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Definition: qubit

(QUantum BIT) A unit of computation in a quantum computer. Pronounced "q-bit," the bit in qubit is somewhat misleading, although when a qubit is read, it does collapse ("decohere") into a 0 or 1. However, for computation and prior to being observed, the qubit can be in a superposition state, which means multiple states at the same time measured by electron motion and direction.

Unlike classical bits, qubits are not used for storage. Data are transferred to the qubits for computation and then read out for answers. Rather than a charge or pulse of electricity in a bit, it is the electrons in the qubit that are manipulated based on the laws of quantum mechanics.

In addition, while a classical bit is made of transistors, there are different qubit designs and constructions.

Each Qubit Adds Exponentially More Power
Qubits function like artificial atoms, and unlike classical bits, each additional qubit adds much greater computational power. For example, while five bits in a classical computer provides 32 values, five qubits in a quantum computer may generate a million values. See binary values.

A Description from an Expert
Interviewed on "60 Minutes" in December 2023, renouned quantum physicist Michio Kaku describes the qubit by saying "there is a fantastic amount of information stored when you can look at all possible angles, not just up or down." Kaku's example is navigating a maze. In classical computing, the pathway to exit is determined by moving through the maze one turn at a time. In quantum computing, all possible routes are computed simultaneously. See quantum computing.

From 433 to 100 Thousand Qubits
In 2022, IBM unveiled the 433-qubit Osprey gate model quantum processor, more than quadruple the 100 qubits of Eagle in 2021. It is expected to unveil the 1,121-qubit Condor in 2023, and the company forecasts 100,000 qubits in a decade. Gate model computers use fewer qubits than D-wave's quantum annealing approach; thus, 433 qubits is a milestone, and 100 thousand is sublime. (Image courtesy of IBM.)