So why are quantum computers so much faster? To understand this, it’s best first to look at how a classical or regular computer works. It will contain a processor which manipulates strings made up of bits. These bits can only have a value of either 0 or 1, depending on the electrical charge applied to them. A pair of bits can produce four values: 10, 01, 00, and 11. With three bits you get eight values. Input is added as a string of 0s and 1s, manipulated by an algorithm and then output as another long string of 0s and 1s.
A quantum computer replaces these binary bits with quantum bits - or qubits for short. These are quantum particles which contain multiple states existing simultaneously in superposition. Their information may be stored as the spin property of that particle, or its momentum, even location.
This superposed state means that the particle’s spin could be up, down, or in fact any value between. These spin values are stored as probabilities. There’s no way of observing the true value in superposition without collapsing the quantum effect. One potential way of getting around this is to take measurements indirectly by entangling two quantum particles. You do this by simply disturbing them. After entanglement the two particles will have complementary properties. For example, if one electron adopts a positive spin, its entangled partner will adopt a negative one.
Entanglement keeps the quantum system valid. A qubit is not limited like regular binary bits to two states. It can have many states, and it's this which gives the quantum computer its exponential processing power. This effect of superposition allows a qubit to perform many times more calculations at once.
At first it was believed that the operating speed of a quantum computer would be restricted to the energy in the underlying physical system. This condition is implied by current quantum mechanics theory. But Steve Johnson of NIST mathematically proved that this was not the case. He showed that it was theoretically possible to get qubits to flip at speeds unlimited by energy aspects. That isn’t to say there aren’t other physical constraints which could affect a quantum computer’s ‘clock speed’. An entirely different architecture has to be designed to allow the qubit to behave in a quantum manner.
A classical computer has a clock speed measured in gigahertz. This translates to a processing speed of a few billion simple logic operations per second. To add context, consider that the processing power of quantum computers is measured in teraflops. Or trillions of logic operations per second.
In 2015, Google and NASA reported that their new 1097-qubit D-Wave quantum computer had solved an optimization problem in a few seconds. That’s 100 million times faster than a regular computer chip. They claimed that a problem their D-Wave 2X machine processed inside one second would take a classical computer 10,000 years to solve.
That's a mind boggling comparison, and all driven by the exponential power of quantum mechanics!
