Photonics team use laser technology to produce significant improvement in accuracy of counting element in compact atomic clocks
Timekeeping has been vital to navigation for centuries. The Royal Observatory at Greenwich proudly displays the chronometers designed and built by John Harrison in the 18th century that allowed longitude to be determined by ships at sea, with the result that the zero meridian runs through London. Today, the hyper-accurate clocks that allow us navigate are mainly housed on satellites, such as the American-owned global positioning system (GPS) and the European Union’s Galileo consolation, the subject of some controversy in the UK owing to legal aspects of Brexit.
A team at the emerging photonics laboratory (EPic Lab) at Sussex University is working on technology to make super accurate clocks portable: something that would free users from the dependants on GPS or Galileo for navigation. This would reduce their exposure to the whims of international politics, while also allowing them to navigate where there is no satellite signal.
Their breakthrough is in improving the accuracy of the lancet – the device in the clock responsible for counting, analogous to the pendulum in a traditional mechanical clock – by 80 per cent, outperforming other teams around the world working on similar projects.
The device is a component of an optical atomic clock, the most accurate kind of timekeeper ever devised. Currently, such clocks are huge, weighing hundreds of kilograms. Their lancets derive from the quantum property of a single confined atom, using a device known as an optical frequency comb – a laser emitting many colours, equally and precisely separated in frequency – to observe the electromagnetic field of a light beam oscillating hundreds of millions of times a second.
The EPic Lab team is working with micro-combs – devices that reduce the size of frequency comb equipment using a microprocessor component called an optical micro-resonator. Previously, these have proved too delicate, difficult to operate and not as accurate as optical frequency combs.
In a paper in Nature Photonics, the team explains how it achieved its improved results by using a laser cavity soliton. “Solitons are special waves that are particularly robust to perturbation. Tsunamis, for instance, are water solitons. They can travel unperturbed for incredible distances; after the Japan earthquake in 2011 some of them even reached as far as the coast of California,” explained Dr Alessia Pasquazi, a mathematician and a member of the research team.
“Instead of using water, in our experiments performed by Dr Hualong Bao, we use pulses of light, confined in a tiny cavity on a chip. Our distinctive approach is to insert the chip in a laser based on optical fibres, the same used to deliver internet in our homes.” The soliton wave produced in the chip can generate many colours, while also offering the robustness and versatility of control of much larger pulsed lasers, she added.
The next stage in the project is to integrate the soliton device with an ultra-compact atomic reference developed by Prof Matthias Keller at Sussex University.
“Working together, we plan to develop a portable atomic clock that could revolutionise the way we count time in the future,” said Prof Marco Peccianti of the EPic Lab. This could lead to partnerships with the aerospace industry within five years and eventually portable atomic clocks that could be housed in mobile phones or vehicles, he added. Advantages of this might include ambulances being able to access mapping inside tunnels or out in the countryside where there is no reliable mobile phone signal, said Pasquazi.
Can someone explain why a portable atomic clock “allow(s) them to navigate where there is no satellite signal”? Are they going to use a sextant?
My understanding is that the GPS receiver listens to the satellites and, by knowing the time the signals were sent out, knows the distance of each of them. [Trilateration (lengths) is much more accurate than triangulation]. Naturally knowing the time at the receiver is important but by knowing the timing of the signals corrections can be made for the local clock to achieve required accuracy.
I think that the improvement of accuracy of clocks is commendable (and useful for improving the satellites too) but your current mobile GPS can compensate for the accuracy of its clock as it is – so would like to see some more in the way of why a more accurate clock is required.
And it should be noted that the GPS on your mobile phone/GPS system does not require a mobile telephone signal – it looks at how many satellites it can “see”.
No wonder we are moving to driver less AI cars! The former pilot is now demoted to navigator, and he/she/it must pull out the old compass and sextant for this, along with the super-accurate clock.
Hopefully one of those magic Viking crystals that allow to find the sun on overcast days also.
I really have no idea how to navigate now, based on the information in the article.
The abstract says nothing about geolocation, and measuring time with exquisite detail gives you absolutely NO CLUE on where you are, so dear author: could you please explain how it works and/or quote the original authors?
Anyway, here’s what I got when emailing the original researcher:
“Long story short, precision clocks are needed for what is called ‘inertial navigation’, where you map your position with time using accelerometers. ships have used for a long time, and a version of this navigation is already on our phones. it is how they get the direction when you start the navigation.
because you calculate the path by measuring time and acceleration/angular moment, if you do not have a good clock you make a lot of errors, and this is why portable atomic clocks are needed. exciting research by our colleagues on quantum gyroscopes should make this thing even better, but the first bottleneck at this point is to make a portable high accurate clock.”
I then pointed out that the gyros and accelerometers are by far the weakest links in a mobile phone’s INS system, not the relatively accurate clock. Her response:
“As a photonic researcher I believe that at this point the micro-comb part of the optical atomic clock has almost all the bits and pieces needed for the full integration on chip (there are already some demonstration of this). The last ten years of research on this topic has been pretty impressive, so I believe that the community should get there soon, and this is likely to be the first bit of the clock to be completed. From what I know from my atomic physicist collaborators, they have a much bigger challenge ahead in integrating the atomic reference, but there is a lot of drive and I think that they will be soon able to provide a reference of the size of a shoe box, that is already a lot for many kind of applications. Atomic community is probably also the best placed for getting small highly accurate gyros, for which they need portable time references.
that’s why I think there is good 20 years to go to get there…. :)”
I’m not entirely sure the reality justifies the lofty and vague claims made in various posts about this, but it’s good research.