Álvaro Parra-López

• Bergli, Joakim & Lopez, Alvaro Parra (2020). Synchronization in two-level quantum systems. Physical Review A (PRA). ISSN 2469-9926. 101, s. 062104–062104. doi: 10.1103/PhysRevA.101.062104. Fulltekst i vitenarkiv Vis sammendrag

  Recently, it was shown that dissipative quantum systems with three or more levels are able to synchronize to an external signal. Some researchers have stated that this is not possible for two-level systems, as those systems lack a stable limit cycle in unperturbed dynamics, but others have demonstrated, under a different definition of synchronization, that it is possible in qubits in models which include other elements. We show how a quantum two-level system can be understood as containing a valid limit cycle as the starting point of synchronization and that it can synchronize its dynamics to an external weak signal. This is demonstrated by analytically solving the Lindblad equation of a two-level system coupled to an environment, determining the steady state. This is a mixed state with contributions from many pure states, each of which provides a valid limit cycle. We show that this is sufficient to phase lock the dynamics to a weak external signal, hence clarifying synchronization in two-level systems. We use the Husimi Q representation to analyze the synchronization region, defining a synchronization measure which characterizes the strength of the phase locking. Also, we study the stability of the limit cycle and its deformation with the strength of the signal in terms of the components of the Bloch vector of the system. Finally, we generalize a model of the three-level system to illustrate how the stationary fixed point of that model can be changed into a limit cycle similar to the one that we describe for the two-level system.

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• Parra-López, Álvaro (2026). Gravitational dark matter production, its uncertainties, and its interplay with freeze-in. doi: https:/indico.capa.unizar.es/event/40/contributions/873/. Fulltekst i vitenarkiv Vis sammendrag

  The persistent absence of non-gravitational dark matter signals has increased interest in candidates that interact extremely weakly with the Standard Model—if at all. (Non-perturbative) gravitational particle production provides an unavoidable mechanism for generating such dark matter via the expansion of spacetime. However, predicting the exact relic abundance is subject to significant theoretical uncertainties arising from the choice of inflationary potential, field spin, and the details of the reheating phase. In this talk, I will present an estimation of these uncertainties based on recent results for scalar and vector spectator fields across different inflationary backgrounds. Furthermore, I explore the conceptual and technical challenges of reconciling this gravitational production—rooted in QFT in curved spacetimes—with the freeze-in mechanism, typical in astroparticle physics

• Parra-López, Álvaro (2026). Towards tackling the inherent uncertainties of gravitational dark matter production. doi: https:/indico2.uis.no/event/64/contributions/1989/. Fulltekst i vitenarkiv Vis sammendrag

  The persistent absence of non-gravitational dark matter signals has increased interest in candidates that interact extremely weakly with the Standard Model—if at all. (Non-perturbative) gravitational particle production provides an unavoidable mechanism for generating such dark matter via the expansion of spacetime. However, predicting the exact relic abundance is subject to significant theoretical ambiguities tied to the framework of QFT in curved spacetimes, as well as uncertainties coming from inflationary and reheating dynamics. In this talk, I will present an overview of these uncertainties based on recent results for scalar and vector spectator fields across different inflationary backgrounds. These ambiguities become especially problematic for masses below the scale of inflation due to tachyonic instabilities and the non-adiabaticity of the field modes. Since this regime is of particular interest for other non-thermal production mechanisms, such as freeze-in, it is crucial to address these conceptual and technical challenges to ensure a robust phenomenological approach.

• Parra-López, Álvaro (2026). Ambiguities and uncertainties in gravitational dark matter production. doi: https:/indico.global/event/15863/contributions/155854/. Fulltekst i vitenarkiv Vis sammendrag

  The persistent absence of non-gravitational dark matter signals has increased interest in candidates that interact extremely weakly with the Standard Model—if at all. (Non-perturbative) gravitational particle production provides an unavoidable mechanism for generating such dark matter via the expansion of spacetime. However, predicting the exact relic abundance is subject to significant theoretical ambiguities tied to the framework of QFT in curved spacetimes, as well as uncertainties coming from inflationary and reheating dynamics. In this talk, I will present an overview of these uncertainties based on recent results for scalar and vector spectator fields across different inflationary backgrounds. These ambiguities become especially problematic for masses below the scale of inflation due to tachyonic instabilities and the non-adiabaticity of the field modes. Since this regime is of particular interest for other non-thermal production mechanisms, such as freeze-in, it is crucial to address these conceptual and technical challenges to ensure a robust phenomenological approach.

Se alle arbeider i NVA