Single-photon emitters in van der Waals materials
Jiandong Qiao (乔建东)
1
, Fuhong Mei (梅伏洪)
1
, and Yu Ye (叶 堉)
2,3,
*
1
Key Laboratory of Interface Science and Engineering in Advanced Materials, Ministry of Education, Taiyuan University
of Technology, Taiyuan 030024, China
2
State Key Laboratory for Artificial Microstructure & Mesoscopic Physics, School of Physics, Peking University, Beijing
100871, China
3
Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
*Corresponding author: ye_yu@pku.edu.cn
Received November 16, 2018; accepted December 27, 2018; posted online January 31, 2019
Solid-state sources of single-photon emitters are highly desired for scalable quantum photonic applications, such
as quantum communication, optical quantum information processing, and metrology. In the past year, great
strides have been made in the characterization of single defects in wide-bandgap materials, such as silicon carbide
and diamond, as well as single molecules, quantum dots, and carbon nanotubes. More recently, single-photon
emitters in layered van der Waals materials attracted tremendous attention, because the two-dimensional (2D)
lattice allows for high photon extraction efficiency and easy integration into photonic circuits. In this review, we
discuss recent advances in mastering single-photon emitters in 2D materials, electrical generation pathways,
detuning, and resonator coupling towards use as quantum light sources. Finally, we discuss the remaining
challenges and the outlooks for layered material-based quantum photonic sources.
OCIS codes: 270.5565, 270.5585, 160.2100, 160.2220, 160.4760, 250.5590.
doi: 10.3788/COL201917.020011.
Emerging quantum technologies for cryptography, com-
munication, computing, and metrology exploit non-
classical states for enhanced information processing and
nanoscale sensing
[1,2]
. Though different platform systems
are currentl y being explored
[3]
, light-based quantum tech-
nologies using single-photon emitters as the basic building
block are among the frontrunners. A long-standing hurdle,
however, has been the realization of robust, device-
compatible single-photon emitters that can be activated
and controlled on demand
[4]
. In the past, several different
material systems have been used to realize deterministic
single-photon sources in the solid state, including quan-
tum dots (QDs), single molecules, carbon nanotubes,
and point defects in wide-bandgap materials, such as dia-
mond and silicon carbide
[3,5–15]
. However, these solid-state
emitters are usually embedded in bulk materials with a
high refractive index, where internal reflection may limit
their integration capability and photon extraction
efficiency
[3]
. Using carbon nanotube-based single-photon
emitters in scalable quantum photonic applications
requires precise placement and orientation using complex
fabrication techniques
[16,17]
. Recently, the discovered
single-photon emitters in crystalline two-dimensional
(2D) materials
[18–22]
, with their ultimate atomic thickness,
have shown promise for precise placement, high extraction
efficiency, and easy integration into photonic circuits
[23–26]
.
Up to date, mechanical exfoliation of single crystals is still
the most common way for producing 2D materials. Stride
steps have been made recently in wafer-scale synthesis of
2D crystals, such as MoS
2
[27]
and hexagonal boron nitride
(hBN)
[28]
, opening a new route for large-scale quantum
photonic applications. In addition, due to their flexibility,
transfer 2D materials can be integrated with any other
material that may alleviate the stringent requirement of
epitaxial growth in traditional semiconductor materials.
The van der Waals (vdW) materials containing
single-photon emitters can potentially be compatible with
other photonic components to fabricate vdW materials-
based quantum photonic devices.
The discovered 2D systems hosting single-photon
emitters include transition-metal dichalcogenides
(TMDCs) (WSe
2
,WS
2
, and MoS
2
) and hBN
[18–22,29]
. In par-
ticular, a defect hosted by 2D hBN is a promising candi-
date for next-generation single-photon sources, due to its
chemical and thermal robustness and high brightness at
room temperature
[22]
. Here, we will first briefly review
the available and most-studied single-photon emitters in
layered materials and their photophysical properties. We
will then discuss important steps towards deterministic
generation of scalable 2D single-photon sources, electri-
cally pumped quantum sources, detuning, and integration
of emitters with optical resonators. We conclude with a dis-
cussion of challenges and highlight new research directions.
Single-photon emitters in 2D materials. Recently,
a number of 2D materials have been shown to host single-
photon emitters. The first observation of a single-photon
emitter in layered materials was reported by four indepen-
dent studies in the presence of isolated defects in single-
layer WSe
2
[Fig. 1(a)]
[18–21]
. TMDC monolayers have
moved to the forefront of solid-state research due to their
unique band structure featuring a large bandgap with
non-equivalent valleys and non-zero Berry curvature
[30]
.
The single-photon emitters in single-layer WSe
2
induced
by the quantum defects are ascribed to localized, weakly
bound excitons. Similarly to QDs, the TMDCs only
exhibit quantum emission at cryogenic temperatures.
COL 17(2), 020011(2019) CHINESE OPTICS LETTERS February 10, 2019
1671-7694/2019/020011(9) 020011-1 © 2019 Chinese Optics Letters