In this project, we study the theory behind nanoscale quantum devices that interact with light. At the nanoscale, light can be made to strongly interact with matter, where quantum mechanical effects govern its behavior and the concept of a photon emerges. Here, we seek to fully understand the quantum changes in the light as it interacts with nano-sized pieces of matter.

Throughout the history of quantum optics, experiments focused primarily on understanding the internal dynamics of the

*matter*when interacting with the light field. For instance, in an ion trap quantum computer the motional states of the ions are of interest while the state of the light field is secondary. However, a new paradigm for information processing is becoming experimentally accessible where many quantum-optical devices are integrated in nanophotonic circuits. Then, the relevant information is encoded in the quantum states of the photons as they fly around the nanophotonic chip. Hence, we are now interested in understanding the converse problem: the way the state of the*photon*field changes after interacting with the piece of matter.The effect of an individual device on a photon can now be formally described in a so-called scattering experiment. First, a photon wavepacket is prepared far away from the device. It travels freely towards the device and as it hits the interaction region forms a strongly entangled state of light and matter. Afterwards, the character of the interaction is imprinted on the outgoing wavepacket. This concept of a scattering experiment was originally envisioned in high-energy field theories with static Hamiltonians, and we are adopting it to nanophotonic devices driven by pulses of laser light. Our formalism will thus be of relevance to design and analysis of quantum information processing systems in which the information is encoded in the state of the photonic field, with the piece of matter implementing either a source of photons or implementing a unitary operation on the photonic state.

## Python tutorials

We are also working to make our theory and simulations accessible through contributions to the Quantum Toolbox in Python (QuTiP). In particular, please check out our tutorials illustrating photon scattering calculations:

## Relevant Publications

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**ew-photon scattering and emission from open quantum systems**, Rahul Trivedi, Kevin Fischer, Shanshan Xu, Shanhui Fan, Jelena Vučković. Phys. Rev. B 98, 144112 (2018) [arXiv:1806.01958] - Scattering into one-dimensional waveguides from a coherently-driven quantum-optical system, Kevin A. Fischer, Rahul Trivedi, Vinay Ramasesh, Irfan Siddiqi, Jelena Vučković. Quantum 2, 69 (2018) [arXiv:1710.02875]
- Quantum dot single photon sources with ultra-low multi-photon probability, Lukas Hanschke, Kevin A. Fischer, Stefan Appel, Daniil Lukin, Jakob Wierzbowski, Shuo Sun, Rahul Trivedi, Jelena Vučković, Jonathan J. Finley, Kai Müller. (2018) [arXiv:1801.01672]
- Signatures of two-photon pulses from a quantum two-level system, Kevin A. Fischer, Lukas Hanschke, Jakob Wierzbowski, Tobias Simmet, Constantin Dory, Jonathan J. Finley, Jelena Vučković, Kai Müller.
*Nature Physics*(2017) - Pulsed Rabi oscillations in quantum two-level systems: beyond the Area Theorem, Kevin A. Fischer, Lukas Hanschke, Malte Kremser, Jonathan J. Finley, Kai Müller, Jelena Vučković.
*Quantum Sci. Technol.*3, 014006 - On-Chip Architecture for Self-Homodyned Nonclassical Light, Kevin A. Fischer, Yousif A. Kelaita, Neil V. Sapra, Constantin Dory, Konstantinos G. Lagoudakis, Kai Müller, and Jelena Vučković.
*Phys. Rev. Applied*7, 044002 (2017) [arXiv:1611.01566] [Supplemental Material] - Dynamical modeling of pulsed two-photon interference, Kevin A. Fischer, Kai Müller, Konstantinos G. Lagoudakis, Jelena Vučković.
*New J. Phys.*18 113053 (2016) [arXiv:1608.07626] [Supplemental Material 1, 2, 3, 4] Featured in New Journal of Physics Highlights of 2016