What's the meaning of the phrase 'Quantum leap'?
A sudden, very noticable and significant advance.
What's the origin of the phrase 'Quantum leap'?
Before quantum leaps there were quantum jumps, which had the same meaning. This has a defined meaning in physics and it is the change that occurs in an atom when an electron jumps from one energy level to another with the emission or absorbaion of a photon. The term 'quantum jump' began to be used around 1920 following the theories and discoveries that were made in quantum physics by many notable scientists in the late 19th and early 20th centuries, notably Bohr and Einstein.
The first use of the phrase that I've found is from the Procedings of the National Academy of Science U.S.A., March 1924:
The second column gives the quantum numbers designating the quantum jump under consideration.
'Quantum leap' comes a little later, as in this example from the Journal of Philosophy, 1930:
We may refer the arbitrary character of a single ultimate physical event, such as a quantum leap, to the arbitrary character of the whole universe of which the single event is a part.
Of course, the expression 'quantum leap' is now almost always used figuratively, that is with no atomic particles being involved and in reference to some sudden dramatic change.
Again 'quantum jump' is used in that wider context first. The Indianapolis Star, November 1930, reported thus:
As science moves forward, slowly as a rule, but with a quantum jump now and again.
The figurative usage of 'quantum leap' (which is what this piece is about) is much more recent. An early example is found in H. L. Roberts' book Russia & America, 1956: :
The enormous multiplication of power, the 'quantum leap' to a new order of magnitude of destruction, is something very real and comprehensible.