FUTURE OF CONNECTIVITY
Quantum communication is a giant leap for humanity
The Chinese have demonstrated a quantum link across 1,200km in space
The Structured Light Laboratory at the University of the Witwatersrand is pushing the limits of fast, secure communication with new research into quantum technologies for communication systems.
Under the leadership of Prof Andrew Forbes, the laboratory has published its third major paper in 2017 on quantum advances, describing the building blocks of a quantum communication system with high dimensional states.
This paper, published in Nature’s Scientific Reports, follows one on demonstrating quantum teleportation (published in Nature Communications) and a means to correct quantum errors in real time (in Nature Physics).
In combination, these advances provide a platform for a new technology for secure and fast data transmission.
"We are currently building a prototype device with the support of the Technology Innovation Agency, which will allow a secure quantum communication link to be established across a long distance between two parties — say two banks or between military bases," says Forbes.
He and his team have been a driving force in developing quantum technologies for SA, with the first quantum correlations ever seen in Africa observed in his laboratory.
Quantum mechanics is a theory that has been in existence for more than a century. It describes the physics of the small scales and energies that are seen when delving deep into matter — such as sub-atomic systems and single particles of light.
The theory has given birth to technologies such as the laser and transistor. It suggests something very strange: the concept of quantum entanglement. When two particles are entangled, they are connected: a measurement on one immediately changes the properties of the other, no matter how far apart they are.
The properties of the particles are described by "states". Much like people, who can be in a "peaceful state" or "agitated state", so quantum states capture the physical properties of the system.
Recent advances in the engineering of quantum states has given hope for a "second quantum revolution", with the promise to realise new technologies such as enhanced medical imaging, efficient light harvesting materials (to be used for clean energy), secure optical communication networks, exponentially faster computers and more precise measurement systems.
National and regional strategies have been developed in the past few years by the UK, EU, Canada, US and China, to name but a few.
It is estimated that by 2020, classical systems (on which computer devices operate) will be replaced by their quantum counterparts, with the lion’s share of investment in these technologies going to quantum cryptography, a fundamentally secure quantum communication system.
No technology will ever exist to help someone hack into this system as the principle behind the encryption is the laws of physicsProf Andrew Forbe
"The major beneficiaries of quantum cryptographic technology will be institutions that require long-term, ultra-high communication and data storage security, such as the banking and defence industries," says Forbes.
Quantum mechanical states cannot be duplicated without destroying the original state. For example, a photon (single particle of light) that is entangled in energy cannot be cloned or duplicated without destruction of the state itself. In other words, that information, in this case energy, is lost.
This property can be exploited to implement a secure quantum communication system. This is based on the entanglement of photons and offers secure communication over an insecure communication channel. This channel would be secure, irrespective of the abilities of anyone who would be trying to hack the system.
"No technology will ever exist to help someone hack into this system as the principle behind the encryption is the laws of physics," says Forbes.
Quantum cryptography differs from classical cryptography at the most fundamental level, as it is physical laws — rather than computational complexity, which is the basis of current cryptographical systems — that provide the security basis of quantum information science.
"Classical cryptography systems are algorithmic procedures that exploit mathematical complexities and computational inefficiencies to distribute encryption keys. The security provided by these classical techniques are, however, bound by advancements in mathematics and computing power," says Forbes, explaining that the development of an efficient inverse function to any such algorithm would expose the encryption key.
Quantum cryptography physically encodes the encryption key within quantum systems, so measurements or manipulation of the physical properties are necessary to extract information from the encryption scheme.
"The properties of a quantum system change when you measure it, so once an illegitimate measurement is taken, it will modify the cryptographic key and alert the legitimate parties involved," says Forbes.
Traditionally, quantum communication experiments have been done with a two-letter alphabet, exploiting the polarisation of light as the quantum state. Polarisation comes in just two flavours, twisted clockwise or anticlockwise. This allows the encoding of information with just two options, which limits how much data can be sent.
"The Chinese recently demonstrated a quantum link across 1,200km in space," says Forbes. "Our novelty is to increase the alphabet by using patterns of light. As there are an infinite number of patterns, the information we can send is also in principle infinitely large."
Forbes’s group has shown up to 25 dimensions in the laboratory. "By combining our large alphabet with our noise-cancellation schemes, we plan to have a robust prototype that works even under noisy conditions," he says.
A consortium of the key national players has been formed in SA and is devising a strategy to take the country into a quantum future.
"We would like to devise a strategy that would see the community bind together for critical mass and impact," says Forbes. "The Department of Science and Technology have mandated this and are waiting for our roadmap."
• Mouton is a senior communications officer at Wits University.