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Item Twist-and-turn dynamics of spin squeezing in bosonic Josephson junctions: Enhanced shortcuts-to-adiabaticity approach(American Physical Society, 2024-08-12) Odelli, Manuel; Ruschhaupt, Andreas; Stojanović, Vladimir M.; Science Foundation Ireland; Deutsche ForschungsgemeinschaftThe twist-and-turn dynamics of spin squeezing results from the interplay of the one-axis-twisting (nonlinear in the collective-spin operators) and the transverse-field turning (linear) term in the underlying Lipkin-Meshkov-Glick-type Hamiltonian, both with constant (time-independent) prefactors. Using shortcuts to adiabaticity (STA) and the recently developed enhanced version thereof (eSTA), we demonstrate here that dynamics of this type can be utilized for a fast and robust preparation of spin-squeezed states in internal bosonic Josephson junctions, i.e., condensates of cold bosonic atoms in two different internal (hyperfine) states (single-boson modes) coupled through Rabi rotations. Assuming that the initial state of this system is its ground state for a given initial value of the (time-dependent) linear coupling strength and that the nonlinear coupling strength remains constant, we set out to determine the time dependence of the linear (Rabi) coupling strength that allows for the generation of spin-squeezed states using the STA- and eSTA-based approaches. We then characterize the modified twist-and-turn dynamics of this system by evaluating the coherent spin-squeezing and number-squeezing parameters, as well as the fidelity of the target spin-squeezed states. In this way, we show that the eSTA approach allows for a particularly robust realization of strongly spin-squeezed states in this system, consistently outperforming its adiabatic and STA-based counterparts, even for systems with several hundred particles. Our method could also be employed for the generation of metrologically-useful non-Gaussian states.Item Impact of random alloy fluctuations on the carrier distribution in multicolor (In,Ga)N/GaN quantum well systems(American Physical Society, 2024-02-27) O’Donovan, Michael; Farrell, Patricio; Moatti, Julien; Streckenbach, Timo; Koprucki, Thomas; Schulz, Stefan; Sustainable Energy Authority of Ireland; Science Foundation Ireland; Deutsche Forschungsgemeinschaft; Austrian Science FundThe efficiency of (In,Ga)N-based light-emitting diodes (LEDs) is limited by the failure of holes to evenly distribute across the (In,Ga)N/GaN multiquantum well stack that forms the active region. To tackle this problem, it is important to understand carrier transport in these alloys. In this work, we study the impact that random alloy fluctuations have on the distribution of electrons and holes in such devices. To do so, an atomistic tight-binding model is employed to account for alloy fluctuations on a microscopic level and the resulting tight-binding energy landscape forms input to a quantum corrected drift-diffusion model. Here, quantum corrections are introduced via localization-landscape theory. Similar to experimental studies in the literature, we have focused on a multiquantum well system in which two of the three wells have the same In content, while the third well differs in In content. By changing the order of wells in this “multicolor” quantum well structure and looking at the relative radiative-recombination rates of the different emitted wavelengths, we (i) gain insight into the distribution of carriers in such a system and (ii) can compare our findings to trends observed in experiment. We focus on three factors and evaluate the impact that each have on carrier distribution: an electron blocking layer, quantum corrections, and random alloy fluctuations. We find that the electron blocking layer is of secondary importance. However, in order to recover experimentally observed features—namely, that the 𝑝-side quantum well dominates the light emission—both quantum corrections and random alloy fluctuations should be considered. The widely assumed homogeneous virtual-crystal approximation fails to capture the characteristic light emission distribution across a multiquantum well stack.Item Harmonic frequency locking and tuning of comb frequency spacing through optical injection(Optica Publishing Group, 2019) Shortiss, Kevin; Lingnau, Benjamin; Dubois, Fabien; Kelleher, Bryan; Peters, Frank H.; Science Foundation Ireland; Deutsche ForschungsgemeinschaftWe show, both experimentally and theoretically, that a slave laser injected with an optical frequency comb can undergo two distinct locking mechanisms, both of which decrease the output optical comb’s frequency spacing. We report that, for certain detuning and relative injection strengths, slave laser relaxation oscillations can become undamped and lock to rational frequencies of the optical comb spacing, creating extra comb tones by nonlinear dynamics of the injected laser. We also study the frequency locking of the slave laser at detunings in between the injected comb lines, which add the slave laser’s frequency to the comb. Our results demonstrate the effect of the 𝛼 parameter and stability of the locked states and indicate how the frequency of the relaxation oscillations affect both of these locking mechanisms. These optical locking mechanisms can be applied to regenerate or multiply optical combs.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.