@inproceedings {730,
	title = {Efficiency and power output of a two-stroke quantum heat engine with a collisional model consisting of N <= 5 qubits},
	booktitle = {Proceedings of the 44th Samahang Pisika ng Pilipinas Physics Conference},
	year = {2026},
	month = {17-20 Jun 2026},
	pages = {SPP-2026-2H-06},
	address = {Los Ba{\~n}os},
	abstract = {Heat engines are thermal devices that convert input energy from a thermal reservoir to generate useful work. However, not all energy is converted into mechanical work{\textemdash}some is discarded into a heat sink, such that the measure of the ratio of work output to heat input is called efficiency. The power of a heat engine characterizes the work-output rate. In the quantum regime, quantum heat engines (QHEs) operate the same way but use quantum matter as a working substance. In this paper, the efficiency and power output of a stroboscopic two-stroke QHE with a collisional model are evaluated, where the working substance is a linear chain of N uncoupled qubits. The numerical calculations show that as the interaction strength is increased between qubits, the QHE yields higher efficiency and power output. However, it takes a larger number of cycles for the engine to reach the Otto efficiency as the qubit size is increased. In addition, the QHE yields a stable power output, where the smaller qubit system sizes have higher power outputs. },
	url = {https://proceedings.spp-online.org/article/view/SPP-2026-2H-06},
	author = {Andrei Espencer M Ordonio and Villagonzalo, Cristine D.}
}
@inproceedings {625,
	title = {Entropy and specific heat features of a four spin system at its energy level crossings},
	booktitle = {Proceedings of the 41st Samahang Pisika ng Pilipinas Physics Conference},
	year = {2023},
	month = {19{\textendash}21 July 2023},
	pages = {SPP-2023-PA-33},
	address = {Siargao},
	abstract = {A previous study showed that the efficiency of a quantum heat engine utilizing the Lipkin-Meshkov-Glick (LMG) spin system can reach the Carnot limit at low temperatures when the external field reaches the energy level cross points of the ground states. These points occur when different energy levels become degenerate. To delve more into the quantum behavior at the crossing points, this work considered the thermodynamic characteristics of an LMG model consisting of four spins. Using the eigenenergies for the N = 4 spin system with anisotropy, the entropy, and specific heat were numerically obtained in the canonical ensemble and studied as a function of its energy level crossings. It is found that lower values of energy level crossings correspond to more stable entropies and higher specific heat values of the system. These features make the LMG spin system suitable as a working substance in heat engine applications.},
	url = {https://proceedings.spp-online.org/article/view/SPP-2023-PA-33},
	author = {Andrei Espencer M Ordonio and Cristine D. Villagonzalo}
}
@inproceedings {581,
	title = {Crossing and anti-crossing of the Lipkin-Meshkov-Glick model for N = 4 spin system},
	booktitle = {Proceedings of the 40th Samahang Pisika ng Pilipinas Physics Conference},
	year = {2022},
	month = {19{\textendash}21 Oct 2022},
	pages = {SPP-2022-2G-06},
	address = {Legazpi City},
	abstract = {Energy level crossings are degeneracies of two or more energy levels which occur when two levels coincide due to the tuning of an external parameter. In this work, we observe the "motion" of the energy levels in terms of the applied external magnetic field and anisotropy. We demonstrate how the eigenenergies of the anisotropic Lipkin-Meshkov-Glick (LMG) model for the N = 4 spin system shift as a function of the aforementioned parameters. The resulting plots show multiple level crossings as the system becomes isotropic where the LMG model has degenerate ground states along the critical lines determined by the anisotropy parameter. This work has also verified that for the isotropic case, energy level crossings occur exactly at the critical points.},
	url = {https://proceedings.spp-online.org/article/view/SPP-2022-2G-06},
	author = {Andrei Espencer M Ordonio and Klarence Anne M. Feri and Cristine D. Villagonzalo}
}