New technologies require new thinking and new materials.
Progress in micro- and nanotechnologies has been a key element in the highly successful quest to satisfy the need for evermore powerful information processing and communication devices during the last decades. This route of progress, however, has a principle limit as smaller structures are necessarily made from fewer and fewer particles and industry is rapidly progressing towards a regime wherein transistors will be made from only a single electron. One can easily see that achieving this goal will lead to a fundamental barrier: due to the indivisibility of electrons the current miniaturisation processes will have reached their final step and new ideas and technologies for enhancing computational power will have to be developed. At the same time, reaching this barrier will also require to develop a completely new set of engineering techniques, since single particles do no longer behave according to the laws of classical mechanics, but instead have to be described quantum mechanically.
As a result, researching the physics of single particles on the quantum scale is of significant importance and has, in recent years, led to a wealth of knowledge and technologies that have underpinned and revolutionised our fundamental understanding of the world. A particularly successful approach has been the application of concepts of information theory to the theory of quantum mechanics, which has led to the development of so-called quantum information devices. The existence of additional resources, such as entanglement, in the quantum regime means that these new devices can have superior qualities to classical devices and solve problems for which no classical algorithms are known. The theoretical work on these issues has been accompanied by tremendous progress in experimental possibilities, and controlled coherent evolution and high fidelity measurements of single particles are, by today, feasible in several synthetic quantum systems. The area is, however, still in its infancy and the development of new ideas for quantum engineering techniques is of large importance for future advances in information and communication technologies. While quantum devices initially only seemed unavoidable, they have turned out to be a highly desirable part of the technological landscape of the future.
Isolating single quantum particles in such a way that they can be deterministically engineered is a very difficult task, due to the often unavoidable environmental interactions or thermal noise. Identifying appropriate systems is, therefore, of large importance and currently a very active strand of research is to test and characterise different candidates for their suitability. One area in which systems that satisfy the basic conditions of good isolations, low noise and high controllability can be found is the area of ultracold atoms and various experimental systems have been build in recent years that allow one to simulate Hamiltonians of importance in quantum information. However, many other systems, ranging from man-made quantum dots in solid state devices to exotic low-dimensional electronic structures are under heavy investigation as well.
Two groups at University College Cork, one experimental and one theoretical, work in this area using ultracold atomic systems. One of their aims is to explore different methods to build interfaces that connect the quantum mechanical world of single atoms to our macroscopic one. A promising method for this is to guide light to the ultracold atom using an optical fibre, have it interact with the atom, and guide is back to the detector. For this we are using a commercial-grade optical fibre, which in the interaction region is stretched to a diameter smaller than 1 micro-meter. The light then no longer fits into the fibre and instead travels on the outside, where it can be accessed by the ultracold atoms. While this technology is still in its infancy, the large flexibility of such a setup makes it a very promising tool for future developments.
The basic entity in a quantum computer is, just as in a classical computer, the bit, now called a quantum bit or qubit. However, while classically a bit can only have two possible states, 0 and 1, a quantum bit can be in any possible combination of these two at the same time. This allows for a powerful parallelism in the computational process, which can be helpful in speeding up algorithms. One common example is the database search, in which one piece of information has to be identified among a large number of elements: instead of sequentially looking at each entry of the database, as required classically, quantum mechanics allows to look at all elements in one operation.
While a full scale quantum computer might still be a long way off, by today almost all fundamental entities and processes have been demonstrated. In fact, first devices using quantum technologies, such as cryptographic systems and random number generators, are already commercially available. Research has started on scaling up the number of quantum bits to carry out more complex processes, as well as improving the stability of the individual qubits. This has helped to significantly increase our understanding of two of the basic properties of quantum mechanics, coherence and entanglement, and is leading the way to explore more complex systems and technologies in the future. Since we are only at the beginning of this journey, the future is likely to hold many unexpected surprises.
Department of Physics
University College Cork