• Getting in a state about quantum states. "Ye cannae change the laws of physics, Captain"
• Both military and potentially commercial quantum computers already exist
• Hundreds of millions of times faster than current computing technology

In the latest skirmish of the deepening trade war of the US, the UK, parts of Europe, Australia and New Zealand versus China, late last week the Chinese government passed a new control law that prohibits the exportation from the PRC of encryption technology and cryptanalysis machines. The ban includes quantum cryptographic hardware and software.

Encryption technology has been officially classified as a "state secret" in China since 1999 and the legislation was expanded in 2005 and 2007. Importation of some comms technologies is also prohibited under the new legislation, including password generators, VPNs, fax machines and telephones! 

It seems the use of faxes to distribute the huge welter of samizdat literature and government-banned information that spread across the Soviet Union as it creaked at the seams in 1989 before imploding and completely falling apart on December 26, 1991, is, a generation later,  still putting a bit of breeze up the wide trouser legs of the members of China's politburo. 

With that news in mind, yesterday I spent an hour and a half on an ale-lubricated video call with one my oldest friends, an eminent computer scientist, who is part of a team made of top boffins from various universities that is researching the outer limits of the arcane discipline-cum-mind-bogglingly complex dreamscape that is quantum cryptography.

Ninety-nine per cent of the population of the planet know naught of the subject and care even less, but it is of astonishing global potential because it can encrypt and protect data from any and every attempt of anyone or anything to decrypt it - unless some faster-than-light aliens from beyond the Horsehead Nebula get involved.

Commonly when quantum cryptology is covered in the popular media what is actually described is "post-quantum cryptography". This refers to cryptographic algorithms (such as ECC and RSA) that are promoted as being secure against any attempt to breach them via a quantum computer. However, the reality is that such algorithms could be cracked within a matter of a few hours by a sufficiently powerful quantum computer and the reason they are not being decrypted in any number (as far as we know) is because there are, ostensibly, so few of them yet in existence.

Estimates are there are probably about 15 such devices publicly-acknowledged to exist and owned by the likes of mega-corporations such as IBM and Google. They are all experimental and while they are evolving rapidly they are not yet ready for commercial deployment. That's the civilian domain. The military is different. It is thought that military labs in countries including China, France, Germany, Japan, Russia and the UK have been working on quantum computing for years and may well have some advanced working prototypes, although none will yet admit to it.

Quantum computers will be able to process and analyse monumental amounts of data at immense speed. For example, Google says its machine will be "at least a hundred million times faster than any system available today." Post-quantum cryptography algorithms (and these are usually public key algorithms) are pretty good in that they take traditional binary computers many months or years to decrypt and by that time the mathematical keys will have changed as will the rest of the world

However, a quantum computer running "Shor's Algorithm" would be able to crack the code in a matter of minutes. This ability was demonstrated last year when Craig Gidney, a Google scientist, and Martin Ekera of Sweden's Royal Institute of Technology in Stockholm showed that quantum system could crack 2,048-bit RSA encryption with a mere 20 million quantum bits (qubits) in just eight hours with this technique. The same feat using a traditional computer would have taken several tens of years.

The times will always be uncertain where quantum cryptology is concerned

So, this is the part where I try to translate and truncate what my chum told me about quantum cryptography and how it works. Despite referring to page upon page of my scrawled notes it's an odds-on bet that I'll miss something out or mess something up, so please bear with me, there simply isn't enough room in an article like this to do the subject any more than rough justice.

It all starts with elementary particles, of which photons are one classification. A definition of a photon is that it is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons do not have mass and always travel at the speed of light in a vacuum, which is 299792458 metres per second, so quite literally faster than a speeding bullet, and then some.

The particles that make up the universe are in and of themselves "uncertain" (aren't we all?) and therefore can exist, simultaneously in more that one place at any time or in more than one state of creation. Thus, photons are generated, entirely randomly, in one of two quantum states. Those quantum states or properties cannot be observed or measured without observing or disturbing the quantum state and, by doing that, changing it. 

In quantum computing, a quantum bit (or qubit) is a unit of quantum data and is analogous to the "bit " in traditional computing. A bit is the smallest unit of storage in a computer memory and can take a binary state value of either a 0 or a 1 (One/Zero. Yes/No. On/Off) and nothing more. In quantum computing a qubit can be in a "superposition" state of either a  0 and 1, simultaneously. In other words a qubit can be "one thing or the other, maybe" or "both, at once."

Putting it (very) simply when a quantum message is transmitted a light source is used to provide a photon which passes through a polariser. If the polariser is set to horizontal the qubit will also have horizontal polarisation. If the polariser is vertical, the qubit too will be vertically polarised.

When a horizontally-polarised passes through a horizontally/vertically polarised polarising beam splitter it will always keep its state of horizontal polarisation. In the case of the BB84 Protocol a photon goes through a polariser and is randomly given one of four possible polarisation and bit designations, ie, Vertical (One bit), Horizontal (Zero bit), 45 degree right (One bit), or 45 degree left (Zero bit). In essence, if a hacker attempts to read or copy a message the photon's quantum state will change and the hack attempt will be detected. As that happens, the message deletes itself. 

Strange, isn't it? That's why there are those who understand quantum computing, those who do not understand quantum computing and those who both don't understand quantum computing but at the same time do understand it. Which category do you belong to? I'm firmly in the third. 

As we finished our distanced pints and the conversation with my old pal drew to a close, he told me that there'll be a lot of problems when quantum computers become as ubiquitous as laptops. That's because people will turn them on, look to see if they have booted-up and then won't be able to find them ever again. I think he was joking but them again, maybe he wasn't.