Quantum emitters can be integrated into a single-piece nanoscale plasma circuit through a low loss plasma configuration to limit light to well below the diffraction limit. In integrated quantum plasmons, a waveguide based on a surface plasmon (SPP) mode propagates electromagnetic waves along a metal-dielectric or metal-air interface over a photonic waveguide based on a dielectric (and thus diffraction limited). Observations are for optical signal processing and integrated circuits for the integration and miniaturization of the Xerox enhanced from embedded quantum emitters and to the trend of development chips. Different metal-dielectric configurations have been developed for glare-substance interactions on a single photon scale to support propagation of plasma modes that are outside the diffraction limit. The property enables unique prospects to design highly integrated photonic signal processing systems with nanoscale resolution, sensors and optical imaging technology.
The efficiency of the GeV-DLSPPW platform compared to other hybrid quantum systems, a) the dependence of the simulated plasma decay rate of the DLSPPW coupled GeV center is observed. The inset shows the cross section of the y-oriented dipole emitter located in the DLSPPW waveguide, and b) the distribution curve of the emission efficiency (β factor) of the internal distribution of the GeV center in the nano-diamond, where each colored square represents the corresponding in-plane dipole The center value of the sub-location, c) the quality factor (FOM) and transmission length of the hybrid quantum plasma system of GeV-DLSPPW on the AgV crystal compared to other quantum emitter plasma waveguide (QE PW) hybrid systems. Image source: Light Science & Applications, doi: 10.1038 / s41377-018-0062-5.
Various SPP-based structures created in the past include metal nanowires (NW), parallel NW, V-grooves (VG), and wedge waveguides, which have demonstrated single plasma guidance for potential quantum applications. The practical implementation of this integrated quantum photonics is still elusive due to several challenges, including the high propagation loss of the SPP mode and the limited control of the single quantum emitter. Recently, a low-loss, dielectric-loaded SPP waveguide (DLSPPW) for nanofabrication was constructed on a silver film for a simple quantum plasma circuit consisting of embedded nanodiamonds and nitrogen vacancy centers.
Now writing in the field of optical science and applications, Hamidreza Siampour and colleagues have taken a step forward in the field of integrated quantum chemistry by demonstrating the on-chip coupling between a single photon source and a plasmonic waveguide. In this approach, physicists designed nanodiamonds with a single-photon emitting space (GeV) center embedded in a dielectric hydrogen silsesquioxane (HSQ) on top of a silver layer fabricated using electron beam lithography. ) constituting a plasma waveguide. When a green laser (532 nm) is coupled through a grating coupler to one end of the waveguide to propagate to the nanodiamond, it excites the GeV center, which emits a single photon that is coupled to the plasma mode of the waveguide. In this work, the researchers realized long waveguide transmission length (33μm) and efficient coupling (56%), thus opening up a new way for chip-based quantum circuit development.
The green laser (532 nm) is transmitted along the low loss plasma waveguide, a) the SEM image of the single wafer (top) and the DLSPP waveguide (bottom) fabricated on top of the Ag plate, b) the optical characterization of the 532 nm laser for the waveguide ( Top) and vertical (bottom) polarization, c) bright field microscope images of fabricated waveguides of different lengths on the Ag sheet (illustration shows the image of the grating coupler at the end of the waveguide used) in order to maximize the coupling efficiency of DLSPPW, d) at 532 nm The propagation length of DLSPPW measured on the Ag sheet was 11.8 μm. Image source: Light Science & Applications, doi: 10.1038 / s41377-018-0062-5.
This study is the first to detail the synthesis and characterization of GeV nanodiamonds. Nanodiamonds are produced using high pressure high temperature (HPHT) methods; Ge is introduced during growth to integrate a single GeV center. The scientists proposed and demonstrated a hybrid method using NLSPPW for nanofabrication, which uses a single silver (Ag) crystal structure, which significantly reduces the SPP damping rate compared to other films produced by Ag. This method contributes to a sufficiently long SPP propagation at the excitation and emission wavelengths of the GeV center in the nanodiamond incorporated within the plasma chip.
The structures of the synthesized GeV nano and microdiamonds were observed in the original samples using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The synthesized nanodiamonds were spin coated onto an Ag coated silicon wafer and scanned with a confocal fluorescence microscope. The measured data indicates a super-bright, narrow-spectrum, stable single-photon source based on a single GeV center in nanodiamonds for highly integrated circuits. The polarization characteristics of the GeV nanodiamonds were measured using an analyzer in the detector to determine the projection of a single photon emitted on the surface plane. The data measured for a single GeV nanodiamond conforms to the model polarization characteristics of the diamond color center based on the Group IV elements of the periodic table (eg silicon vacancy SiV)
Characterization of nanodiamonds: a) SEM images of GeV nano and microdiamonds of the original samples after HPHT synthesis. b) Ge atoms are located in the middle of two empty lattice positions, including reverse symmetry, c) the system includes electronic structures and optical transitions similar to the family of the Group IV diamond color, d) normalized photon rate is a single in the Ag plane GeV nanodiamond and analyzer angle, measurement (point) and model fit (solid). Image source: Light Science & Applications, doi: 10.1038 / s41377-018-0062-5.
The observed ability to single-photon emission in diamond nanocrystals enables a hybrid quantum plasma system that can facilitate remote excitation of the GeV center incorporated in the plasma chip. Siampour et al. Efficient remote delivery of the GeV-DLSPPW system is elegantly demonstrated compared to other hybrid quantum plasma systems. A special figure of merit of 180 (FOM) was revealed in the study due to the six-fold Cels enhancement, 56% coupled at one wavelength (efficiency and ? micron transmission length λ of 602 nm).
Electron beam lithography was used to fabricate a waveguide with an HSQ resist on an Ag coated substrate to contain nanodiamonds with a single GeV center - added to the device by controlled placement. The technology provides an accurate placement of ~30 nm, enhanced by SEM imaging observations, limited by the size of the nanodiamond, and can be fabricated down to 1 nm using existing diamond synthesis techniques. After the nanodiamonds were excited by a green pump laser, the fabricated waveguides were observed using an atomic force microscope (AFM) and a charge coupled device (CCD) camera.
On-chip excitation of a single GeV nanodiamond (ND) is controlled by a controlled placement of a device fabricated with hydrogen silsesquioxane (HSQ) on top of an Ag film. a) Sample layout and direct excitation of GeV nanodiamonds embedded in a plasmonic waveguide. The working principle, b) the AFM image of the manufactured waveguide (left), the CCD image of the entire structure excited by the nanodiamond (right). The three points ND, A and B show the excitation and emission of the GeV emitter (ND) and the coupling of the GeV to the DLSPPW mode, the propagation and outcoupling radiation from both ends (A and B). Image source: Light Science & Applications, doi: 10.1038 / s41377-018-0062-5.
In addition, the authors used a single crystal Ag sheet instead of the Ag film to significantly enhance the DLSPPW propagation length. The green laser transmitted through the DLSPPW mode is optically characterized as polarization along the waveguide axis. The transmittance of several different lengths of waveguide was measured to show the very long propagation length (~11.8 μm) of the green laser through the low loss DLSPPW.
Schematic diagram of device layout and operation principle for on-chip excitation of nanodiamonds. Nanodiamonds carry a narrow-spectrum single GeV quantum emitter embedded in a DLSPP waveguide. Image source: Light Science & Applications, doi: 10.1038 / s41377-018-0062-5.
Using a similar setup, the scientists began demonstrating and confirming the remote excitation of the GeV center coupled to the DLSPPW mode. Subsequently, the finite element modeling (FEM) method was used to simulate the GeV decay rate, and the attenuation rate of the GeV center in the predicted waveguide was up to four times compared to its emission in vacuum. The system exhibits superior performance compared to previously demonstrated systems, and the use of larger refractive index dielectrics such as titanium dioxide (TiO 2 ) can further enhance the observed Purcell factor in future studies.
This research opens up a way to integrate excitation lasers, quantum emitters and plasma circuits onto the same chip. Previous strategies have demonstrated the detection of a single plasma and double plasma interference on the chip. By combining all three technologies on a single chip, the authors envision that all elements of a quantum plasma circuit can be integrated on a chip in the near future.
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