Tuesday, 17 March 2015

Are We At Risk from Quantum Computers

by Reetobrata Chatterjee


A quantum computer is a computer which makes use of the quantum states of sub-atomic particles in order to store and manipulate information. Put simply, this allows us to have a computer which works MUCH faster than normal computers. If a semi-decent quantum computer could be constructed (current efforts have very small amounts of computing power), then the entire banking industry and others could collapse before our very eyes.

A standard computer works very simply. All the data you provide is stored as a combination of 1s and 0s, using ever tinier devices called transistors, which have an on (1) or off (0) state. The data in each transistor is known as a bit, and they work in groups of 8, as bytes. As these bytes build up, you get kilobytes, megabytes and so on. This allows a group of n transistors to be in one of 2n states. More powerful computers have more transistors or those of a higher quality which fail less often.

But not quantum computers.

They use an entirely different way to store the data. This is called a qubit. Unlike a transistor, which can either be 1 or 0, using the ideas of quantum superposition to be 1 or 0 or both at once. This is similar to Schrodinger's cat, which was both dead and alive until the box was opened (If you don’t know what Schrödinger’s cat is, the video explains it really well).

This is achieved by using coils of a special metal called Niobium. If the current goes through the loop counter-clockwise, it will create a tiny magnetic field pointing up, whereas a clockwise current will have a downwards facing magnetic field. These are the equivalent of the classical 1 and 0 states. Drop this however to 0.2° C above absolute zero and the coils begin behaving like superconductors, wires with basically 0 resistance. This allows the system to enter the mysterious expanses of quantum superposition, where each individual qubit, could be 1 or 0, or since it’s superposed, both.

How will this affect us?

The government, banks and Facebook (and all other websites) all use encryption to keep your data safe and away from people who might want it for malicious purposes. The tightest security around this data, is while it’s being transmitted and stored. Generally this is in the form of public key encryption.

Take the number 10. If someone asked you to find its factors, it would be very simple (5 and 2). Now take the number 4453. Finding the factors of this are just a little bit harder. But a computer could do it. (The factors are 61 and 73 by the way, what makes this so difficult is that they have only 2 prime factors). If you now replace this number by one which is hundreds of thousands of digits long, which have only 2 prime factors, each thousands of digits long, the task becomes rather difficult. The current estimation to crack a 1024 bit RSA key, which is essentially a really, really large number with only 2 factors is 5.95 x 10211 years. 

As a comparison the universe is 13.75 x 109 years old.

But this calculation is only limited to traditional computers.

A powerful quantum computer, on the other hand, could do this calculation in a few hours purely passed on the fact that for every bit you add to it, it becomes exponentially as powerful.

Fear not however, your money, messages and snapchats are safe (for now) because the largest number factorised on a quantum computer is 56153, not small, but insignificant compared to the largeness of the numbers in current encryption techniques.

1 comment:

  1. Michael Crichton's novel 'Timeline' deals with quantum computers quite well and accurately, well worth a read (as well as quantum teleportation and medieval France)

    Tim Bustin

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