The National Physical Laboratory relaunched this September with a showcase of its technology, and senior professor for time and frequency Patrick Gill told Techworld why the utmost precision of the centre's newest atomic clock is so important for the future of technology.

The National Physical Laboratory (NPL) is Britain's national measurement institute and has developed and maintained the country's measurements standards since it was established at the turn of the 20th century in at Bushy Park, Teddington.

Image: iStock/in-future
Image: iStock/in-future

Quantum technology, 5G testing chambers and biometric analysis, were all on display at its headquarters, alongside the most famous of all the innovations in the NPL's 102-year history: a device that redefined time known as the caesium atomic clock.

Today the institute's Caesium Fountain, or CsF2, atomic clock provides the ultra-precise time standard for global satellite services as well as in the finance sector, for telcos, energy supplies, computer systems and the military. It provides a foundation for the time boards on GPS that power aircraft navigation, and the nanosecond-accurate timestamps used to record financial transactions.

How atomic time works

The original caesium atomic clock was the first device of its kind when it was unveiled at the NPL in 1955.

For thousands of years before it, time standards had been set by the position of the sun in relation to the rotation of the Earth. The atomic clock replaced this with a measurement of energy in the atom of caesium.

That device was used to set the standard second throughout the country. Inventor Louis Essen invited NPL director Edward Bullard "to come and witness the death of the astronomical second and the birth of atomic time".

His prediction soon proved true. In 1967 the atomic second became the new international time standard, replacing Ephemeris Time – the standard developed by ancient Egyptian astronomers in 1500BC based on the earth's rotation.

The previous system relied on the rotation of the Earth on its axis, but the gravitational pull of the moon gradually slows this down, with this irregular orbit leading to a fluctuation in the length of the day.

The atomic clock follows the frequency of an electron's transition energy as it moves within an atom.

Essen and his collaborator J.V.L. Parry designed a system that assesses the vibrations of caesium atoms when an electrical charge is applied to them, an effect known as a resonant frequency. The measurement functions in a similar manner to the swinging of a pendulum in a grandfather clock to mark a single second.

The vibration in caesium at a high resonant frequency can be connected to extremely precise time markers. The accuracy was the equivalent to the loss of roughly one second every 300 years.

At the 13th General Conference on Weights and Measures in 1067, the International System (SI) of Units definition of a second was redefined according to the transition between two energy levels of the caesium-133 atom. Physicists had taken over from astronomers as the guardians of timekeeping.

In 2011, the CsF2 atomic clock was found to be the world's most precise timekeeper with an accuracy fluctuation of one second every 138 million years, twice the length of time between now and the extinction of the dinosaurs.

Keeping ships on course

The NPL has applied its unrivaled precision timing to a wide range of applications, including Global Navigation Satellite System (GNSS), the term for satellite navigation positioning including GPS and Galileo.

"It's feeding into all location-based services," senior NPL fellow for time and frequency Professor Patrick Gill told Techworld. "It's used for transport, retail, safety of life, critical infrastructure, and energy management on the grid, and emerging needs such as timing for high-frequency trading in the city."

The invisible utility can have an eye-popping economic impact.

According to research conducted by London Economics (LE), GNSS directly supports sectors generating 11.3 percent of domestic GDP and provides economic benefits of roughly £6.7 billion per annum. The study estimates that a five-day loss of GNSS would cost the country a total of £5.2 billion.

The NPL is also developing atomic timekeeping systems to support communication between military personnel deployed in war zones.

"We're looking to make very small clocks that could go into a scenario where it might need to be collapsed a little bit more to wear on your clothing or fit into vehicles that are transporting personnel around," said Gill.

He explained: "The reliance factor is really serious. If you lose the GPS, how do you continue? One of the ways of doing that is having atomic clocks as backups in critical situations.

"The amount of power you get in your receiver from a GPS satellite is tiny so it's very easy to jam or lose a signal. That doesn't have to be intentional. It can be unintentional due to things like solar flares, it can be because you're in a bit of an urban jungle and you can't see the satellites properly, or because there are multiple reflections, or you're underground or inside and lose your links.

"But of course, it can be intentional as well. That recently has become quite significant issue for governments to try to improve that resilience."

In 2013, a team of researchers from the University of Texas spoofed the GPS-system on a 213-foot superyacht and sent the ship hundreds of yards off its course.

And a series of accidents suffered by the US Navy in 2017 – culminating with the deadly collision of guided-missile destroyer the USS John S. McCain with a tanker in Singapore – led to speculation that a foreign state was using GPS spoofing to crash the vessels.

Space and time

Atomic clock systems typically sit in radio stations on the ground to deal with this increased timing requirement but the NPL is also developing atomic clocks for space.

"There is this concept that actually the best place to put a very accurate clock is not on the ground because it suffers from the gravitational pull of the earth," says Gill.

"If you put it up in space, you much reduce that sensitivity. So there is this long-term future opportunity to have master clocks in space."

The European Space Agency is supporting this development. The clocks will first have to be capable of resisting a rocket launch to survive, and deployment in the solar system will also have to account for the interference and noise in international space stations. A fully operational system could be ready to go in the mid-2020s.

Another common current use is providing timing and synchronisation for telecoms and communication networks.

This will only become more vital to serve future communication needs as technologies like autonomous vehicles and data streaming all require accurate time synchronisation to stitch that data together.


The NPL's timekeeping technology is also becoming an essential part of high-speed financial trading. The rapid speed of contemporary financial trading makes it difficult to accurately track, and automated high-frequency trading uses algorithms to spot emerging market trends within billionths of a second.

The revised Markets in Financial Instruments Directive (MiFID II) will make accurate recording of the times of transaction a legal requirement once the regulation comes into force on 3 January 2018.

The European Union law on investment services requires financial institutions to make their trading events traceable to a 100-microsecond level. The NPL's technology can help ensure compliance with the directive.

The NPL claims this system can track trade times down to a single microsecond, the equivalent of one millionth (0.000001) of a second.

New York Stock Exchange owner Intercontinental Exchange (ICE) has joined Swiss bank UBS in signing up to use the system, which delivers atomic timing to a company's rack over fibre optic links.

The NPL predicts that its next generation of atomic clocks will use laser-cooled trapped ions or atoms to achieve accuracies around 100 times better than today's standard-bearers.

And that will mean what first replaced a system that had existed since Ancient Egyptians told the time by shadows will then have an accuracy equivalent to a swing of one second in the age of the universe.