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.
How Did the Qubit Come About?
Benjamin Schumacher coined the term “qubit.” He said that it was used in jest while he conversed with William Wootters in the acknowledgments section of Schumacher’s 1995 paper.
Schumacher is an American theoretical physicist who works mostly in the field of quantum information theory. He, in fact, discovered a way to interpret quantum states as information. He came up with a way to compress information in a state and stored it in a smaller number of states, which became known as the “Schumacher compression.” It helped start the field we now know as “quantum information theory.”
Wootters, meanwhile, is an American theoretical physicist, who is also considered one of the founders of the field of quantum information theory.
How Does a Qubit Differ from a Bit?
The primary difference between a qubit and a bit lies in the concept of superposition. Qubits are capable of superposition while bits are not. As such, qubits can have an infinite number of values while bits cannot.
Illustrating with an example, a system built with two bits can only manifest four states. Another system built with two qubits can manifest an infinite number of states based on four basis states.
How Are Qubits Made?
Creating a qubit requires scientists to find a spot in a material where they can access and control quantum properties. Once the properties are accessed, scientists can use light or magnetic fields to create superposition, entanglement, and other properties required of qubits.
Can You Store Qubits?
According to some scientists, it is possible to store qubits in so-called “quantum memory.” Photon qubits, according to Alan Kessel and Sergey Andreevich Moiseev, can be stored when these are in the single photon state. Optical data storage, meanwhile, can be achieved by using absorbers to absorb different frequencies of light, which are then directed to beam space points and stored.
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.
We hope you can now answer the question “What is a qubit?” after reading this post.