What is Quantum Computing

Early October 2015, and researchers at the University of New South Wales have built a logic gate that looks to make quantum computers feasible. But what is a quantum computer?

We know a classic computer uses bits of information, either ones or zeros (on/off, true/false, depending how you notate them). These bits are process by a variety of logic gates; logic gates take two bits of information and give a one bit response; An AND type logic gate takes two bits of information and outputs a ‘one’ (on, true …etc.) if both inputs are one, and outputs a zero under any other circumstance. And OR logic gate takes two bit and out a ‘one’ if either input bit is ‘one’. There are also NAND, NOR, XOR, NOT gates. All classic computing uses complex combinations of these logic functions.

In the past bits in classic computers have consisted of voltages between zero and a set higher value, usually 5 or 10 volts. A zero bit was represented by a zero (or near zero) voltage; a one was represented by a higher voltage. With enough bits a complex pattern of ones and zeros could be represented. With 2 bits there were 4 representations; with 3 there were 8 representations. It there were N bits there were 2 to the Nth combinations.

Quantum computers are different from classic computers in several ways. One difference is that where a classic computer has exactly one state amongst 2 to the Nth possibilities the quantum computer simultaneously has many states, up to 2 to the Nth power. The initial state of the quantum qubits (quantum bits) represents a piece of data; these are applied to a series of gates know as a quantum algorithm, and the resulting state (one of 2 to the Nth possibilities) is the outcome. Because of the non-deterministic nature of the quantum algorithm this outcome is only considered correct within a certain probability.

The new development at the UNSW is the invention of a logic gate that works with qubits. This has basically been the last major hurdle in building a quantum computer; all the necessary building blocks for operational quantum computers are now here.

The benefits of quantum computers are numerous. Their massively increased speed is one factor. Massively increased speed means programs can now be much more complex and still produce results in a reasonable amount of time. Programs to predict the weather once took several days to run, by which time the weather conditions had already come and gone. Modern computers caught up with this at least a generation ago, but faster computers would allow more complex programs and quicker calculation results. Computer models for the human body, very useful for medical research, are now quite feasible and potential quite complex. Other applications and models are numerous. And because quantum computers use tiny particles such as photons for their qubits, and equally tiny logic gates, their size is much smaller than any present technology.