The Best Information Is Quantum Information


Joseph Emerson – Al Jazeera

Quantum computing could revolutionise the field of cryptography, with major implications for privacy and security.

For some time now we have been immersed in the information age – if you’re reading this online, you’re proving the point. Our immersion in the information age is reflected in almost every social setting; it has become hard not to find at least one face, if not several faces, aglow with the cool blue light of a smartphone screen. Google, Facebook, and Twitter have changed the way we learn about the world and each other.

The digitisation of information has brought about Marshall McLuhan’s “global village”, in which nearly everyone is – or soon will be – fully connected. The explosive growth of information technology has transformed our world into one that is now draped in a network of fiber-optic cables, dotted with cell-phone towers and encircled by a drone army of communication satellites, all of which enable the flow of digital information around the globe.

Privacy, security, knowledge and power

A major unresolved question is the role, or even the possibility, of private communication and information security in this brave new digital world – a topic in which governments, corporations and private citizens all have a vested interest. This issue has come sharply into focus as various governments attempt to monitor the communications of their citizens, and even threaten to ban some services, such as Blackberry’s BBM, because of the incredibly secure encryption such services provide to end users. But it’s important to emphasise that private and secure communication is broadly relevant to users of the internet. For example, if I want to do some online banking, I want to be sure my financial data is protected from online prying eyes.

A fundamental, scientific question is this: how much privacy is even possible over networks controlled and monitored by others? Under what physical conditions can Person A communicate privately with Person B over a public network?  Fortunately, we currently have efficient encryption systems to reliably protect online activities such as personal banking. But practical systems can be cracked, depending on the resources the would-be eavesdroppers have at their disposal.

One of the most widely used encryption schemes on the internet today is the RSA scheme. The basic idea is that one can encode information with a key – which is some very large number – that is made publicly available. With RSA, the encoded information can only be decoded by someone who knows the two prime factors that, when multiplied together, produce this very large number. While it is easy to multiply two numbers together, it turns out to be extremely difficult to find the two prime factors that are multiplied to create a large product. This difficulty is what enables privacy. I make my locking-key publicly available and anyone who wants to send me information privately encodes that information with this locking-key. If I do not disclose the prime factors to anyone – that is, if I keep my unlocking key private – then only I can decipher the encoded message. To anyone else, the message looks like random binary gibberish.

How secure is this? The answer depends on a number of practical considerations, but fundamentally, RSA remains only as secure as the difficulty of finding the two prime factors for the locking-key. For large enough locking-key numbers this problem is believed to be unfeasibly hard to solve – even with vast amounts of conventional computing power – because finding the prime factors gets exponentially more difficult as you increase the number of digits in the key.

What can quantum physics do for you … or to you?

Information is an abstract concept – it can comprise names, numbers, dates, places, almost anything. The important point is that any information is ultimately represented as some physical quantity – it is always encoded in some physical medium, whether the physical medium involves sound waves from one person’s mouth to another’s ear, blotches of ink on paper, pulses of light in a fiber-optic cable or the magnetised regions of a hard drive. When the physical medium is manipulated according to the laws of classical physics – for example, the laws of classical electromagnetism which completely describe conventional computers – then these laws imply certain physical limits on how the encoded information can be manipulated and accessed. And when the information is encoded in physical media that obey the laws of quantum physics, then a different set of rules describes how the information can be manipulated and accessed.

The laws of quantum physics are now well established as the appropriate rules that govern the way that world works. However, the special features of the quantum laws that make them different from the classical laws are typically only manifest when we manipulate objects at the level of individual atoms and photons. So the idea of quantum information technology is based on the possibility of encoding information at this tiny scale. But before we discuss the practical issues associated with this technological challenge, let’s first address the following question: how do the unique features of the quantum laws – and any quantum technology based upon them – affect information privacy?

The quantum information age

The quantum information age was born about 20 years ago from a somewhat unexpected union between quantum physicists and computing scientists. One of the major insights that brought quantum information to the forefront of science was the discovery by Peter Shor that a “quantum computer” (a computer built out of components that can be manipulated according to the full extent allowed by the laws of quantum physics) could easily solve the factoring problem. Hence a quantum computer, if one could be built, would spell an end to the security of the most practical encryption method used for private communication today.

Shor’s algorithm and a host of other quantum algorithms that have been discovered subsequently have stimulated a major global research effort investigating practical ways to build a large-scale quantum computer. However, there are major technological obstacles to realising large-scale quantum computers. It turns out that the same special features of quantum mechanics that give power to quantum computing also make them tricky to build. Quantum systems are fragile, fickle and tough to control. While small-scale quantum computers consisting of up to a dozen quantum bits, or “qubits”, have been realised in the most advanced research labs, currently there is no known technological pathway to building a large-scale quantum computer with thousands or even tens of thousands of qubits, which would be required to crack present-day encryption.

The quantum world taketh … but also giveth

Quantum technology creates a threat to the possibility of private communication using current encryption methods – but, interestingly, it also provides a new and more secure solution to achieving private communication. While a quantum computer would break current practical encryption schemes, quantum technology also enables a new means of establishing unconditionally secure private communication through a protocol known as quantum key distribution, which was actually discovered a decade before Shor’s algorithm.

Quantum key distribution exploits one of the fundamental features of quantum mechanics known as the Heisenberg uncertainty principle. This principle holds that, when dealing with quantum systems, it is impossible to observe one property of that system without disturbing some other property. The significance of this for private communication is this: if a Sender A transmits some (random) data to a Receiver B using quantum bits encoded in the right way, then the receiver can always detect whether an eavesdropper has snooped on the transmission.

If no eavesdropper is detected, then B is certain that the random data is private, and this private random data can then be used to establish a secure communication channel over a regular (classical) network. Unlike the RSA scheme currently in use, private communication with quantum key distribution remains secure even if an adversary has access to a quantum computer.

The technological threshold for creating and using quantum communication in practice is much lower than that for creating a practical quantum computer. In fact, we already have the technology – researchers have shown that it is possible to transmit quantum bits over hundreds of kilometers using commercial-grade fiber-optic cables. Moreover, there are already private companies offering quantum cryptographic systems. For example, quantum key distribution was used to establish secure communication during the federal election in Switzerland in 2007. Moreover, a multi-national research group led by one of my colleagues, Thomas Jennewein at the Institute for Quantum Computing, is now undertaking a research program to transmit quantum bits to an orbiting communications satellite, which would enable quantum key distribution on a truly global scale.

Of course, the extra security afforded by quantum key distribution is currently unnecessary for most applications. Current encryption methods, and the information it protects, can be decrypted only in the future, from an adversary who gains eventual access to a quantum computer. Although for most applications this level of security is not relevant, for others the threat of this future technology can be a serious security concern.

We live at a time when rapid developments in conventional information technology have led to an equally rapidly adapting social and political landscape surrounding private communication over public networks. The advent of quantum information technology will further shape the future of communication privacy in our expanding global village.


Joseph Emerson is a professor in the Department of Applied Mathematics, at the University of Waterloo, Canada, and a member of the University of Waterloo’s Institute for Quantum Computing. He is a scholar of the Canadian Institute for Advanced Research and recipient of the province of Ontario’s Early Researcher Award. Prof. Emerson is co-writer of the award-winning documentary The Quantum Tamers. He is currently a visiting professor at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario. 

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