Photodetection plays a key role in basic science and technology, with exquisite performance having been achieved down to the single photon level. Further improvements would open new possibilities across a broad range of scientific disciplines, and enable new types of applications. However, it is still unclear what is possible in terms of ultimate performance, and what properties are needed to achieve such performance. Here, we present a general modeling framework for photodetectors whereby the photon field, the absorption process, and the amplification process are all treated as one coupled quantum system. The formalism naturally handles field states with single or multiple photons as well as a variety of detector configurations, and includes a mathematical definition of ideal photodetector performance. The framework reveals how specific photodetector architectures introduce limitations and tradeoffs for various performance metrics, providing guidance for optimization and design.
Identification of non-trivial quantum mechanical effects in the functioning of biological systems has been a
long-standing and elusive goal in the fields of physics, chemistry and biology. Recent progress in control and
measurement technologies, especially in the optical spectroscopy domain, have made possible the identification
of such effects. In particular, electronic coherence was recently shown to survive for relatively long times in
photosynthetic light harvesting complexes despite the effects of noisy biomolecular environments. Motivated by
this experimental discovery, several recent studies have combined techniques from quantum information, quantum
dynamical theory and chemical physics to characterize the extent and nature of quantum dynamics in light
harvesting structures. I will review these results and summarize our understanding of the subtle quantum effects
in photosynthetic complexes. Then I will outline the remarkable properties of light harvesting complexes that
allow quantum effects to be significant at dynamically relevant timescales, despite the decohering biomolecular
environment. Finally, I will conclude by discussing the implications of quantum effects in light harvesting
complexes, and in biological systems in general.
Quantum error correction is an essential ingredient for quantum computation. The standard descriptions of how to implement active error correction assume ideal resources such as projective measurements and instantaneous gate operations. Unfortunately in practice such resources are not realizable in most quantum computing architectures and it is not clear how such error correction implementations will perform under more realistic conditions. Motivated by this we examine schemes for implementing active error correction that use a more modest set of resources. This leads to new implementations of error correction that are continuous in time, and thus described by continuous dynamical maps. We evaluate the performance of such schemes using numerical simulations and comment on the applicability and effectiveness of continuous error correction for quantum computing.