Spin ice draws continuing interest since its discovery in 1999, due to its outstanding character as a magnetic counterpart of water ice. The quantum version of spin ice, a quantum spin ice, gives a typical example of quantum spin liquid state, which is described by a gauge theory analogous to quantum electrodynamics. It is usually quite hard to describe the dynamics of strong-coupling gauge theory. However, recent theoretical progress enables a precise description of the fractional excitation, called magnetic monopole, which sheds light on the experimental identification of quantum spin liquid phase in spin ice materials.
It is a non-trivial issue to define higher-dimensional gauge theories at any energy scale since their interactions become stronger at high energies. In the presence of supersymmetry, it was argued that certain five-dimensional gauge theories make sense by showing the existence of their ultraviolet fixed points. An attempt of classifying supersymmetric five-dimensional gauge theories had been performed both from quantum field theory and string theory but there was inconsistency between the two approaches. Recently, the inconsistency has been resolved and a lot of new five-dimensional supersymmetric gauge theories which have ultraviolet fixed points have been discovered. In this article, we review such progress in five-dimensional supersymmetric gauge theories. We also comment on applications of string theory to compute various physical quantities of five-dimensional gauge theories.
In superconducting qubits composed of aluminum based Josephson junctions (JJs), the decoherence from microscopic two-level systems in amorphous aluminum oxide has long been a concern. As an alternative material for the qubits, fully epitaxial NbN/AlN/ NbN JJs are an attractive candidate with the potential to solve the above problems because of crystal quality, chemical stability against oxidization, and relatively high transition temperature (～16 K) of NbN. Early studies of superconducting qubits using epitaxially grown nitride JJs have shown significant potential, but their coherence time was limited due to dielectric loss from the MgO substrate. To improve this, we have employed a Si substrate with TiN buffer layer for the epitaxial growth of the nitride JJs and fabricated an all-nitride capacitively-shunted flux qubit coupled to a half-wavelength coplanar waveguide resonator. As the results, this nitride qubit has demonstrated a significant improvement in coherence times, such as T1=16.3 μs and T2=21.5 μs as the mean values of a hundred measurements, which are more than an order of magnitude longer than those reported in the literature using MgO substrates. These results are an important step towards constructing a new platform for superconducting quantum hardware.
Experimentally investigated Turing patterns have typical length scales of millimeters to centimeters in biological morphogenesis, and to sub-millimeters in purely chemical systems. Herein, we report strong evidence that the minimum wavelength of Turing patterns observed thus far which lowers the known scale of Turing patterns substantially. We numerically obtained stripe patterns and domain walls with Y-junctions that are highly similar to those recently observed in bismuth monolayers on NbSe2.