[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

We demonstrate first room temperature, and ultrabright single photon emission from a color center in two-dimensional multilayer hexagonal boron nitride. Density Functional Theory calculations indicate that vacancy-related centers are a likely source of the emission.

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Quantum emission from hexagonal boron nitride monolayers

Graphene plasmons were predicted to possess ultra-strong field confinement and very low damping at the same time, enabling new classes of devices for deep subwavelength metamaterials, single-photon nonlinearities, extraordinarily strong light-matter interactions and nano-optoelectronic switches. While all of these great prospects require low damping, thus far strong plasmon damping was observed, with both impurity scattering and many-body effects in graphene proposed as possible explanations. With the advent of van der Waals heterostructures, new methods have been developed to integrate graphene with other atomically flat materials. In this letter we exploit near-field microscopy to image propagating plasmons in high quality graphene encapsulated between two films of hexagonal boron nitride (h-BN). We determine dispersion and particularly plasmon damping in real space. We find unprecedented low plasmon damping combined with strong field confinement, and identify the main damping channels as intrinsic thermal phonons in the graphene and dielectric losses in the h-BN. The observation and in-depth understanding of low plasmon damping is the key for the development of graphene nano-photonic and nano-optoelectronic devices.

Highly confined low-loss plasmons in graphene-boron nitride heterostructures

For more than seven decades, hexagonal boron nitride (hBN) has been employed as an inert, thermally stable engineering ceramic; since 2010, it has also been used as the optimal substrate for graphene in nanoelectronic and optoelectronic devices. Recent research has revealed that hBN exhibits a unique combination of optical properties that enable novel (nano)photonic functionalities. Specifically, hBN is a natural hyperbolic material in the mid-IR range, in which photonic material options are sparse. Furthermore, hBN hosts defects that can be engineered to obtain room-temperature, single-photon emission; exhibits strong second-order nonlinearities with broad implications for practical devices; and is a wide-bandgap semiconductor well suited for deep UV emitters and detectors. Inspired by these promising attributes, research on the properties of hBN and the development of large-area bulk and thin-film growth techniques has dramatically expanded. This Review offers a snapshot of current research exploring the properties underlying the use of hBN for future photonics functionalities and potential applications, and covers some of the remaining obstacles. Hexagonal boron nitride (hBN) is highly sought after for mid-IR nanophotonics, nonlinear and quantum optics, and as an efficient UV emitter. This Review surveys its fundamental physical properties, applications and synthesis.

Photonics with hexagonal boron nitride

Single-photon emitters (SPEs) in hexagonal boron nitride (hBN) have garnered increasing attention over the last few years due to their superior optical properties. However, despite the vast range of experimental results and theoretical calculations, the defect structure responsible for the observed emission has remained elusive. Here, by controlling the incorporation of impurities into hBN via various bottom-up synthesis methods and directly through ion implantation, we provide direct evidence that the visible SPEs are carbon related. Room-temperature optically detected magnetic resonance is demonstrated on ensembles of these defects. We perform ion-implantation experiments and confirm that only carbon implantation creates SPEs in the visible spectral range. Computational analysis of the simplest 12 carbon-containing defect species suggest the negatively charged $${\rm{V}}_{\rm{B}}{\rm{C}}_{\rm{N}}^ -$$
 defect as a viable candidate and predict that out-of-plane deformations make the defect environmentally sensitive. Our results resolve a long-standing debate about the origin of single emitters at the visible range in hBN and will be key to the deterministic engineering of these defects for quantum photonic devices. Comparison of hexagonal boron nitride samples grown with different techniques and with varying carbon-doping content provides evidence that the defects emitting single photons in the visible range are carbon related.

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Identifying carbon as the source of visible single-photon emission from hexagonal boron nitride

Combining solid state single photon emitters (SPE) with nanophotonic platforms is a key goal in integrated quantum photonics. In order to realize functionality in potentially scalable elements, suitable SPEs have to be bright, stable, and widely tunable at room temperature. In this work we show that selected SPEs embedded in a few layer hexagonal boron nitride (hBN) meet these demands. In order to show the wide tunability of these SPEs we employ an AFM with a conductive tip to apply an electrostatic field to individual hBN emitters sandwiched between the tip and an indium tin oxide coated glass slide. A very large and reversible Stark shift of $(5.5 \pm 3)\,$nm at a zero field wavelength of $670\,$nm was induced by applying just $20\,$V, which exceeds the typical resonance linewidths of nanodielectric and even nanoplasmonic resonators. Our results are important to further understand the physical origin of SPEs in hBN as well as for practical quantum photonic applications where wide spectral tuning and on/off resonance switching are required.

Very Large and Reversible Stark Shift Tuning of Single Emitters in Layered Hexagonal Boron Nitride

Thermally grown silica is one of the most desirable materials for the realization of optical waveguides and whispering-gallery mode micro-resonators due to the ultra-low propagation loss and broad transparency window from UV to mid-IR. Here, we present the design, fabrication, and characterization of a high-Q ring-resonator device with a monolithically integrated evanescent rib waveguide coupler made solely from silica thermally grown on a Si substrate. The device delivered an intrinsic Q-factor of $3.7\,\times \, 10^{6}$ and operated close to the critical coupling regime for both TE and TM polarizations. The achieved Q-factors were more than three orders of magnitude higher than those of comparable silica resonator devices. Furthermore, we showcase the ultra-low parasitic fluorescence unique to thermally grown silica and compare it to a device fabricated in Si3N4.

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Integrated Thermal Silica Micro-Resonator Waveguide System With Ultra-Low Fluorescence

Microwave pulse sequences are the basis of coherent manipulation of the electronic spin ground state in nitrogen vacancy (NV) centers. In this work we demonstrate stimulated Raman transitions (SRTs) and stimulated Raman adiabatic passage (STIRAP), two ways to drive the dipole-forbidden transition between two spin sublevels in the electronic triplet ground state of the NV center. This driving is achieved by a two-photon Raman microwave pulse which simultaneously drives two detuned transitions via a virtual level for SRTs or via two adiabatic and partially overlapping resonant microwave pulses for STIRAP. We lay the theoretical framework of SRT and STIRAP dynamics and verify experimentally the theoretical predictions of population inversion by observing the dipole-forbidden transition in the ground state of a single NV center. A comparison of the two schemes showed better robustness and success of the spin swap for STIRAP compared to SRT.

Ground-state microwave-stimulated Raman transitions and adiabatic spin transfer in the N 15 nitrogen vacancy center

Efficient coupling of single quantum emitters to guided optical modes of integrated optical devices is of high importance for applications in quantum information science as well as in the field of sensing. Here we present the design and fabrication of a platform for on-chip experiments based on dielectric optical single-mode waveguides(Ta2O5 on SiO2). The design of the waveguide is optimized for broadband (600-800 nm) evanescent coupling to a single quantum emitter (expected efficiency: up to 36%) and efficient off-chip coupling to single-mode optical fibers using inverted tapers. First test samples exhibit propagation losses below 1.8 dB/mm and off-chip coupling efficiencies exceeding 57%. These results are promising for efficient coupling of solid state quantum emitters like NV- and SiV-centers to a single optical mode of a nanoscale waveguide.

Design, Fabrication, and Characterization of Ta2O5 Photonic Strip Waveguides

Diamond can host a variety of point defects, some of which are already well known and utilized for quantum applications, others are just coming up as new promising candidates. As quantum applications often require the interaction of a light field with a single or only a few emitters at the same time, it is crucial to increase the number of collected photons, as well as to tailor the interaction with the light field. After a brief discussion on how an increase of the detected photons would affect different quantum applications, two different hybrid approaches, including their respective experimental implementation, are discussed in detail. First, the concept of a bullseye antenna is discussed, which mainly focuses on a simple and robust way to enhance the collection via free-space optics and into low collection angles. With this structure a collection efficiency of up to 85% into an NA of 0.9 could be realized. The second structure goes toward a fiber-coupled device, in order to prototype a fully integrated single-photon source. Here a single defect center is coupled to an on-chip silica waveguide, and its emitted photons are routed to single-mode fibers.

Florian Böhm

Papers

Very Large and Reversible Stark Shift Tuning of Single Emitters in Layered Hexagonal Boron Nitride

Integrated Thermal Silica Micro-Resonator Waveguide System With Ultra-Low Fluorescence

Ground-state microwave-stimulated Raman transitions and adiabatic spin transfer in the N 15 nitrogen vacancy center

Design, Fabrication, and Characterization of Ta2O5 Photonic Strip Waveguides

Hybrid light collection