Quantum Feedback Networks

A unified framework for describing open quantum systems interconnected by bosonic quantum fields (such as optical or microwave fields) has recently been developed. This is enabling the development of engineering strategies to design physical systems for the purpose of quantum enhanced information processing applications. Our group is working on tools for working with quantum feedback networks, model reduction methods for dealing with the inherent complexity of such systems as well as concrete applications that demonstrate the power of our approach.

Optical and Coherent Control

In order to capitalize on their promise of high-bandwidth, ultra-low power operation, future nanophotonic devices will have to contend with quantum and coherent effects inherent to the small-volume, few-photon limit. The theoretical development of general, systematic frameworks for describing quantum feedback networks enables us to leverage established optical technologies—from single- and multi-atom cavity quantum electrodynamics to ultrafast multimode optics—as an essential testbed for establishing direct contact between coherent-feedback control theory and first generation nanophotonic circuits.

Nonlinear and Multimode Optics

Circuits of nonlinear optical devices could provide novel, practical functionality relevant for communication, sensing and computing. Power-dependent (nonlinear) absorption and refraction by atoms, molecules and materials is the key ingredient for devices that mediate interaction of multiple laser beams. For now the laser intensities usually needed to induce significant nonlinear optical interaction are impractically high for all but niche applications. This is a significant hurdle that must be overcome to achieve nonlinear optical devices that can be practically scaled to operate in a circuit. To address this challenge we study materials that we believe to be promising for construction of scalable, low-power nonlinear-optical devices.

Biophysics with Feedback Control

A lot of interesting biology inside the cell emerges from the dynamics of large molecular complexes. The length scales involved are on the order of tens of nanometers and are typically difficult to probe because of fundamental limits in optical microscopy. We are interested in developing new fluorescence spectroscopy techniques which can measure organization at these length scales.  Our favorite tool is Single Molecule Tracking Microscopy, where we use feedback techniques to observe individual molecules diffusing in solution for long periods of time, and glean information about their conformation.

Information Theory and Distributed Computing

We are interested in analyzing the computational power of networks of nonlinear nodes both in the classical regime and the quantum regime. Interesting questions that arise are how rates of computation scale with the overall power consumption but also with the size of a given network.