### Hybrid Quantum Networks

#### (supervisor: John Gough)

Nature of project: **theory**, theory

Available to
students on full-time physics degree schemes only.

#### Project description and methodology

Quantum transducers play a crucial role in hybrid quantum networks.

The goal is to convert a quantum signal contained in a mode from one form to another - eg., microwave to photonic - with minimum decoherence.

The standard approach is direct mode conversion. But alternatives using adaptive control have been proposed.

The project will look at the underlying physics, the physical systems considered, and the protocols proposed.

*A successful project will develop beyond the above in one/some of the following directions:*

The topic is extra-curricular and so detailing the underlying physics would already be an achievement. A description of applications would extend the core project.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

*Additional scope or challenge if taken as a Year-4 project:* Investigating continuous time modes in addition to discrete ones.

Please speak to **John Gough** (jug) if you consider doing this project.

*Initial literature for students:*

- Quantum transduction with adaptive control, Mengzhen Zhang, Chang-Ling Zou, Liang Jiang, Phys. Rev. Lett. 120, 020502 (2018)
- A. Furusawa, J. L. Sazrensen, S. L. Braunstein, C. A. Fuchs, H. J. Kimble, and E. S. Polzik, Science 282, 706 (1998).
- S. L. Braunstein and C. M. Caves, Statistical distance and the geometry of quantum states, Phys. Rev. Lett. 72, 3439 (1994).
- Jing Zhang, Yu-xi Liu, Re-Bing Wu, Kurt Jacobs, Franco Nori, Quantum feedback: theory, experiments, and applications, Physics Reports 679, 1-60 (2017)

#### Novelty, degree of difficulty and amount of assistance required

Topic would suit someone with an interest in quantum mechanics. Topic is extracurricular.

#### Project milestones and deliverables (including timescale)

milestone | to be completed by |

Locating source material/additional material/gaining understanding of the background concepts | end of October |

overview of theory | end of November |

looking at applications/ underlying principles | Christmas |

Developing ideas further | mid-March |