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Item At least one in a dozen stars shows evidence of planetary ingestion(Springer Nature Ltd., 2024-03-20) Liu, Fan; Ting, Yuan-Sen; Yong, David; Bitsch, Bertram; Karakas, Amanda; Murphy, Michael T.; Joyce, Meridith; Dotter, Aaron; Dai, FeiStellar chemical compositions can be altered by ingestion of planetary material1,2 and/or planet formation, which removes refractory material from the protostellar disk3,4. These ‘planet signatures’ appear as correlations between elemental abundance differences and the dust condensation temperature3,5,6. Detecting these planet signatures, however, is challenging owing to unknown occurrence rates, small amplitudes and heterogeneous star samples with large differences in stellar ages7,8. Therefore, stars born together (that is, co-natal) with identical compositions can facilitate the detection of planet signatures. Although previous spectroscopic studies have been limited to a small number of binary stars9,10,11,12,13, the Gaia satellite14 provides opportunities for detecting stellar chemical signatures of planets among co-moving pairs of stars confirmed to be co-natal15,16. Here we report high-precision chemical abundances for a homogeneous sample of ninety-one co-natal pairs of stars with a well defined selection function and identify at least seven instances of planetary ingestion, corresponding to an occurrence rate of eight per cent. An independent Bayesian indicator is deployed, which can effectively disentangle the planet signatures from other factors, such as random abundance variation and atomic diffusion17. Our study provides evidence of planet signatures and facilitates a deeper understanding of the star–planet–chemistry connection by providing observational constraints on the mechanisms of planet engulfment, formation and evolution.Item Teaching about magnetic materials - A pedagogical dilemma(American Institute of Physics; American Association of Physics Teachers, 2024-03-07) O'Sullivan, Colm T.; Fahy, StephenAlthough magnetic materials had been studied for over 2000 years, it was not until the development of quantum mechanics in the early years of the 20th century that any satisfactory explanation of their properties could be provided. This paper outlines some of the difficulties that this fact presents for teachers attempting to explain permanent magnetism to learners at different levels who do not have a background in quantum physics. The authors suggest how a consistent and physically correct approach may be achieved.Item Neuromorphic dynamics with optically injected quantum dot lasers(Springer Heidelberg, 2019) Dillane, Michael; Robertson, Joshua; Peters, Matthew; Hurtado, Antonio; Kelleher, BryanAbstract: Optically injected quantum dot lasers display many unique nonlinear phenomena and are in particular, excellent testbeds for different forms of excitability. We analyse the recent discovery of Type II excitability in such devices. An optothermal instability leads to the phenomenon and while an underlying Hopf bifurcation is ultimately responsible for the observation, intriguingly there are two potential routes: One via a subcritical bifurcation and an associated bistable region and the other via a supercritical bifurcation and an associated canard explosion.Item Spin squeezing in internal bosonic Josephson junctions via enhanced shortcuts to adiabaticity(American Physical Society., 2023-11-17) Odelli, Manuel; Stojanović, Vladimir M.; Ruschhaupt, Andreas; Science Foundation Ireland; Deutsche ForschungsgemeinschaftWe investigate a time-efficient and robust preparation of spin-squeezed states—a class of states of interest for quantum enhanced metrology—in internal bosonic Josephson junctions with a time-dependent nonlinear coupling strength between atoms in two different hyperfine states. We treat this state-preparation problem, which had previously been addressed using shortcuts to adiabaticity (STA), using the recently proposed analytical modification of this class of quantum control protocols that has become known as the enhanced STA (eSTA) method. We characterize the state-preparation process by evaluating the time dependence of the coherent spin-squeezing and number-squeezing parameters and the target-state fidelity. We show that the state-preparation times obtained using the eSTA method compare favorably to those found in previously proposed approaches. We also demonstrate that the increased robustness of the eSTA approach—compared to its STA counterpart—leads to additional advantages for potential experimental realizations of strongly spin-squeezed states in internal bosonic Josephson junctions.Item Multicolour optical light curves of the companion star to the millisecond pulsar PSR J2051-0827(Oxford University Press, 2022-08-25) Dhillon, V. S.; Kennedy, Mark R.; Breton, R. P.; Clark, C. J.; Mata Sánchez, D.; Voisin, G.; Breedt, E.; Brown, A. J.; Dyer, M. J.; Green, M. J.; Kerry, P.; Littlefair, S. P.; Marsh, T. R.; Parsons, S. G.; Pelisoli, I.; Sahman, D. I.; Wild, J. F.; van Kerkwijk, M. H.; Stappers, B. W.; Seventh Framework Programme; European Research Council; Science and Technology Facilities Council; Horizon 2020; Irish Research Council; European Regional Development Fund; Consejería de Educación, Universidades, Cultura y Deportes, Gobierno de Canarias; Science and Technology Facilities CouncilWe present simultaneous, multicolour optical light curves of the companion star to the black-widow pulsar PSR J2051−0827, obtained approximately 10 yr apart using ULTRACAM and HiPERCAM, respectively. The ULTRACAM light curves confirm the previously reported asymmetry in which the leading hemisphere of the companion star appears to be brighter than the trailing hemisphere. The HiPERCAM light curves, however, do not show this asymmetry, demonstrating that whatever mechanism is responsible for it varies on time-scales of a decade or less. We fit the symmetrical HiPERCAM light curves with a direct-heating model to derive the system parameters, finding an orbital inclination of 55.9+4.8−4.1 degrees, in good agreement with radio-eclipse constraints. We find that approximately half of the pulsar’s spin-down energy is converted to optical luminosity, resulting in temperatures ranging from approximately 5150+190−190 K on the day side to 2750+130−150 K on the night side of the companion star. The companion star is close to filling its Roche lobe (fRL=0.88+0.02−0.02) and has a mass of 0.039+0.010−0.011 M⊙, giving a mean density of 20.24+0.59−0.44 g cm−3 and an apsidal motion constant in the range 0.0036 < k2 < 0.0047. The companion mass and mean density values are consistent with those of brown dwarfs, but the apsidal motion constant implies a significantly more centrally condensed internal structure than is typical for such objects.