Impossibility of Cloning a Quantum State

A theorem in out textbook (p. 532, see event comments, below), states that it is impossible to build a device that, given an unknown quantum state as input, produces a copy of that state. I will explain the proof of the theorem.

Exercise 1.2 on page 57 asks us to show that if a circuit could distinguish between two quantum states, it could be used for cloning. I will do that.

The last 30 minutes of the planned 1.5 hours are reserved for question and answer.

Familiarity with matrices will be quite helpful, as will an awareness of Dirac notation (bras and kets).