ESE Seminar: “Synthetic dimensions: harnessing light’s internal degrees of freedom for quantum, nonlinear and topological photonics”

Scaling up next-generation photonic systems in a resource-efficient manner is a ubiquitous challenge for quantum technologies such as quantum networks, quantum simulation and computation, and for classical technologies such as photonic neural networks, LiDAR and communications. From a fundamental perspective, high-dimensional lattices hold promise for realizing and manipulating exotic states of light and matter, complementing the recent surge in studying low-dimensional physics using 2D materials, quantum materials and cold atoms.

I will show how we can endow photons with “synthetic dimensions” to overcome these challenges of scalability, resource efficiency and dimensionality. The concept of synthetic dimensions replaces one or more spatial dimensions with intrinsic properties of photons such as frequency, spin or temporal modes. I will introduce a novel synthetic-dimension spectroscopy technique to directly read out band structures from a time-resolved transmission. Using this technique, we probed 2D quantum Hall physics in a single modulated cavity by simultaneously harnessing two synthetic dimensions of frequency and spin, thus elucidating how higher-dimensional physics can be implemented in simpler, experimentally feasible lower-dimensional structures. In such a cavity, neutral photons experience an artificial magnetic field, allowing us to observe a wide variety of condensed matter phenomena such as spin-orbit coupling, spin-momentum locking, chiral edge currents and a Meissner-to-vortex phase transition, completely in synthetic dimensions. Examples of the extreme tunability of synthetic-space photonic circuits to realize flexibly reprogrammable long-range complex coupling and reconfigurable lattice Hamiltonians will also be provided, in a manner that is unmatched in real-space architectures.

Quantum technologies not only require reprogrammable photonic circuits, but also need quantum sources to excite these circuits. In the second part of my talk, I will discuss the first nanophotonic quantum squeezed-light source, built by harnessing the ultralow-loss and strong nonlinearity of the silicon nitride microresonator platform. I will also explain how we generated broadband low-noise frequency combs on the same platform, and performed ultrafast real-time spectroscopy of molecules using these combs. The talk will conclude with an outlook for combining quantum and nonlinear optics with coherent synthetic-space circuits in high dimensions to enable scalable, reconfigurable nanophotonic systems for emerging applications.