We demonstrate a chip-scale quantum emitter-metamaterial device that emits highly directional photons. Our device opens the door for quantum imaging of yveak sources by adding photon(s) to manipulate the photon statistics for improved signal-to-noise ratio

Akbari, Hamidreza

Atwater, Harry A.

Grajower, Meir Y.

Jha, Pankaj K.

Koltenbah, Benjamin E. C.

Parazzoli, Claudio G.

Shirmanesh, Ghazaleh K.

English

Caltech Authors - Main

FM4C.2.pdf CLEO 2020 © OSA 2020
Emitter-Metasurface Interface for Manipulating Emission 
Characteristics of Quantum Defects 
 
Pankaj K. Jha1, *, Ghazaleh K. Shirmanesh1, Hamidreza Akbari1, Meir Y. Grajower1, Claudio G. Parazzoli2, 
Benjamin E. C. Koltenbah3, Harry A. Atwater1  
1Thomas J. Watson Laboratory of Applied Physics and Materials Science, California Institute of Technology, Pasadena CA 91125 USA 
2North West Quantum Science, Seattle WA 98198 USA 
3The Boeing Company, P. O. Box 3703 Seattle WA 98124 USA  
*Author e-mail address: pkjha@caltech.edu 
 
       Abstract: We demonstrate a chip-scale quantum emitter-metamaterial device that emits highly directional 
photons. Our device opens the door for quantum imaging of weak sources by adding photon(s) to manipulate the 
photon statistics for improved signal-to-noise ratio.  
 
1. Introduction 
 Single-photon sources are elementary building blocks for photonic quantum networks, quantum information 
processing, and quantum metrology, where the photons are used as “flying” qubits [1]. Several solid-state sources [2] 
like single organic molecules, self-assembled quantum dots, and 
semiconductor nanocrystals have been presented as potential 
emitter candidates. However, the ideal emitter candidate should be 
photostable, work at room temperature, and easy to control and 
manipulate. Recent discovery of quantum light emission from two-
dimensional (2D) van der Waals (vdW) materials, such as transition 
metal dichalcogenides (TMDCs) [3] and hexagonal boron nitride 
(hBN) [4] have opened the door to a new class of single-photon 
sources. In contrast to other solid-state emitter candidates, these 
emitters have much narrower emission spectra at room temperature 
and they can be controlled electrically. Moreover, 2D materials may 
facilitate easier integration into complex photonic structures for on-
chip quantum applications. 
Here, we report a chip-scale optical interface configuration for 
coupling hBN color-centers with planar arrays of classical 
nanoantennas, configured as a metasurface [5,6]. A schematic 
representation of our hBN-metasurface interface is shown in Fig. 1. 
Here, an atomically thin layer of hBN is transferred onto a phase 
gradient metasurface.  This hybrid device, when illuminated by 532 
nm laser, will emit single-photons from a color-center in hBN along the surface-normal direction, thus creating highly 
directional single-photon source.  
 
1.1 Spectroscopy of color-centers in exfoliated hBN 
In our experiments, we exfoliated few-layer hBN samples on silicon (Si/SiO2) substrates. The sample (hBN-Si/SiO2) 
was annealed in an inert environment (Ar-N2) at 850 Celsius and we performed optical characterization using a 
confocal Raman microscope. Figure 2 
(a) shows one of the exfoliated flakes. 
Fig. 2(b) illustrates the 
photoluminescence (PL) spectrum from 
a location highlighted by the black 
circle indicated on the image. We 
observed a sharp emission line 
characteristic of zero-phonon line 
(ZPL) in hBN at ~665 nm. The full-
width at half-maximum (FWHM) of the 
ZPL is ~2-3 nm at room temperature 
with characteristic vibronic sidebands 
redshifted by ~ 160 meV. We also 
performed PL mapping of the flake in 
Figure 1: Emitter-Metasurface Interface. A color 
center in hexagonal boron nitride in the vicinity of a 
phase gradient metasurface. One such color centers
are shown in the inset where two oxygen atom have 
replaced two boron atoms and vacancy at the site of
a nitrogen atom. 
20μm
550 600 650 700 750
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Fl
uo
re
sc
en
ce
 In
te
ns
ity
[c
p
s]
 x
 1
03
Wavelength, [nm]
ZPL
PSBs
RhBN
RSi
hBN
Si/SiO2
Figure 2: Photoluminescence spectrum from one of the color centers in an 
exfoliated hBN flake on silicon substrate which was annealed at 850 degrees 
Celsius in an inert environment.   
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the region shown by the white dashed line and we found several color centers with characteristic ZPL in the range 
600-700 nm with photon counts as high as several thousand per second. 
 
1.2 Design and fabrication of a phase-gradient metasurface 
We designed a phase gradient metasurface configured so that emission from a dipole located at (0,0, z) is highly 
directional (as shown in Fig. 3 left panel). We used six different silver bar nanoantenna elements to realsize a 
metasurface whose phase gradient ranges 
from 0-2π with a step size of π/6. The 
thickness of the nanoantennas is 30 nm and 
the thickness of the dielectric spacer layer 
(aluminum dioxide) is 65 nm. The phase 
shift and reflection efficiency is calculated 
using a commercial full-wavelength 
simulation package (COMSOL 
Multiphysics). The average reflection 
intensity of the nanoantennas was ~ 81%. In 
Fig. 3, we have plotted far-field radiation 
pattern of an atomic-dipole with dipole 
orientation along the surface of the 
metasurface. Our simulation shows a highly 
directional (surface-normal) emission from the emitter (solid blue). The dashed curve shows the radiation pattern 
without the metasurface.  
 
To summarize, we have introduced and theoretically demonstrated a chip-scale interface between a defect-based 
quantum emitter and a phase gradient metasurface. We show that a judiciously designed metasurface can engineer 
far-field radiation pattern of an emitter located at its focal spot such that the emission is highly directional. Our device 
also opens the door a similar system that favorably modifies photon statistics of a weak input thermal beam, increases 
photon count leading to larger signal-to-noise ratio and enhanced images of the source [7].  
 
2. References: 
(1) J. P. Dowling and G. J. Milburn, “Quantum technology: the second quantum revolution,” Phil. Trans. R. Soc. Lond. A 361, 1655 (2003). 
(2) W. E. Moerner, “Single-photon sources based on single molecules in solids,” New J. Phys. 6, 88 (2004).  
(3) A. Srivastava, M. Sidler, A. V. Allain, et al., “Optically active quantum dots in monolayer WSe2,” Nat. Nanotechnol. 10, 491 (2015). 
(4) T. T. Tran, K. Bray, M. J. Ford, et al., “Quantum emission from hexagonal boron nitride monolayers,” Nat. Nanotechnol. 11, 37 (2016). 
(5) P. K. Jha, X. Ni, C. Wu, et al., “Metasurface-Enabled Remote Quantum Interference,” Phys. Rev. Lett. 115, 025501 (2015). 
(6) P. K. Jha, N. Shitrit, X. Ren, et al., “Spontaneous Exciton Valley Coherence in Transition Metal Dichalcogenide Monolayers Interfaced with 
an Anisotropic Metasurface,” Phys. Rev. Lett. 121, 116102 (2018). 
(7) C. G. Parazzoli, B. E. Koltenbah, D. R. Gerwe, et. al., “Enhanced Thermal Objective Imaging by Photon Addition or Subtraction”, arXiv 
160902780(2016). 
 
 
 
Figure 3: Metasurface design and far-field radiation pattern of an atomic 
dipole located at the focal spot of the metasurface.   
Authorized licensed use limited to: CALIFORNIA INSTITUTE OF TECHNOLOGY. Downloaded on September 22,2020 at 00:27:09 UTC from IEEE Xplore.  Restrictions apply. 


Emitter-Metasurface Interface for Manipulating Emission Characteristics of Quantum Defects

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Emitter-Metasurface Interface for Manipulating Emission Characteristics of Quantum Defects

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