Durham University: Lumiere 2021 – Researching the fundamentals of time

Atoms, lasers and optical tweezers
From GPS to the internet, much of the technology we take for granted relies on precision timekeeping. Accuracy to within a trillionth of a second is achieved with the use of atomic clocks, which is where technology and physics meet.

Atomic clocks use the electrons of an atom to measure time. The electrons are excited and de-excited millions of times each second by a laser, and these cycles are counted – like the ticking of a clock, but much faster. But first you need to catch the atoms!

Laser cooling is used to slow the atoms down so that another laser, known as an optical tweezer, can hold the atoms in place and stop them from falling under gravity.

With challenges of motion and gravity overcome, atoms provide a highly accurate and stable way to measure time, and one that has revolutionised navigation and communications systems.

Shifts in time
Einstein discovered that clocks run at different speeds depending on location. A clock at the top of a mountain will run at a different rate to one at sea level, a phenomenon now known as gravitational red shift.

Understanding this phenomenon, which was part of the initial motivation for building better clocks, has led to remarkable spin offs that have changed the way we navigate and compute.

Our Quantum Light Matter (QLM) research group runs a number of different experiments based on the technology of atomic clocks. These include using quantum computing to develop even greater accuracy and exploring how to enable the atoms within atomic clocks to communicate and synchronise with each other through a process known as quantum entanglement.

Keeping time with nature
Whilst this may all sound very scientific and remote, the applications of this hyper-accurate time keeping are all around us. From instant messaging to financial trading, synchronised time signals support many digital and commercial activities in our everyday lives.

It has also given rise to ‘leap seconds’ which, like leap years, correct our timekeeping to account for the fact that the number of seconds in a year is not perfectly constant.

In a world driven by science, atomic clocks show that nature ultimately gives us time.

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