Sejeong Kim graduated from Sogang University (Summa Cum Laude), Korea in 2009 with a degree in Physics and Integrated Biotechnology. She received her Ph.D. in Physics from Korea Advanced Institute of Science and Technology (KAIST) in 2014. Dr. Sejeong Kim spent two and half years as a postdoctoral researcher at KAIST. She joined the University of Technology Sydney (UTS) as a postdoctoral researcher since 2017. Her doctoral research interests include semiconductor optical resonator design, fabrication and optical characterization. The title of doctoral thesis is “Study of photonic crystal nanobeam lasers and their applications”. Since then, her interest was to efficiently collect light from GaN single emitters. Sejeong Kim’s research at UTS will focus on the introduction of micro/nano cavities for new materials.
Can supervise: YES
We propose and design photonic crystal cavities (PCCs) in hexagonal boron nitride (hBN) for diverse photonic and quantum applications. Two dimensional (2D) hBN flakes contain quantum emitters which are ultra-bright and photostable at room temperature. To achieve optimal coupling of these emitters to optical resonators, fabrication of cavities from hBN is therefore required to maximize the overlap between cavity optical modes and the emitters. Here, we design 2D and 1D PCCs using anisotropic indices of hBN. The influence of underlying substrates and material absorption are investigated, and spontaneous emission rate enhancements are calculated. Our results are promising for future quantum photonic experiments with hBN.
Zhou, Y., Wang, Z., Rasmita, A., Kim, S., Berhane, A., Bodrog, Z., Adamo, G., Gali, A., Aharonovich, I. & Gao, W.-.B. 2018, 'Room temperature solid-state quantum emitters in the telecom range.', Science advances, vol. 4, no. 3, p. eaar3580.View/Download from: Publisher's site
On-demand, single-photon emitters (SPEs) play a key role across a broad range of quantum technologies. In quantum networks and quantum key distribution protocols, where photons are used as flying qubits, telecom wavelength operation is preferred because of the reduced fiber loss. However, despite the tremendous efforts to develop various triggered SPE platforms, a robust source of triggered SPEs operating at room temperature and the telecom wavelength is still missing. We report a triggered, optically stable, room temperature solid-state SPE operating at telecom wavelengths. The emitters exhibit high photon purity (~5% multiphoton events) and a record-high brightness of ~1.5 MHz. The emission is attributed to localized defects in a gallium nitride (GaN) crystal. The high-performance SPEs embedded in a technologically mature semiconductor are promising for on-chip quantum simulators and practical quantum communication technologies.
Kianinia, M., Bradac, C., Sontheimer, B., Wang, F., Tran, T.T., Nguyen, M., Kim, S., Xu, Z.-.Q., Jin, D., Schell, A.W., Lobo, C.J., Aharonovich, I. & Toth, M. 2018, 'All-optical control and super-resolution imaging of quantum emitters in layered materials.', Nature communications, vol. 9, no. 1, p. 874.View/Download from: UTS OPUS or Publisher's site
Layered van der Waals materials are emerging as compelling two-dimensional platforms for nanophotonics, polaritonics, valleytronics and spintronics, and have the potential to transform applications in sensing, imaging and quantum information processing. Among these, hexagonal boron nitride (hBN) is known to host ultra-bright, room-temperature quantum emitters, whose nature is yet to be fully understood. Here we present a set of measurements that give unique insight into the photophysical properties and level structure of hBN quantum emitters. Specifically, we report the existence of a class of hBN quantum emitters with a fast-decaying intermediate and a long-lived metastable state accessible from the first excited electronic state. Furthermore, by means of a two-laser repumping scheme, we show an enhanced photoluminescence and emission intensity, which can be utilized to realize a new modality of far-field super-resolution imaging. Our findings expand current understanding of quantum emitters in hBN and show new potential ways of harnessing their nonlinear optical properties in sub-diffraction nanoscopy.
Nguyen, M., Kim, S., Tran, T.T., Xu, Z.-.Q., Kianinia, M., Toth, M. & Aharonovich, I. 2018, 'Nanoassembly of quantum emitters in hexagonal boron nitride and gold nanospheres.', Nanoscale, vol. 10, no. 5, pp. 2267-2274.View/Download from: Publisher's site
The assembly of quantum nanophotonic systems with plasmonic resonators is important for fundamental studies of single photon sources as well as for on-chip information processing. In this work, we demonstrate the controllable nanoassembly of gold nanospheres with ultra-bright narrow-band quantum emitters in 2D layered hexagonal boron nitride (hBN). We utilize an atomic force microscope (AFM) tip to precisely position gold nanospheres to close proximity to the quantum emitters and observe the resulting emission enhancement and fluorescence lifetime reduction. The extreme emitter photostability permits analysis at high excitation powers, and delineation of absorption and emission enhancement caused by the plasmonic resonators. A fluorescence enhancement of over 300% is achieved experimentally for quantum emitters in hBN, with a radiative quantum efficiency of up to 40% and a saturated count rate in excess of 5 106 counts per s. Our results are promising for the future employment of quantum emitters in hBN for integrated nanophotonic devices and plasmonic based nanosensors.
Kim, S., Gong, S., Cho, J. & Cho, Y. 2016, 'Unidirectional emission of a site-controlled single quantum dot from a pyramidal structure', Nano Letters, vol. 16, no. 10, pp. 6117-6123.View/Download from: UTS OPUS or Publisher's site
Emission control of a quantum emitter made of semiconductor materials is of significance in various optical applications. Specifically, the realization of efficient quantum emitters is important because typical semiconductor quantum dots are associated with low extraction efficiency levels due to their high refractive index contrast. Here, we report bright and unidirectional emission from a site-controlled InGaN quantum dot formed on the apex of a silver-coated GaN nanopyramidal structure. We show that the majority of the extracted light from the quantum dot is guided toward the bottom of the pyramid with high directionality. We also demonstrate that nanopyramid structures can be detached from a substrate, thus demonstrating great potential of this structure in various applications. To clarify the directional radiation, the far-field radiation pattern is measured using Fourier microscopy. This scheme will pave the way toward the realization of a bright and unidirectional quantum emitter along with easy fabrication and large-area reproducibility
Kim, S., Ko, H., Lee, C., Kim, M., Kim, K.S., Lee, Y., Shin, K. & Cho, Y. 2016, 'Semiconductor Photonic Nanocavity on a Paper Substrate', Advanced Materials, vol. 28, no. 44, pp. 9765-9769.View/Download from: UTS OPUS or Publisher's site
Direct integration of semiconductor photonic nanocavities with paper substrates is demonstrated for the first time. 1D photonic crystal nanocavities successfully show lasing action on paper substrates. The device has great synergy as a sensor because paper has good wicking ability while a photonic crystal cavity has high figure of merit. The research provides a platform for eco-friendly and sustainable devices.
Kim, S., Kim, H. & Lee, Y. 2015, 'Single nanobeam optical sensor with a high Q-factor and high sensitivity', Optics Letters, vol. 40, no. 22, pp. 5351-5354.View/Download from: UTS OPUS or Publisher's site
The miniaturization of optical sensors is essential for the realization of compact, portable, and cost-effective devices. Photonic crystal-based optical sensors, which have an ultra-small mode volume and footprint, have demonstrated remarkable recent progress in achieving a high figure-of-merit (FOM) in a sensor. Here, we report an optical sensor with a high Q-factor and high sensitivity based on a photonic crystal nanobeam using the second lowest air band-edge mode. We calculated that a nanobeam ( =3.4)(n=3.4) in a water environment ( =1.33)(n=1.33) has refractive-index sensitivity of 631nm/RIU631nm/RIU, while the quality factor is greater than 23,300. Accordingly, a theoretical FOM of the sensor corresponds to >9500>9500. To the best of our knowledge, experimental refractive-index sensitivity of 461 nm/RIU is the highest value among photonic crystal single nanobeam geometry. The simple geometry of uniform air hole sizes and lattice constants in the proposed nanobeam sensor allows easy fabrication and mechanical stability.
Kim, S., Kim, H., Son, J., Kim, Y., Ok, J.M., Kim, K.S., Jung, H., Min, B. & Lee, Y. 2014, 'Low-voltage-tunable nanobeam lasers immersed in liquid crystals', Optics express, vol. 22, no. 25, pp. 30707-30712.View/Download from: UTS OPUS or Publisher's site
A low-voltage-tunable one-dimensional nanobeam laser is realized by employing lithographically defined lateral electrodes. An InGaAsP nanobeam with a sub-micrometer width is transfer-printed in the middle of two electrodes using a polydimethylsiloxane stamp. Spectral tuning is achieved by controlling the molecular alignment of the surrounding liquid crystals (LCs). From m-scale-gap structures, a total wavelength shift that exceed 6 nm is observed at a low voltage of less than 10 V. A measured spectral tuning rate of 0.87 nm/V, which is the largest value ever reported to our knowledge among LC-tuned photonic crystal lasers, was also noted.
Son, B., Kim, S., Kim, Y.H., Käläntär, K., Kim, H., Jeong, H., Choi, S.Q., Shin, J., Jung, H. & Lee, Y. 2014, 'Optical vortex arrays from smectic liquid crystals', Optics express, vol. 22, no. 4, pp. 4699-4704.View/Download from: UTS OPUS or Publisher's site
We demonstrate large-area, closely-packed optical vortex arrays using self-assembled defects in smectic liquid crystals. Self-assembled smectic liquid crystals in a three-dimensional torus structure are called focal conic domains. Each FCD, having a micro-scale feature size, produces an optical vortex with consistent topological charge of 2. The spiral profile in the interferometry confirms the formation of an optical vortex, which is predicted by Jones matrix calculations.
Kim, S., Fröch, J.E., Christian, J., Straw, M., Bishop, J., Totonjian, D., Watanabe, K., Taniguchi, T., Toth, M. & Aharonovich, I., 'Photonic Crystal Cavities from Hexagonal Boron Nitride'.
Development of scalable quantum photonic technologies requires on-chip
integration of components such as photonic crystal cavities and waveguides with
nonclassical light sources. Recently, hexagonal boron nitride (hBN) has emerged
as a promising platform for nanophotonics, following reports of hyperbolic
phonon-polaritons and optically stable, ultra-bright quantum emitters. However,
exploitation of hBN in scalable, on-chip nanophotonic circuits, quantum
information processing and cavity quantum electrodynamics (QED) experiments
requires robust techniques for the fabrication of monolithic optical
resonators. In this letter, we design and engineer high quality photonic
crystal cavities from hBN. We employ two approaches based on a focused ion beam
method and a minimally-invasive electron beam induced etching (EBIE) technique
to fabricate suspended two dimensional (2D) and one dimensional (1D) cavities
with quality (Q) factors in excess of 2,000. Subsequently, we show
deterministic, iterative tuning of individual cavities by direct-write,
single-step EBIE without significant degradation of the Q-factor. The
demonstration of tunable, high Q cavities made from hBN is an unprecedented
advance in nanophotonics based on van der Waals materials. Our results and hBN
processing methods open up promising new avenues for solid-state systems with
applications in integrated quantum photonics, polaritonics and cavity QED