Atomic clocks are established as the most precise timekeepers created. Atomic clocks work by deploying lasers to measure the vibrations of atoms (electromagnetic signals). By atoms oscillating at a constant frequency it enables precise movements of time to be recorded. Here the atoms are functioning as tiny microscopic pendulums swinging in synchronicity.
Current generations of atomic clocks cool atoms to near absolute zero temperature by slowing them with lasers. The measurements are made by creating atomic fountains within a microwave-filled cavity. One example is the NIST-F1 atomic clock, which was developed in the U.S. (a cesium fountain clock).
Despite the advances made to date, atomic clocks can be approved. This is based on atomic clocks more accurately measuring atomic vibrations. To develop the technology scientists needed to work out what effect gravity has upon the passage of time. This includes wrestling the conundrum whether time itself changes as the universe ages.
The new variant of the atomic clock comes from MIT scientists. What is different about this clock is that it does not measure a cloud of randomly oscillating atoms. Instead the new system assesses atoms which have been quantumly entangled. This enables the vibrations to be measured more accurately.
In terms of improvement, the MIT clock provides improved precision to the level of one second better than current technology.
This improvement arises because according to quantum mechanics, as an atom is measured it will behave much like spinning a coin and calling ‘heads’ or ‘tails’, It is only by flipping the coin multiple times that the collected data can be used to make the correct probabilities. This is called the Standard Quantum Limit. This means any restriction on measurement due to quantum effects.
The researchers speculate that if the new generation atomic clocks are adapted to assess entangled atoms the overall timing would improve such that, across the entire age of the universe, the clocks would only run less than 100 milliseconds off. In other words, time keeping of immense precision.
Quantum entanglement
The new approach assesses multiple atoms so that the average is assessed at one time point, which significantly increases the accuracy. Through the principle of quantum entanglement, atoms in a group display correlated measurement results. This means that while any individual atom behaves like the random toss of a coin, the collective assessment of atoms provides and accurate measurement. Hence the individual oscillations tighten up around a common frequency.
Or, to put it another way, imagine a pair of particles are generated. Here the individual quantum states of each particle are indefinite until they are measured. With the act of measuring one particle, this determines the result of measuring the other particle, even when the two particles are at a distance from each other.
The MIT clock is based around 350 atoms of ytterbium, which is the most volatile rare-earth metal. It comes in the form of a soft, malleable silvery metal. The metal oscillates at the same frequency as visible light. Compared with conventional atomic clocks, this means that any one atom vibrates at a rate 100,000 times more frequently within one second than cesium.
The main complexity with developing the MIT atomic clock was with the process used to cool the atoms and the method used to trap them, which required to use of a special optical cavity composed of two mirrors. This effectively quantumly entangles the atoms. In this state a laser is then used to assess the average frequency.
Practical use
As to what the new atomic clock will be used for, this includes helping scientists to solve such theoretical imponderables as considering when the universe ages, does the speed of light change? Another inquiry is with considering the extent that a charge of an electron changes. Both of these areas are impossible to answer with current technology.
Research paper
The research has been published in the science journal Nature. Here the paper is titled “Entanglement on an optical atomic-clock transition.”
Essential Science
This article forms part of Digital Journal’s long-running Essential Science series, where new research relating to wider science stories of interest are presented on a weekly basis.
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The week before we looked at technological solutions for those with impaired vision. We learned that by using a brain implant, researchers have restored a rudimentary form of vision in the blind.
