arXiv subjects

David Ziemkiewicz

Publications and source records attributed to David Ziemkiewicz.

At least 19 recordsLinked to original sources

arXiv2026

Propagation processing of short pulses in Rydberg exciton medium under blockade conditions

Propagation of short pulses through Cu$_2$O crystal containing Rydberg excitons is studied with the use of density matrix formalism and FDTD method. Saturation effects related to the so-called Rydberg blockade are studied extensively, exploring not only reduction of absorption (bleaching) but also power-dependent changes of the dispersive properties of the medium. The role of exciton lifetime and coherent population oscillations in the dynamics of the system is investigated. A pump-probe setup with two pulses is also studied, showing good agreement with recent experimental studies.

cond-mat.mes-hall↗

arXiv2026

Emission Dynamics of Rydberg Excitons in $\mathbf{\mathrm{Cu_2O}}$: Distinguishing Second Harmonic Generation from Secondary Emission

Rydberg excitons in $\mathrm{Cu_2O}$ simultaneously give rise to two very different optical responses under resonant two-photon excitation: a coherent second-harmonic signal mediated by the excitonic second order susceptibility tensor $\chi^{(2)}$, and a secondary emission originating from the radiative decay of real exciton populations. Distinguishing these two channels is essential for interpreting nonlinear and quantum-optical experiments based on high-$n$ states, yet their temporal, spectral, and power-dependent signatures often overlap. Here we use time-resolved resonant two-photon excitation to cleanly separate SHG and SE and to map how each depends on $n$, temperature, excitation power, and crystal quality. This approach reveals the markedly different sensitivities of the two processes to phonons, defects, and many-body effects, and establishes practical criteria for identifying SE and SHG in a wide range of experimental conditions. Our results provide a unified framework for interpreting emission from Rydberg excitons and offer guidelines for future studies aiming to exploit their nonlinear response and long-range interactions.

cond-mat.quant-gas↗

arXiv2025

Plasmon-enhanced quadrupole transitions of Rydberg excitons in Cu2O

A mechanism for amplification of weak quadrupole transitions of Rydberg excitons in Cu$_2$O by a plasmonic nanostructure is investigated. The theoretical description of exciton-plasmon interaction is presented and a field averaging approximation is proposed for calculations involving large excitons. Various types of copper, silver and gold-based plasmonic nanostructures are considered and their potential for enhancing quadrupole transitions is evaluated.

physics.optics↗

arXiv2025

Quantum interference of Rydberg excitons in Cu$_2$0: quantum beats

A density matrix formalism is employed to calculate the emission of multi-level excitonic system, highlighting picosecond-scale dynamics and coherent effects such as quantum beats. The results are compared with recent experimental results and indicate some directions of further study. In particular, the effect of Rydberg blockade on the quantum beat phenomenon is discussed.

physics.optics↗

arXiv2024

Optical properties of excitons in CdSe nanoplatelets and disks: real density matrix approach

We show how to calculate the optical functions of a nanoplatelet, taking into account the effect of a dielectric confinement on excitonic states. Real density matrix approach is employed to obtain analytical and semi-analytical relations for the absorption coefficient, the exciton resonance energy and binding energy of nanoplatelets and nanodisks. The impact of plate geometry (thickness, area) on the spectrum is discussed and the results are compared with the available experimental data.

physics.optics↗

arXiv2024

Two-photon absorption in silicon using real density matrix approach

Two-photon absorption in indirect gap semiconductors is an frequently encountered, but not well-understood phenomenon. To address this, the Real Density Matrix Approach is applied to describe two-photon absorption in silicon through the excitonic response to the interacting fields. This approach produces an analytical expression for the dispersion of the two-photon absorption coefficient for indirect-gap materials, and can be used to explain trends in reported experimental data for bulk silicon both old and new with minimal fitting.

physics.optics↗

arXiv2023

Optical properties of Rydberg excitons in Cu$_2$O based superlattices

Combining the microscopic calculation of superlattice minibands and the macroscopic real density matrix approach one can obtain electric susceptibilities of the superlattice system irradiated by an electromagnetical wave. It is shown how to compute the dispersion relation, excitonic resonances positions and susceptibility of Cu$_2$O/MgO based superlattice (SL), when Rydberg Exciton-Polaritons appear, including the effect of the coherence between the electron-hole pair and the electromagnetic field and the polaritonic effect. Using the Kronig-Penney model for computing miniband SL parameters the analytical expressions for optical functions are obtained and the numerical calculations for Cu$_2$O/MgO SL are performed.

physics.optics↗

arXiv2023

Optical to microwave frequency conversion with Rydberg excitons

A novel, copper-based plasmonic system is presented to provide optical to microwave photon conversion. The process uses highly excited levels in Cu2O Rydberg excitons and takes advantage of spoof plasmons, which allow for significant enhancement of the transition probability between specific excitonic energy levels. The theoretical results are verified with numerical simulations. The proposed system is very flexible, allowing for emission of microwaves wavelength from 0.1 mm to 10 mm.

physics.optics↗

arXiv2022

Superlens with copper and copper oxide

We investigate the imaging properties of copper-based superlens surrounded by copper oxide (Cu$_2$O). A subwavelength image resolution of the order $\lambda/9$ is demonstrated theoretically and verified in numerical simulations. It is shown that the existence of excitons in Cu$_2$O influence the static and dynamical optical properties of the lens. In particular, an improvement of image quality caused by absorption in the spectral region of excitonic resonances is investigated. The plasmon-exciton interaction in the system may pave the way to a tunable, highly nonlinear superlens designs.

cond-mat.mes-hall↗

arXiv2022

Copper plasmonics with excitons

We investigate the propagation of surface plasmons (SPPs) in a thin layer of copper surrounded by copper oxide Cu$_2$O. It is shown that particularly strong excitons in Cu$_2$O can have considerable impact on plasmon propagation, providing many opportunities for plasmon-exciton and plasmon-plasmon interactions. It is demonstrated that by the use of sufficiently thin metal layer, one can excite the so-called long range plasmons (LRSPPs) which can overcome the inherently high ohmic losses of Cu as compared to usual plasmonic metals such as silver. Analytical results are confirmed by numerical calculations.

cond-mat.mes-hall↗

arXiv2022

Nonlinear optical properties and Kerr nonlinearity of Rydberg excitons in Cu$_2$O quantum wells

The quantum confiment of Rydberg excitons (REs) in quantum structures opens the way towards considering nonlinear interactions in such systems. We present a theoretical calculation of optical functions in the case of a nonlinear coupling between REs in a quantum well with an electromagnetic wave. Using the Real Density Matrix Approach (RDMA), the analytical expressions for a linear and nonlinear absorption are derived and numerical calculations for Cu$_2$0 quantum wells are performed. The results indicate the conditions in which quantum well confinement states can be observed in linear and nonlinear optical spectra. The Kerr nonlinearity and self-phase modulation in such a system are studied. The effect of Rydberg blockade and the associated optical bleaching are also discussed and confronted with available experimental data.

cond-mat.mes-hall↗

arXiv2022

Self-Kerr effect across the yellow $\mathrm{Cu_2O}$ Rydberg series

We investigate the nonlinear refraction induced by Rydberg excitons in $\mathrm{Cu_2O}$. Using a high-precision interferometry imaging technique that spatially resolves the nonlinear phase shift, we observe significant shifts at extremely low laser intensity near each exciton resonance. From this, we derive the nonlinear index $\mathrm{n_2}$, present the $\mathrm{n_2}$ spectrum for $n\geq 5$ and report large $\mathrm{n_2}$ values of order $10^{-3}$ mm$^2$/mW. Moreover, we observe a rapid saturation of the Kerr nonlinearity and find that the saturation intensity $\mathrm{I_{sat}}$ decreases as $n^{-7}$. We explain this with the Rydberg blockade mechanism, whereby giant Rydberg interactions limit the exciton density, resulting in a maximum phase shift of 0.5 rad in our setup.

quant-ph↗

arXiv2021

Entropy of timekeeping in a mechanical clock

The dynamics of an unique type of clock mechanism known as grasshopper escapement is investigated with the aim of evaluating its accuracy in a noisy environment. It is demonstrated that the clock's precision scales linearly with the rate of its entropy production, consistently with recently reported results regarding nanoscale and quantum clocks. Moreover, it is shown that the inevitable force variations present in the mechanism can be modelled with a Maxwell-Boltzmann statistic. Finally, the function of clock error is compared with Brownian motion and its fractal-like properties are discussed. The numerical results are confirmed with experimental data.

physics.app-ph↗

arXiv2021

Quantum confined Rydberg excitons in Cu$_2$O nanoparticles

The quantum confinement of Rydberg excitons is an important step towards exploiting their large nonlinearities for quantum applications. We observe Rydberg excitons in natural nanoparticles of Cu$_2$O. We resolve up to the principal quantum number $n=12$ in a bulk Cu$_2$O crystal and up to $n=6$ in nanoparticles extracted from the same crystal. The exciton transitions in nanoparticles are broadened and their oscillator strengths decrease as $\propto n^{-4}$ compared to those in the bulk (decreasing as $\propto n^{-3}$). We explain our results by including the effect of quantum confinement of exciton states in the nanoparticles. Our results provide an understanding of the physics of Cu$_2$O Rydberg excitons in confined dimensions.

cond-mat.mes-hall↗

arXiv2021

Electro-optical properties of excitons in Cu$_2$O quantum wells: I discrete states

We present theoretical results of the calculations of optical functions for Cu$_2$O quantum well (QW) with Rydberg excitons in an external homogeneous electric field of an arbitrary field strength. Two configurations of an external electric field perpendicular and parallel to the QW planes are considered in the energetic region for discrete excitonic states and continuum states. With the help of the real density matrix approach, which enables the derivation of the analytical expressions for the QW electro-optical functions, absorption spectra are calculated for the case of the excitation energy below the gap energy.

cond-mat.mes-hall↗

arXiv2021

Electro-optical properties of excitons in Cu$_2$O quantum wells: II continuum states

We present theoretically calculated optical functions for Cu$_2$O quantum well (QW) with Rydberg excitons in an external, homogeneous electric field parallel to the QW planes for the energy region above the gap, suitable to observe the Franz-Keldysh (FK) oscillations. We quantitatively describe the amplitudes and periodicity of FK modulations and the influence of both Rydberg excitons and confinement effect on this phenomenon.

cond-mat.mes-hall↗

arXiv2021

Numerical analysis of grasshopper escapement

The dynamics of driven, damped pendulum as used in mechanical clocks is numerically investigated. In addition to the analysis of a well-known mechanisms such as chronometer escapement, the unusual properties of Harrison's grasshopper escapement are explored, giving some insights regarding the dynamics of this system. Both steady state operation and transient effects are discussed, indicating the optimal condition for stable long-term clock accuracy. Possibility of chaotic motion is investigated.

physics.class-ph↗

arXiv2021

Fractional Derivative Modification of a Drude Model

A modification of the Drude dispersive model based on fractional time derivative is presented. The dielectric susceptibility is calculated analytically and simulated numerically, showing a good agreement between theoretical description and numerical results. The absorption coefficient and wave vector -- key parameters describing the propagation of waves in such a medium -- are shown to follow a power law in the frequency domain, which is a common phenomenon in many real life applications. The introduction of two separate parameters provides a more flexible model than some other approaches found in literature and is well suited for numerical implementation.

physics.comp-ph↗