qubit
noun
qu·bit ˈkyü-bət 
plural qubits
: a unit of computing information that is represented by a state of an atom or elementary particle (such as the spin) and can store multiple values at once due to the principles of quantum mechanics
And the most basic truth of quantum mechanics dictates that you cannot measure a qubit without destroying the superposition. The register that said 1 and 0 will randomly collapse into 1 or 0.
George Johnson
compare bit entry 3 sense 1 George Johnson
Word History
Etymology
qu- (in quantum entry 2) + bit entry 4, probably formed with punning allusion to cubit
Note: According to the American physicist Benjamin Schumacher, in the acknowledgements to a paper ("Quantum coding," Physical Review A, vol. 51, issue 4 [April, 1995], p. 2747), "The term 'qubit' was coined in jest during one of the author's many intriguing and valuable conversations with W. K. Wootters, and became the initial impetus for this work."
First Known Use
1994, in the meaning defined above