Recent advances in realizing optical frequency combs using nonlinear parametric processes in integrated photonic resonators have revolutionized on-chip optical clocks, spectroscopy, and multi-channel optical communications. At the same time, the intr
oduction of topological physics in photonic systems has provided a new paradigm to engineer the flow of photons, and thereby, design photonic devices with novel functionalities and inherent robustness against fabrication disorders. Here, we use topological design principles to theoretically propose the generation of optical frequency combs and temporal Kerr solitons in a two-dimensional array of coupled ring resonators that creates a synthetic magnetic field for photons and exhibits topological edge states. We show that these topological edge states constitute a traveling-wave super-ring resonator that leads to the generation of coherent nested optical frequency combs, and self-formation of nested temporal solitons and Turing rolls that are remarkably phase-locked over >40 rings. In the nested soliton regime, our system operates as a pulsed optical frequency comb and achieves a mode efficiency of >50%, an order of magnitude higher than single ring frequency combs that are theoretically limited to only ~5%. Furthermore, we show that the topological nested solitons are robust against defects in the lattice. This topological frequency comb works in a parameter regime that can be readily accessed using existing low loss integrated photonic platforms like silicon-nitride. Our results could pave the way for efficient on-chip optical frequency combs, and investigations of various other soliton solutions in conjunction with synthetic gauge fields and topological phenomena in large arrays of coupled resonators.
Sources of quantum light, in particular correlated photon pairs that are indistinguishable in all degrees of freedom, are the fundamental resource that enables continuous-variable quantum computation and paradigms such as Gaussian boson sampling. Nan
ophotonic systems offer a scalable platform for implementing sources of indistinguishable correlated photon pairs. However, such sources have so far relied on the use of a single component, such as a single waveguide or a ring resonator, which offers limited ability to tune the spectral and temporal correlations between photons. Here, we demonstrate the use of a topological photonic system comprising a two-dimensional array of ring resonators to generate indistinguishable photon pairs with dynamically tunable spectral and temporal correlations. Specifically, we realize dual-pump spontaneous four-wave mixing in this array of silicon ring resonators that exhibits topological edge states. We show that the linear dispersion of the edge states over a broad bandwidth allows us to tune the correlations, and therefore, quantum interference between photons by simply tuning the two pump frequencies in the edge band. Furthermore, we demonstrate energy-time entanglement between generated photons. We also show that our topological source is inherently protected against fabrication disorders. Our results pave the way for scalable and tunable sources of squeezed light that are indispensable for quantum information processing using continuous variables.
We demonstrate quantum interference of three photons that are distinguishable in time, by resolving them in the conjugate parameter, frequency. We show that the multiphoton interference pattern in our setup can be manipulated by tuning the relative d
elays between the photons, without the need for reconfiguring the optical network. Furthermore, we observe that the symmetries of our optical network and the spectral amplitude of the input photons are manifested in the interference pattern. Moreover, we demonstrate time-reversed HOM-like interference in the spectral correlations using time-bin entangled photon pairs. By adding a time-varying dispersion using a phase modulator, our setup can be used to realize dynamically reconfigurable and scalable boson sampling in the time domain as well as frequency-resolved multiboson correlation sampling.
We experimentally realize a photonic analogue of the anomalous quantum Hall insulator using a two-dimensional (2D) array of coupled ring resonators. Similar to the Haldane model, our 2D array is translation invariant, has zero net gauge flux threadin
g the lattice, and exploits next-nearest neighbor couplings to achieve a topologically non-trivial bandgap. Using direct imaging and on-chip transmission measurements, we show that the bandgap hosts topologically robust edge states. We demonstrate a topological phase transition to a conventional insulator by frequency detuning the ring resonators and thereby breaking the inversion symmetry of the lattice. Furthermore, the clockwise or the counter-clockwise circulation of photons in the ring resonators constitutes a pseudospin degree of freedom. We show that the two pseudospins acquire opposite hopping phases and their respective edge states propagate in opposite directions. These results are promising for the development of robust reconfigurable integrated nanophotonic devices for applications in classical and quantum information processing.
Quantum light sources are characterized by their distinctive statistical distribution of photons. For example, single photons and correlated photon pairs exhibit antibunching and reduced variance in the number distribution that is impossible with cla
ssical light. Most common realizations of quantum light sources have relied on spontaneous parametric processes such as down-conversion (SPDC) and four-wave mixing (SFWM). These processes are mediated by vacuum fluctuations of the electromagnetic field. Therefore, by manipulating the electromagnetic mode structure, for example, using nanophotonic systems, one can engineer the spectrum of generated photons. However, such manipulations are susceptible to fabrication disorders which are ubiquitous in nanophotonic systems and lead to device-to-device variations in the spectrum of generated photons. Here, we demonstrate topologically robust mode engineering of the electromagnetic vacuum fluctuations and implement a nanophotonic quantum light source where the spectrum of generated photons is robust against fabrication disorders. Specifically, we use the topological edge states to achieve an enhanced and robust generation of correlated photon pairs using SFWM and show that they outperform their topologically-trivial counterparts. We demonstrate the non-classical nature of our source using conditional antibunching of photons which confirms that we have realized a robust source of heralded single photons. Such topological effects, which are unique to bosonic systems, could pave the way for the development of robust quantum photonic devices.
A common challenge in quantum information processing with photons is the limited ability to manipulate and measure correlated states. An example is the inability to measure picosecond scale temporal correlations of a multi-photon state, given state-o
f-the-art detectors have a temporal resolution of about 100 ps. Here, we demonstrate temporal magnification of time-bin entangled two-photon states using a time-lens, and measure their temporal correlation function which is otherwise not accessible because of the limited temporal resolution of single photon detectors. Furthermore, we show that the time-lens maps temporal correlations of photons to frequency correlations and could be used to manipulate frequency-bin entangled photons. This demonstration opens a new avenue to manipulate and analyze spectral and temporal wavefunctions of many-photon states.
