Cogs in machine

Developing optical lattice clocks to test gravity theory

A new class of optical clocks are set to revolutionize timekeeping by offering a level of precision that significantly exceeds standard atomic clocks, say leading experts at the UK Quantum Technology Hub Sensors and Timing, which is led by the University of Birmingham.

These new so-called optical lattice clocks can be used to test the limits of gravity to a high level of precision and also enable further study of the Earth’s geodesy, comment Dr Yeshpal Singh and Professor Kai Bongs in an article published in Nature.

In the article, Dr Singh and Professor Bongs discuss how Albert Einstein’s general theory of relativity, which explains gravity as a “consequence of the curvature of space-time that is deformed by mass”, has been held as the “best theory of gravity we currently have” since it was published in 1915.

Dr Singh, of the University of Birmingham’s School of Physics and Astronomy and academic lead for quantum clocks at the UK Quantum Technology Hub Sensors and Timing, said: “It has not yet been possible to unify the theory of relativity with quantum field theory, meaning that there is not yet a complete theory of nature”.

“For instance, dark energy and dark matter - subjects used to describe observations of an accelerating expansion of the Universe contradicting predictions from Einstein’s theory - remain unexplained.

“So how do we develop more precise tests of relativity? At the Quantum Technology Hub, my team and I are working closely with industry to develop portable, robust quantum clocks, which aim to give ultra-precise, ultra-accurate time to more than one billionth of a second.

“These clocks, along with the rest of the sensor technology in development at the Hub, are specifically being created to be robust and transportable, capable of performing in deployable conditions. Once developed, quantum clocks can be implemented in a number of sectors, such as in finance, navigation, and even space.”

Optical Lattice clocks were first proposed by Professor Hidetoshi Katori at the University of Tokyo in the early 2000s.  They store atoms tight enough to remove unwanted Doppler frequency shifts, hence allowing long interrogation times, and not interfering with the frequency of the clock transition.

The clocks will also present an opportunity to test general relativity and geodesy. This will be done by placing clocks at differing heights to determine the geoid height via a frequency comparison between the clocks, providing competition with the best geophysical approaches.

One example is the recent breakthrough by Professor Katori and his team, when two portable, robust optical clocks were created, with precision surpassing many of the best clocks available in the world. A six-month long measurement campaign was undertaken to achieve results comparable with the “best space tests of general relativity, and open[ing] up fascinating new applications on Earth using such clocks”.

Professor Katori and his team’s impressive achievement, and the potential of optical lattice clock projects all over the world, paves the way for exciting industrial collaboration with researchers at the Quantum Technology Hub to revolutionise oil and mineral exploration, ultra-precise satellite navigation systems and performing time synchronization for quantum communication networks.

This article was originally posted on the UK Quantum Technology Hub Sensors and Timing website

Global communications networks
Quantum secured communications across continents

Could quantum key distribution (QKD) in space enable quantum secured communications around the world, across continents and oceans?

Data transfer and secure communications are absolutely essential today - for individuals, institutions, businesses, governments and nations. Society relies upon cybersecurity to ensure that data is stored and transferred securely. Quantum secure communications, and in particular QKD, a mature quantum technology for the distribution of encryption keys, have the potential to one day underpin the world’s digital communications. At present, data transfer by QKD usually takes place by optical fibre, but this is not possible in all situations due to distance limitations – particularly under the sea! To deliver quantum secured communication between continents, techniques need to be developed to transfer quantum encryption keys between ground stations and satellites, and between satellites.

Researchers at the Quantum Communications Hub are working on developing satellite-to-ground quantum communications, which will one day enable data to be transferred around the world, over coming any distance limitations and ensuring data security, no matter how far the data needs to travel. The Hub will soon be launching a satellite equipped with Hub developed quantum technologies into space to enable testing of the technologies which will ultimately bring the technologies closer to implementation within communications infrastructure around the world.

Dr Amrute Gadge, University of Sussex
Researcher creates fifth state of matter in living room

A researcher from the UK Quantum Technology Hub Sensors and Timing has created the fifth state of matter working from home using quantum technology

Dr Amruta Gadge, Research Fellow in Quantum Physics and Technologies at the University of Sussex, successfully created a Bose-Einstein Condensate (BEC) at Sussex’s facilities despite working remotely from her living room two miles away.

It is believed to be the first time that BEC has been created remotely in a lab that did not have one before.

The research team believe the achievement could provide a blueprint for operating quantum technology in inaccessible environments such as space.

A BEC consists of a cloud of hundreds of thousands of rubidium atoms cooled down to nanokelvin temperatures, which is more than a billion times colder than freezing.  At this point the atoms take on a different property and behave all together as a single quantum object. This quantum object has special properties which can sense very low magnetic fields.

Dr Gadge was able to make complex calculations, optimise, and run the sequence from her home by accessing the lab computers remotely. Just prior to lockdown, researchers set-up a 2D magnetic optical trap and have returned only a couple of times to carry out essential maintenance.

She said: “The research team has been observing lockdown and working from home and so we have not been able to access our labs for weeks.  But we were determined to keep our research going so we have been exploring new ways of running our experiments remotely. It has been a massive team effort.”

Peter Krüger, Professor of Experimental Physics at the University of Sussex, said: “We believe this may be the first time that someone has established a BEC remotely in a lab that didn’t have one before. We are all extremely excited that we can continue to conduct our experiments remotely during lockdown, and any possible future lockdowns.

"But there are also wider implications beyond our team. Enhancing the capabilities of remote lab control is relevant for research applications aimed at operating quantum technology in inaccessible environments such as space, underground, in a submarine, or in extreme climates.” 

The Quantum Systems and Devices Group have been working on having a second lab with a BEC running consistently over the past nine months as part of a wider project developing a new type of magnetic microscopy and other quantum sensors. 

The research team uses atomic gases as magnetic sensors close to various objects including novel advanced materials, ion channels in cells, and the human brain. Trapped cold quantum gases are controlled to create extremely accurate and precise sensors that are ideal for detecting and studying new materials, geometries and devices.The research team are developing their sensors to be applied in many areas including electrical vehicle batteries, touch screens, solar cells and medical advancements such as brain imaging.

Satellite in space
Developing a quantum inertial navigation system

Understanding the 'invisible utility'

If our Global Navigation Satellite System (GNSS) fails, it ranges anywhere between inconvenient to catastrophic. It is easy to underestimate how reliant we have become on navigation systems in our daily lives, and we often do not realise how dependent our services and national infrastructure are on GNSS, so much so that it has now become known as the ‘invisible utility’.

Railways, telecommunications and emergency services are just a few areas now reliant on GNSS for their operations. And yet, when GNSS was first developed by the US Department of Defence, its vulnerabilities were well-known enough to ensure they did not critically depend on it. Global Positioning System (GPS) was created in the 1970s, and now consists of up to 24 satellites circling the Earth in a precise orbit. It was originally intended to be used solely for military applications, but this remit was broadened to the wider public in the 1980s. Over time, GPS was adopted by service providers, companies and consumers, who became both increasingly dependent and oblivious to the weaknesses of the system over time. It has been estimated that by 2020, 80% of the world’s adult population will have access to a smart phone and therefore access to GNSS.

So what happens when our GNSS system fails? According to the Satellite-derived time and position: Blackett review (2018), “all GNSS receivers are vulnerable to natural and man-made interference”. Jamming, spoofing and even space weather can result in inaccuracies or loss of signal, and given the level of dependence on the navigation system across main services, this can severely weaken a country’s infrastructure.

At the UK Quantum Technology Hub Sensors and Timing, led by the University of Birmingham, one of our key areas of work is to create a quantum inertial navigation system. This is a standalone navigation system which does not rely on satellite signals and is therefore invulnerable to the same external risks experienced by GNSS.

Researchers at Imperial College London, one of the Quantum Technology Hub’s partners (alongside Southampton, Sussex, NPL, Strathclyde, Glasgow, Nottingham and the British Geological Survey) are leading the research and development of the quantum inertial navigation system.

And how does it work? Classical microelectromechanical systems (MEMs) can already provide high precision sensors for inertial navigation systems. However, MEMs devices are prone to drift, which limits how long they can provide accurate location information. Quantum inertial sensors overcome the problem of drift by measuring properties of atoms supercooled using lasers. At extremely low temperatures, the atoms ‘quantum’ nature dominates and they behave like waves, which can be used to encode inertial information. By hybridising MEMs and quantum inertial sensors we get the best of both – drifts are minimised, and measurement speed is maintained.

Dr Joseph Cotter, Research Fellow at the Centre for Cold Matter at Imperial College London, said: "The quantum navigation systems being developed by the UK Quantum Technology Hub Sensors and Timing offer the exciting prospect of new technologies that provide better and more reliable location information, without the need for a satellite link.”

The quantum inertial navigation system promises huge benefits to the UK. It will free large sections of our services and many professions from reliance on GNSS and the fear of it failing. As with much of the sensor research at the UK Quantum Technology Hub Sensors and Timing, the system will ensure that the country’s critical infrastructure is more secure and resilient.

Quantum Internet
Quantum Internet

What is a Quantum Internet and what does it mean for regular internet users?

What is a quantum internet?

In the simplest of terms, a quantum internet would be one that uses quantum signals instead of radio waves to send information.  The internet we know and love uses radio waves to connect multiple computers through a 'world-wide-web' in which electronic signals are sent back and forth. In a quantum internet, signals would be sent through a quantum network using quantum particles - like photons (particles of light).

What does a quantum internet mean for regular internet users?

As far as typical internet surfing goes, probably not much. It’s highly unlikely that you’ll be using the quantum internet to update Twitter for example. The quantum internet would excel, however, at sending information securely. Through what’s known as quantum encryption or quantum cryptography, people would be able to send “unhackable” data over a quantum network. This is because quantum cryptography sends an encrypted message and its keys separately. Quantum physics means that tampering with the message causes it to change, which something both the sender and receiver can detect. Work on how to send these "un-hackable" signals is being conducted by NQIT

Are we close?

Scientists and engineers have recently made huge strides in building this quantum communication network. China launched the world’s first quantum communication satellite last year, and more recently they conducted the first unhackable video call with it between Beijing and Vienna.

Anything else it can be used for?

A quantum internet could also speed up access to a working quantum computer by putting quantum computing in the cloud. Instead of trying to get your hands on a physical quantum computer, (which are fragile and hard to make) you could access one through the cloud or interface separate quantum computers around the world to boost computing power.

NPL Optical atomic clocks
Optical atomic clocks

The reference against which other clocks are evaluated

NPL's leading-edge optical atomic clocks have stabilities and uncertainties that surpass the performance of present-day primary frequency standards. As national standards, they provide the reference against which other clocks are evaluated. Building on the expertise gained in developing these laboratory systems, NPL are now engineering portable and compact versions, which will bring improved frequency and timing precision to navigation, sensing, communications and space-based applications.

Optical clocks generate a frequency output in the form of ultra-stable laser light. These frequencies are at several hundred terahertz, but can be divided down into microwave or radio frequencies, without loss of precision, using optical frequency combs. Optical clocks are at the leading edge of performance for both uncertainty and stability in frequency standards.

NPL is working on laboratory-based systems that will be used for the highest accuracy realisation of SI units, contributing to international time scales and ensuring consistency of time and frequency measurements around the globe. They are also used to test fundamental physical theories at unprecedented levels of precision. These compact and portable optical clocks will find much wider use; for example they could provide improved autonomy of on-board clocks in future satellite navigation systems. They could also be used as sensors of gravity potential for oil and mineral surveying or for monitoring volcanic activity, ocean currents and rising sea levels.

Key facts and data

  • NPL optical clock types: Sr, Sr+ and Yb+
  • Frequency uncertainty: approaching 1 part in 1018
  • Frequency stability: approaching 1 part in 1016 at 1 s averaging   time
  • Future gravity potential sensing capability corresponding to 1 cm height change at the Earth’s surface