Starting from the problem of steam engines, Sadi Carnot’s ideal cycle became a way to compare real processes with physical limits. Physicist and historian of the physical and mathematical sciences Raffaele Pisano traces how machines, diagrams, later theoretical reinterpretation and archival evidence turned an engineering problem into a durable thermodynamic law.
An article in Science Advances introduces a method for measuring the temperature inside living cells.
Levitodynamics aims to control micro-objects and nano-objects levitated in vacuum. For years, the field had worked towards one goal — the ground-state cooling of optically trapped nanoparticles — providing the community with a direction and a justification for many of its activities. As this crucial demonstration of quantum control of mechanical motion has now been achieved, it is a good time to stop and consider which objectives may serve as the main drivers for the levitodynamics community in the future. With all the progress made in the past decade, further and even more ambitious experiments have come within reach and will open up opportunities to probe the quantum nature of mechanical motion more deeply. At the same time, the increasing level of technological refinement and the growing level of experience and routine in handling and controlling optically levitated mechanical systems has initiated a drive towards technological applications. In this Perspective, we provide a forward-looking view on the field of optical levitodynamics. We detail where we believe the field stands and which recent technological developments stand out to arrive at an educated, but certainly biased and potentially controversial, opinion on where the future may lead our community. We focus on two research areas that we consider particularly promising — sensing and the generation of non-classical states of mechanical motion. For both areas, we summarize the state of the art and we collate possible future directions together with foreseeable challenges. Ground-state cooling of levitated particles has brought the field of levitodynamics into the quantum regime, but the next steps are less clear. This Perspective highlights advances and challenges in two key frontiers — precision sensing and generation of non-classical states of motion.
Paul Bate has gone from particle physics to Number 10 Downing Street to the UK Space Agency and beyond. Throughout, he has delivered on big ideas by recognizing expertise in others.
The excitonic insulator is a many-body ground state of condensed, spontaneously formed excitons (electron–hole pairs) in equilibrium. Unlike conventional band or Mott insulators, excitonic insulators are difficult to realize experimentally and demonstrate unambiguously. In recent years, the concept has gained renewed experimental traction thanks to advances in spectroscopic resolution, ultrafast probes and materials synthesis. In this Review, we outline the essential theoretical ingredients underpinning excitonic order and then examine the diverse experimental fingerprints of the excitonic state. We propose strategies to disentangle excitonic order from competing phases such as charge density waves, Mott insulating states and hybridization-driven insulators. We survey the rapidly expanding family of candidate materials, from layered chalcogenides in 2D and 3D to artificial excitonic platforms. Finally, we discuss the key challenges and emerging opportunities in the field, identifying the theoretical and experimental frontiers that promise to shape the next decade of research. Excitonic insulators are many-body states in which electron–hole pairing drives insulating behaviour with coherent condensate properties. This Review examines diverse experimental fingerprints of the excitonic state and proposes strategies to disentangle excitonic order from competing phases.
