7 research outputs found
Thickness Insensitive Nanocavities for 2D Heterostructures using Photonic Molecules
Two-dimensional (2D) heterostructures integrated into nanophotonic cavities
have emerged as a promising approach towards novel photonic and opto-electronic
devices. However, the thickness of the 2D heterostructure has a strong
influence on the resonance frequency of the nanocavity. For a single cavity,
the resonance frequency shifts approximately linearly with the thickness. Here,
we propose to use the inherent non-linearity of the mode coupling to render the
cavity mode insensitive to the thickness of the 2D heterostructure. Based on
the couple mode theory, we reveal that this goal can be achieved using either a
homoatomic molecule with a filtered coupling or heteroatomic molecules. We
perform numerical simulations to further demonstrate the robustness of the
eigenfrequency in the proposed photonic molecules. Our results render
nanophotonic structures insensitive to the thickness of 2D materials, thus
owing appealing potential in energy- or detuning-sensitive applications such as
cavity quantum electrodynamics
Probing the Dark Exciton in Monolayer MoS by Quantum Interference in Second Harmonic Generation Spectroscopy
We report resonant second harmonic generation (SHG) spectroscopy of an
hBN-encapsulated monolayer of MoS. By tuning the energy of the excitation
laser, we identify a dark state transition (D) that is blue detuned by +25 meV
from the neutral exciton X. We observe a splitting of the SHG spectrum into
two distinct peaks and a clear anticrossing between them as the SHG resonance
is tuned through the energy of the dark exciton D. This observation is
indicative of quantum interference arising from the strong two-photon
light-matter interaction. We further probe the incoherent relaxation from the
dark state to the bright excitons, including X and localized excitons LX,
by the resonant enhancement of their intensities at the SHG-D resonance. The
relaxation of D to bright excitons is strongly suppressed on the bare substrate
whilst enabled when the hBN/MoS/hBN heterostructure is integrated in a
nanobeam cavity. The relaxation enabled by the cavity is explained by the
phonon scattering enhanced by the cavity phononic effects. Our work reveals the
two-photon quantum interference with long-lived dark states and enables the
control through nanostructuring of the substrate. These results indicate the
great potential of dark excitons in 2D-material based nonlinear quantum
devices
Extending the coherence time of spin defects in hBN enables advanced qubit control and quantum sensing
Spin defects in hexagonal Boron Nitride (hBN) attract increasing interest for
quantum technology since they represent optically-addressable qubits in a van
der Waals material. In particular, negatively-charged boron vacancy centers
() in hBN have shown promise as sensors of temperature, pressure, and
static magnetic fields. However, the short spin coherence time of this defect
currently limits its scope for quantum technology. Here, we apply dynamical
decoupling techniques to suppress magnetic noise and extend the spin coherence
time by nearly two orders of magnitude, approaching the fundamental
relaxation limit. Based on this improvement, we demonstrate advanced spin
control and a set of quantum sensing protocols to detect electromagnetic
signals in the MHz range with sub-Hz resolution. This work lays the foundation
for nanoscale sensing using spin defects in an exfoliable material and opens a
promising path to quantum sensors and quantum networks integrated into
ultra-thin structures
Thickness insensitive nanocavities for 2D heterostructures using photonic molecules
Two-dimensional (2D) heterostructures integrated into nanophotonic cavities have emerged as a promising approach towards novel photonic and opto-electronic devices. However, the thickness of the 2D heterostructure has a strong influence on the resonance frequency of the nanocavity. For a single cavity, the resonance frequency shifts approximately linearly with the thickness. Here, we propose to use the inherent non-linearity of the mode coupling to render the cavity mode insensitive to the thickness of the 2D heterostructure. Based on the coupled mode theory, we reveal that this goal can be achieved using either a homoatomic molecule with a filtered coupling or heteroatomic molecules. We perform numerical simulations to further demonstrate the robustness of the eigenfrequency in the proposed photonic molecules. Our results render nanophotonic structures insensitive to the thickness of 2D materials, thus owing appealing potential in energy- or detuning-sensitive applications such as cavity quantum electrodynamics
Sharp-Hook Acupuncture ( Feng Gou Zhen
The Feng Gou Zhen (sharp-hook acupuncture) as a traditional form of ancient acupuncture is said to be particularly effective for managing periarthritis of shoulder. We conducted this randomized controlled trial to evaluate the effectiveness of Feng Gou Zhen as an add-on compared to conventional analgesics for patients with PAS. 132 patients were randomly assigned in a 1 : 1 ratio to either a acupuncture group receiving sharp-hook acupuncture plus acupoint injection with conventional analgesics or a control group. Patients from both groups were evaluated at week 0 (baseline), week 1, and week 4. The primary outcome measure was the change from baseline shoulder pain, measured by Visual Analogue Scale at 7 days after treatment. Secondary outcome measures include the (i) function of shoulder joint and (ii) McGill pain questionnaire. The results showed that patients in acupuncture group had better pain relief and function recovery compared with control group (P<0.05) at 1 week after treatment. Moreover, there were statistical differences between two groups in VAS and shoulder joint function and McGill pain questionnaire at 4 weeks after treatment (P<0.05). Therefore, the sharp-hook acupuncture helps to relieve the pain and restore the shoulder function for patients with periarthritis of shoulder
High-performance broadband flexible photodetector based on Gd3Fe5O12-assisted double van der Waals heterojunctions
Abstract Flexible photodetectors are fundamental components for developing wearable systems, which can be widely used for medical detection, environmental monitoring and flexible imaging. However, compared with 3D materials, low-dimensional materials have degraded performance, a key challenge for current flexible photodetectors. Here, a high-performance broadband photodetector has been proposed and fabricated. By combining the high mobility of graphene (Gr) with the strong light–matter interactions of single-walled carbon nanotubes (SWCNTs) and molybdenum disulfide (MoS2), the flexible photodetector exhibits a greatly improved photoresponse covering the visible to near-infrared range. Additionally, a thin layer of gadolinium iron garnet (Gd3Fe5O12, GdlG) film is introduced to improve the interface of the double van der Waals heterojunctions to reduce the dark current. The SWCNT/GdIG/Gr/GdIG/MoS2 flexible photodetector exhibits a high photoresponsivity of 47.375 A/W and a high detectivity of 1.952 × 1012 Jones at 450 nm, a high photoresponsivity of 109.311 A/W and a high detectivity of 4.504 × 1012 Jones at 1080 nm, and good mechanical stability at room temperature. This work demonstrates the good capacity of GdIG-assisted double van der Waals heterojunctions on flexible substrates and provides a new solution for constructing high-performance flexible photodetectors
Extending the coherence of spin defects in hBN enables advanced qubit control and quantum sensing
Abstract Negatively-charged boron vacancy centers ( V B − ) in hexagonal Boron Nitride (hBN) are attracting increasing interest since they represent optically-addressable qubits in a van der Waals material. In particular, these spin defects have shown promise as sensors for temperature, pressure, and static magnetic fields. However, their short spin coherence time limits their scope for quantum technology. Here, we apply dynamical decoupling techniques to suppress magnetic noise and extend the spin coherence time by two orders of magnitude, approaching the fundamental T 1 relaxation limit. Based on this improvement, we demonstrate advanced spin control and a set of quantum sensing protocols to detect radiofrequency signals with sub-Hz resolution. The corresponding sensitivity is benchmarked against that of state-of-the-art NV-diamond quantum sensors. This work lays the foundation for nanoscale sensing using spin defects in an exfoliable material and opens a promising path to quantum sensors and quantum networks integrated into ultra-thin structures