Reserchers have solved a major stumbling block in the development of portable atomic clocks, by working out how to reliably switch 'on' their counting device and keep them running.
From: University of Sussex
August 12, 2022 -- Precision
timing, measured with ultraprecise atomic clocks, is essential for systems such
as global navigation, satellite mapping, establishing the composition of
exoplanets and the next generations of telecommunication. But atomic clocks are
currently massive devices -- weighing hundreds of kilograms -- which need to be
housed within precise, difficult-to-maintain conditions. That's why scientists
around the world are racing to build portable versions that will work in
real-world settings, and could replace existing satellite navigation systems,
such as GPS and Galileo.
Now, research
undertaken at the University of Sussex, and continued at Loughborough
University, has solved a major stumbling block in the development of these
portable atomic clocks, by working out how to reliably switch 'on' their
counting device -- and keep them running.
Microcombs are a
fundamental part of future optical atomic clocks -- they allow one to count the
oscillation of the 'atomic pendulum' in the clock, converting the atomic
oscillation at hundreds of trillions of times per second to a billion times a
second -- a gigahertz frequency, that modern electronic systems can easily
measure.
Based on electronic
compatible optical microchips, microcombs are the best candidates to
miniaturise the next generation of ultraprecise timekeeping. They are
cutting-edge laser technology sources, made up of ultraprecise laser lines, equally
spaced in the spectrum, which resemble a comb.
This peculiar spectrum
opens an array of applications blending ultraprecise time keeping and
spectroscopy which could lead to the discovery of exoplanets, or
ultra-sensitive medical instruments based simply on breath scans.
"None of this will
ever be possible if the microcombs are so sensitive that they cannot maintain
their state even if someone just enters in the lab," said Professor
Alessia Pasquazi, who began this ERC and EPSRC funded project at the University
of Sussex before moving to Loughborough University with her team, last month.
In a new paper
published in the journal Nature, research undertaken at the
University of Sussex by Prof Pasquazi and her team has identified a way to
allow the system to start by itself and remain in a stable state -- essentially
being self-recovering.
"We have basically
an 'eternal engine' -- like Snowpiercer if you watch it -- which always comes
back to the same state if something happens to disrupt it," said Prof Pasquazi.
"A well-behaved
microcomb uses a special type of wave, called a cavity-soliton, which is not
simple to get. Like the engine of a petrol car, a microcomb prefers to stay in
an 'off-state'. When you start your car, you need a starter motor that makes
the engine rotate properly.
"At the moment,
microcombs do not have a good 'starter-motor'. It is like having your car with
the battery constantly broken, and you need someone to push it downhill every
time you need to use it, hoping that it will start. If you imagine that usually
a cavity-soliton disappears in a microcomb laser when someone simply talks in
the room, you see that we have a problem here."
Professor Marco
Peccianti, who worked on the research at the University of Sussex and directs
the newly funded Emergent Photonic Research Centre at Loughborough University,
added: "In 2019 we had already demonstrated that we could use a different
type of wave to get microcombs.
"We called them
laser cavity solitons because we embedded directly the microchip in a standard
laser and we obtained a great boost in the efficiency."
"We have shown now
that our soliton can be naturally turned into the only state of the system, and
we call this process 'self-emergence'."
Dr Juan Sebastian
Totero Gongora, EPSRC research fellow in quantum technologies in Loughborough
explained: "It works like a simple thermodynamical system, which is ruled
by 'global variables,' like temperature and pressure."
"At atmospheric
pressure, you are always sure to find water as ice at -5 degrees or as vapour
above 100 degrees, whatever has happened to the water molecules before."
Dr Maxwell Rowley, who
obtained his PhD at the University of Sussex developing this system with Prof
Pasquazi, and who now works with CPI TMD Technologies, a division of
Communications & Power Industries (CPI), where work continues to
commercialize the microcomb, added: "Similarly, when we set the electrical
current driving the laser to the appropriate value, here we are guaranteed that
the microcomb will operate in our desired soliton state.
"It is a
set-and-forget system -- an 'eternal engine' that always recover the correct
state."
The paper,
"Self-emergence of robust solitons in a micro-cavity," has been
published this week in collaboration with colleagues at the University of
Sussex, City University of Hong Kong, the Xi'an Institute of Optics and
Precision Mechanics, in China, Swinburne University of Technology in Australia,
the INRS-EMT in Canada and the University of Strathclyde.
The pursuit of this
technology is a key goal of the newly funded Emergent Photonics Laboratory
Research Centre, which will focus on cutting edge optical technologies at
Loughborough.
The microcomb is a core
component for creating a portable and ultra-accurate time reference, which is
critically needed for the current and next generation of telecommunication (5
and 6G+ and fibre communication), network synchronization (e.g. electrical network)
and it will reduce our dependence on the GPS.
The self-emergent
microcombs will be directly used in optical-fibre based calcium ion references,
being pursued under Innovate UK support and the leadership of Professor
Matthias Keller at the University of Sussex with CPI TMD technologies, and in a
broader collaboration on Quantum Technologies including co-author Professor
Roberto Morandotti at the Canadian Institut national de la recherche
scientifique (INRS).
Prof Pasquazi said:
"Microcombs are expected to revolutionize the telecommunication networks,
which use many different colours to transfer as much information as possible.
"While networks
currently use separate lasers for every colour, microcombs will provide a
compact and power-efficient alternative, with the possibility of also
transferring ultra-precise timekeeping.
"The pursuit of
next generation telecom technologies is one of the goals of our collaboration
with Swinburne University and co-author Professor David Moss.
"We are
collaborating with their astronomy department, hopefully one day these 'optical
rulers' will enable their search for exoplanets."
https://www.sciencedaily.com/releases/2022/08/220810123646.htm
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