arXiv subjects

Yong-Hoon Cho

Publications and source records attributed to Yong-Hoon Cho.

13 recordsLinked to original sources

arXiv2026

Topological charge switching in trapped polariton condensates

Topological charges in photonic systems provide a robust degree of freedom with direct applications in optical information processing. Bound states in the continuum (BICs) in photonic crystal slabs inherently carry such quantized topological charges, yet they are topologically protected, making active reconfiguration fundamentally challenging. Here, we demonstrate topological charge switching in trapped BIC polariton condensates in a photonic crystal, where spatial modulation of the photonic crystals supports multiple confined states, each carrying a distinct charge. Trapped condensates within the Dirac bandgap are expelled into the leaky band via polariton blueshift, enabling single-mode selection by solely tuning the excitation power. This work offers a platform for optically controlling topological charges by harnessing polariton nonlinearity.

physics.optics↗

arXiv2026

Subcritical bifurcation and on-off bistability in ballistic polariton condensates

Dynamics of exciton-polariton condensates under continuous-wave incoherent Gaussian optical pumping is considered. It is shown that the conventional supercritical Stuart-Landau picture is invalid in a certain domain of the parameter space. For strong polariton repulsion from the reservoir and relatively small pump spots, the dynamics is adequately described by the quintic Stuart-Landau equation. The corresponding subcritical pitchfork bifurcation leads to condensate formation, accompanied by bistability between the trivial and nontrivial states over a finite pump-power range and a one-bit memory. Further increase of the repulsion parameter or decrease of the spot size breaks down the perturbative approach and leads to a peculiar self-trapping regime with complex dynamics. Experimental evidence of the emergence of the proposed behavior is provided. Our findings can be used to design polaritonic setups that exploit the predicted memory effect.

cond-mat.mes-hall↗

arXiv2026

Purcell enhanced and blinking free single photons from InAs/GaAs quantum dots in deterministically placed circular Bragg gratings

The development of efficient, deterministic, and tunable single-photon sources is a cornerstone for the realization of long-distance quantum communication, quantum repeaters, and photonic quantum computing technologies. In this study, we demonstrate a bright, charge-tunable single-photon source in the 900 nm wavelength range based on InAs quantum dots (QDs) embedded in a p-i-n doped GaAs membrane, which shows blinking free emission. We use a modified circular Bragg grating (CBG) as a micro-resonator. By adding fourfold symmetric bridges in a labyrinth-like geometry, we provide a conductive pathway to the central disk, thereby enabling electrical contact to the QD while maintaining high Purcell enhancement and photon extraction efficiency (PEE). For the negative trion (X-), we demonstrate a lifetime of $44.3 \pm 0.2$ ps - corresponding to a Purcell factor of $18.0 \pm 0.7$ and a PEE of $68.1% \pm 3.1$ %. Furthermore, the device is blinking-free with very low multi-photon contribution, evidenced by a second-order autocorrelation value $g(2)(0) < 0.017 \pm 0.015$. By applying a vertical diode bias, we demonstrate precise charge-state control, resolving distinct emission plateaus ranging from the single negatively charged trion ($X^-$) to triply negatively charged excitons ($X^{3-}$). These results showcase a robust architecture that simultaneously provides high efficiency, high repetition rates, and deterministic charge control, fulfilling key requirements for the next generation of quantum network hardware.

cond-mat.mes-hall↗

arXiv2025

A Spin-Photon Interface in the Telecom C-Band with Long Hole Spin Dephasing Time

Matter qubits that maintain coherence over extended timescales are essential for many pursued applications in quantum communication and quantum computing. Significant progress has already been made on extending coherence times of spins in semiconductor quantum dots while interfacing them with photons in the near-infrared wavelength range. However, similar results for quantum dots emitting at the telecom range, crucial for many applications, have so far lagged behind. Here, we report on InAs/InAlGaAs quantum dots integrated in a deterministically placed circular Bragg grating emitting at $1.55\,μ\mathrm{m}$. We quantify the g-factors of electrons and holes from polarization-resolved measurements of a positive trion in an in-plane magnetic field and study the dynamics of the ground-state hole spin qubit. We then herald the hole spin in a pulsed two-photon correlation measurement and determine its inhomogeneous dephasing time to $T_{2}^{*}=(15.9 \pm 1.7)$ ns.

quant-ph↗

arXiv2025

Two-Photon Interference from an InAs Quantum Dot emitting in the Telecom C-Band

Two-photon interference from an InAs/InAlGaAs quantum dot (QD) emitting in the telecom C-band with a raw two-photon interference visibility of $V_{HOM}=(71.9\pm0.2)$ % is demonstrated. This is achieved by a two-fold approach: an improvement of the molecular beam epitaxial growth for better QDs, and integration of the QDs into an optical circular Bragg grating resonator for a Purcell enhancement of the radiative decay rate. The quantum optical properties of the fabricated device are studied by means of time-correlated single-photon counting under quasi-resonant excitation of the charged exciton line. A reduced lifetime of $T_1=(257.5\pm0.2)$ ps is found corresponding to a Purcell factor of $F_P\geqq(4.7\pm0.5)$. Pronounced anti-bunching of the second-order autocorrelation function at zero time delay $g^{(2)} (0)=(0.0307\pm0.0004)$ confirms the single-photon emission character. The two-photon interference is demonstrated with an unbalanced Mach-Zehnder interferometer in Hong-Ou-Mandel configuration. We discuss strategies how to further improve the indistinguishability, and provide a survey of the state-of-the art.

quant-ph↗

arXiv2023

Ultrafast and Bright Quantum Emitters from the Cavity Coupled Single Perovskite Nanocrystals

Perovskite nanocrystals (NCs) have attracted increasing interest for the realization of single-photon emitters, owing to their ease of chemical synthesis, wide spectral tunability, fast recombination rate, scalability, and high quantum yield. However, the integration of a single perovskite NC into a photonic structure is yet to be accomplished. We successfully coupled a highly stable individual zwitterionic ligand-based CsPbBr3 perovskite NC with a circular Bragg grating (CBG). The far-field radiation pattern of the NC inside the CBG exhibits high directionality toward a low azimuthal angle, which is consistent with the simulation results. We observed a 5.4-fold enhancement in brightness due to an increase in collection efficiency. Moreover, we achieved a 1.95-fold increase in the recombination rate. This study offers ultrafast (< 100 ps) single-photon emission and an improved brightness of perovskite NCs, which are critical factors for practical quantum optical applications.

physics.optics↗

arXiv2022

Single quantum dot selection and tailor-made photonic device integration using nanoscale focus pinspot

Among the diverse platforms of quantum light sources, epitaxially grown semiconductor quantum dots (QDs) are one of the most attractive workhorses for realizing various quantum photonic technologies owing to their outstanding brightness and scalability. There exist various material systems for these QDs based on their appropriate emission bandwidth; however, only a few material systems have successfully grown single or low-density QDs, which are essential for quantum light sources. In most other material systems, it is difficult to realize low-density QDs, and the mesa-etching process is usually undergone in order to reduce their density. Nevertheless, the etching process irreversibly destroys the medium near the QD, which is detrimental to in-plane device integration. In this study, we apply a nondestructive luminescence picking method termed as nanoscale focus pinspot (NFP) using helium ion microscopy to reduce the luminous QD density while retaining the surrounding medium. Given that the NFP can precisely manipulate the luminescence at nanoscale resolution, a photonic device can be deterministically fabricated on the target QD matched from both spatial and spectral points of view. After applying the NFP, we extract only a single QD emission out of the high-density ensemble QD emission. Moreover, the photonic structure of a circular Bragg reflector is deterministically integrated with the selected QD, and the extraction efficiency of the QD emission has been improved 27 times. Furthermore, this technique does not destroy the medium and only controls the luminescence. Hence, it is highly applicable to various photonic structures, including photonic waveguides or photonic crystal cavities regardless of their materials.

physics.app-ph↗

arXiv2021

1D photonic crystal direct bandgap GeSn-on-insulator laser

GeSn alloys have been regarded as a potential lasing material for a complementary metal-oxide-semiconductor (CMOS)-compatible light source. Despite their remarkable progress, all GeSn lasers reported to date have large device footprints and active areas, which prevent the realization of densely integrated on-chip lasers operating at low power consumption. Here, we present a 1D photonic crystal (PC) nanobeam with a very small device footprint of 7 $μm^2$ and a compact active area of ~1.2 $μm^2$ on a high-quality GeSn-on-insulator (GeSnOI) substrate. We also report that the improved directness in our strain-free nanobeam lasers leads to a lower threshold density and a higher operating temperature compared to the compressive strained counterparts. The threshold density of the strain-free nanobeam laser is ~18.2 kW cm$^{ -2}$ at 4 K, which is significantly lower than that of the unreleased nanobeam laser (~38.4 kW cm$^{ -2}$ at 4 K). Lasing in the strain-free nanobeam device persists up to 90 K, whereas the unreleased nanobeam shows a quenching of the lasing at a temperature of 70 K. Our demonstration offers a new avenue towards developing practical group-IV light sources with high-density integration and low power consumption.

physics.optics↗

arXiv2020

Observation of a partially rotating superfluid of exciton-polariton

Rotation of a container holding a viscous fluid forms a vortex which grows with increasing angular velocity. A superfluid, however, is intrinsically different from these normal fluids because its rotation is quantized. Even if a container of superfluid is rotating, the fluid itself remains still until a critical velocity is reached. Beyond the critical velocity, all the particles conspire to suddenly pick up an angular momentum of $\hbar$ each and forms a quantized vortex. As a result, a superfluid is known to increase its rotation by a total angular momentum of $N\hbar$. In this letter, we show that exciton-polariton superfluid can split into an irrotational part and a rotational part. The relative ratio between the two states can be controlled by either pump beam's power or spot size. Consequently, angular momentum of exciton-polariton superfluid can be tuned from zero to $N\hbar$ continuously. This striking observation sets the stage for studying non-equilibrium properties of a superfluid with exciton-polaritons.

cond-mat.quant-gas↗

arXiv2018

Direct Transfer of Light's Orbital Angular Momentum onto Non-resonantly Excited Polariton Superfluid

Recently, exciton-polaritons in a semiconductor microcavity were found to condense into a coherent ground state much like a Bose-Einstein condensate and a superfluid. They have become a unique testbed for generating and manipulating quantum vortices in a driven-dissipative superfluid. Here, we generate exciton-polariton condensate with non-resonant Laguerre-Gaussian (LG) optical beam and verify the direct transfer of light's orbital angular momentum to exciton-polariton quantum fluid. Quantized vortices are found in spite of large energy relaxation involved in non-resonant pumping. We identified phase singularity, density distribution and energy eigenstates for the vortex states. Our observations confirm that non-resonant optical LG beam can be used to manipulate chirality, topological charge, and stability of non-equilibrium quantum fluid. These vortices are quite robust, only sensitive to the OAM of light and not other parameters such as energy, intensity, size or shape of the pump beam. Therefore, optical information can be transferred between photon and exciton-polariton with ease and the technique is potentially useful to form the controllable network of multiple topological charges even in the presence of spectral randomness in solid state system.

cond-mat.quant-gas↗

arXiv2016

Time-reversing a monochromatic subwavelength optical focus by optical phase conjugation of multiply-scattered light

Due to its time-reversal nature, optical phase conjugation generates a monochromatic light wave which retraces its propagation paths. Here, we demonstrate the regeneration of a subwavelength optical focus by phase conjugation. Monochromatic light from a subwavelength source is scattered by random nanoparticles, and the scattered light is phase conjugated at the far-field region by coupling its wavefront into a single-mode optical reflector using a spatial light modulator. Then the conjugated beam retraces its propagation paths and forms a refocus on the source at the subwavelength scale. This is the first direct experimental realization of subwavelength focusing beyond the diffraction limit with far-field time reversal in the optical domain.

physics.optics↗

arXiv2016

Scattering optical elements: stand-alone optical elements exploiting multiple light scattering

Optical design and fabrication techniques are crucial for making optical elements. From conventional lenses to diffractive optical elements, and to recent metasurfaces, various types of optical elements have been proposed to manipulate light where optical materials are fabricated into desired structures. Here, we propose a scattering optical element (SOE) which exploits multiple light scattering and wavefront shaping. Instead of fabricating optical materials, the SOE consists of a disordered medium and a photopolymer-based wavefront recorder, with shapes the wavefront of impinging light on demand. With the proposed stand-alone SOEs, we experimentally demonstrate control of various properties of light, including intensity, polarisation, spectral frequency and near field. Due to the tremendous freedom brought about by disordered media, the proposed approach will provide unexplored routes to manipulate arbitrary optical fields in stand-alone optical elements.

physics.optics↗

arXiv2014

Multi-color broadband visible light source via three-dimensional GaN hexagonal annular microstructures

Broadband visible light emitting, three-dimensional hexagonal annular microstructures with InGaN/GaN multiple quantum wells (MQWs) are fabricated via selective-area epitaxial growth. The single hexagonal annular structure is composed of not only polar facet of (0001) on top surface but also semi-polar facets of {10-11} and {11-22} in inner and outer sidewalls, exhibiting multi-color visible light emission from InGaN/GaN MQWs formed on the different facets. The InGaN MQWs on (0001) facet emits the longer wavelength (green color) due to the larger well thickness and the higher In composition, while those on semi-polar facets of {10-11} and {11-22} had highly-efficient shorter wavelength (violet to blue color) emission caused by smaller well thickness and smaller In composition. By combining the multiple color emission depending on different facets, high efficiency broadband visible light emission could be achieved. The emission color can be changed with excitation power density owing to the built-in electric field on the (0001) facet, which is confirmed by time-resolved luminescence experiments. The hexagonal annular structures can be a critical building block for highly efficient broadband visible light emitting sources, providing a solution to previous problems related to the fabrication issues for phosphor-free white light emitting devices.

cond-mat.mes-hall↗