Daemonic ergotropy of Gaussian quantum states and the role of measurement-induced purification via general-dyne detection

• URL: http://arxiv.org/abs/2506.22288v1
• Date: Fri, 27 Jun 2025 15:02:14 GMT
• Title: Daemonic ergotropy of Gaussian quantum states and the role of measurement-induced purification via general-dyne detection
• Authors: K. H. Kua, Alessio Serafini, Marco G. Genoni,
• Abstract summary: In quantum systems, the maximum work extractable via unitary operations is referred to as daemonic ergotropy.<n>We show that for single-mode Gaussian states, the ergotropy depends solely on the state's energy and purity.
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• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: According to the Maxwell demon paradigm, additional work can be extracted from a classical or quantum system by exploiting information obtained through measurements on a correlated ancillary system. In the quantum setting, the maximum work extractable via unitary operations in such measurement-assisted protocols is referred to as daemonic ergotropy. In this work, we explore this concept in the context of continuous-variable quantum systems, focusing on Gaussian states and general-dyne (Gaussian) measurements. We derive a general expression for the daemonic ergotropy and examine two key scenarios: (i) bipartite Gaussian states where a general-dyne measurement is performed on one of the two parties, and (ii) open Gaussian quantum systems under continuous general-dyne monitoring of the environment. Remarkably, we show that for single-mode Gaussian states, the ergotropy depends solely on the state's energy and purity. This enables us to express the daemonic ergotropy as a simple function of the unconditional energy and the purity of the conditional states, revealing that enhanced daemonic work extraction is directly linked to measurement-induced purification. We illustrate our findings through two paradigmatic examples: extracting daemonic work from a two-mode squeezed thermal state and from a continuously monitored optical parametric oscillator. In both case we identify the optimal general-dyne strategies that maximize the conditional purity and, in turn, the daemonic ergotropy.

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