### Symmetry, Integrability and Geometry: Methods and Applications (SIGMA)

SIGMA 18 (2022), 071, 8 pages      arXiv:0809.3538      https://doi.org/10.3842/SIGMA.2022.071
Contribution to the Special Issue on Non-Commutative Algebra, Probability and Analysis in Action

### Spatial Markov Semigroups Admit Hudson-Parthasarathy Dilations

Michael Skeide
Università degli Studi del Molise, Dipartimento di Economia, Via de Sanctis, 86100 Campobasso, Italy

Received February 23, 2022, in final form September 23, 2022; Published online October 03, 2022

Abstract
We present, for the first time, the result (from 2008) that (normal, strongly continuous) Markov semigroups on $\mathscr{B}(G)$ ($G$ a separable Hilbert space) admit a Hudson-Parthasarathy dilation (that is, a dilation to a cocycle perturbation of a noise) if and only if the Markov semigroup is spatial (that is, if it dominates an elementary CP-semigroup). The proof is by general abstract nonsense (taken from Arveson's classification of $E_0$-semigroups on $\mathscr{B}(H)$ by Arveson systems up to cocycle conjugacy) and not, as usual, by constructing the cocycle as a solution of a quantum stochastic differential equation in the sense of Hudson and Parthasarathy. All other results that make similar statements (especially, [Mem. Amer. Math. Soc. 240 (2016), vi+126 pages, arXiv:0901.1798]) for more general $C^*$-algebras) have been proved later by suitable adaptations of the methods exposed here. (They use Hilbert module techniques, which we carefully avoid here in order to make the result available without any appeal to Hilbert modules.)

Key words: quantum dynamics; quantum probability; quantum Markov semigroups; dilations; product systems.

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