Search Results for « Work extraction »

Abstract In the standard framework of thermodynamics, work is a random variable whose average is bounded by the change in free energy of the system. This average work is calculated without regard for the size of its fluctuations. Here we show that for some processes, such as reversible cooling, the fluctuations in work diverge. Realistic thermal machines may be unable to cope with arbitrarily large fluctuations. Hence, it is important to understand how thermodynamic efficiency rates are modified by bounding fluctuations. We quantify the work content and work of formation of arbitrary finite dimensional quantum states when the fluctuations in work are bounded by a given amount c . By varying c we interpolate between the standard and minimum free energies. We derive fundamental trade-offs between the magnitude of work and its fluctuations. As one application of these results, we derive the corrected Carnot efficiency of a qubit heat engine with bounded fluctuations.

We consider a quasi-probability distribution of work for an isolated quantum system coupled to the energy-storage device given by the ideal weight. Specifically, we analyze a trade-off between changes in average energy and changes in weight's variance, where work is extracted from the coherent and incoherent ergotropy of the system. Primarily, we reveal that the extraction of positive coherent ergotropy can be accompanied by the reduction of work fluctuations (quantified by a variance loss) by utilizing the non-classical states of a work reservoir. On the other hand, we derive a fluctuation-decoherence relation for a quantum weight, defining a lower bound of its energy dispersion via a dumping function of the coherent contribution to the system's ergotropy. Specifically, it reveals that unlocking ergotropy from coherences results in high fluctuations, which diverge when the total coherent energy is unlocked. The proposed autonomous protocol of work extraction shows a significant difference between extracting coherent and incoherent ergotropy: The former can decrease the variance, but its absolute value diverges if more and more energy is extracted, whereas for the latter, the gain is always non-negative, but a total (incoherent) ergotropy can be extracted with finite work fluctuations. Furthermore, we present the framework in terms of the introduced quasi-probability distribution, which has a physical interpretation of its cumulants, is free from the invasive nature of measurements, and reduces to the two-point measurement scheme (TPM) for incoherent states. Finally, we analytically solve the work-variance trade-off for a qubit, explicitly revealing all the above quantum and classical regimes.

Clinical case notes provide researchers with a rare yet unsettling insight into the intimate realities of children’s mental health. These records capture fragments of lived experience that demand rigorous ethical attention in how they are accessed, interpreted, and re-presented. This paper examines the ethical tensions between data extraction and narrative witnessing through the reflections of a Social Work practitioner, through a collaboration with professionals, and Experts by Experience. Drawing on a year-long reflexive study of clinical case notes from children in state care, this paper explores how professional language, institutional framing, and systemic pressures influence both the production and interpretation of such records. Divergent professional positions and discourses often collide, shaping children’s representation and obscuring their voices within clinical and administrative documentation. The analysis also considers the emotional labour and moral unease experienced by researchers when encountering recorded suffering, including the risks of vicarious trauma and moral distress. By reframing clinical case notes as testimonies rather than data alone, the paper argues for the practice of narrative care, an approach that prioritises attentive anonymisation, reflexive interpretation, and dignified representation. Narrative care acknowledges the methodological and emotional dimensions of engaging with trauma-saturated texts, enabling ethically responsive research that bears witness to children’s experiences. In doing so, this study highlights how researchers can uphold humanity within the constraints of research governance, transforming analysis into an act of ethical witnessing that recognises, rather than erases, the suffering and resilience contained within clinical records.