Features of Quantum Computing

 

SUPERPOSITION

To explain superposition, some people evoke someone's cat while others point to the moments a coin is in the air during a coin toss. 

Put simply, quantum superposition is a mode when quantum particles are a combination of all possible states. The particles continue to fluctuate and move while the quantum computer measures and observes each particle.

The more interesting fact about superposition — rather than the two-things-at-once point of focus — is the ability to look at quantum states in multiple ways, and ask it different questions, said John Donohue, scientific outreach manager at the University of Waterloo’s Institute for Quantum Computing. That is, rather than having to perform tasks sequentially, like a traditional computer, quantum computers can run vast numbers of parallel computations.

That’s about as simplified as we can get before trotting out equations. But the top-line takeaway is that that superposition is what lets a quantum computer “try all paths at once.”

ENTANGLEMENT

Quantum particles are able to correspond measurements with one another, and when they are engaged in this state, it’s called entanglement. During entanglement, measurements from one qubit can be used to reach conclusions about other units. Entanglement helps quantum computers solve larger problems and calculate bigger stores of data and information.

Entanglement particles are entangled pairs of qubits that exist in a state where changing one qubit directly changes the other. Knowing the spin state of one entangled particle -- up or down -- gives away the spin of the other in the opposite direction. In addition, because of the superposition, the measured particle has no single spin direction before being measured. The spin state of the particle being measured is determined at the time of measurement and communicated to the connected particle, which simultaneously assumes the opposite spin direction.

Quantum entanglement enables qubits separated by large distances to interact with each other instantaneously. No matter how great the distance between the correlated particles, they remain entangled as long as they're isolated.

Quantum superposition and entanglement together create enormously enhanced computing power. If more qubits are added, the increased capacity is expanded exponentially.

Decoherence

Decoherence occurs when the quantum behavior of qubits decays. The quantum state can be disturbed instantly by vibrations or temperature changes. This can cause qubits to fall out of superposition and cause errors to appear in computing. It's important that qubits be protected from such interference by, for instance, supercooled refrigerators, insulation, and vacuum chambers.