Qubit is short for “quantum bit,” which is the unit of measure for quantum information. It is the quantum computing version of a binary digit or a bit.
In classical computing, bits are used to communicate encoded information. They represent two possible states represented by 0 and 1. These two states could mean “true” or “false,” “empty” or “full,” or “on” or “off.” Bits can only operate in one of two states at one time. They can switch from one state to another at a slow speed and under low electronic voltage.
A qubit is similar to a bit in the sense that it encodes information on two levels. Unlike a bit, though, a qubit does so in two quantum states at the same time. That said, you can only manipulate qubits to accomplish complicated tasks or calculations using so-called quantum principles such as quantum superposition or entanglement. Because of this property, a qubit can encode a more expansive array of information than a bit.
In Dirac notation, which is a way to describe quantum states, the following equation represents a qubit:
|0〉 + |1〉
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Within every laptop or desktop computer is a transistor (a type of semiconductor) that is responsible for the creation of bits. Think of it as a box that can either be empty or full.
With a qubit, a specially designed system such as a superconductor replaces the transistor. This new and improved version of the transistor is capable of either being full or empty at the same time, which is also known as a superposition state. A qubit can also exist in multiple entangled states, where each qubit’s behavior affects another, even when great distances separate them.
The infinite computational possibilities offered by qubits allow quantum computers to reduce the number of steps necessary and thus the amount of time needed to solve a problem. As a result, quantum computers can complete complex processes faster than a standard computer.
What are Some Examples of a Qubit?
A basic example of a qubit in its most natural state is a spinning electron. The spin states of electrons or atoms (when they’re either spinning up or down) are considered qubits.
Another example is photon polarization. In the simplest terms, this describes the phenomenon by which a single photon rotates in two simultaneous states, either vertically or horizontally. This rotation is perpendicular to the motion of an electromagnetic wave.
How do You Build and Control a Qubit?
There are various ways to build and control qubit, but these require specialized systems. One example is a superconducting circuit that works in low temperatures. This device can create and control quantum particles that behave like qubits.
Trapped ion quantum computers also operate using qubits. These quantum computers store qubits in suspended, electrically charged ions. These ions are trapped using electromagnetic fields. Meanwhile, lasers manipulate qubit states.
Currently, the trapped ion system is one of the most promising incarnations of quantum computers in an experimental phase. It meets the basic requirements for universal quantum computers.