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Advanced Quantum Technologies

Unidirectional Photon Coupling Using Asymmetric Diamond Emitters with Enhanced Spontaneous Emission

Satyajit Murmu, Avijit Kumar, Rajan Jha

Published May 21, 2022• 10 citations
Publisher

Abstract

Abstract The directional coupling of single photon emission from nitrogen vacancy (NV – ) emitters to optical systems for various applications requires a suitable interface between NV – emitters and optical waveguides. Unidirectional coupling of photons may have significant importance in next generation quantum technology such as quantum and complex optical networks, quantum communication, and multi‐scale quantum photonics devices including quantum non‐linearity and quantum metrology. Here, a hybrid asymmetric structure of elliptically faceted (ELFA) diamond nanowire with Bragg grating (BG) containing negatively charged NV – center for efficient and unidirectional optical coupling to optical nanowire (waveguide) is proposed. The calculations indicate that the structure can provide coupling efficiency of ≈90% toward the elliptically facet direction and ≈1% in the opposite direction. Further, Purcell factor is enhanced due to the augmented electric field intensity in the ELFA structure. This structure is significantly robust against imperfect placement and rotational alignment of dipole from its intended position.

DOI
10.1002/qute.202100160

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We present a novel design of optical nanostructure for efficient light extraction from nitrogen vacancy (NV) center in diamond. Numerical simulations of the optimal structure exhibit significant collection efficiency along with a stable radiation profile. We achieved a photon collection efficiency of 70% even with a lower numerical aperture of 0.5. Two different approaches (simple cone and encapsulated cone) have been adopted to reach a high geometrical tolerance without affecting much to the efficiency and emission profile. Besides that, our structure adds an extra benefit in terms of emission enhancement near zero phonon line (ZPL) region of NV spectra. Overall, this cone shaped diamond structure provides a robust, highly efficient and directional emission which can be integrated with a quantum optical network for various applications.

Results in Optics•Sep 22, 2023•2 citations
Abstract The directional coupling of single photon emission from nitrogen vacancy (NV – ) emitters to optical systems for various applications requires a suitable interface between NV – emitters and optical waveguides. Unidirectional coupling of photons may have significant importance in next generation quantum technology such as quantum and complex optical networks, quantum communication, and multi‐scale quantum photonics devices including quantum non‐linearity and quantum metrology. Here, a hybrid asymmetric structure of elliptically faceted (ELFA) diamond nanowire with Bragg grating (BG) containing negatively charged NV – center for efficient and unidirectional optical coupling to optical nanowire (waveguide) is proposed. The calculations indicate that the structure can provide coupling efficiency of ≈90% toward the elliptically facet direction and ≈1% in the opposite direction. Further, Purcell factor is enhanced due to the augmented electric field intensity in the ELFA structure. This structure is significantly robust against imperfect placement and rotational alignment of dipole from its intended position.
The demand of single photon coupling to optical systems requires a suitable interface between negatively charged Nitrogen Vacancy (NV-) emitters in diamond to waveguides or optical circuits for applications in quantum network systems and in unidirectional emission with controlled photon states. Here, we propose a hybrid asymmetric structure of elliptically faceted (ELFA) diamond nanowire with Bragg Grating containing negatively charged NV center for efficient and unidirectional optical coupling to optical nanowire. Our calculations indicate that the structure can provide coupling efficiency of ~90% towards the elliptically facet direction and ~1% towards the opposite direction. Further, Purcell factor is enhanced due to the augmented electric field intensity in the Bragg Grating assisted ELFA structure. Further, we observe higher chirality constant for ELFA+BG structure -- an indicative of efficient unidirectional photon coupling. By integrating two ELFA diamond nanowire having opposite aligned elliptical facet can be used to design and develop complex optical circuits. Further, this structure can also be used as an inline polarizer filter where it can reflect only one particular mode (e.g. TE mode or TM mode) with higher extinct ratio. The hybrid structure can potentially be used for various applications in quantum photonics, quantum-nonlinear systems.
Abstract The resonant modes associated with engineered photonic structures of different spatial‐dimension are essential to obtain bright on‐demand single photon sources for quantum technologies. Negatively‐charged nitrogen‐vacancy (NV‐) center in diamond is proposed as an excellent single‐photon source at room temperature. The possible optical readout of spin states in diamond makes it a good candidate for the spin‐photon interface. However, poor light collection, feeble zero‐phonon line, low emission rate, and broad phonon‐induced emission limit the use of NV‐ centers in quantum technologies. Here, a feasible, easy‐to‐fabricate, asymmetric Tamm structure coupled with a single NV‐ center to enhance the emission rate of zero phonon line (ZPL) with better light collection efficiency is presented. The asymmetric Tamm structure shows dual resonant mode with one of the modes coinciding with NV‐ ZPL wavelength of 640 nm. The mode quality factor ( Q ‐factor) is 140, which is greater than the Q ‐factor of conventional Tamm structure and hence, improved field intensity localization. The authors achieved four times Purcell enhancement and five times enhanced light collection efficiency at 640 nm. The proposed asymmetric Tamm structure helps to generate bright single photons using NV‐ center and improves the efficacy of the spin‐photon interface.
Abstract A fiber inline compatible hybrid diamond cavity system manifesting Fano resonance in transmission, as well as emission spectra, is presented. This system comprises a 1D Bragg cavity structured elliptically faceted diamond nanowire coupled to an optical nanowire. The device exhibits ≈47% transmission variation within a wavelength range ≈522 pm with a moderate Q ‐factor ≈1100. The dual supermode‐based photon coupling enables ≈80% photon coupling efficiency. The tunability of the Fano lineshape and the Purcell factor as high as 223 is attained by altering the dipole position of the quantum emitter. Such significantly high Purcell factor results in ≈150 times reduction in the decay time of quantum emitter emission, thereby allowing faster data transmission. It is believed that the proposed hybrid cavity Fano system may provide a new pathway for quantum optical switches, sensors, and applications at a single photon level.
Nitrogen-Vacancy (NV) centers in diamond are promising solid-state quantum emitters that can be utilized for photonic quantum applications. Various diamond nanophotonic devices have been fabricated for efficient extraction of single photons emitted from NV centers to a single guided mode. However, for constructing scalable quantum networks, further efficient coupling of single photons to a guided mode of a single-mode fiber (SMF) is indispensable and a difficult challenge. Here, we propose a novel efficient hybrid system between an optical nanofiber and a cylindrical-structured diamond nanowire. The maximum coupling efficiency as high as 75% for the sum of both fiber ends is obtained by numerical simulations. The proposed hybrid system will provide a simple and efficient interface between solid-state quantum emitters and a SMF suitable for constructing scalable quantum networks.
Solid-state quantum emitters embedded in a semiconductor crystal environment are potentially scalable platforms for quantum optical networks operated at room temperature. Prominent representatives are nitrogen-vacancy (NV) centers in diamond showing coherent entanglement and interference with each other. However, these emitters suffer from inefficient optical outcoupling from the diamond and from fluctuations of their charge state. Here, we demonstrate the implementation of regular n-type gallium nitride nanowire arrays on diamond as photonic waveguides to tailor the emission direction of surface-near NV centers and to electrically control their charge state in a p-i-n nanodiode. We show that the electrical excitation of single NV centers in such a diode can efficiently replace optical pumping. By the engineering of the array parameters, we find an optical read-out efficiency enhanced by a factor of 10 and predict a lateral NV-NV coupling 3 orders of magnitude stronger through evanescently coupled nanowire antennas compared to planar diamond not covered by nanowires, which opens up new possibilities for large-scale on-chip quantum-computing applications.
We present a novel design of optical nanostructure for efficient light extraction from nitrogen vacancy (NV) center in diamond. Numerical simulations of the optimal structure exhibit significant collection efficiency along with a stable radiation profile. We achieved a photon collection efficiency of 70% even with a lower numerical aperture of 0.5. Two different approaches (simple cone and encapsulated cone) have been adopted to reach a high geometrical tolerance without affecting much to the efficiency and emission profile. Besides that, our structure adds an extra benefit in terms of emission enhancement near zero phonon line (ZPL) region of NV spectra. Overall, this cone shaped diamond structure provides a robust, highly efficient and directional emission which can be integrated with a quantum optical network for various applications.