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Distributed quantum computing (DQC) combines the computing power of multiple networked quantum processing modules, ideally enabling the execution of large quantum circuits without compromising performance or qubit connectivity 1 , 2 . Photonic networks are well suited as a versatile and reconfigurable interconnect layer for DQC; remote entanglement shared between matter qubits across the network enables all-to-all logical connectivity through quantum gate teleportation (QGT) 3 , 4 . For a scalable DQC architecture, the QGT implementation must be deterministic and repeatable; until now, no demonstration has satisfied these requirements. Here we experimentally demonstrate the distribution of quantum computations between two photonically interconnected trapped-ion modules. The modules, separated by about two metres, each contain dedicated network and circuit qubits. By using heralded remote entanglement between the network qubits, we deterministically teleport a controlled-Z (CZ) gate between two circuit qubits in separate modules, achieving 86% fidelity. We then execute Grover’s search algorithm 5 —to our knowledge, the first implementation of a distributed quantum algorithm comprising several non-local two-qubit gates—and measure a 71% success rate. Furthermore, we implement distributed iSWAP and SWAP circuits, compiled with two and three instances of QGT, respectively, demonstrating the ability to distribute arbitrary two-qubit operations 6 . As photons can be interfaced with a variety of systems, the versatile DQC architecture demonstrated here provides a viable pathway towards large-scale quantum computing for a range of physical platforms. The distribution of quantum computations is demonstrated between two photonically interconnected trapped-ion modules, using repeatable, deterministic teleported controlled-Z gates to perform Grover’s search algorithm.

Cryptographic key exchange protocols traditionally rely on computational conjectures such as the hardness of prime factorization 1 to provide security against eavesdropping attacks. Remarkably, quantum key distribution protocols such as the Bennett–Brassard scheme 2 provide information-theoretic security against such attacks, a much stronger form of security unreachable by classical means. However, quantum protocols realized so far are subject to a new class of attacks exploiting a mismatch between the quantum states or measurements implemented and their theoretical modelling, as demonstrated in numerous experiments 3 – 6 . Here we present the experimental realization of a complete quantum key distribution protocol immune to these vulnerabilities, following Ekert’s pioneering proposal 7 to use entanglement to bound an adversary’s information from Bell’s theorem 8 . By combining theoretical developments with an improved optical fibre link generating entanglement between two trapped-ion qubits, we obtain 95,628 key bits with device-independent security 9 – 12 from 1.5 million Bell pairs created during eight hours of run time. We take steps to ensure that information on the measurement results is inaccessible to an eavesdropper. These measurements are performed without space-like separation. Our result shows that provably secure cryptography under general assumptions is possible with real-world devices, and paves the way for further quantum information applications based on the device-independence principle. This study demonstrates the experimental realization of a complete protocol for quantum key distribution using entangled trapped strontium ions with device-independent quantum security guarantees.

Optical atomic clocks are our most precise tools to measure time and frequency 1 – 3 . Precision frequency comparisons between clocks in separate locations enable one to probe the space–time variation of fundamental constants 4 , 5 and the properties of dark matter 6 , 7 , to perform geodesy 8 – 10 and to evaluate systematic clock shifts. Measurements on independent systems are limited by the standard quantum limit; measurements on entangled systems can surpass the standard quantum limit to reach the ultimate precision allowed by quantum theory—the Heisenberg limit. Although local entangling operations have demonstrated this enhancement at microscopic distances 11 – 16 , comparisons between remote atomic clocks require the rapid generation of high-fidelity entanglement between systems that have no intrinsic interactions. Here we report the use of a photonic link 17 , 18 to entangle two 88 Sr + ions separated by a macroscopic distance 19 (approximately 2 m) to demonstrate an elementary quantum network of entangled optical clocks. For frequency comparisons between the ions, we find that entanglement reduces the measurement uncertainty by nearly 2 , the value predicted for the Heisenberg limit. Today’s optical clocks are typically limited by dephasing of the probe laser 20 ; in this regime, we find that entanglement yields a factor of 2 reduction in the measurement uncertainty compared with conventional correlation spectroscopy techniques 20 – 22 . We demonstrate this enhancement for the measurement of a frequency shift applied to one of the clocks. This two-node network could be extended to additional nodes 23 , to other species of trapped particles or—through local operations—to larger entangled systems. An elementary quantum network of two entangled atomic clocks is demonstrated; the high fidelity and speed of entanglement generation show that entangled clocks can offer practical enhancement for metrology.

The Welfare Quality ® protocols provide a multidimensional assessment of welfare, which is lengthy, and hence limited in terms of practicality. The aim of this study was to investigate potential ‘iceberg indicators’ which could reliably predict the overall classification as a means of reducing the length of time for an assessment and so increase the feasibility of the Welfare Quality ® protocol as a multidimensional assessment of welfare. Full Welfare Quality ® assessments were carried out on 92 dairy farms in England and Wales. The farms were all classified as Acceptable or Enhanced. Logistic regression models with cross validation were used to compare model fit for the overall classification on farms. ‘Absence of prolonged thirst’, on its own, was found to correctly classify farms 88% of the time. More generally, the inclusion of more measures in the models was not associated with greater predictive ability for the overall classification. Absence of prolonged thirst could thus, in theory, be considered to be an iceberg indicator for the Welfare Quality ® protocol, and could reduce the length of time for a farm assessment to 15 min. Previous work has shown that the parameters within the Welfare Quality ® protocol are important and relevant for welfare assessment. However, it is argued that the credibility of the published aggregation system is compromised by the finding that one resource measure (Absence of prolonged thirst) is a major driver for the overall classification. It is therefore suggested that the prominence of Absence of prolonged thirst in this role may be better understood as an unintended consequence of the published measure aggregation system rather than as reflecting a realistic iceberg indicator.

Infrared thermometry is a non-invasive tool shown to be useful in detecting claw abnormalities in cattle at an individual and herd level. This study used the technology to monitor foot temperature and investigate the association with lesion presence over time. A 990 cow dairy herd was enrolled and followed for six months, with data collection fortnightly, lesions were identified by examination of any cow with a mobility score >2, using the 0–3 scale. Two level, multilevel analysis of the association between ambient temperature and foot temperature found that the former was a significant predictor of the latter (coefficient estimate (se)=0.277 (0.02)). Actual foot temperatures were calculated by adjusting for this covariate to allow monitoring over time. Presence of a lesion was also found to be a significant predictor of foot temperature (coefficient estimate (se)=0.623 (0.19)), when added to the model, furthermore some lesion types, claw horn and multiple lesions, were found to be associated with differential foot temperatures. When monitoring lesions over time, the mean adjusted foot temperature was highest at the point of lesion identification. A marked drop in temperature then followed after the lesion was trimmed, with the lowest mean temperature recorded six weeks after treatment, significantly different from the point of lesion identification (P=0.003). This temperature was also lower than the six weeks prior to diagnosis of the lesion, suggesting inflammation was present for at least six weeks prior to the behavioural sign of lameness was seen.

To obtain information on euthanasia decisions from practising veterinary surgeons, respondents were asked to estimate how often during their time in practice they had refused to euthanase a dog and how often they had wanted to refuse to euthanase a dog but not done so because of other pressures. For each, respondents were then asked to state their most common reasons for refusing/not refusing in free text. The responses of clinicians were considered in the light of established ethical concepts to produce an evidence-based ethical framework for decision making. In total, 58 practitioners responded. Common reasons given for decisions on whether to refuse euthanasia referred to the patient's interests, such as the possibility of treatment or rehoming, and the fear of other unacceptable outcomes for the dog. Other reasons were based on concern for owners' interests. Some respondents reported being pressured into euthanasia by clients and other veterinary surgeons. This gives insight into the ethical principles that explicitly underlie veterinary surgeons' euthanasia decisions and the resultant framework may be useful for discussing and teaching euthanasia.

Veterinary surgeons are often asked to provide reports to courts describing factual observations and their expert opinion on the presence or absence of unnecessary suffering in animals. This study reviewed 42 expert witness reports in order to describe the approach taken to the assessment of unnecessary suffering. While most reports suitably described factual observations, there was significant variation in the opinions on suffering and the actions of the owner. Severity and duration of potential suffering was commented upon in 26 and 29 reports, respectively. Experts used terms associated with negative mental states and physical states in 28 and 27 reports, respectively. The necessity of suffering was commented upon in 27 reports, with minimal commentary on the actions of the owner. External references supporting the opinion of the expert were only provided in 13 reports. There was evidence of disputes between experts concerning the definition of suffering, the significance of clinical findings and the relevance of different assessment methods. It is suggested that expert witness reports should include a systematic consideration of the animal's mental and physical states, severity of harm, duration of harm and a commentary on the necessity of suffering as defined by legislation.

In the UK, the pig industry is leading the way in the adoption of welfare outcome measures as part of their farm assurance scheme. The welfare outcome assessment (WOA), known as Real Welfare, is conducted by the farmers’ own veterinary surgeon. For the first time this has allowed the pig industry to evaluate welfare by directly assessing the animal itself, and to document the welfare of the UK pig industry as a whole. Farmer perspectives of the addition of a welfare outcome assessment to their farm assurance scheme have yet to be explored. Here we investigate how the introduction of the Real Welfare protocol has been perceived by the farmers involved, what value it has (if any), whether any practical changes on farm have been a direct consequence of Real Welfare, and ultimately whether they consider that the welfare of their pigs has been improved by the introduction of the Real Welfare protocol. Semi-structured interviews with 15 English pig farmers were conducted to explore their perceptions and experiences of the Real Welfare process. Our findings fall into three key areas: the lived experience of Real Welfare, on farm changes resulting from Real Welfare and suggested improvements to the Real Welfare process as it currently stands. In all three areas, the value farmers placed on the addition of WOA appeared to reflect their veterinary surgeon’s attitude towards the Real Welfare protocol. If the vet was engaged in the process and actively included the farmer, e.g. through discussion of their findings, the farmers interviewed had a greater appreciation of the benefits of Real Welfare themselves. It is recommended that future similar schemes should work with veterinary surgeons to ensure their understanding and engagement with the process, as well as identifying and promoting how the scheme will practically benefit individual farmers rather than assuming that they will be motivated to engage for the good of the industry alone. Retailers should be encouraged to use Real Welfare as a marketing tool for pig products to enhance the perceived commercial value of this protocol to farmers.