Lateral computing
In a quantum computer, the fundamental unit of information (called a quantum bit or qubit), is not binary but rather more quaternary in nature. This qubit property arises as a direct consequence of its adherence to the laws of quantum mechanics, which differ radically from the laws of classical physics. A qubit can exist not only in a state corresponding to the logical state 0 or 1 as in a classical bit, but also in states corresponding to a blend or quantum superposition of these classical states. In other words, a qubit can exist as a zero, a one, or simultaneously as both 0 and 1, with a numerical coefficient representing the probability for each state. A quantum computer manipulates qubits by executing a series of quantum gates, each a unitary transformation acting on a single qubit or pair of qubits. In applying these gates in succession, a quantum computer can perform a complicated unitary transformation to a set of qubits in some initial state.
Bell state
In this example, Alice is trying to communicate two bits of classical information, one of four two bit strings: formula_13or formula_14. If Alice chooses to send the two bit message formula_15, she would perform the phase flip formula_16to her qubit. Similarly, if Alice wants to send formula_17, she would apply a CNOT gate; if she wanted to send formula_14, she would apply the formula_19gate to her qubit; and finally, if Alice wanted to send the to bit message formula_20, she would do nothing to her qubit. Alice performs these quantum gate transformations locally, transforming the initial entangled state formula_21 into one of the four Bell states.