Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences最新文献

Historically, the realization of the base unit kelvin was exclusively possible via International Temperature Scales (ITS). The new definition of the kelvin and the accompanying Mise en Pratique of the kelvin (MeP-K) enables the alternative to use primary thermometry for the realization of the kelvin. During the last years, considerable improvements in primary thermometry in the low-temperature range have been achieved. Thereby, above 300 K, still a lot of work is necessary to be competitive with the existing ITS realization. In this contribution, the interplay between primary thermometry, ITS and scale carriers (platinum resistance thermometers, thermocouples) in a historical perspective is sketched. After a short introduction to primary thermometry in general and the established techniques within the MeP-K, the focus will lie on the challenges connected with thermodynamic temperature measurement above 300 K. The advantages and disadvantages of the different techniques will be discussed briefly, and a summary will be given showing that thermodynamic temperature T, TITS and scale carriers are highly connected and improvement in one field relies on improvement in the others. The background of the discussion will be the deficiencies of the existing ITS and thus the requirements for the temperature-measurement community. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.

In the perspective, some new methods for measuring thermodynamic (or primary) temperature that exploit quantum effects are discussed. The techniques discussed are at various stages of development, so for each, the principles of operation, current and anticipated challenges and current status and progress are presented. First, the development of a thermometer based on cavity magnomechanics for cryogenic applications is discussed. This technique links temperature to a signal derived from the phonon modes in a magnetic element coupled to a microwave cavity. Second, progress in Coulomb blockade thermometry is discussed. Advances in the manipulation of atoms using scanning probe microscopy (SPM) have led to the creation of structures, such as single-electron transistors (SETs), with physical dimensions smaller than can be achieved using traditional lithography. A Coulomb blockade thermometer (CBT) fabricated at such small scales could operate at higher temperatures than previously demonstrated. Third, Rydberg thermal radiometry is discussed. The excited states of Rydberg atoms possess large dipole moments and interact strongly with blackbody radiation (BBR). Rydberg radiometry leverages these interactions to infer a source's temperature from the effect of its emitted BBR upon the quantum dynamics of Rydberg states. Fourth, thermometry via temperature-dependent optical emission from nanoparticles is discussed, which is expected to be particularly useful for biological applications; in addition, efforts are underway to achieve primary thermometry by this mechanism. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.

The international system of units (the SI) is currently defined in terms of fundamental constants with defined values. The kelvin is defined in terms of the Boltzmann constant (k). The new definitions have their associated mise en pratique (MeP) to indicate how the definition of the SI base unit, such as the kelvin, symbol K, may be realized in practice. For the case of temperature, the MeP-K enables the practical implementation of primary thermometry techniques which provide thermodynamic temperature, T. The MeP provides guidelines for the realization and dissemination of the kelvin using thermodynamic thermometry while also recognizing the continued use of International Temperature Scales (ITS-90 and PLTS-2000) as practical references for most temperature measurements, T90. Above the freezing point of silver (1234.93 K ), T₉₀ temperatures, defined by the ITS-90, are determined using the Planck radiation law in a relative manner. The primary method included in the MeP-K for this range is primary radiometric thermometry, which applies the same law in both absolute and relative forms. In this article, a description of the primary methods for measuring T in comparison with T90, above the silver point is presented. A review of the different possibilities using absolute and relative primary radiometric thermometry is provided and the uncertainties and feasibility studied. We illustrate our findings with some examples of primary thermometry measurements performed at the Centro Español de Metrología. These examples provide a comprehensive overview of the advantages or disadvantages of using ITS-90 and the MeP-K primary thermometry above the silver point. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.

We have implemented absolute acoustic gas thermometry at 10 K, 13.8 K, 19 K and 24.6 K to evaluate the performance of this primary method for the direct thermodynamic calibration of capsule-type resistance thermometers, including both platinum and rhodium-iron types. Our implementation is based on speed of sound measurements in helium at a single pressure, chosen in the range 65 to 130 kPa, with non-ideality corrections relying on accurate ab initio calculations of the thermodynamic properties. The overall accuracy achieved in the determination of the thermodynamic temperature T varies between a minimum of 0.1 mK at 13.8 K to a maximum of 0.2 mK at 24.6 K. From the acoustic results and the calibration of thermometers on the international temperature scale ITS-90 providing T90, we determined the differences (T-T90), finding them in good agreement with the 2022 consensus estimates within the combined uncertainties. These results include a determination of the thermodynamic temperature at the triple point of neon TNe = (24.55502 ± 0.00030) K. This new value of TNe is consistent with other recent determinations obtained with various primary methods. Finally, we provide an example of a rapid, yet accurate, simplified thermodynamic calibration procedure. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.

Atoms and simple molecules are excellent candidates for new standards and sensors because they are both identical and their properties are determined by the immutable laws of quantum physics. Here, we introduce the concept of building a standard and sensor of radiative temperature using atoms and molecules. Such standards are based on precise measurement of the rate at which blackbody radiation (BBR) either excites or stimulates emission for a given atomic transition. We summarize the recent results of two experiments while detailing the rate equation models required for their interpretation. The cold atom thermometer (CAT) uses a gas of laser-cooled 85Rb Rydberg atoms to probe the BBR spectrum near 130 GHz. This primary, i.e. not traceable to a measurement of like kind, temperature measurement currently has a total uncertainty of approximately 1%, with clear paths toward improvement. The compact BBR atomic sensor (CoBRAS) uses a vapour of 85Rb and monitors fluorescence from states that are either populated by BBR or populated by spontaneous emission to measure the blackbody spectrum near 24.5 THz. The CoBRAS has an excellent relative precision of u(T) ≈ 0.13 K, with a clear path toward implementing a primary measurement. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.

The redefinition of the kelvin has ushered in a new era for thermometry, emphasizing the need for robust global interoperability and traceability. This paper explores the multifaceted challenges associated with maintaining these standards in a rapidly evolving scientific landscape. Central to this discussion is the role of the Consultative Committee for Thermometry (CCT), which oversees the establishment, realization and dissemination of the international temperature scales and thermodynamic temperature. CCT plays a critical role in harmonizing international standards, ensuring there is global consistency in temperature measurement. Furthermore, the evolving role of National Metrology Institutes (NMIs) in the International System of Units, post the redefinition of the kelvin in 2019, highlights the increasing importance of decentralized and quantum-based measurement techniques. NMIs are now tasked with developing and disseminating advanced, intrinsically accurate sensors that could operate reliably and independently of traditional standards. That is through delivering in situ traceability and reliability of temperature measurement across diverse applications. This paper discusses these critical topics, examining the collaborative efforts and the long-term CCT strategy required to sustain global interoperability in thermometry. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.

The redefinition of the kelvin motivates the realization of thermodynamic temperature standards and their improvement up to the stage where they become sufficiently accurate, reliable and practically useful for the purpose of disseminating the unit by direct calibration of temperature sensors. We review progress milestones in the development of gas-based primary thermometry methods, assess their current state of the art and discuss the remaining challenges and the perspectives of using thermodynamic methods as an alternative to traditional dissemination based on the realization of the International Temperature Scale. We give an account of research initiatives which are underway to test the maturity of this perspective, including an international blind comparison of thermodynamic calibrations of capsule-type resistance thermometers using different methods of primary gas thermometry in the range 4 to 300 K. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.

The revised definition of the kelvin has created new interest in alternative paths of traceability to the SI. In particular, the development of methods for the direct realization of the kelvin is ongoing, establishing traceability without the need to go through the international-consensus temperature scale, the ITS-90. These direct realization methods are in contrast to the ITS-90 and the measurement infrastructure of reference materials and artefact thermometer calibration chains. This infrastructure has been built up over a century or more of industrialization and scientific progress, and while very robust, is not well suited to address the requirements of the most demanding of application environments. We examine how direct traceability to the kelvin can be applied to address those applications and assess the relative practical merits of various direct realization approaches. Primary thermometry methods are surveyed from the standpoint of achievable uncertainties over the range 4 K to 1800 K with examples of practical direct-realization technologies. This assessment points to a narrow application space of long-term missions, or those occurring in remote or hazardous environments, as the most compelling cases for the direct realization approach. We present two special application environments where direct realizations are well suited for point-of-use temperature measurement. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.

We demonstrate a photonic temperature sensor based on three silicon cascaded ring resonators (CRRs) integrated on a 3 µm thick silicon-on-insulator (SOI) platform for contact thermometry. A CRR-based sensor achieves an expanded free spectral range (FSR) of 23 nm, enabling a broader operational temperature range compared with the FSR of 1 nm for the single ring resonator. The thick SOI platform offers several advantages, including low propagation loss (less than 0.1 dB cm-1), negligible polarization dependence (approaching zero birefringence) and high-power handling capability (greater than 10 mW) without any resonance shape deformation from two-photon absorption (TPA). Optical coupling was achieved through edge-coupled fibre packaging to the photonic chip. The sensor exhibits a temperature sensitivity of 85 pm K-1 with an uncertainty of 16.1 mK, measured over a temperature range from -20 to 90°C. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.