Plasmonics are open systems, which means that they efficiently send measurable energy far away from the system. They also concentrate light at very small regions, which increases their interaction with quantum matter and allows for much quicker interactions to occur.“ Until recently, there was no proper theory to describe such open cavity systems, apart from phenomenological models that cannot capture all the interactions occurring. Recently, we derived and published the first method that allows us to see how the interactions happen in such open systems and it has been enormously revealing. Based on this new theory, we were able to visualise the “shape” of a photon in such nanophotonic systems. This method is the first step to making it easier to design new nanophotonic devices for the next generation of quantum technologies”, said Demetriadou. These new technologies will change how we communicate securely, detect pathogens and control chemical reactions at the single molecule level.
Quantum phenomena are foundational to the development of innovations in quantum technologies, and these are enabled by the discovery and characterisation of quantum materials. Clark described some of the desirable properties she would like to see in her research: quantum fluctuations, entanglement and superposition.
Quantum fluctuation is a temporary change in state at a particular point in space, according to the Heisenberg Uncertainty Principle which states that a particle’s location and momentum cannot be known at the same time. This can be explained with the analogy of a marble in a bowl: according to quantum mechanics, this marble is constantly moving, preventing knowledge of its exact position and momentum.
“My group is interested in the fluctuations of the electron's spin. At high temperatures, the electron spins are in a disordered, fluctuating state which slows as the material cools until they all point in the same direction”, explained Clark. “We explore quantum materials in which fluctuations destroy this conventional behaviour at any temperature.” The phenomenon of quantum fluctuation has applications in quantum sensing.
Quantum fluctuations of electrons occurring in an intricately connected system of magnetic moments cannot be described independently of the state of the other particles in the group, introducing the concept of quantum entanglement. This can be described with an analogy of two dice in separate boxes that are brought together to form a link. Even when separated and shaken, the number facing up will be identical for both dice. The dice represent individual particles and bringing them together entangles them. Demetriadou noted that phenomena such as entanglement can happen at the strong coupling regime, allowing us to generate new quantum states. Her group is trying to demonstrate entanglement in nanoplasmonic systems.
The spin of entangled particles is in a state of quantum superposition, where they exist in all possible orientations simultaneously. This concept is often described using Schrödinger’s cat thought experiment: a cat along with a harmful substance both placed in a box has an equal chance of being dead or alive within an hour. Schrödinger suggested that the cat is both dead and alive in a superposition of states until the box is opened, at which time it is dead or alive. According to Clark, entanglement and superposition are important properties and would be useful in quantum computation to develop a platform for quantum bits of information, or [qubits](https://www.ibm.com/think/topics/qubit).
The challenge of quantum
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Clark underscores the importance of understanding the synthesis of quantum materials as her group works towards developing and characterising new classes of materials. “Characterising quantum materials can be challenging, both from an experimental point of view and understanding the data collected. The computational tools used to extract information from measurements of quantum materials often push the limits of what can be done. New ways of analysing measurements would be a breakthrough,” she said.
She compared silicon wafers, which are generated using reliable processing methods, to quantum materials. “Unlike silicon wafers, the pattern of results \[for quantum materials\] that we often see in literature is that different samples of nominally the same material display different properties. We don’t understand fundamentally how synthetic methods impact properties, and we don’t have reliable methods for generating pure, defect-free products”, she said.
The hope is that new approaches, including machine learning, will help drive the development of new classes of quantum materials. “The scope for new discoveries is enormous. We have many possible combinations of different elements in the periodic table that we can use to make new materials.”
Future of Quantum Research in the UK
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In the UK, future investment in quantum materials research is key. “Quantum materials are more challenging to fund from an industry perspective, due to their more fundamental nature. However, globally, there is substantial investment in quantum materials research, and it is important that the UK continues to play a leading role in this to secure the translational pipeline to new applications”, said Clark.
As research groups across the country produce world-leading work on fundamental science and quantum materials, University of Birmingham researchers hope there will be a framework that provides secure longer-term funding that allows them to progress.