Integrated optical combs: Towards single photon applications
Roberto Morandotti, Michael Kues, Christian Reimer, Benjamin Wetzel, Piotr Roztocki, Lucia Caspani, Fabio Grazioso, Brent E. Little, William J. Munro, Chu, Sai T., David Moss
The implementation of a novel microring pumping scheme allows for highly stable and potettially fully integratable sources of multiplexed headed photons, as well the first time two ring modes can be pumped in a stable configuration. This in turn led to the first demonstration of a new nonlinear process on the integrated platform (type II spontaneous four-wave mixing) and the first direct generation of polarization diverse photon pairs.
The implementation of a novel microring pumping scheme allows for highly stable and potettially fully integratable sources of multiplexed headed photons, as well the first time two ring modes can be pumped in a stable configuration. This in turn led to the first demonstration of a new nonlinear process on the integrated platform (type II spontaneous four-wave mixing) and the first direct generation of polarization diverse photon pairs.
In this talk, the physics of microring resonators is discussed in the classical and quantum regimes, in the context of the exploitation of chi-3 effects in these cavities as done by our group. Through the implementation of a novel microring pumping scheme and a quantum reinterpretation of the frequency comb, we present an integrated platform for the generation of quantum optical states spread over multiple optical modes. The scheme allows for highly stable and potentially fullyintegrable quantum light sources. Following the demonstration of a multiplexed heralded photon source, the scheme also enabled the first demonstration of a new nonlinear process on the integrated platform (type II spontaneous four-wave mixing) allowing the first direct generation of polarization-diverse photon pairs, where the first time two ring modes can be pumped in a stable configuration.
The on-chip generation of optical quantum states will enable accessible advances for quantum technologies. We demonstrate that integrated quantum frequency combs (based on high-Q microring resonators made from a CMOS-compatible, high refractive-index doped-glass platform) can enable the generation of pure heralded single photons, cross-polarized photon pairs, as well as bi- and multi-photon entangled qubit states over a broad frequency comb covering the S, C, L telecommunications band, with photon frequencies corresponding to standard telecommunication channels spaced by 200 GHz. Exploiting a self-locked, intra-cavity excitation configuration, a highly-stable source of multiplexed heralded single photons is demonstrated, operating continuously for several weeks with less than 5% fluctuations. The photon bandwidth of 110 MHz is compatible with quantum memories, and high photon purity was confirmed through single-photon auto-correlation measurements. In turn, by simultaneously exciting two orthogonal polarization mode resonances, we demonstrate the first realization of type-II spontaneous FWM (in analogy to type-II spontaneous parametric down-conversion), allowing the direct generation of orthogonally-polarized photon pairs on a chip. By using a double-pulse excitation, we demonstrate the generation of time-bin entangled photon pairs. We measure qubit entanglement with visibilities above 90%, enabling the implementation of quantum information processing protocols. Finally, the excitation field and the generated photons are intrinsically bandwidth-matched due to the resonant characteristics of the ring cavity, enabling the multiplication of Bell states and the generation of a four-photon time-bin entangled state. We confirm the generation of this four-photon entangled state through four-photon quantum interference.
Quantum correlations, where two or more parties exhibit strong correlations in a particular degree of freedom are important resources for fundamental science [1], such as the exploration of non-locality and entanglement, as well as non-classical technologies including quantum computation, quantum key distribution and quantum metrology. One typical way to generate correlated photon pairs is to use the spontaneous four-wave mixing process, with demonstrations on various platforms [2]. So far, single-photon stimulated four-wave mixing (FWM) has been demonstrated in optical fibers [3]. Here we show induced correlation by single photon seeded FWM through exploiting the orthogonal polarization modes in an integrated ring resonator [4]. We allow two different four-wave mixing processes to occur simultaneously with the same signal frequency mode but different idler frequency modes (see Fig.1(a)). The single-photon induced FWM process, named here seeded FWM, was created through the link of type-0 SFWM and type-2 SFWM. In the type-0 process, two excitation photons from the same field are converted into two new photons, signal and idler, with the same polarization as the pump field. While in the type-2 FWM, two annihilated photons, each one from a different polarized pump field, namely TE and TM, generate an orthogonal-polarized photon pair. More importantly, spatial and temporal overlapping of two processes and their sharing of one common resonance lead to correlation between the other two signal photons, one from each process. For example, an idler photon created in type-0 FWM seeds the type-2 FWM process or vice versa, i.e. the TM idler photon in Fig. 1, induces correlation between the signal TM and TE photons. This is proven by the observation of a clear coincidence peak for both signal photons in Fig.1(b). Furthermore, we confirmed our observation via power-dependent correlation measurements (see Fig.1 (c)). We summarized the true coincidence count (C) and its coincidence to accidental ratio (CAR) when only the TE pump power is increased while maintaining the TM mode pump power (black squares), and both pump powers are increased with a constant ratio (blue dots). We found that the seeded FWM scales with the square of both pump powers (C ∝ PjePtm) and that the CAR reach its maxima of 1.5 at the available pump power, indicating thermal statistics. Our findings are relevant to the fundamental understanding of spontaneous parametric effects as well as single-photon induced processes and single photon cloning.
Compact, efficient, high-quality and scalable non-classical photon sources are one of the most critical building blocks for quantum information processing and communications. Photon pair generation via spontaneous four wave mixing is being recognized as an attractive platform for quantum optics which is compatible with the rapidly-maturing classical integrated photonics technology using silicon wafers, which is adopted in industry for its low cost, high performance and scalability. Traditionally, the photon pairs generated from silicon photonic devices, however, have not compared favorably with traditional nonlinear crystals in terms of overall rate, quality and efficiency. This dissertation discusses the factors that affect the quality and efficiency of photon pair generation in silicon integrated photonic microrings, together with their design and characterization. Furthermore, we show how the microrings can be integrated with other photonic devices on the silicon-on-insulator platform, and using proof-of-concept experiments, discuss the feasibility of using these photon-pair sources with technology that is already present in, or will soon be present in, practical fiber-optic networks, such as integrated lasers and modulated classical data streams.