arXiv subjects

Hanz Y. Ramírez-Gómez

Publications and source records attributed to Hanz Y. Ramírez-Gómez.

4 recordsLinked to original sources

arXiv2026

A framework for extracting the rates of photophysical processes from biexponentially decaying photon emission data

There is strong interest in designing and realizing optically-active semiconductor nanostructures of greater complexity for applications in fields ranging from biomedical engineering to quantum computing. While these increasingly complex nanostructures can implement progressively sophisticated optical functions, the presence of more material constituents and interfaces also leads to increasingly complex exciton dynamics. In particular, the rates of carrier trapping and detrapping in complex heterostructures are critically important for advanced optical functionality, but they can rarely be directly measured. In this work, we develop a model that includes trapping and release of carriers by optically inactive states. The model explains the widely observed biexponential decay of the photoluminescence signal from neutral excitons in low dimensional semiconductor emitters. The model also allows determination of likelihood intervals for all the transition rates involved in the emission dynamics, without the use of approximations. Furthermore, in cases for which the high temperature limit is suitable, the model leads to specific values of such rates, outperforming reduced models previously used to estimate those quantities. We demonstrate the value of this model by applying it to time resolved photoluminescence measurements of CdSeTe/CdS heterostructures. We obtain values not only for the radiative and nonradiative lifetimes, but also for the delayed photoluminescence originating in trapping and release.

cond-mat.mes-hall↗

arXiv2026

Exciton localization in two-dimensional semiconductors through modification of the dielectric environment

Monolayer semiconductors, given their thickness at the atomic scale, present unique electrostatic environments due to the sharp interfaces between the semiconductor film and surrounding materials. These interfaces significantly impact both the quasiparticle band structure and the electrostatic interactions between charge carriers. Akey area of interest in these materials is the behavior of bound electron-hole pairs (excitons) within the ultra-thin layer, which plays a crucial role in its optoelectronic properties. In this work, we investigate the feasibility of generating potential traps that completely confine excitons in the thin semiconductor by engineering the surrounding dielectric environment. By evaluating the simultaneous effects on bandgap renormalization and modifications to the strength of the electron-hole Coulomb-interaction, both associated to the modulation of the screening by the materials sandwiching the monolayer, we anticipate the existence of low-energy regions in which the localization of the exciton center of mass may be achieved. Our results suggest that for certain dielectric configurations, it is possible to generate complete discretization of exciton eigenenergies in the order of tens of meV. Such quantization of energy levels of two-dimensional excitons could be harnessed for applications in new-generation optoelectronic devices, which are necessary for the advancement of technologies like quantum computing and quantum communication.

cond-mat.mes-hall↗

arXiv2025

Impact of dephased entangled states and varying measurement orientations on the reliability of cryptographic keys generated via the quantum protocol E91: A quantum simulation approach

One of the main requirements to achieve reliable quantum communications are on-demand sources of highly entangled photon pairs, and semiconductor quantum dots have emerged as prominent candidates to satisfy the necessary conditions of brightness and entanglement fidelity. However, in most cases the biexciton-exciton-vacuum cascade produces a pair of maximally polarization-entangled photons with a dephasing, due to a non-negligible exciton fine structure splitting in the emitting nanostructure. This work focuses on the performance of the E91 quantum key distribution protocol under the variation of two elements: first, the phase in the input state when the protocol is implemented using entangled photons generated via the radiative cascade, and second, the relative directions of the polarization analyzers. We use a quantum computational approach by means of the IBM's API Qiskit to simulate the optical implementation of the studied cryptographic protocol and thus to validate analytical expressions derived for the secret key rate and the Bell's parameter. Our results show that the performance of the quantum transmission is highly impacted by the product between the exciton lifetime and the quantum dot's fine structure splitting and that such an impact may be modulated through the orientation of the polarizers. Under some specific conditions, the studied E91 protocol is shown to turn into the BBM92 protocol, to which the results can be extended. These findings provide important insight for the scalable implementation of quantum key distribution protocols with realistic entanglement sources. Furthermore, this study constitutes an illustrative example of how quantum computation can be used as a tool for simulating physical processes whose experimental realization can be substituted by short algorithms run on quantum software.

quant-ph↗

arXiv2024

Exciton Coulomb correlations in axially symmetric II-VI nanocrystals

Because of their conveniently tunable optoelectronic properties, semiconductor nanocrystals have become established components for new devices and emergent technologies, in a broad range of applications which include agriculture, medicine, energy harvesting and quantum information. In this work we study the dielectric and quantum confinement effects on excitons confined in single axially symmetric quantum dots, and systematically calculate by means of the configuration interaction method the corresponding Coulomb correlations in the cases of CdSe, CdTe and ZnTe nanocrystals. % to quantify the effects on the system energy due to the Coulomb interaction. We show that effects from the dielectric confinement, although one order of magnitude bigger than those from the quantum confinement, are negligible in the exciton energies because of mutual cancellation of the electron and hole contributions. Regarding the electrostatic interaction, we found for all analyzed cases that the exciton binding energy is below 2\% of the non-interacting electron-hole pair energy. Furthermore, our calculations reveal that the in general the first-order-perturbation correction accounts for 70 \% to 90 \% of the binding energy. These results provide useful information on the magnitude of the confinement effects in II-VI semiconductor nanocrystals, suggesting that a simple perturbative approach may be accurate enough for including the electrostatic interaction in most cases.

cond-mat.mes-hall↗