The pulse of an atom is one of the most consistent rhythms
in the universe. When stressed, even the most sophisticated "atomic"
clocks based on these quantum timekeepers begin to lose accuracy. Although most
tests have only been able to show this on the smallest scales, physicists have
known for some time that entangling atoms can help hold particles down in order
to squeeze a little more tick from every tock.
This limit has been extended by a group of researchers from
the University of Oxford in the UK to a distance of two metres (approximately
six feet), demonstrating that the mathematics is still valid for wider areas. Not
only may this increase the overall accuracy of optical atomic clocks, but it
also permits a level of comparison in the split-second timing of various clocks
to a degree that might disclose signals in a variety of physical processes that
were previously invisible.
As their name suggests, optical atomic clocks track time by
using light to track the motion of atoms. Atomic parts swing back and forth
like children on a swing while being constrained by a constant set of rules.
All that is required to start the swinging is a dependable kick, like a laser
photon.
Over time, a variety of methods and materials have been
tried to advance technology to the point where variations in their frequencies
barely add up to a second's worth of error over the 13 or so billion years of
the Universe. Because of this level of accuracy, we may need to reconsider how
we define time itself. Even while this technology is extremely precise, there
comes a time when the very laws of timekeeping themselves become a little hazy
due to the quantum landscape's uncertainties, which create a number of
paradoxical circumstances. For instance, increasing the frequency of light can
increase accuracy, but at the expense of making little errors between the
photon's kick and the atom's reaction more significant.
These can then be resolved by repeatedly reading the atom,
albeit this method is not without flaws. The optimum reading would be a
"one shot" measurement using the proper kind of laser beam. The
uncertainty of this method can be reduced, according to physicists, if the fate
of the atom being examined has previously been intertwined with that of
another.
The idea of entanglement is both logical and strange. Until
an object is observed, it is impossible to say that it has a value or a state, according
to quantum mechanics. All of the system's components will be destined to
produce a largely predictable result if they are already a part of a larger
system, perhaps through an exchange of photons with other atoms. It's like
flipping two coins from the same wallet, knowing that even as they spin in the
air, if one comes up heads, the other will come up tails.
The test itself did not yield any revolutionary levels of
precision in optic atomic clocks, but that was not its intended outcome. The
two "coins" in this case were a pair of strontium ions that were
entangled with a photon that was shot down a short distance. Instead, the
scientists demonstrated that using entangled strontium's charged atoms, they
could lower measurement uncertainty under circumstances that should enable them
to increase accuracy in the future.
It is not difficult to determine distances of a few metres on a macroscopic scale, and it is now theoretically possible to entangle optical atomic clocks all over the world to increase their accuracy. The absolute precision we attain is a few orders of magnitude below the state-of-the-art, and our work is very much a proof-of-principle, but physicist Raghavendra Srinivas adds, "We hope that the techniques described here can someday improve state-of-the-art systems."
Entanglement will eventually be necessary because it offers
access to the highest level of precision permitted by quantum theory. To
quantify the minute variations in time caused by masses travelling over the
smallest possible distances, we may need to squeeze a little more accuracy out
of each tick-tock of an atomic clock. This technique could lead to the
development of quantum theories of gravity.
Even outside of science, exploiting entanglement to lessen
uncertainty in quantum measurements may have uses in quantum computers,
cryptography, and communications, among other things. fibre optics.
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