Resolving Phonon Fock States in a Multimode Cavity with a Double-Slit Qubit

We resolve phonon number states in the spectrum of a superconducting qubit coupled to a multimode acoustic cavity. Crucial to this resolution is the sharp frequency dependence in the qubit-phonon interaction engineered by coupling the qubit to surface acoustic waves in two locations separated by $\sim40$ acoustic wavelengths. In analogy to double-slit diffraction, the resulting self-interference generates high-contrast frequency structure in the qubit-phonon interaction. We observe this frequency structure both in the coupling rate to multiple cavity modes and in the qubit spontaneous emission rate into unconfined modes. We use this sharp frequency structure to resolve single phonons by tuning the qubit to a frequency of destructive interference where all acoustic interactions are dispersive. By exciting several detuned yet strongly-coupled phononic modes and measuring the resulting qubit spectrum, we observe that, for two modes, the device enters the strong dispersive regime where single phonons are spectrally resolved.Comment: 9 pages, 8 figures; revised arguments in paragraphs 3 and 8, added Hamiltonian description, and corrected typo

Comprehensive structural model of the mechanochemical cycle of a mitotic motor highlights molecular adaptations in the kinesin family

Kinesins are responsible for a wide variety of microtubule-based, ATP-dependent functions. Their motor domain drives these activities but the molecular adaptations that specify these diverse and essential cellular activities are poorly understood. It has been assumed that the first identified kinesin - the transport motor kinesin-1 – is the mechanistic paradigm for the entire superfamily, but accumulating evidence suggests that this is not the case. To address the deficits in our understanding of the molecular basis of functional divergence within the kinesin superfamily, we studied kinesin-5s, which are essential mitotic motors whose inhibition blocks cell division. Using cryo-electron microscopy and subnanometer resolution structure determination, we have visualised conformations of microtubule-bound human kinesin-5 motor domain at successive steps in its ATPase cycle. Following ATP hydrolysis, nucleotide-dependent conformational changes in the active site are allosterically propagated into rotations of the motor domain and uncurling of the drugbinding loop L5. In addition, the mechanical neck-linker element that is crucial for motor stepping undergoes discrete, ordered displacements. We also observed large reorientations of the motor N-terminus that indicate its importance for kinesin-5 function through control of neck-linker conformation. A kinesin-5 mutant lacking this N-terminus is enzymatically active, and ATP-dependent neck-linker movement and motility is defective although not ablated. All these aspects of kinesin-5 mechanochemistry are distinct from kinesin-1. Our findings directly demonstrate the regulatory role of the kinesin-5 N-terminus in collaboration with the motor’s structured neck-linker, and highlight the multiple adaptations within kinesin motor domains that tune their mechanochemistries according to distinct functional requirements

Lucky 13-microtubule depolymerisation by kinesin-13 motors

The kinesin-13 class of motors catalyses microtubule depolymerisation by bending tubulins at microtubule ends. Depolymerisation activity is intrinsic to the kinesin-13 motor core but the activity of the core alone is very low compared with that of constructs that also contain a conserved neck sequence. The full-length dimeric motor is an efficient depolymeriser and also diffuses along the microtubule lattice, which helps it to find microtubule ends. Current evidence supports the idea of a generic mechanism for kinesin-13-catalysed depolymerisation. However, the activity of kinesin-13 motors is precisely localised and regulated in vivo to enable a wide range of cellular roles. The proteins are involved in global control of microtubule dynamics. They also localise to mitotic and meiotic spindles, where they contribute to formation and maintenance of spindle bipolarity, chromosomal congression, attachment correction and chromatid separation. In interphase cells, intricate and subtle mechanisms appear to allow kinesin-13 motors to act on specific populations of microtubules. Such carefully controlled localisation and regulation makes these kinesins efficient, multi-tasking molecular motors

Widening access to Higher Education:an evaluative case study of a foundation year alternative to access

Universities are encouraged to widen access to a broad range of applicants, including mature students taking Access qualifications. Admissions tutors can find it difficult to compare and choose between Access and A-level applications, and Access applicants for popular courses may be disadvantaged relative to students with good A-levels. In this evaluative case study a foundation year designed to avoid Access selection problems and widen participation in psychology, biology, optometry and pharmacy is reviewed. Progression and success rates are compared to national averages for Access courses and issues in Foundation Year management considered. The Foundation Year is rejected as unsatisfactory and it is concluded that widening participation for mature students can be achieved through Access courses. Difficulties in achieving this for high-demand courses in leading universities are discussed

No regrets? Measuring the career benefits of a psychology placement year

We report an analysis of whether a psychology placement year provides a significant benefit to graduates’ careers. Destination of Leavers from Higher Education (DLHE) survey data six months post-graduation suggested that placement programme graduates across the university are more likely to be (i) in work and (ii) in graduate level jobs. For psychology, the association between graduates’ placement status and employment status at six months post graduation was not significant overall. However, when analyses were split by degree classification obtained, it was shown that amongst those graduates with 2.1 classification degrees reporting themselves as working, more placement programme vs. non-placement programme graduates had obtained graduate level jobs (63% vs. 33%). In 2.2 graduates there was no significant association. This pattern persisted in the data from a survey of psychology alumni (from 18 months to six and a half years post graduation). Psychology placement programme alumni were more satisfied with their careers even when ethnicity, gender, degree classification and entry year were taken into account. They also earn more, although not when background factors are taken into account. This study was therefore able to show some measurable and persistent effects of a psychology placement year, although whether the benefits can be claimed to outweigh the costs is inconclusive. Limitations and implications are discussed