Topological Field Theory Far from Equilibrium.

The observable properties of topological quantum matter are often described by topological field theories. Here, we demonstrate that this principle extends beyond thermal equilibrium. To this end, we construct a model of two-dimensional driven open dynamics with a Chern insulator steady state. Within a Keldysh field theory approach, we show that under mild assumptions-particle number conservation and purity of the stationary state-an abelian Chern-Simons theory describes its response to external perturbations. As a corollary, we predict chiral edge modes stabilized by a dissipative bulk.

Weak Measurement Protocols for Majorana Bound State Identification.

We propose a continuous weak measurement protocol testing the nonlocality of Majorana bound states through current shot noise correlations. The experimental setup contains a topological superconductor island with three normal-conducting leads weakly coupled to different Majorana states. Putting one lead at finite voltage and measuring the shot noise correlations between the other two (grounded) leads, devices with true Majorana states are distinguished from those without by strong current correlations. The presence of true Majorana states manifests itself in unusually high noise levels or the near absence of noise, depending on the chosen device configuration. Monitoring the noise statistics amounts to a weak continuous measurement of the Majorana qubit and yields information similar to that of a full braiding protocol, but at much lower experimental effort. Our theory can be adapted to different platforms and should allow for the clear identification of Majorana states.

Towards Realistic Implementations of a Majorana Surface Code.

Surface codes have emerged as promising candidates for quantum information processing. Building on the previous idea to realize the physical qubits of such systems in terms of Majorana bound states supported by topological semiconductor nanowires, we show that the basic code operations, namely projective stabilizer measurements and qubit manipulations, can be implemented by conventional tunnel conductance probes and charge pumping via single-electron transistors, respectively. The simplicity of the access scheme suggests that a functional code might be in close experimental reach.

Multichannel Kondo impurity dynamics in a Majorana device.

We study the multichannel Kondo impurity dynamics realized in a mesoscopic superconducting island connected to metallic leads. The effective "impurity spin" is nonlocally realized by Majorana bound states and strongly coupled to lead electrons by non-Fermi liquid correlations. We explore the spin dynamics and its observable ramifications near the low-temperature fixed point. The topological protection of the system raises the perspective to observe multichannel Kondo impurity dynamics in experimentally realistic environments.

Strong Anderson localization in cold atom quantum quenches.

Signatures of Anderson localization in the momentum distribution of a cold atom cloud after a quantum quench are studied. We consider a quasi-one-dimensional cloud initially prepared in a well-defined momentum state, and expanding for some time in a disorder speckle potential. Quantum interference generates a peak in the forward scattering amplitude which, unlike the common weak localization backscattering peak, is a signature of strong Anderson localization. We present a nonperturbative, and fully time resolved description of the phenomenon, covering the entire diffusion-to-localization crossover. Our results should be observable by present day experiments.

Universal dephasing rate due to diluted Kondo impurities.

We calculate the dephasing rate due to magnetic impurities in a weakly disordered metal as measured in a weak-localization experiment. If the density nS of magnetic impurities is sufficiently low, the dephasing rate 1/tauphi is a universal function, 1/tauphi=(nS/nu)f(T/TK), where TK is the Kondo temperature and nu is the density of states. We show that inelastic vertex corrections with a typical energy transfer DeltaE are suppressed by powers of 1/(tauphiDeltaE) proportional to nS. Therefore, the dephasing rate can be calculated from the inelastic cross section proportional to pinu ImT-/pinuT/2, where T is the T matrix which is evaluated numerically exactly using the numerical renormalization group.

Wigner-Dyson statistics from the Keldysh sigma-model.

The level statistics of disordered metallic grains with broken time reversal invariance is obtained from the Keldysh nonlinear sigma-model. The basic strategy of the approach--a nonperturbative integration over all saddle points of the sigma-model manifold--might prove useful in the analysis of problems involving disorder and interactions.

Pouring wide-range immobilized pH gradient gels with a window of extremely flattened slope.

A gradient mixing device has been designed to pour polyacrylamide gels with a wide-range immobilized pH gradient including a "window" of extremely flattened slope. The device consists of an IBM-compatible personal computer controlling 8 step-motor-driven burettes, with four producing a density gradient from glycerol and delivering acrylamides and catalysts for gel polymerization, two delivering Immobilines for a wide-range pH gradient and the other two burettes responsible for the delivery of Immobilines for a partial pH range inside the wide range. The effect on a complex separation pattern of proteins with a wide range of pI is that resolution can be increased reproducibly to any reasonable extent at any location of the separation pattern.

Pouring reproducible gradients in gels under computer control: new devices for simultaneous delivery of two independent gradients, for more flexible slope and pH range of immobilized pH gradients.

Recently we described (Electrophoresis 5: 143-147, 1984) a new device for producing density and solute gradients, involving computer-controlled coöperation of stepmotor-driven high-precision burettes, the purpose being to substantially improve reproducibility, flexibility, and documentation of gradients used in gels and in other applications in biochemistry. Here we present the functional principle of three modified and partly alternative devices, based on simultaneous delivery of a density gradient and a non-density gradient. They provide unlimited flexibility of choice for the slope of the non-density gradient, which is stabilized by the density gradient. They seem especially useful for pouring immobilized pH gradients in gels of wide pH ranges (between pH 3.5 and 10) where localized flattening of the gradient is needed to selectively improve resolution. Used in two-dimensional electrophoretic analysis, they should considerably improve control of spot coördinates, standardization of the technique, and interlaboratory data exchange.