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Younghee Kim

Publications and source records attributed to Younghee Kim.

6 recordsLinked to original sources
arXiv2021

Single Photon Sources with Near Unity Collection Efficiencies by Deterministic Placement of Quantum Dots in Nanoantennas

Deterministic coupling between photonic nodes in a quantum network is an essential step towards implementing various quantum technologies. The omnidirectionality of free-standing emitters, however, makes this coupling highly inefficient, in particular if the distant nodes are coupled via low numerical aperture (NA) channels such as optical fibers. This limitation requires placing quantum emitters in nanoantennas that can direct the photons into the channels with very high efficiency. Moreover, to be able to scale such technologies to a large number of channels, the placing of the emitters should be deterministic. In this work we present a method for directly locating single free-standing quantum emitters with high spatial accuracy at the center of highly directional bullseye metal-dielectric nanoantennas. We further employ non-blinking, high quantum yield colloidal quantum dots (QDs) for on-demand single-photon emission that is uncompromised by instabilities or non-radiative exciton recombination processes. Taken together this approach results in a record-high collection efficiency of 85% of the single photons into a low NA of 0.5, setting the stage for efficient coupling between on-chip, room temperature nanoantenna-emitter devices and a fiber or a remote free-space node without the need for additional optics.

quant-ph↗
arXiv2015

Anomalous Lattice Dynamics of Mono-, Bi-, and Tri-layer WTe2

Tungsten ditelluride (WTe2) is a layered material that exhibits excellent magnetoresistance and thermoelectric behaviors, which are deeply related with its distorted orthorhombic phase that may critically affect the lattice dynamics. Here, for the first time, we present comprehensive characterization of the Raman spectroscopic behavior of WTe2 from bulk to monolayer using experimental and computational methods. We discover that mono and bi-layer WTe2 can be easily identified by Raman spectroscopy since double or single Raman modes that are observed in higher-layer WTe2 are substantially suppressed in the monolayer and bilayer WTe2, respectively. In addition, different from hexagonal metal dichalcogenides, the frequency of in-plane mode of WTe2 remains almost constant as the layer number decreases, while the other Raman modes consistently blueshift. First-principles calculation validates the experiments and reveals that the negligible shift of the mode is attributed to the lattice vibration along the tungsten chains that make WTe2 structurally one-dimensional.

cond-mat.mes-hall↗
arXiv2009

On the q-Extensions of the Bernoulli and Euler Numbers, Related Identities and Lerch Zeta Function

Recently, $λ$-Bernoulli and $λ$-Euler numbers are studied in [5, 10]. The purpose of this paper is to present a systematic study of some families of the $q$-extensions of the $λ$-Bernoulli and the $λ$-Euler numbers by using the bosonic $p$-adic $q$-integral and the fermionic $p$-adic $q$-integral. The investigation of these $λ$-$q$-Bernoulli and $λ$-$q$-Euler numbers leads to interesting identities related to these objects. The results of the present paper cover earlier results concerning $q$-Bernoulli and $q$-Euler numbers. By using derivative operator to the generating functions of $λ$-$q$-Bernoulli and $λ$-$q$-Euler numbers, we give the $q$-extensions of Lerch zeta function.

math.NT↗