Speaker
Prof.
Klaus Mølmer
(Aarhus)
Description
The state of a quantum system is described by a wavefunction
evolving in time according to the Schroedinger equation. If
a measurement is carried out on the system, its wave
function collapses, i.e., it changes according to the random
outcome of the measurement. During a sequence of
measurements on a single system, its quantum state thus
follows a stochastic trajectory composed of the normal
quantum mechanical time evolution interrupted by collapses
at each measurement.
The resulting state of the system, at any time, successfully
predicts the probabilities and mean values for the
measurement of physical observables. In this talk we ask
whether the sequence of measurements also adds to our
knowledge about the state of the system at earlier times
during the experiment.
I shall show how such “hindsight” knowledge can be formally
defined in quantum mechanics and how we can represent it via
a time evolving (past) state, which at any time depends on
both earlier and later measurement outcomes. I will show
applications of this theory to experiments on atoms and
superconducting qubits, and I will discuss how the concept
and formalism of hindsight quantum states relate to
questions of more foundational character.
Primary author
Prof.
Klaus Mølmer
(Aarhus)
