Scientists used quantumly entangled two optical atomic clocks at a distance of two meters, reports a new study. The achievement opens the door to probing fundamental reality on a deep level.
It’s hard to be precise, especially when it comes to time. Not even your iPhone is a perfect timekeeper, and in fact, the best device is something that’s not easily available. Atomic clocks use an atom’s vibrational patterns to measure time and frequency. The upgraded version, the optical atomic clock, can do an even better job by pairing elements like strontium or ytterbium with lasers.
And while the main application of optical atomic clocks has been timekeeping and navigation, their precision can also be used in searching for dark matter, looking at the space-time variation of fundamental constants, and understanding Earth’s figure, orientation in space, and gravity. The idea of using these clocks to expand our understanding of these natural phenomena is the focus of the study, published on Wednesday in Nature by researchers at Oxford University.
“When two atoms are entangled, then you cannot describe the state of one without describing the state of the other,” Bethan Nichols, one of the study’s authors, wrote in an email to Motherboard. "This is what Einstein is describing with the phrase ‘spooky action at a distance,’ i.e., if something happens to one atom, it can immediately affect the other with no apparent communication between them.”
Entanglement with atomic clocks allows researchers to go beyond traditional boundaries of measurement.
“In order to measure very small changes in the relative atomic frequencies between two atoms in separate locations, we need very high measurement precision,” Nichols wrote. “There is a limit on the measurement precision of independent systems. Entanglement can be used to go past that limit to the ultimate limit allowed by quantum theory.”
Nichols emphasized that there are many groups that have made accurate measurements of optical atomic clock frequencies and that have been working in this field for a long time. But while previous studies have demonstrated that clock entanglement could potentially improve measuring quality, this experiment differs in that the clocks are not actually in the same quantum system.
“There have been demonstrations of entanglement enhanced measurements on optical atomic clocks for atoms that are close to one another in the same system,” Nichols wrote. “However, this is the first demonstration for atoms that are further apart in separate systems.”