Advancing classical simulators by measuring the magic of quantum computation

Stabiliser operations and state preparations are efficiently simulable by classical computers. Stabiliser circuits play a key role in quantum error correction and fault-tolerance, and can be promoted to universal quantum computation by the addition of "magic" resource states or non-Clifford gates. It is believed that classically simulating stabiliser circuits supplemented by magic must incur a performance overhead scaling exponentially with the amount of magic. Early simulation methods were limited to circuits with very few Clifford gates, but the need to simulate larger quantum circuits has motivated the development of new methods with reduced overhead. A common theme is that algorithm performance can often be linked to quantifiers of computational resource known as magic monotones. Previous methods have typically been restricted to specific types of circuit, such as unitary or gadgetised circuits. In this thesis we develop a framework for quantifying the resourcefulness of general qubit quantum circuits, and present improved classical simulation methods. We first introduce a family of magic state monotones that reveal a previously unknown formal connection between stabiliser rank and quasiprobability methods. We extend this family by presenting channel monotones that measure the magic of general qubit quantum operations. Next, we introduce a suite of classical algorithms for simulating quantum circuits, which improve on and extend previous methods. Each classical simulator has performance quantified by a related resource measure. We extend the stabiliser rank simulation method to admit mixed states and noisy operations, and refine a previously known sparsification method to yield improved performance. We present a generalisation of quasiprobability sampling techniques with significantly reduced exponential scaling. Finally, we evaluate the simulation cost per use for practically relevant quantum operations, and illustrate how to use our framework to realistically estimate resource costs for particular ideal or noisy quantum circuit instances

Knudsen gas provides nanobubble stability

We provide a model for the remarkable stability of surface nanobubbles to bulk dissolution. The key to the solution is that the gas in a nanobubble is of Knudsen type. This leads to the generation of a bulk liquid flow which effectively forces the diffusive gas to remain local. Our model predicts the presence of a vertical water jet immediately above a nanobubble, with an estimated speed of $\sim3.3\,\mathrm{m/s}$, in good agreement with our experimental atomic force microscopy measurement of $\sim2.7\,\mathrm{m/s}$. In addition, our model also predicts an upper bound for the size of nanobubbles, which is consistent with the available experimental data

Surface bubble nucleation phase space

Recent research has revealed several different techniques for nanoscopic gas nucleation on submerged surfaces, with findings seemingly in contradiction with each other. In response to this, we have systematically investigated the occurrence of surface nanobubbles on a hydrophobised silicon substrate for various different liquid temperatures and gas concentrations, which we controlled independently. We found that nanobubbles occupy a distinct region of this phase space, occurring for gas concentrations of approximately 100-110%. Below the nanobubble phase we did not detect any gaseous formations on the substrate, whereas micropancakes (micron wide, nanometer high gaseous domains) were found at higher temperatures and gas concentrations. We moreover find that supersaturation of dissolved gases is not a requirement for nucleation of bubbles.Comment: 4 pages, 4 figure

Towards an understanding of the learning processes that occur in synchronous online seminars for the professional development of experienced educators

notes: Published through online firstpublication-status: Publishedtypes: ArticleThe National College for School Leadership (now the National College) exists to serve the development needs of school leaders in England. The College has begun to use web conferencing in several areas of its work including its professional development programmes, strategic initiatives and support and networking opportunities. Web conferencing tools offer a range of modes of interaction including audio, chat, text, desktop sharing, presentations and video conferencing. It thus has the potential for multi-process learning. The research reported here investigated the ways in which multi-process learning using these tools can be understood. It asked ‘What insights can be gained into the learning processes occurring in synchronous online seminars involving experienced educators? A literature review was carried out to provide background on the current thinking about learning through web conferencing and to explore factors that might be essential for the collective construction of knowledge in this context. Recorded internal and external NCSL web conferences were chosen as case studies; these provided the data for independent qualitative analysis by each of the researchers. From this analysis a model of the learning processes, identified in the data, was developed and related to the current literature. The major findings and model were further reviewed, in the light of their own web-conferencing experiences, by a large number of expert College educators. The resulting ‘model of multi-process learning in web conferencing’ identifies the part played by social, informational, individual internalisation and coconstruction stages in multi-process learning

Non-symmetric liquid crystal dimer containing a carbohydrate-based moiety

Peer reviewedPublisher PD

Retooling existing tuberculosis drugs for children.

Please help populate SUNScholar with the full text of SU research output. Also - should you need this item urgently, please send us the details and we will try to get hold of the full text as quick possible. E-mail to [email protected]. Thank you.Journal Articles (subsidised)Geneeskunde en GesondheidswetenskappePediatrie En Kindergesondhei