The integration of quantum emitters with integrated photonics enables complex quantum photonic circuits that are necessary for photonic implementation of quantum simulators, computers, and networks. Thin-film lithium niobate is an ideal material substrate for quantum photonics because it can tightly confine light in small waveguides and has a strong electro-optic effect that can switch and modulate single photons at low power and high speed. However, lithium niobate lacks efficient single-photon emitters, which are essential for scalable quantum photonic circuits. We demonstrate deterministic coupling of single-photon emitters with a lithium niobate photonic chip. The emitters are composed of InAs quantum dots embedded in an InP nanobeam, which we transfer to a lithium niobate waveguide with nanoscale accuracy using a pick-and-place approach. An adiabatic taper transfers single photons emitted into the nanobeam to the lithium niobate waveguide with high efficiency. We verify the single photon nature of the emission using photon correlation measurements performed with an on-chip beamsplitter. Our results demonstrate an important step toward fast, reconfigurable quantum photonic circuits for quantum information processing.

Telecom-wavelength single photons are essential components for long-distance quantum networks. However, bright and pure single photon sources at telecom wavelengths remain challenging to achieve. Here, we demonstrate a bright telecomwavelength single photon source based on a tapered nanobeam containing InAs/InP quantum dots. The tapered nanobeam enables directional and Gaussian-like far-field emission of the quantum dots. As a result, using above-band excitation we obtain an end-to-end brightness of 4.1 ± 0.1% and first-lens brightness of 27.0 ± 0.1% at the ∼1300 nm wavelength. Furthermore, we adopt quasi-resonant excitation to reduce both multiphoton emission and decoherence from unwanted charge carriers. As a result, we achieve a coherence time of 523 ± 16 ps and postselected Hong−Ou−Mandel visibility of 0.91 ± 0.09 along with a comparable first-lens brightness of 21.0 ± 0.1%. These results represent a major step toward a practical fiber-based single photon source at telecom wavelengths for long-distance quantum networks.

Fiber-coupled single photon sources are essential components of photonics-based quantum information processors. Most fiber-coupled single photon sources require careful alignment between fibers and quantum emitters. In this work, we present an alignment-free fiber-integrated single photon source based on an InAs/InP quantum dot emitting at telecom wavelengths. We designed a nanobeam containing the quantum dots attached to a fiber taper. The adiabatic tapered coupler of the nanobeam enables efficient light coupling to the fiber taper. Using a tungsten probe in a focused ion beam system, we transferred the nanobeam to the fiber taper. The observed fibercoupled single photon emission occurs with a brightness of 1.5% and purity of 86%.This device provides a building block for fiber-optic quantum circuits that have various applications, such as quantum communication and distributed quantum computing.

Coupling single photon emitters to surface plasmons provides a versatile ground for on chip quantum photonics. However, achieving good coupling efficiency requires precise alignment of both the position and dipole orientation of the emitter relative to the plasmonic mode. We demonstrate coupling of single emitters in the 2-D semiconductor, WSe2 self-aligned with propagating surface plasmon polaritons in silver-air-silver, metal-insulator-metal waveguides. The waveguide produces strain induced defects in the monolayer which are close to the surface plasmon mode with favorable dipole orientations for optimal coupling. We measure an average enhancement in the rate of spontaneous emission by a factor of 1.89 for coupling the single defects to the plasmonic waveguide. This architecture provides an efficient way of coupling single photon emitters to propagating plasmons which is an important step towards realizing active plasmonic circuits on chip.In recent years, defects bound excitons in two dimensional semiconductors have emerged as a new class of single photon emitters with ultra-narrow linewidths of 100 µeVs, as well as high single photon purity. [1][2][3][4] These emitters are located at the surface of an atomically thin monolayer which allows them to come in close proximity to photonic nanostructures. Another characteristic feature is that they can be deterministically induced by strain engineering allowing for site specific positioning. 5-7 Thus, with the ability to position these atomically thin quantum emitters, one can efficiently couple to the confined mode of optical nanostructures providing a platform for coherent light-matter interactions. Such a platform is critical for applications such as quantum communication and quantum information processing 8,9 . 2D materials with their narrow linewidths and flexibility in terms of positioning, offer a promising path to tailoring strong light matter interactions. However, apart from nanoscale positioning of emitters, the nanostructure must also exhibit a high optical density of states. A strong contender for the photonic nanostructures are surface plasmon polaritons generated at a metaldielectric interface. Surface plasmons exhibit extreme subwavelength confinement of light 10,11 and an atom-like dipole emitter placed near the metal-dielectric interface, preferentially emits into the surface plasmon mode due to its high optical density of states. 12 The strong optical decay of emitters into the surface plasmon results in efficient coupling of emitters to a common plasmonic mode that can lead to strong photon-photon interactions. 13 Coupling also produces a significant enhancement in the rate of spontaneous emission of the emitters 12,14,15 which can help realize a fast single photon source on-chip. Thus, single photon emitters in 2D materials, coupled to surface plasmon polaritons establishes a platform for compact active photonic circuits essential for quantum information processing [16][17][18] .Several previous works reported deterministic coupling of quantu...

InAs/InP quantum dots are excellent sources of telecom single-photon emission and are among the most promising candidates for scalable quantum photonic circuits. However, geometric differences in each quantum dot leads to slightly different emission wavelengths and hinders the possibility of generating multiple identical quantum emitters on the same chip. Stark tuning is an efficient technique to overcome this issue as it can control the emission energy of individual quantum dots through the quantum-confined Stark effect. Realizing this technique in InAs/InP quantum dots has previously been limited to shifts of less than 0.8 meV due to jumps in the emission energy because of additional charges at high electric field intensities. We demonstrate up to 5.1 meV of Stark tuning in the emission wavelength of InAs/InP quantum dots. To eliminate undesirable jumps to charged state, we use a thin oxide insulator to prevent carrier injection from the contacts, thereby significantly improves the tuning range of the Stark effect. Moreover, the single-photon nature and narrow linewidth of the quantum dot emission is preserved under a wide range of applied electric fields. Using photoluminescence intensity measurements and timeresolved lifetime spectroscopy we confirmed that this Stark tuning range is limited by carrier tunneling at high electric fields. This result is an important step toward integrating multiple identical quantum emitters at telecom wavelengths on-a-chip, which is crucial for realizing complex quantum photonic circuits for quantum information processing. a) Corresponding Author,