Past exam of the mathematics course of the University of Cambridge 2020 ii Paper 1 34A Solution Created 2026-09-24 Updated 2026-09-29
For part (a), the adjoint operator isUsing the canonical commutation relation ,Thus and are the annihilation and creation operators of the quantum harmonic oscillator.
For part (b), writeSince and , differentiation of the unitary conjugation givesThe initial conditions are and . Solving this pair of linear ordinary differential equations gives the Bogoliubov transformationThis is the transformation implemented by the single-mode squeeze operator.
For part (c), invert the definition of :The transformation above impliesThe ground state has zero position and momentum means and variances and . Hence the squeezed vacuum state hasThe reciprocal squeezing factors cancel, soThe state therefore continues to saturate the Heisenberg uncertainty relation.