Engineers at UNSW say exciting new developments in the way optical clocks can be synchronised has the potential to radically change global positioning systems – as well as fundamental cosmological theories.
Satellites in space need to synchronise very precisely in order for communications to proceed efficiently. Synchronisation also allows the time taken for signals to be sent across a network to be calculated, which then allows positioning to be determined.
Currently global positioning is accurate in most circumstances to within about 1 metre, but if the timing of signals is miscalculated by just 1 nanosecond the error would be a distance of around 30cm.
Now, a team from UNSW – in partnership with NASA and aerospace company Northrop Grumman Corporation – have determined that so-called quantum frequency combs could make network synchronisation using future optical clocks times orders of magnitude more accurate than the current standard.
Professor Robert Malaney, from UNSW's School of Electrical Engineering and Telecommunications, led a team including Ronakraj Gosalia analysing and interpreting a wide range of studies as part of a perspective paper published in APL Photonics.
And they say that frequency combs – a special type of laser beam where light pulses are emitted in the form of extremely short-duration pulses – have the potential to profoundly change the way network synchronisation and GPS might be designed in the future.
"The bottleneck for network synchronisation and GPS being even more accurate is the wavelength of the signals you send out and receive, and that's what we are analysing with this paper, to present the potential advancements possible with quantum frequency combs.
"We've calculated the optical clocks in satellites could improve by orders of magnitude if quantum effects are included , which obviously would make an enormous difference in terms of synchronisation.
"You may ask, 'But who cares?' Well, it turns out you can potentially then test some fundamental physics, or try to detect the presence of dark matter, or even evaluate some different alternatives for what the space-time structure may be."
Squeezing and entanglement
The UNSW researchers specifically analysed the potential to exploit quantum properties in the frequency combs of the signals as they are being sent across a network of satellites in space, particularly related to squeezing and entanglement.
Squeezing is reducing the uncertainty of one property below its usual limit, at the expense of increasing the uncertainty in a complementary property. Entanglement occurs when particles become linked such as the state of one instantly determines the state of another, no matter how far apart they are, enabling unique correlations that defy classical physics.
"If we can exploit the quantum properties in the frequency combs, we can use those exotic attributes such as squeezing and entanglement to achieve an advantage in terms of the signals and therefore improve the performance of GPS systems," says PhD candidate Mr Gosalia.
"The satellites would send out and receive a pulsed laser beam, where each of the pulses lasts just a very short time, around a hundred femtoseconds, or just 0.1 trillionth of a second.
"However, some people are even proposing these signals can be down to the attosecond, which is one quintillionth of a second, and that's why everyone is very excited about this technology."
Prof. Malaney acknowledges that real-world testing in space of the quantum frequency comb technology has not yet been undertaken, with his team's analysis based purely on simulations and theoretical work.
Real-world application would also need to overcome the effect of Doppler shifts during satellite motion, whereby the frequencies of the light beamed out from the laser would change as the objects in space move closer or further apart.
But he believes within around five to ten years the theories could well be turned into reality.
"Doing anything related to space is very hard from an engineering perspective, and also very expensive, so it isn't easy to test these things in the real world," he says.
"But our collaborators at NASA have been involved in experimental projects utilising these types of technologies, albeit not yet incorporating the quantum effects that we describe in our paper.
"What we are ultimately talking about is potentially having the opportunity to detect ripples in space-time at one satellite and then detecting that ripple ever so slightly later at another, which would offer new ways to study the very fabric of the universe."
Key Facts:
Research by engineers at UNSW Sydney proposes the next generation of optical clocks within satellites may be precise enough to detect ripples in space-time.
