Coherent Resonant Tunneling Through an Artificial Molecule

Coherent resonant tunneling through an artificial molecule of quantum dots in an inhomogeneous magnetic field is investigated using an extended Hubbard model. Both the multiterminal conductance of an array of quantum dots and the persistent current of a quantum dot molecule embedded in an Aharanov-Bohm ring are calculated. The conductance and persistent current are calculated analytically for the case of a double quantum dot and numerically for larger arrays using a multi-terminal Breit-Wigner type formula, which allows for the explicit inclusion of inelastic processes. Cotunneling corrections to the persistent current are also investigated, and it is shown that the sign of the persistent current on resonance may be used to determine the spin quantum numbers of the ground state and low-lying excited states of an artificial molecule. An inhomogeneous magnetic field is found to strongly suppress transport due to pinning of the spin-density-wave ground state of the system, and giant magnetoresistance is predicted to result from the ferromagnetic transition induced by a uniform external magnetic field.Comment: 23 pages, 12 figure

Probing many-body dynamics on a 51-atom quantum simulator

Controllable, coherent many-body systems can provide insights into the fundamental properties of quantum matter, enable the realization of new quantum phases and could ultimately lead to computational systems that outperform existing computers based on classical approaches. Here we demonstrate a method for creating controlled many-body quantum matter that combines deterministically prepared, reconfigurable arrays of individually trapped cold atoms with strong, coherent interactions enabled by excitation to Rydberg states. We realize a programmable Ising-type quantum spin model with tunable interactions and system sizes of up to 51 qubits. Within this model, we observe phase transitions into spatially ordered states that break various discrete symmetries, verify the high-fidelity preparation of these states and investigate the dynamics across the phase transition in large arrays of atoms. In particular, we observe robust manybody dynamics corresponding to persistent oscillations of the order after a rapid quantum quench that results from a sudden transition across the phase boundary. Our method provides a way of exploring many-body phenomena on a programmable quantum simulator and could enable realizations of new quantum algorithms.Comment: 17 pages, 13 figure

Demonstration of hyper-programming in Java

We demonstrate the use of a hyper-programming system to build persistent Java applications in PJama, an orthogonally persistent version of Java. This allows program representations to contain type-safe links to persistent objects embedded directly within the source code. The potential benefits include greater potential for static program checking, improved efficiency, and reduced programming effort.Postprin

Fingerprinting and characterisation of Escherichia coli isolates using DNA arrays

Two commercially available DNA whole genome Escherichia coli K12 arrays were compared to identify a subset of markers for typing. The arrays were identical in probe composition but different in substrate (membrane and glass slide arrays) and probe preparation (radio- and fluorescent-labelled). Labelled genomic E. coli DNA from five strains of the E. coli reference (ECOR) collection (ATCT35320 - ATCX35324) and E. coli K12 were hybridised against these arrays. A group of 1240 putative markers was identified on the membrane arrays and 649 were found on the glass slide arrays. Only a small proportion of these sequences (8%) was found through both platforms. Variability in the hybridisation signals from duplicate experiments made it difficult to identify useful markers. In order to investigate whether this technology could be used for characterising or typing E. coli strains, an array for the detection of 29 pathogenicity markers in E. coli strains was produced. This array was used with eight reference strains, including different pathotypes, 72 strains from the ECOR collection, and 49 clinical isolates. A wide range of E. coli pathogenicity markers was detected. The pathogenicity markers that were most common include chuA and iucC, which are both involved in iron metabolism. Additionally, the clinical isolates were grouped into clusters different from groupings based on biochemical tests. This demonstrates that the use of pathogenicity array typing can complement diagnostic tests on clinical E. coli isolates. An extended, second-generation, pathogenicity marker array containing 75 probes was made. The extended array successfully distinguished between ten closely related isolates from an outbreak of urinary tract infections, while previous tests were unable to do so. This array has the potential for providing a rapid and novel means of characterising pathogenic isolates

Quantitative Decoding of Interactions in Tunable Nanomagnet Arrays Using First Order Reversal Curves

To develop a full understanding of interactions in nanomagnet arrays is a persistent challenge, critically impacting their technological acceptance. This paper reports the experimental, numerical and analytical investigation of interactions in arrays of Co nanoellipses using the first-order reversal curve (FORC) technique. A mean-field analysis has revealed the physical mechanisms giving rise to all of the observed features: a shift of the non-interacting FORC-ridge at the low-H$_c$ end off the local coercivity H$_c$ axis; a stretch of the FORC-ridge at the high-H$_c$ end without shifting it off the H$_c$ axis; and a formation of a tilted edge connected to the ridge at the low-H$_c$ end. Changing from flat to Gaussian coercivity distribution produces a negative feature, bends the ridge, and broadens the edge. Finally, nearest neighbor interactions segment the FORC-ridge. These results demonstrate that the FORC approach provides a comprehensive framework to qualitatively and quantitatively decode interactions in nanomagnet arrays.Comment: 19 pages, 4 figures. 9 page supplemental material including 3 figure