Physical and logical qubits
In quantum computing, a qubit is a unit of information analogous to a bit (binary digit) in classical computing, but it is affected by quantum mechanical properties such as superposition and entanglement which allow qubits to be in some ways more powerful than classical bits for some tasks. Qubits are used in quantum circuits and quantum algorithms composed of quantum logic gates to solve computational problems, where they are used for input/output and intermediate computations.
Superconducting quantum computing
where formula_23 is the shape of the microwave pulse in time, formula_24 is the resonance frequency of the second qubit, formula_25 are the Pauli matrices, formula_26 is the coupling coefficient between the two qubits via the resonator, formula_27 is the qubit detuning, formula_28 is the stray (unwanted) coupling between qubits and formula_29 is Planck constant divided by formula_30. The time integral over formula_23 determines the angle of rotation. Unwanted rotations due to the first and third terms of the Hamiltonian can be compensated with single qubit operations. The remaining part is exactly the controlled-X gate.