Macroscopic Coherence

Benjamin Yadin, Vlatko Vedral

We propose a universal language to assess macroscopic quantumness in terms of coherence, with a set of conditions that should be satisfied by any measure of macroscopic coherence. We link the framework to the resource theory of asymmetry. We show that the quantum Fisher information gives a good measure of macroscopic coherence, enabling a rigorous justification of a previously proposed measure of macroscopicity. This picture lets us draw connections between different measures of macroscopicity and evaluate them; we show that another widely studied measure fails one of our criteria.

Jan Peřina

Hyukjoon Kwon, Chae-Yeun Park, Kok Chuan Tan +2 more

We investigate a measure of quantum coherence and its extension to quantify quantum macroscopicity. The coherence measure can also quantify the asymmetry of a quantum state with respect to a given group transformation. We then show that a weighted sum of asymmetry in each mode can be applied as a measure of macroscopic coherence. To exclude the effects of microscopic superpositions, we suggest a method to introduce a cutoff to the weighted sum that will specify the macroscopic portion of the coherence. This cutoff may be interpreted as the fuzziness for a given measurement outcome. Based on the suggested measures, we investigate the quantum macroscopicity for particular concrete examples in $N$-partite spin systems.

Л.М. Сороко

Anupam Garg

The phenomenon of macroscopic quantum coherence is examined within the framework of a two-level system coupled to an Ohmic bath. A bound is obtained for the temperature above which the macroscopic variable cannot display the oscillatory behavior characteristic of quantum coherence. Different approximations for the dynamical behavior of the macroscopic variable in the low-dissipation limit are compared.