Physics - Journal Articles

Permanent URI for this collection

Browse

Recent Submissions

Now showing 1 - 5 of 402
  • 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, Stephen
    Although 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, Bryan
    Abstract: 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 Forschungsgemeinschaft
    We 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 Council
    We 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.
  • Item
    A black widow population dissection through HiPERCAM multiband light-curve modelling
    (Oxford University Press, 2023-01-19) Mata Sánchez, D.; Kennedy, Mark R.; Clark, C. J.; Breton, R. P.; Dhillon, V. S.; Voisin, G.; Camilo, F.; Littlefair, S.; Marsh, T. R.; Horizon 2020; European Regional Development Fund; Consejería de Educación, Universidades, Cultura y Deportes, Gobierno de Canarias; Ministerio de Ciencia e Innovación; Royal Society
    Black widows are extreme millisecond pulsar binaries where the pulsar wind ablates their low-mass companion stars. In the optical range, their light curves vary periodically due to the high irradiation and tidal distortion of the companion, which allows us to infer the binary parameters. We present simultaneous multiband observations obtained with the HIPERCAM instrument at the 10.4-m GTC telescope for six of these systems. The combination of this five-band (us, gs,rs, is, zs) fast photometer with the world’s largest optical telescope enables us to inspect the light curve range near minima. We present the first light curve for PSR J1641+8049, as well as attain a significant increase in signal to noise and cadence compared with previous publications for the remaining five targets: PSR J0023+0923, PSR J0251+2606, PSR J0636+5129, PSR J0952−0607, and PSR J1544+4937. We report on the results of the light-curve modelling with the ICARUS code for all six systems, which reveals some of the hottest and densest companion stars known. We compare the parameters derived with the limited but steadily growing black widow population for which optical modelling is available. We find some expected correlations, such as that between the companion star mean density and the orbital period of the system, which can be attributed to the high number of Roche-lobe filling companions. On the other hand, the positive correlation between the orbital inclination and the irradiation temperature of the companion is puzzling. We propose such a correlation would arise if pulsars with magnetic axis orthogonal to their spin axis are capable of irradiating their companions to a higher degre