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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.
[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]
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.
99.944 (1 qubit max) 98.25 (2 qubits median) 99.1 (2 qubits max) 20 October 9, 2023 [33] 16 [34] M Squared Lasers: Maxwell Neutral atoms in optical lattices 99.5 (3-qubit gate), 99.1 (4-qubit gate) [35] 200 [36] November 2022: Oxford Quantum Circuits Lucy [37] Superconducting 8 2022: Oxford Quantum Circuits OQC Toshiko [38] Superconducting 32 ...
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.
Consider an arbitrary set of rank-1 projectors () = such that = / is a POVM, and thus =.Asking the projectors to have equal pairwise inner products, () = for all , fixes the value of .
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).
The global phase gate introduces a global phase to the whole qubit quantum state. A quantum state is uniquely defined up to a phase. A quantum state is uniquely defined up to a phase. Because of the Born rule , a phase factor has no effect on a measurement outcome: | e i φ | = 1 {\displaystyle |e^{i\varphi }|=1} for any φ {\displaystyle ...