SiGe quantum wells with oscillating Ge concentrations for quantum dot qubits.

Large-scale arrays of quantum-dot spin qubits in Si/SiGe quantum wells require large or tunable energy splittings of the valley states associated with degenerate conduction band minima. Existing proposals to deterministically enhance the valley splitting rely on sharp interfaces or modifications in the quantum well barriers that can be difficult to grow. Here, we propose and demonstrate a new heterostructure, the "Wiggle Well", whose key feature is Ge concentration oscillations inside the quantum well.

A phylogenetic and evolutionary analysis of antimycin biosynthesis.

Streptomyces species and other Actinobacteria are ubiquitous in diverse environments worldwide and are the source of, or inspiration for, the majority of antibiotics. The genomic era has enhanced biosynthetic understanding of these valuable chemical entities and has also provided a window into the diversity and distribution of natural product biosynthetic gene clusters. Antimycin is an inhibitor of mitochondrial cytochrome c reductase and more recently was shown to inhibit Bcl-2/Bcl-XL-related anti-apoptotic proteins commonly overproduced by cancerous cells.

Superconductivity in Empty Bands and Multiple Order Parameter Chirality.

Recent experiments have shown rotation of the plane of polarization of light reflected from the surface of some superconductors. The photon energy exceeds the electronic bandwidth, so that completely filled or completely empty bands must play a role. We show that in strong-coupling theory a Coulomb interaction can produce an order parameter in the unoccupied band that explains the observations.

Improved Error Thresholds for Measurement-Free Error Correction.

Motivated by limitations and capabilities of neutral atom qubits, we examine whether measurement-free error correction can produce practical error thresholds. We show that this can be achieved by extracting redundant syndrome information, giving our procedure extra fault tolerance and eliminating the need for ancilla verification. The procedure is particularly favorable when multiqubit gates are available for the correction step.

Reflections: Neurology and The Humanities. The case of the locked house. The finished mystery.

After the death in 2012 of Dr. Robert Joynt, who served Neurology® as CPC Section Editor, an unfinished manuscript was found on his computer. It would have been his sixth Sherlock Holmes pastiche.

Single-shot measurement of triplet-singlet relaxation in a Si/SiGe double quantum dot.

We investigate the lifetime of two-electron spin states in a few-electron Si/SiGe double dot. At the transition between the (1,1) and (0,2) charge occupations, Pauli spin blockade provides a readout mechanism for the spin state. We use the statistics of repeated single-shot measurements to extract the lifetimes of multiple states simultaneously.

Tunable spin loading and T1 of a silicon spin qubit measured by single-shot readout.

We demonstrate single-shot readout of a silicon quantum dot spin qubit, and we measure the spin relaxation time T1. We show that the rate of spin loading can be tuned by an order of magnitude by changing the amplitude of a pulsed-gate voltage, and the fraction of spin-up electrons loaded can also be controlled. This tunability arises because electron spins can be loaded through an orbital excited state.

Charge sensing and controllable tunnel coupling in a Si/SiGe double quantum dot.

We report integrated charge sensing measurements on a Si/SiGe double quantum dot. The quantum dot is shown to be tunable from a single, large dot to a well-isolated double dot. Charge sensing measurements enable the extraction of the tunnel coupling t between the quantum dots as a function of the voltage on the top gates defining the device.

Energy level statistics of quantum dots.

We investigate the charging energy level statistics of disordered interacting electrons in quantum dots by numerical calculations using the Hartree approximation. The aim is to obtain a global picture of the statistics as a function of disorder and interaction strengths. We find Poisson statistics at very strong disorder, Wigner-Dyson statistics for weak disorder and interactions, and a Gaussian intermediate regime.

Spin readout and initialization in a semiconductor quantum dot.

Electron spin qubits in semiconductors are attractive from the viewpoint of long coherence times. However, single spin measurement is challenging. Several promising schemes incorporate ancillary tunnel couplings that may provide unwanted channels for decoherence.

Theory of the transition at 0.2 K in Ni-doped Bi2Sr2CaCu2O8.

A theory is put forward that the electronic phase transition at 0.2 K in Ni-doped Bi2Sr2CaCu2O8 is a result of the formation of a spin density wave in the system of Ni impurities. The driving force for the transition is the exchange interaction between the impurity spins and the spins of the conduction electrons.

Pseudogaps and extrinsic losses in photoemission experiments on poorly conducting solids.

A photoelectron emitted from a conducting solid may suffer a substantial energy change through ohmic losses that can drastically alter the line shape on the millielectron volt scale that is now observable through improved resolution. Almost all of this energy loss occurs after the electron leaves the solid. These losses are expected to be important in isotropic materials with relatively low conductivity, such as certain colossal magnetoresistance manganates, and in very electrically anisotropic materials, such as one-dimensional conductors, and may also affect interpretation of photoemission in superconductors with high transition temperatures.