Year: 2016
Type: article
Abstract: Wave functions and density matrices represent our knowledge about a quantum system and give probabilities for the outcomes of measurements. If the combined dynamics and measurements on a system lead to a density matrix $\ensuremath{\rho}(t)$ with only diagonal elements in a given basis ${|n\ensuremath{\rangle}}$, it may be treated as a classical mixture, i.e., a system which randomly occupies the basis states $|n\ensuremath{\rangle}$ with probabilities ${\ensuremath{\rho}}_{nn}(t)$. Equivalent to so-called smoothing in classical probability theory, subsequent probing of the occupation of the states $|n\ensuremath{\rangle}$ may improve our ability to retrodict what was the outcome of a projective state measurement at time $t$. Here, we show with experiments on a superconducting qubit that the smoothed probabilities do not, in the same way as the diagonal elements of $\ensuremath{\rho}(t)$, permit a classical mixture interpretation of the state of the system at the past time $t$.
Source: Physical Review A
Authors: D. Tan, M. Naghiloo, K. Mølmer, K. W. Murch
Institutions: Washington University in St. Louis, Aarhus University
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: John Templeton Foundation, Villum Fonden
OpenAlex ID: W2467159017