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arXiv:1802.10072

Strong Nonlinear Coupling due to Induced Photon Interaction on a Si$_{3}$N$_{4}$ Chip

Sven Ramelow, Alessandro Farsi, Z. Vernon, Stéphane Clemmen, Xingchen Ji, John E. Sipe, Marco Liscidini, Michal F. Lipson, Alexander L. Gaeta

Published Feb 27, 2018• 2 citations
arXivHTMLPDF

Abstract

Second-order optical processes lead to a host of applications in classical and quantum optics. With the enhancement of parametric interactions that arise due to light confinement, on-chip implementations promise very-large-scale photonic integration. But as yet there is no route to a device that acts at the single photon level. Here we exploit the $χ^{(3)}$ nonlinear response of a Si$_{3}$N$_{4}$ microring resonator to induce a large effective $χ^{(2)}$. Effective second-order upconversion (ESUP) of a seed to an idler can be achieved with 74,000 %/W efficiency, indicating that single photon nonlinearity is within reach of current technology. Moreover, we show a nonlinear coupling rate of seed and idler larger than the energy dissipation rate in the resonator, indicating a strong coupling regime. Consequently we observe a Rabi-like splitting, for which we provide a detailed theoretical description. This yields new insight into the dynamics of ultrastrong effective nonlinear interactions in microresonators, and access to novel phenomena and applications in classical and quantum nonlinear optics.

DOI
10.48550/arxiv.1802.10072

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Strong Nonlinear Coupling due to Induced Photon Interaction on a Si3_{3}3​N4_{4}4​ Chip
Second-order optical processes lead to a host of applications in classical and quantum optics. With the enhancement of parametric interactions that arise due to light confinement, on-chip implementations promise very-large-scale photonic integration. But as yet there is no route to a device that acts at the single photon level. Here we exploit the χ(3)χ^{(3)}χ(3) nonlinear response of a Si3_{3}3​N4_{4}4​ microring resonator to induce a large effective χ(2)χ^{(2)}χ(2). Effective second-order upconversion (ESUP) of a seed to an idler can be achieved with 74,000 %/W efficiency, indicating that single photon nonlinearity is within reach of current technology. Moreover, we show a nonlinear coupling rate of seed and idler larger than the energy dissipation rate in the resonator, indicating a strong coupling regime. Consequently we observe a Rabi-like splitting, for which we provide a detailed theoretical description. This yields new insight into the dynamics of ultrastrong effective nonlinear interactions in microresonators, and access to novel phenomena and applications in classical and quantum nonlinear optics.
We demonstrate that nondegenerate four-wave mixing in a Si_{3}N_{4} microring resonator can result in a nonlinear coupling rate between two optical fields exceeding their energy dissipation rate in the resonator, corresponding to strong nonlinear coupling. We demonstrate that this leads to a Rabi-like splitting, for which we provide a theoretical description in agreement with our experimental results. This yields new insight into the dynamics of nonlinear optical interactions in microresonators and access to novel phenomena.
Abstract Entangled photon pairs from spontaneous parametric down-conversion (SPDC) 1 are central to many quantum applications 2–6 . SPDC is typically performed in non-centrosymmetric systems 7 with an inherent second-order nonlinearity ( χ (2) ) 8–10 . We demonstrate strong narrowband SPDC with an on-chip rate of 0.8 million pairs per second in Si 3 N 4 . Si 3 N 4 is the pre-eminent material for photonic integration and also exhibits the lowest waveguide loss (which is essential for integrated quantum circuits). However, being amorphous, silicon nitride lacks an intrinsic χ (2) , which limits its role in photonic quantum devices. We enabled SPDC in Si 3 N 4 by combining strong light-field enhancement inside a high optical Q -factor microcavity with an optically induced space-charge field. We present narrowband photon pairs with a high spectral brightness. The quantum nature of the down-converted photon pairs is verified through coincidence measurements. This light source, based on Si 3 N 4 integrated photonics technology, unlocks new avenues for quantum systems on a chip.
Quantum-photonic chips, which integrate quantum light sources alongside active and passive optical elements, as well as single-photon detectors, show great potential for photonic quantum information processing and quantum technology. Mature semiconductor nanofabrication processes allow for scaling such photonic integrated circuits to on-chip networks of increasing complexity. Second-order nonlinear materials are the method of choice for generating photonic quantum states in the overwhelming majority of linear optic experiments using bulk components, but integration with waveguide circuitry on a nanophotonic chip proved to be challenging. Here, we demonstrate such an on-chip parametric down-conversion source of photon pairs based on second-order nonlinearity in an aluminum-nitride microring resonator. We show the potential of our source for quantum information processing by measuring the high visibility anti-bunching of heralded single photons with nearly ideal state purity. Our down-conversion source yields measured coincidence rates of 80 Hz, which implies MHz generation rates of correlated photon pairs. Low noise performance is demonstrated by measuring high coincidence-to-accidental ratios. The generated photon pairs are spectrally far separated from the pump field, providing great potential for realizing sufficient on-chip filtering and monolithic integration of quantum light sources, waveguide circuits and single-photon detectors. A chip-based source of photon pairs for applications in quantum information processing has been built by a team of scientists in the US. Xiang Guo and co-workers from Yale University built the quantum light source from an aluminum nitride microring resonator. The strong second-order nonlinearity of the aluminum nitride yields efficient parametric down-conversion. This allows 775-nm-wavelength pump photons to be converted into a pair of entangled photons in the telecommunications window of 1550 nm. Tests indicated that the heralded photons generated by the microring source are anti-bunched and have high visibility and a high purity of state, indicating that they are highly suitable for use in quantum optics experiments. In principle, the on-chip source is compatible with megahertz generation rates and large-scale manufacture of integrated optical circuits.
Abstract Silicon carbide (SiC) polytypes are emerging for integrated nonlinear and quantum photonics due to their wide-bandgap energies, second-order optic nonlinearity and process compatibility with complementary metal-oxide-semiconductor technologies. Among polytypes, 3C-SiC is the only one epitaxially grown on wafer-scale silicon substrates. However, on-chip nonlinear and quantum light sources leveraging the second-order nonlinearity of 3C-SiC have not been reported to our knowledge. Here, we design and fabricate an elliptical microring on 3C-SiC. We demonstrate a nonlinear light source with a second-harmonic generation efficiency of 17.4±0.2%W−117.4\pm 0.2 \% {W}^{-1}17.4±0.2%W−1 17.4 ± 0.2 % W − 1 and difference-frequency generation with a signal-idler bandwidth of 97 nm. We demonstrate a spontaneous parametric down-conversion source with a photon-pair generation rate of 4.8 MHz and a coincidence-to-accidental ratio of 3361±843361\pm 843361±84 3361 ± 84 . We measure a low heralded single-photon second-order coherence gH(2)=0.0007{g}_{H}^{\left(2\right)}=0.0007gH(2)​=0.0007 g H 2 = 0.0007 . We observe time-bin entanglement with a visibility of 86.0±2.4%86.0\pm 2.4 \%86.0±2.4% 86.0 ± 2.4 % using this source. Our work paves a way toward SiC-based on-chip nonlinear and quantum photonic circuits.
Over the last two decades, the emergence of quantum information science has uncovered many practical applications in areas such as communications, imaging, and sensing where harnessing quantum features of Nature provides tremendous benefits over existing methods exploiting classical physical phenomena. In this effort, one of the frontiers of research has been to identify and utilize quantum phenomena that are not susceptible to environmental and parasitic noise processes. Quantum photonics has been at the forefront of these studies because it allows room-temperature access to its inherently quantum-mechanical features, and allows leveraging the mature telecommunication industry. Accompanying the weak environmental influence, however, are also weak optical nonlinearities. Efficient nonlinear optical interactions are indispensible for many of the existing protocols for quantum optical computation and communication, e.g. high-fidelity entangling quantum logic gates rely on large nonlinear responses at the one- or few-photon-level. While this has been addressed to a great extent by interfacing photons with single quantum emitters and cold atomic gases, scalability has remained elusive. In this work, we identify the macroscopic second-order nonlinear polarization as a robust platform to address this challenge, and utilize the recent advances in the burgeoning field of optical microcavities to enhance this nonlinear response. In particular, we show theoretically that by using the quantum Zeno effect, low-noise, single-photon-level optical nonlinearities can be realized in lithium niobate whispering-gallery-mode microcavities, and present experimental progress toward this goal. Using the measured strength of the second-order nonlinear response in lithium niobate, we modeled the nonlinear system in the strong coupling regime using the Schrödinger picture framework and theoretically demonstrated that the single-photon-level operation can be observed for cavity lifetimes in excess of 500 ns for all the three waves in the interaction, provided a cavity of radius R < 10 μm is fabricated. Experimentally, we showed that the absorption-limited quality ( Q) factors for lithium niobate, Qintrinsic ≈ 108, can be achieved using diamond-turning methods for disk radii, R > 100 μm, whereas for the smaller disks, additional rigorous polishing may be required. We also fabricated resonators as small as R ∼ 40 μm via this method. In a millimeter-sized resonator, we experimentally demonstrated triply resonant sum-frequency generation, which allowed for an observation of the classical manifestation of the quantum Zeno effect, wherein line-splitting occurs due to the high efficiency intracavity frequency conversion. For the sub-100 μm resonators, we present phase-matching calculations and dispersion-management techniques using analytical approximations and rigorous finite-element-method simulations. Experimentally, Q -factor measurements are shown, and we identify the specific short-comings of the fabrication procedure that may have led to the lower, surface-roughness-limited Q-factors. Finally, we identify pathways toward achieving the single-photon-level nonlinear optics using off-resonant nonlinear optics, which requires the simultaneous realization of phase-matching, large cavity lifetimes, and small mode volumes. We believe this would be feasible in the near future as more advanced fabrication and processing methods are developed for crystalline materials and novel nonlinear crystals are synthesized.
The realization of strong nonlinear coupling between single photons has been a long-standing goal in quantum optics and quantum information science, promising wide impact applications, such as all-optical deterministic quantum logic and single-photon frequency conversion. Here, we report an experimental observation of the strong coupling between a single-photon and a two-photon Fock state in an ultrastrongly-coupled circuit-QED system. This strong nonlinear interaction is realized by introducing a detuned flux qubit working as an effective coupler between two modes of a superconducting coplanar waveguide resonator. The ultrastrong light–matter interaction breaks the excitation number conservation, and an external flux bias breaks the parity conservation. The combined effect of the two enables the strong one–two-photon coupling. Quantum Rabi-like avoided crossing is resolved when tuning the two-photon resonance frequency of the first mode across the single-photon resonance frequency of the second mode. Within this new photonic regime, we observe the thresholdless second harmonic generation for a mean photon number below one. Our results represent a key step towards a new regime of quantum nonlinear optics, where individual photons can deterministically and coherently interact with each other in the absence of any stimulating fields. Systems with strong photon-photon interactions enable advanced quantum optical applications as well as the study of highly correlated light-matter states. Here the authors report strong coupling between single- and two-photon states in a superconducting circuit, enabling a new regime of nonlinear quantum optics.