What is a Qubit?

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  • Written By: Malcolm Tatum
  • Edited By: Bronwyn Harris
  • Last Modified Date: 08 November 2019
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The qubit is an example of a quantum bit. In quantum computing, the qubit serves as the counterpart to the binary digit, which is normally known as a bit. A binary digit serves as the most basic unit of information in a classical computer. In like manner, the qubit serves as the most basic unit of information in a quantum computer.

With a quantum computer, these quantum bits or qubits are essentially photon or electron particles that carry a polarization or charge that is either positive or negative. The charge of the qubit is read in the actual programming as either a “0” or a “1.” It is the interrelation and performance of these charged particles that provide the basic functionality of quantum computing, as the function is based in quantum theory.


The function of the qubit is governed by two principles that are basic to the idea of quantum physics. One of these principles is superposition. In terms of the qubit, superposition has to do with how the qubit performs within a magnetic field. If the qubit or electron particle is rotating or spinning in alignment with the field, this is known as a spin-up state. Should the qubit rotate or spin in opposition to the field, this is known as a spin-down state. Using an influx of energy can change the spin of the qubit and thus make it possible to manipulate the utility of each qubit contained within the field.

A second principle that has an impact on the function of a qubit is entanglement. This principle has to do with the way that individual qubits interact with one another. Essentially, once a connection of some type is made between qubits, the connection remains in place. This leads to the formation of qubit pairs. The pair contains a qubit that is in a spin-up state, while the second qubit is in a spin-down state. The interesting thing about this phenomenon is that there may be great distances between the two qubits in the pair, yet they still react to one another as opposites.

When superposition and entanglement can be harnessed and manipulated, the result is the establishment of a great deal of computing power. The dual nature of a qubit pair makes it possible to a quantum computer to store more numbers in comparison to a binary computer configuration. This in turn leads to an enhance capacity that allows a wider range of simultaneous functionality, making quantum computers ideal for situations requiring the processing of large amounts of data within a relatively small window of time.


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