‘We need to think out of the box’: physicist Maria Spiropulu on how to build the quantum internet

Computers and the internet have revolutionised our lives, having both a profoundly positive but also, oftentimes, negative impact on society. Yet, it's impossible to imagine life today without the World Wide Web.

And nearly 30 years after its creation, as the limits of Moore's Law – which estimates that chip capacity doubles every two years – gets closer, companies, governments and experts are beginning to consider the next technological leap – the quantum internet.

"When we talk about the quantum internet today, it is a very loaded term," says experimental particle physicist Maria Spiropulu, who is the Shang-Yi Ch'en Professor of Physics at the California Institute of Technology. "As a theoretical concept it is very beautiful; however, in practice, we don't yet have all the components needed to build it."

Spiropulu has previously worked for 10 years on the Tevatron's collider experiments and 15 years at Cern, The European Organization for Nuclear Research, on the Large Hadron Collider (LHC).

Now, the award-wining physicist, alongside her day job working on high-energy physics and the LHC, is leading a collaborative effort to develop all the technologies needed for the future quantum internet.

In 2017, she began building the Alliance for Quantum Technologies (AQT), a novel consortium of academic and research institutions, and directing INQNET – INtelligent Quantum NEtworks & Technologies programme, which has hubs at both Caltech and the AT&T Palo Alto Foundry. The programme is seed-funded by AT&T and in September was awarded government money through the US Department of Energy's $218m investment in quantum technologies.

Spiropulu says she wants AQT to be the "Cern of quantum technologies" with INQNET being a set of projects and experiments that will facilitate the quantum internet.

"This is not a small project; we need to build everything that is in the normal internet: quantum switches, routers, package switching – basically a parallel infrastructure that can sustain, over long periods of time and distance, what I call the beam of quantum entanglement," she says.

Quantum entanglement is a quantum-mechanical phenomenon in which the quantum states of two or more objects, including information, are intimately correlated and connected even though the individual objects may be spatially separated.

Distributing information via quantum entanglement is considered the Holy Grail because it is inherently secure. If someone tries to intercept the information, it is instantly lost or broken.

However, while distribution of quantum entanglement is happening in small-scale lab experiments, it has not been scaled because coherent distribution is notoriously difficult to achieve at long distances. As is creating high production and detection rates of quantum entanglement.

Last year, Chinese researchers conducted a point-to-point demonstration of distributing quantum keys (quantum information) using a satellite trusted relay with optical ground links, for a 75-minute quantum-encrypted video conference call between Asia and Europe, at a distance of 7,600km. They also demonstrated the distribution of two entangled photons from a satellite to two ground stations 1,203km apart and observed the survival of entanglement, which is now considered the baseline to beat, says Spiropulu.

Due to their highly sensitive state, to distribute quantum entanglement it is necessary to either store the signal, rebroadcast it, or amplify it with precision quantum repeaters and quantum memories.

At FQNET, the Fermilab Quantum NETwork hosted at Fermilab, a National Accelerator Laboratory, with contributions from Caltech and the Jet Propulsion Laboratory (JPL), Spiropulu and her team have built a local three-node teleportation test bed to transmit entangled quantum information.

A node is a quantum location that can generate, receive or process quantum information. "It's not exactly a mini quantum computer but a mini quantum information handler or processor," says Spiropulu.

In 2019, the researchers aim to build another three nodes that are kilometres apart, eventually expanding to distances of tens of hundreds of kilometres, with intermediate stations and nodes between that host complex quantum devices such as repeaters and memories.

"What we want is ground to ground, ground to air and air to ground systems, and this requires integration and lots of research and development and, collaboratively, we hope to have some demonstrations in all these areas within the next two to five years," she says.

However, right now, for the most part, all their work is akin to a physics experiment, she says.

'We are developing technologies that could change the fabric of human society – from a physics point of view we are trying to know how we can use these applications'

The quantum internet was first envisioned in a paper written by HJ Kimble in 2008. Several decades on, considering the spooky effects of quantum entanglement, it is incredibly hard – mind-bending even – to try and understand what the quantum internet might mean or do in practice when – or if – it is fully realised.

In theory, the main benefits of the quantum internet are for cryptographic functions – which is driving most of the investment and interest – and to build sensor webs for distributed computing. Due to the increased computing capacity of qubits, this could achieve significant speed-ups for many important tasks.

However, Spiropulu says the quantum internet is likely to have applications that aren't possible to imagine yet.

"The way we describe potential functions now is based on the future of quantum mechanics we know about, namely that there is superposition of states, which in itself is a huge difference between quantum and classical, and entanglement," she says. "However, quantum powers open up spaces for technology and applications that I don't think we know yet how to describe, and we need to think out of the box."

Theoretically, quantum entanglement is a deep physics phenomenon from here to the edge of the universe. And quantum means that instead of describing the universe in terms of particles and forces, it's possible to go a layer deeper and describe it as a quantum information universe.

"The strong correlation of quantum information may have something to do with the fabric of the universe, with space-time, and this is where there is a very deep connection with what I am doing with the programmes in the network; it is not only setting up the technology for the quantum internet, but setting up the experimental infrastructure to say, based on the study of this correlation, if we understand whether space-time is generated, indeed, by quantum entanglement, for example. This would be extremely profound," she explains.

"This quantum revolution is attracting very fundamental, theoretical and experimental thinking about how we consider everything and what might change, and, at the same time, we are developing technologies that could change the fabric of human society. From a physics point of view we are trying to know how we can use these applications and what does it mean when I transfer it to technology."

How might people connect with this otherworldly phenomenon that is the quantum internet in the future?

Spiropulu and her colleagues envision users accessing the quantum internet via classical architecture. "If you are sitting on a laptop, you might interface with a quantum communication centre: you will send information and then the centre will translate it into quantum information and distribute it in the system," she explains.

At Oak Ridge National Laboratory in the US researchers are trying to build software architecture to interface from classical machines onto quantum computing devices. Akin to a compiler, they will take the problem that needs solving or the information that needs sending and translate it into quantum. These are currently operating as small test beds on a few qubit machines working with quantum annealers, such as D-Wave Systems machines.

Spiropulu says she would like the quantum internet to ride on classical infrastructure, so that both have a handshake – "a classical node with a quantum node, for example", she says.

If there is a crossover between classical and quantum devices, will information still be secure at either end or just while being transmitted?

"That is a very interesting question and based on the laws of physics – yes – it will be unbreakable, but if someone interferes all the information will be lost because we do not clone it, we entangle it.

"And this is why we need, on the parallel track, authentication and security protocols, associated with the quantum internet so there are smooth operations and we will know when and where from someone interfered," she explains.

Interestingly, once intercepted, the quantum entangled information is not completely lost to the sender, because they can create an 'entangled copy'. The receiver and the hacker will receive noise, but the sender will have a 'physics acrobatic' to entangle their information instead of copying it. This is, essentially, what Spiropulu calls a "quantum workaround to copying" as copying does not exist in the quantum world.

This issue of security is one that both holds the most promise but equally terrifies, because, in theory, quantum computers and networking can render current cyber security ineffective.

However, to say a quantum computer can break all current passwords is "partially inaccurate", says Spiropulu.

"Yes, you can crack the passwords, but it's a blanket statement to say with quantum everyone will be vulnerable, and we can do nothing about it. That is inaccurate. There is much ongoing work in cryptography to deal with this and there are beautiful mathematical ways to have security, even after the quantum internet, to secure both," she reassures.

Yet, it is security and the idea of quantum enabling technological dominance that is primarily driving a much talked about global race to reach quantum supremacy first, whether it be in security, defence or commercial applications.

Countries and companies are rushing to make investment in quantum development. The US Department of Energy awarded $218m in funding for 85 quantum research groups in September. The Chinese are building a $10bn research centre for quantum applications to open in 2020. And the UK, also a leader in the field, has committed £270m of investment. Commercial companies like Volkswagen, Airbus, AT&T, Lockheed and Northrup Grumman are all investing in quantum.

"This type of competition for advanced technology has always been there, people always want to be first. But is the threat [of quantum supremacy] exaggerated? I think it is," says Spiropulu, "but many, perhaps mostly cryptography experts, think it is not!

"I don't want to be nonchalant and say it's all going to be hunky-dory; it will be significant for the ones that have it first and the best but will the rest of the world be under peril then? I don't think so."

If the classical internet has had a profound effect on society in this and the end of the last century, what impact might the quantum one have?

"You mean, what are the societal consequences? I don't know if people are thinking about that. But the way we have formulated it in the US is 'science first' . We have to understand what it is we are doing," Spiropulu says.

"But no one is sure how this will work in the end, we have to be frank about that. We can't promise this, but we will know in five to ten years. It is not a matter of a half a century any more."