Hollow-core fibre based quantum optical light-atom interface

Since their discovery, about a century ago, the physical laws of quantum mechanics have puzzled researchers and attracted widespread interest. In particular, the philosophical implications for the meaning of reality and objectivity have raised lasting debates. The bone of contention being the concept of entanglement, where two distant objects, upon the act of measurement, appear to agree on random measurement outcomes, although no physical reality could be ascribed to their properties before the measurement and although any communication between them is ruled out by the theory of relativity.
In modern days, immense progress has been made in this area, and beyond the vast amount of devices and applications such as lasers and superfluidity, the pure quantum properties of photons and even individual atoms can now be controlled with unprecedented precision. While such a high level of control was first achieved in quantum optics, i.e. the physics of light, the advent of laser cooling enabled physicists also to engineer new quantum states of matter. These research fields were recognized by the award of Physics Nobel prizes in 1997, 2001 and 2005.

The field became a spectacular topic of interest when potential applications of entanglement for quantum computing and cryptography were discovered. Devices working with quantum units of information, or qubits, could efficiently solve certain computational problems, simulate quantum dynamics, and provide a means for completely secure communication.

An important ingredient for future quantum networks, i.e., linked nodes that are capable of controlling quantum states, will be the ability to interface light and matter. While photons can be easily transported but are very volatile in their very nature, quantum states of matter can be kept, controlled, and designed to interact with each other. A set of small, easily controllable quantum machines can become more powerful by interconnection. The problem of long-distance quantum communication might serve as the prime example. While basic quantum communication devices are already commercially available, current technology is limited to distances of about 150 km due to the noise that is inevitably introduced in any sort of quantum channel. Overcoming this limit will become technically feasible only with nodes that are capable of storing and preserving the transmitted quantum information and performing quantum operations on it. Hence, there is a strong interest in developing light-matter interfaces that fulfil these tasks.

Such interfaces also find other applications. The transfer of well-controlled optical states onto matter can serve for precision measurements such as magnetometry, atomic clocks, and spectroscopy. At the same time, new states of light can be engineered or detected, and applications include squeezed light, single photons, frequency conversion, and efficient or even non-destructive photon counting, where the intensity of light can be precisely measured without absorbing it. All of these are much sought-after resources for a range of quantum optical applications.

The aim of this project is to design and build a fibre optical light-atom interface. By incorporating techniques from cold-atom physics, we want to build a system based on a micro-fabricated chip with integrated hollow-core photonic crystal fibres. With the help of the chip we will magnetically confine laser cooled, ultracold atoms in the 6 micron sized empty core of these light guiding fibres and let them interact with the light field. This system will allow us to explore new parameter regimes and can become the first demonstration of a long-lived (seconds) quantum memory with very fast switching times. The natural compatibility of the proposed implementation with fibre optical communication will bring quantum communication devices closer to a "real world" implementation.

The goal of this project is the development of a novel technology for quantum light-matter interfaces, which offer exciting prospects for new quantum technologies and in particular the realisation of future quantum information networks. The basic ideas, stemming from what was originally considered a curiosity of Physics, have already led to some commercial exploitation for secure communication devices protected by the laws of Physics, but limitations of speed, compatibility, and especially physical range render this technology still far from becoming an everyday reality. This research project strongly builds on fundamental research on quantum information science that has been pursued over the last decade to overcome these limitations, and although still on a rather fundamental side has the potential of bringing global quantum links closer to technological feasibility and exploitation. The project will advance the scope and applicability of quantum optical devices and contribute directly to one of the "key aspects of a Grand Challenge in Physics" identified in the recent EPSRC consultation, i.e. the field of Quantum Physics for New Quantum Technologies. The project is aligned with a worldwide endeavour to utilise quantum technology for the benefit of society, with major funding programs in Europe and the US and increasing effort in, e.g., countries like China and Singapore, and will contribute to maintaining Europe's and the UK's competitive position. The most direct impact will therefore be given through training of directly involved researchers and students, which will enable them to play key roles in future innovation in this field, i.e. the development and elaboration of ideas for better or new technologies, processes, and products with particular consideration of industrial, economical, and societal needs, desires, and compatibility.

The outcomes of the project will be disseminated through publication and communication of scientific results, and also find entry into various outreach activities. These will make this research accessible to the widest possible audience and potential beneficiaries in the most general sense.