Quantum technologies at Imperial
by Ian Mundell
Quantum technologies take advantage of the quantum properties of matter – the properties that exist at the sub-atomic level – to carry out tasks that would otherwise be impossible with conventional approaches. If that sounds futuristic, then remember that some quantum technologies have been with us for some time.
“If you work in semiconductors or you work in lasers, then you are automatically using quantum mechanics,” says Professor Neil Alford, Associate Provost for Academic Planning at Imperial, who has a strategic overview of work in quantum technologies at the College. “But what we are really looking for is how you make use of the stranger properties of quantum mechanics to re-invent technologies such as cryptography or computing.”
Quantum computing is the area that attracts the most attention. Conventional computers are based on ones and zeros, and the idea that a switch can either be on or off. The more 'switches' you can pack into the tiny space of a microprocessor, the better your computer will perform.
But at the sub-atomic level there are particles that exist in three states, as if a switch could be on, off or both at the same time. Computing based on these three states promises to be significantly faster, performing tasks out of reach of conventional computers. “That makes it very interesting, but it also makes it really, really complicated,” Professor Alford says.
First there is the challenge of physically creating and maintaining qubits, the quantum equivalent of the information bit in conventional computing. This might be through the polarisation of photons, the spin state of electrons or a number of other approaches. And however it is stored physically, quantum information is very susceptible to disturbance and background noise, which means developing sophisticated new methods for error correction.
“There are some quite difficult problems to overcome, so I think that quantum computing is quite a long way down the line,” Professor Alford says, “but quantum sensors are already looking quite interesting.”
One of the people leading the way at Imperial when it comes to quantum sensors is Professor Tom Pike, from the Department of Electronic and Electrical Engineering. He and his colleagues were given the task of building a miniaturised low mass, high performance vibration sensor for NASA's InSight mission to Mars. The aim is to detect Martian earthquakes, in order to build up a picture of the planet's structure.
The final microseismometer is capable of measuring a quarter of a nano-g - less than one billionth of Earth's gravity"
“That is challenging because we don't know how many 'marsquakes' we are going to see,” he says. “We are going into an extreme environment and then trying to make a sensitive measurement of something that hasn't been observed up to this point.”
The basis of their micro-machined silicon sensor is quite conventional: a mass on a spring, which responds to external vibrations, and then a displacement transducer to pick up the small movements of the mass. It’s in this transducer that the surface quantum states of the electrons used in the pick up come into play.
“We have to control the energy spread of these quantum states to produce a really good sensor, and here we get an unexpected bonus from miniaturisation,” Professor Pike explains. “By reducing the size of the pickups, we restrict the number of different surface quantum states. This in turn allows us to see smaller marsquakes above the noise of the sensor itself.”
The final microseismometer, which includes three sensors and their electronics, weighs a few hundred grammes and is capable of measuring a quarter of a nano-g (less than one billionth of Earth's gravity), orders of magnitude better than other miniaturised silicon devices. The sensors are currently installed on the spacecraft which is being readied for the mission's expected launch in May 2018.
While measuring earthquakes on Mars is a very specific task, there is considerable scope for adapting such a sensitive sensor for other applications. “It opens up an area which is of great interest in quantum sensing, which is to use gravity as a new imaging mode,” says Professor Pike.
With a sensitive, miniaturised, robust and portable gravity sensor you could look for mineral deposits, or underground voids caused by sinkholes or old mine workings, or even the location of pipes so that they are not cut during building or road works.
Towards the end of 2017 the Quantum Measurement Lab was established at Imperial to advance the development of powerful new quantum sensors. Its speciality is quantum optomechanics, which uses laser light to control the motion of very small mechanical oscillators.
“The 'killer app' is the ability to convert quantum information into light, so that it can be transmitted in low-loss telecommunications," Dr Vanner says
“Think of a micro-scale diving board. Simply by bouncing light off the structure we can control the way it moves, or sense its position very precisely,” says Dr Michael Vanner, the lab's principal investigator.
The ability to pick up movements as small as a femtometre means that the influence of weak forces on the oscillator can be detected. Such forces might be a small electric field, a change in a gravitational field, or the presence of a biological molecule. This opens the way for sensors for use in mineral prospecting, navigation, and medical applications.
The oscillators can also work as transducers, converting quantum information from one form to another, for instance from microwave signals into light, or vice versa. “The 'killer app' for quantum transducers is the ability to convert quantum information in a superconducting microwave quantum computer into light, so that it can be transmitted in low-loss telecommunications optical fibres over large distances,” Dr Vanner says.
He thinks quantum sensors and transducers will be of practical use very soon. “We now have laboratory prototypes that demonstrate the key physics, and in many cases, it’s now a matter of improving the engineering in these systems to make them robust enough to take out of the lab.”
Another quantum technology where applications are within reach is cryptography. Systems are already on the market that use quantum methods to transmit encryption keys between two parties, usually encoded in photons. The advantage here is that the
“If you look at quantum data you automatically change it, because you interact with it, so you can detect if anyone is looking at your data,” explains Dr Mario Berta, a lecturer in the Department of Computing.encoding is physically impossible to break since it is always possible to tell if part of the key has been intercepted and security compromised.
While they work, these systems are both expensive and limited in what they can do. “It's not like a fully fledged quantum internet yet, where you could communicate safely with everyone,” Dr Berta says, “but it's currently more a point-to- point system. If you want to talk to someone, you both need to buy a device and it would only work over that connection.”
The challenge researchers are working on now is to refine these methods or develop others so that quantum cryptography becomes cheap enough and flexible enough for general use.
Quantum cryptography goes hand in hand with the promise, or threat, that quantum computers will be able to break most conventional kinds of encryption. “It's not just that a quantum computer could hack the conversations that we are having nowadays, for example making bank transactions, but it also works retrospectively, so everything that is encrypted now could be hacked later.”
This means business should already be planning its response. “We don't have a fully programmable quantum computer now, but we might have it in five or ten years, and if you want to change all your communications protocols you need a lot of time to prepare.”
Working with light
We want to make a device in which a fluctuation in output comes from quantum processes, so they can't be predicted beforehand" says Dr Kolthammer. "That's a completely new form of randomness generator.”
With light playing such an important role in quantum technologies, it's natural that researchers interested in its fundamental properties, such as Dr Steve Kolthammer in the Physics Department, have also become involved. He has been working on ways that the quantum behaviour of light, usually considered noise in optical devices, can be controlled and exploited.
One line of work involves trying to harness the fundamentally random nature of light's quantum behaviour. “There are lots of protocols, for example in cryptography, in which you want some fundamental randomness that you're sure no-one else can know about and predict,” Kolthammer explains.
“What we want to do is make a device in which we can certify that a certain amount of the fluctuation, or noise, in output comes from these fundamentally quantum processes, so they really can't be predicted beforehand. And that's a completely new form of randomness generator.”
This work already involves a number of enterprising small firms. More broadly, Dr Kolthammer is working with companies interested in making components for future quantum devices. “Although we might not have the architectures of the final devices nailed down, we have some sense that we will need boxes that efficiently generate single photons and detectors that are sensitive enough to count photons,” he says.
A line of research that will take longer to pay off involves boson sampling, an experiment that sets out to demonstrate the superiority of quantum information processing. The challenge is to determine what happens to light passing through the multiple channels of an interferometer. Given the rules for how light behaves, a conventional computer can do this for a few photons, but the task gets harder, and then impossible, as their number increases.
A quantum approach involves finding ways to send photons with precise quantum states into the interferometer and detecting them when they come out. The rules behind the outcome are the same, but the device's capacity for processing the information is far greater.
This experiment sets out to prove a point, rather than solve a practical problem, although applications may emerge in time. “The first step is to find the quantum problems that we can attack very well in the lab, and then identify these correspondences that point to useful applications.”
If quantum stays stand-alone, it will be useful as far as information technology goes." says Professor Yeatman. "But integrated into the fabric, it can change things in a big way."
Quantum computing is likely to have its earliest impact in tandem with traditional computers. “A completely believable paradigm is that we will have a massive computing centre, where amongst the conventional machines there are a few quantum machines doing specific kinds of tasks very efficiently,” says Professor Eric Yeatman, head of the Department of Electrical and Electronic Engineering.
Physically connecting the two kinds of system will be one challenge. “But the more interesting problem is how you efficiently and effectively divide up tasks and distribute them among a number of machines, some of which are quantum and some of which are not,” he goes on. “How do you represent information, and at which points in the system do you switch and translate between forms that are suitable for each domain.”
Imperial is increasingly interested in this area. “Up until now people have concentrated mainly on the physical hardware of quantum devices, but now we also have to start doing things like programming software and control systems for quantum-based machinery.”
Success in this area will make all the difference. “If quantum just stays as stand-alone, niche applications, then that will be useful but it won't be transformational as far as information technology goes. But if it can be integrated into the fabric, it has the potential to change things in a big way.”
The potential threat from these technologies is one reason why interest in quantum has grown over the past two or three years. “The intelligence agencies have started investing more money, as have many of the big companies such as Google, Microsoft and IBM,” Dr Berta says. “There has also been an explosion in start-up companies in this area.”
These technologies are disciplines on their own, and we would really like to emphasise the interdisciplinarity," Professor Alford explains
Similarly there has been an injection of public cash, both from the UK government and the European Union. “So with much more money going into this area, many more things are going to happen.”
Imperial has also responded strategically to the growth in quantum technologies, creating a platform to showcase all of its activities in this area. Called the Imperial Centre for Quantum Engineering, Science and Technology (QuEST), it divides research activities into six headings: quantum sensors; quantum information; quantum materials; quantum chemistry; quantum optics; and theory, which has been dubbed quantum foundations.
“We've got some really nice work going on currently in all six of those areas, in a number of different departments,” Professor Alford explains. “That's mainly physics, but also in chemistry, materials, and civil engineering. And we currently have about £25 million in grant income in this area.”
Thinking of this activity as part of a single endeavour should be helpful. “In a way, these technologies act as little disciplines on their own, and what we would really like to do is to cut across that and emphasise the interdisciplinarity.”
Masers are amazingly sensitive sensors. They could be used where sensitive detection of microwaves is essential" Professor Alford says
Professor Alford's own work with masers is a case in point, demonstrating how quantum chemistry and quantum materials can together inform the development new quantum devices.
Masers are the microwave equivalent of lasers. Both technologies date from the 1950s, but whereas masers only worked if they were cryogenically cooled and wrapped in powerful magnetic fields, lasers worked at room temperature and in the Earth's magnetic field. Naturally enough, people preferred to work with lasers and masers languished.
“Until recently, masers were really only used for deep space exploration, because their noise floor was fantastically low. They are amazingly sensitive sensors,” Professor Alford says. But in 2011 he and his colleagues Mark Oxborrow and Jon Breeze built a maser that worked at room temperature in short bursts, and in March 2018 they announced the world's first continuous room temperature solid-state maser built using diamond. “This technology has a way to go, but I can see it being used where sensitive detection of microwaves is essential,” says Professor Alford. Possible applications include medical imaging, deep space communications and airport security.
Photons on demand
Given a known starting point, a record of any acceleration up, down, left, right, forwards, or backwards, plus rotation, will reveal the new location without referring to an external point. The Ministry of Defence sees this as a way of positioning submarines without the global satellite navigation system."
A similar combination of disciplines lies behind a project in the Blackett Laboratory's Centre for Cold Matter to develop a reliable source of identical photons, for use in quantum applications. “We want to be able to press a button and out comes a photon,” explains Professor Ed Hinds, the Centre's director. “Curiously enough, no such source exists at the moment.”
He and his colleagues have found that individual dye molecules embedded in a crystal can be stimulated to produce identical photons on demand. Better still, the photons are produced in a way that feeds them into an optical fibre.
This approach also opens up a solution to a problem arising from light's lack of interaction with its surroundings, an interaction that is necessary to process the information it may be carrying. “These molecules embedded in a crystal also have the capability of allowing two photons to interact with each other, in such a way that you can make a logic gate or processor for quantum information,” says Professor Hinds.
Another project at the Centre uses a different quantum technology, atom interferometry, to provide navigation off the grid. Atom interferometers can measure acceleration and rotation very sensitively and very accurately. Given a known starting point, a record of any acceleration in perpendicular directions - up/down, left/right. forward/back - plus rotation will reveal the new location without referring to an external point.
The Ministry of Defence, which has funded this research, sees this technology as a way of positioning submarines without relying on the global satellite navigation system. “They want to know, after six months, where their submarine is to within 300m, which is very challenging,” says Professor Hinds.
He admits that this will be a very expensive device. “At the moment it is a niche market for users who want something incredibly accurate,” he says. “But if we could make it cheaper and smaller there's a market in remotely operated submersible vehicles, which look for broken cables under the sea and so on.”
Quantum theory, meanwhile, has a contribution to make across the board. “And we have a very strong quantum theory group here at Imperial,” Professor Alford says.
For instance, Professor Myungshik Kim, in the Department of Physics, is interested in making sure that quantum computers and simulators (quantum computers built up to perform one specific task) are really surpassing their classical counterparts.
“Even though we say that quantum computers and quantum simulators can work much better than the classical machines, the word 'better' is not always well-defined, and it is not easy to prove,” he says.
A particular problem is that quantum simulators are optimised for a single task, yet they are often benchmarked against general machines rather than the best that conventional technology has to offer. “Quantum machines are much more difficult to build, so why spend so much time and money on that when a conventional machine could be optimised to do better? So one part of my work is validation of the claim,” he says.
While this may look like knocking the concept of quantum technology, it is exactly this process that companies will have to go through when considering whether or not to adopt quantum technologies, either as products or by investing in start-ups.
“Companies need to keep a keen eye on what is being developed in universities and by young people,” Professor Kim says. “By working together with these people they create a kind of validation centre so that, if there is a technology that can be adapted to their needs, they can do it.”
In addition to his theoretical work, Professor Kim also runs Imperial's Doctoral Training Centre, together with Professor Ben Sauer. Here he sees the fascination that quantum technology (and quantum computing in particular) exerts on physics graduates. But more recently there has been a drive to open this up to other disciplines. “We have been able to attract some very good students, not only physics graduates, but also engineering graduates who are looking for a new type of engineering and technology,” Professor Kim says.
Even if they return to conventional engineering after their time working on quantum, the investment is a good one. “The success story of Microsoft and IBM is because they opened their code. So, people have to talk about quantum. We have to spread the word, and to do that it needs to go beyond physicists and other scientists to involve engineers.”
“One of the things that we are very keen on is getting the engineering into quantum,” agrees Professor Alford. “We've got to be able to place the engineering foundations alongside the hardcore science, and bring those two things together.” This will also help answer the question of what quantum can do for business.
Companies and quantum
“There are some extremely talented young people who are interested in quantum technology," says Professor Hinds. "Companies should make good use of their brains and curiosity."
Thinking about how companies should respond now to the promise of quantum, Professor Alford points to those who have taken a lead, and in particular Chinese internet giant Alibaba, which has invested $11 billion in funding centres doing quantum science. “That is a very aggressive and a proactive approach, but I do think that the bottom line is that you need to invest in the basic research if you expect anything to emerge from this.”
Dialogue is also important. “Like many disruptive technologies, quantum is a solution looking for a problem,” says Professor Hinds. This is where companies could and should get involved. “They can define the problems, and then maybe we can apply our quantum techniques to solving them.”
And in addition to developing in-house expertise in quantum in order to validate new technologies, Professor Kim thinks companies need to look to the next generation. “There are some extremely talented young people who are interested in quantum technology, and companies should make good use of their brains and curiosity. This is a very good time to do that.”
A Quantum Champion
On top of his contribution to the science of quantum optics, Emeritus Professor Sir Peter Knight has played a prominent role in Britain's quantum technology policy. This included helping shape the National Quantum Technologies Programme, which was launched in 2013 with a five-year budget of £270 million. The total public spend from all government partners over the span of the programme is now estimated to be £383 million. “That's the largest single investment the UK government has ever made in a disruptive technology,” Sir Peter told an audience of business leaders at Imperial College in November. The emphasis from the outset has been on applications. “It was meant to create an ecosystem which pushed quantum technologies out of the labs and into things that people need to use.”
Sir Peter sits on the Quantum Technology Strategic Advisory Board, which oversees the programme and is currently working on its second phase. And in 2016 he co-wrote, with the then government chief scientific adviser Sir Mark Walport, the Blackett review of quantum technologies.
Naturally he remains an enthusiastic advocate for the field. “Quantum is the enabler to do things that you couldn't do before, at a price which is affordable,” he said. “It will enable you to see the invisible by building sensors and secure our information.”
But the largest economic benefits will come through the photonics industry, which underpins many quantum methods. “Photonics is one of the secret jewels of the UK economy,” he said. “It generates more to the GDP of the UK than pharmaceuticals, but it's in 1,500 companies across the supply chain, and has a very complex ecosystem.”
Ensuring that Britain captures the benefits of quantum is one of the challenges that lie ahead. To that end, the Chancellor's autumn statement of 2017 committed an additional £20 million to an Industrial Strategy Challenge Fund Pioneer Programme to address the commercialisation of quantum technologies.
Ian Mundell is a journalist who specialises in research and higher education. He divides his time between London and Brussels.
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