influences the outcome. Basically, when you touch the ruler to the bubble, the bubble breaks. It’s a paradox which has been driving scientists crazy for a century now.
John Bollinger and Ana Maria Rey, of JILA, put their heads together and came up with the breakthrough which could be as earthshaking as Einstein’s aha moment of suddenly realizing that energy is the same as mass times the velocity of light squared, so you can build bombs from it.
Dr. Rey pointed out that entanglement “is beneficial in canceling the ions’ intrinsic quantum noise.” But, she puzzled, “measuring the entangled quantum state without destroying the information shared between spin and motion is difficult.” Bollinger’s group figured out a way to “reverse time” with a pair of lasers. The technique worked so well they built a gizmo with it which they’re using to find some of that dark matter everyone’s been looking for. Let’s hope it doesn’t get used to someday build a “time” bomb.
During the day, Bollinger hangs out at the National Institute of Standards and Technology. In his lab they do freaky things with the fabric of space and time, linking together exactly 150 charged beryllium atoms by “entangling” the “mechanical motion and electronic properties.”
Using a magnetic field, they coax the ions until they “self-arrange into a flat 2D crystal just 200 millionths of a meter in diameter. It’s blue. They can use their creature to detect dark matter because its presence makes the crystal “wiggle in telltale ways” and the breakthrough comes from not just analyzing the collective spin properties of the crystal, but through the use of a “time reversal” strategy to detect the results.
Frequency depends on the mass
Nearby particles of dark matter such as “axions and hidden photons” interact with the ions in the crystal “through a weak electric field.” Dark matter “forms a background signal with an oscillation frequency that depends on the mass of the dark matter particle.” Axions will produce one frequency in the detector, hidden photons another frequency. Scientists have been working on the problem for decades but the breakthrough came when Bollinger figured out a technique to basically “run the film in reverse.”
He tangles up his crystal, reads the measurement, then “untangles” it again, to see how far it moved, quantumly speaking. “This time reversal decouples the spin and the motion, and now the collective spin itself has the displacement information stored on it, and when we measure the spins we can determine the displacement very precisely. This is neat!”
Starting with microwaves, they get each and every one of their pet atoms spinning in the same direction, first up, then horizontal. Picture a plate full of spinning tops. He then shoots laser beams across the crystal crossways, tuning the frequency of the laser beams so that the difference between the two of them becomes “nearly the same as the motion.”
That achieves the entanglement between “collective spin with the motion.” Then they hand their pet a treat. “The crystal was then vibrationally excited.” They record just how excited it gets. Next comes the breakthrough. “The same lasers and microwaves were used to undo the entanglement.”
As Dr. Bollinger explains, it’s easy to “determine how much the crystal moved.” They look at “the ions’ spin level of fluorescence (spin up scatters light, spin down is dark).”
This sensor, they declare, “can measure external electric fields that have the same vibration frequency as the crystal with more than 10 times the sensitivity of any previously demonstrated atomic sensor.” Their breakthrough technology allows the sensor to “measure 240 nanovolts per meter in one second.”
They already have ideas for improvement on the drawing board. “increasing the number of ions to 100,000 by making 3D crystals” could improve the sensing capability by a factor of thirty. Also, “the stability of the crystal’s excited motion might be improved, which would enhance the time reversal process and the precision of the results.” Dr. Rey is as excited as the crystal about the breakthrough.
“If we are able to improve this aspect, this experiment can become a fundamental resource for detecting dark matter. We know 85% of the matter in the universe is made of dark matter, but to date we do not know what dark matter is made of. This experiment could allow us in the future to unveil this mystery.”