Strong coupling and coherence in hybrid solid state quantum systems

In the last half century of human history we have seen an incredible revolution in our ability to process and disseminate information, with the rise of computers, high speed communication networks, and the internet. The pace of progress is still extremely high, but a major challenge is on the horizon, as the size of processing devices shrinks to approach the scale of single atoms. At such tiny length scales, the physics governing the operation of electronic devices changes fundamentally to obey the laws of quantum mechanics, and computer processors could no longer operate in the conventional way that they do today. This approaching horizon is both a challenge and an opportunity. It has now long been known theoretically that quantum mechanics can in fact be used to carry out computing and communication in ways that are impossible with 'classical' systems, and a large research effort is now underway across many scientific disciplines to realize such quantum communication and computation in a practical way.

In this fellowship, a variety of promising candidate systems for use as quantum bits (qubits) on future quantum electronic chips will be brought together and investigated in a truly quantum coherent manner. Static qubits made from superconducting electric circuits, and electrons trapped in islands on semiconductor chips will be coupled to 'flying' qubits in the form of quanta of light (photons) and quanta of vibrational motion (phonons) on electronic chips cooled to their lowest quantum mechanical energy state at close to absolute zero. The research will address key questions of how long the fragile quantum nature of information can last in such systems, how the different systems can be made to interact and exchange quantum information, and how they can be brought together to ultimately form the basic building blocks of future quantum computers, such as quantum logic gates and quantum memories.

A particular focus of the research is to explore the potential of a system known as cavity QED in which the interaction between atoms (or static qubits) and light (or flying qubits) is enhanced by trapping the light between mirrors that form a cavity. Such a system makes it possible to observe the exchange of energy or information between the atoms/qubits and the light at a much higher rate than in free space. In this particular project, this scenario is realized with microwave frequency photons or phonons trapped on the surface of an electronic chip, with static qubits fabricated in place inside the on-chip cavities. This architecture for cavity QED, and for quantum computing, is thought to be highly promising since scaling it up to larger numbers of qubits may be achieved using conventional processor fabrication techniques that exist today.

The new technology of quantum information processing (QIP) has the potential to have a major impact on society once realized. This is expected to occur within a timescale of several decades. Some already well identified applications will be in secure communication, high performance computing, and complex simulation (in particular of intrinsically quantum systems, which are at the heart of chemistry, biochemistry and nanotechnology). The work to be carried out in this project will contribute to the advancement of this global field, and will raise the profile of UK research within it. Large IT corporations are already beginning to invest in QIP research, and the published results of the work to be pursued in this project will be directly usable in their R&D departments. Direct engagement with such companies will be considered as the project progresses, dependent on success.

The practical and exploratory nature of the specific investigation of surface phonons at a quantum level in this proposal may lead to near-term applications in highly sensitive detectors, benefitting the UK economy through generation of IP and potentially spin-off companies.

Active communication of the new research with young people in both universities and schools will inform and raise awareness of quantum science in general, enhance science education, and motivate more young people to consider higher science education and scientific careers, in particular in physics. Participation in local outreach programmes will contribute to local culture, and improve general public understanding and awareness of quantum mechanics and related research. Explanation of published research results in layman's terms through various media will be undertaken, and will contribute to the communication of the impact of public research funding.