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Ouri Karni

Publications and source records attributed to Ouri Karni.

8 recordsLinked to original sources
arXiv2025

Ultrafast optical gating in a nonlinear lithium niobate microcavity

Recent advances in optical simulation and computational techniques have renewed interest in high-finesse optical cavities for applications such as enhancing light-matter interactions, engineering complex photonic band structures, and storing quantum information. However, the extended interaction times enabled by these cavities often come at the cost of slow optical read-out protocols and limited control over system transients. To address this challenge, we demonstrate an ultrafast intra-cavity optical gating scheme in a high-finesse, second-order nonlinear microcavity incorporating a thin-film of lithium niobate. A femtosecond optical gate pulse -- tuned to the transparency region of the cavity's dielectric mirrors -- achieves instantaneous up-conversion of the intra-cavity field via sum-frequency generation. The resulting upconverted signal exits the cavity as a short pulse, providing space- and time-resolved, on-demand access to the intra-cavity state. We validate this approach by tracking the dynamics of multiple resonant modes excited in a plano-concave distributed Bragg reflector microcavity, showing close agreement with analytical models. Additionally, we demonstrate that stimulated intra-cavity difference-frequency generation can efficiently instantiate cavity modes on femtosecond timescales. This gating scheme is fully compatible with low-temperature microcavity experiments, paving the way for advanced quantum state storage, retrieval, and real-time control of light-matter interactions.

physics.optics↗
arXiv2023

Achiral dielectric metasurfaces for spectral and polarization control of valley specific light emission from monolayer MoS2

Excitons in two-dimensional transition metal dichalcogenides have a valley degree of freedom that can be optically accessed and manipulated for quantum information processing. Here, we integrate MoS2 with achiral silicon disk array metasurfaces to enhance and control valley-specific absorption and emission. Through the coupling to the metasurface Mie modes, the intensity and lifetime of the emission of neutral excitons, trions and defect bound excitons can be enhanced, while the spectral shape can be modified. Additionally, we demonstrate the symmetric enhancement of the degree-of-polarization (DOP) of neutral exciton and trions via valley-resolved PL measurements, and find that the DOP can be as high as 24% for exciton emission and 34% for trion emission at 100K. These results can be understood by analyzing the near-field impact of metasurface resonators on both the chiral absorption of MoS2 emitters as well as the enhanced emission from the Purcell effect. Combining Si-compatible photonic design with large-scale (mm-scale) 2D materials integration, our work makes an important step towards on-chip valleytronic applications approaching room-temperature operation.

physics.optics↗
arXiv2021

Moiré-localized interlayer exciton wavefunctions captured by imaging its electron and hole constituents

Interlayer excitons (ILXs) - electron-hole pairs bound across two atomically thin layered semiconductors - have emerged as attractive platforms to study exciton condensation, single-photon emission and other quantum-information applications. Yet, despite extensive optical spectroscopic investigations, critical information about their size, valley configuration and the influence of the moiré potential remains unknown. Here, we captured images of the time- and momentum-resolved distribution of both the electron and the hole that bind to form the ILX in a WSe2/MoS2 heterostructure. We thereby obtain a direct measurement of the interlayer exciton diameter of ~5.4 nm, comparable to the moiré unit-cell length of 6.1 nm. Surprisingly, this large ILX is well localized within the moiré cell to a region of only 1.8 nm - smaller than the size of the exciton itself. This high degree of localization of the interlayer exciton is backed by Bethe-Salpeter equation calculations and demonstrates that the ILX can be localized within small moiré unit cells. Unlike large moiré cells, these are uniform over large regions, thus allowing the formation of extended arrays of localized excitations for quantum technology.

physics.optics↗
arXiv2017

Ramsey fringes in a room temperature quantum dot semiconductor optical amplifier

The ability to induce, observe and control quantum coherent interactions in room temperature, electrically driven optoelectronic devices is of outmost significance for advancing quantum science and engineering towards practical applications. We demonstrate here a quantum interference phenomena, Ramsey fringes, in an inhomogeneously broadened InAs/InP quantum dot (QD) ensemble in the form of a 1.5 mm long optical amplifier operating at room temperature. Observation of Ramsey fringes in semiconductor QD was previously achieved only at cryogenic temperatures and only in isolated single dot systems. A high-resolution pump probe scheme where both pulses are characterized by cross frequency resolved optical gating (X-FROG) reveals a clear oscillatory behavior both in the amplitude and the instantaneous frequency of the probe pulse with a period that equals one optical cycle at operational wavelength. Using nominal input delays of 600 to 900 fs and scanning the separation around each delay in 1 fs steps, we map the evolution of the material de-coherence and extract a coherence time. Moreover we notice a unique phenomenon, which can not be observed in single dot systems, that the temporal position of the output probe pulse also oscillates with the same periodicity but with a quarter cycle delay relative to the intensity variations. This delay is the time domain manifestation of coupling between the real and imaginary parts of the complex susceptibility.

quant-ph↗
arXiv2016

Coherent control in room-temperature quantum dot semiconductor optical amplifiers using shaped pulses

We demonstrate the ability to control quantum coherent Rabi-oscillations in a room-temperature quantum dot semiconductor optical amplifier (SOA) by shaping the light pulses that trigger them. The experiments described here show that when the excitation is resonant with the short wavelength slope of the SOA gain spectrum, a linear frequency chirp affects its ability to trigger Rabi-oscillations within the SOA: A negative chirp inhibits Rabi-oscillations whereas a positive chirp can enhance them, relative to the interaction of a transform limited pulse. The experiments are confirmed by a numerical calculation that models the propagation of the experimentally shaped pulses through the SOA.

physics.optics↗
arXiv2014

Nonlinear pulse propagation in InAs/InP quantum-dot optical amplifiers: Rabi-oscillations in the presence of non-resonant nonlinearities

We study the interplay between coherent light-matter interactions and non-resonant pulse propagation effects when ultra-short pulses propagate in room-temperature quantum-dot (QD) semiconductor optical amplifiers (SOAs). The signatures observed on a pulse envelope after propagating in a transparent SOA, when coherent Rabi-oscillations are absent, highlight the contribution of two-photon absorption (TPA), and its accompanying Kerr-like effect, as well as of linear dispersion, to the modification of the pulse complex electric field profile. These effects are incorporated into our previously developed finite-difference time-domain comprehensive model that describes the interaction between the pulses and the QD SOA. The present, generalized, model is used to investigate the combined effect of coherent and non-resonant phenomena in the gain and absorption regimes of the QD SOA. It confirms that in the QD SOA we examined, linear dispersion in the presence of the Kerr-like effect causes pulse compression, which counteracts the pulse peak suppression due to TPA, and also modifies the patterns which the coherent Rabi-oscillations imprint on the pulse envelope under both gain and absorption conditions. The inclusion of these effects leads to a better fit with experiments and to a better understanding of the interplay among the various mechanisms so as to be able to better analyze more complex future experiments of coherent light-matter interaction induced by short pulses propagating along an SOA.

physics.optics↗
arXiv2012

Electron wavefunction probing in room-temperature semiconductors: direct observation of Rabi oscillations and self-induced transparency

Quantum coherent light-matter interactions have been at the forefront of scientific interest since the fundamental predictions of Einstein and the later work of Rabi. Direct observation of quantum coherent interactions entails probing the electronic wavefunction which requires that the electronic state of the matter does not de-phase during the measurement, a condition that can be satisfied by lengthening the coherence time or by shortening the observation time. The short de-phasing time in semiconductors has dictated that all coherent effects reported to date have been recorded directly only at cryogenic temperatures. Here we report on the first direct electronic wavefunction probing in a room-temperature semiconductor. Employing an ultrafast characterization scheme we have demonstrated Rabi oscillations and self-induced transparency in an electrically driven, room-temperature semiconductor laser amplifier, revealing the most intimate details of the light-matter interactions seen to date. The ability to employ quantum effects in solid-state media, which operate at elevated temperatures, will finally bring true quantum mechanical concepts into the realm of practical devices.

cond-mat.mes-hall↗