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The general definition of a qubit as the quantum state of a two-level quantum system.In quantum computing, a qubit (/ ˈ k juː b ɪ t /) or quantum bit is a basic unit of quantum information—the quantum version of the classic binary bit physically realized with a two-state device.
The purpose of quantum computing focuses on building an information theory with the features of quantum mechanics: instead of encoding a binary unit of information (), which can be switched to 1 or 0, a quantum binary unit of information (qubit) can simultaneously turn to be 0 and 1 at the same time, thanks to the phenomenon called superposition.
[1] [2] A logical qubit is a physical or abstract qubit that performs as specified in a quantum algorithm or quantum circuit [3] subject to unitary transformations, has a long enough coherence time to be usable by quantum logic gates (c.f. propagation delay for classical logic gates). [1] [4] [5]
Global single qubit gates on all the atoms can be done either by applying a microwave field for qubits encoded in the Hyperfine manifold such as Rb and Cs or by applying an RF magnetic field for qubits encoded in the nuclear spin such as Yb and Sr. Focused laser beams can be used to do single-site one qubit rotation using a lambda-type three level Raman scheme (see figure).
Just as the bit is the basic concept of classical information theory, the qubit is the fundamental unit of quantum information.The same term qubit is used to refer to an abstract mathematical model and to any physical system that is represented by that model.
A qubit is a two-level system, and when we measure one qubit, we can have either 1 or 0 as a result. One corresponds to odd parity, and zero corresponds to even parity. This is what a parity check is. This idea can be generalized beyond single qubits. This can be generalized beyond a single qubit and it is useful in QEC.
The √ SWAP gate performs half-way of a two-qubit swap (see Clifford gates). It is universal such that any many-qubit gate can be constructed from only √ SWAP and single qubit gates. More than one application of the √ SWAP is required to produce a Bell state from product states.
The quantum volume of a quantum computer was originally defined in 2018 by Nikolaj Moll et al. [10] However, since around 2021 that definition has been supplanted by IBM's 2019 redefinition. [ 11 ] [ 12 ] The original definition depends on the number of qubits N as well as the number of steps that can be executed, the circuit depth d