Color-charge separation in trapped SU(3) fermionic atoms

Cold fermionic atoms with three different hyperfine states with SU(3) symmetry confined in one-dimensional optical lattices show color-charge separation, generalizing the conventional spin charge separation for interacting SU(2) fermions in one dimension. Through time-dependent DMRG simulations, we explore the features of this phenomenon for a generalized SU(3) Hubbard Hamiltonian. In our numerical simulations of finite size systems, we observe different velocities of the charge and color degrees of freedom when a Gaussian wave packet or a charge (color) density response to a local perturbation is evolved. The differences between attractive and repulsive interactions are explored and we note that neither a small anisotropy of the interaction, breaking the SU(3) symmetry, nor the filling impedes the basic observation of these effects

Testing collapse models with levitated nanoparticles: the detection challenge

We consider a nanoparticle levitated in a Paul trap in ultrahigh cryogenic vacuum, and look for the conditions which allow for a stringent noninterferometric test of spontaneous collapse models. In particular we compare different possible techniques to detect the particle motion. Key conditions which need to be achieved are extremely low residual pressure and the ability to detect the particle at ultralow power. We compare three different detection approaches based respectively on a optical cavity, optical tweezer and a electrical readout, and for each one we assess advantages, drawbacks and technical challenges

Tracking spin and charge with spectroscopy in spin-polarised 1D systems

We calculate the spectral function of a one-dimensional strongly interacting chain of fermions, where the response can be well understood in terms of spinon and holon excitations. Upon increasing the spin imbalance between the spin species, we observe the single-electron response of the fully polarised system to emanate from the holon peak while the spinon response vanishes. For experimental setups that probe one-dimensional properties, we propose this method as an additional generic tool to aid the identification of spectral structures, e.g. in ARPES measurements. We show that this applies even to trapped systems having cold atomic gas experiments in mind.Comment: 5 pages, 4 figure

Microscale Modeling of Magnetoactive Composites Undergoing Large Deformations

This paper is concerned with the development of a material model for the constituents of a magnetoactive composite. Special attention is paid to magnetorheological elastomers which are synthesized from a soft polymeric matrix material with embedded magnetizable particles. Because the particles interact under an applied magnetic load, a coupled magneto-mechanical field problem has to be solved. The mechanical properties of the polymer matrix motivate the consideration of large deformations. We present the balance equations with boundary conditions and an appropriate material model. The corresponding boundary value problems are solved by the Finite-Element-Method. A weak numerical coupling scheme enables the staggered solution of two subproblems, the stationary magnetic and mechanical one. The coupling between both is realized by a surrounding iterative loop

Is spin-charge separation observable in a transport experiment?

We consider a one-dimensional chain consisting of an interacting area coupled to non-interacting leads. Within the area, interaction is mediated by a local on-site repulsion. Using real time evolution within the Density Matrix Renormalisation Group (DMRG) scheme, we study the dynamics of wave packets in this two-terminal transport setup. In contrast to previous works, where excitations were created by adding potentials to the Hamiltonian, we explicitly create left moving single particle excitations in the right lead as the starting condition. Our simulations show that such a transport setup allows for a clear detection of spin-charge separation using time-resolved spin-polarised density measurements.Comment: 5 pages, 4 figures. accepted by Europhysics Letter

Modelling and control of a water jet cutting probe for flexible surgical robot

Surgical removal of cancerous tissue from the spine is limited by the inability of hand held drills and cutting tools to reach small crevices present in complex bones such as the spinal column, especially on the anterior side. In addition, the high speed rotating mechanisms used presently are subject to stability issues when manoeuvring around tortuous bone forms. We report on the design and experimental testing of a novel flexible robotic surgical system which addresses these issues. The robot consists of a flexible probe, a water jet cutting system, and a haptic feedback controller. The water jet cutting system consists of a flexible end effector capable of bending around the anterior of the spinal column for tissue removal. A new experimental method of controlling the depth of water jet cut is described. The haptic feedback controller is based on a constraint set approach to define 3D boundaries, based on five key types of constraints. Experimental outcomes of measuring the depth of water jet cut were combined with haptic regional constraints with the aim of improving the safety of surgical procedures. The reliability, accuracy and performance of the prototype robot were tested in a mock surgical procedure on the lower lumbar vertebrae. Results show promise for the implementation of water jet cutting for robotic surgical spinal procedures

nanite: using machine learning to assess the quality of atomic force microscopy-enabled nano-indentation data

Atomic force microscopy (AFM) allows the mechanical characterization of single cells and live tissue by quantifying force-distance (FD) data in nano-indentation experiments. One of the main problems when dealing with biological tissue is the fact that the measured FD curves can be disturbed. These disturbances are caused, for instance, by passive cell movement, adhesive forces between the AFM probe and the cell, or insufficient attachment of the tissue to the supporting cover slide. In practice, the resulting artifacts are easily spotted by an experimenter who then manually sorts out curves before proceeding with data evaluation. However, this manual sorting step becomes increasingly cumbersome for studies that involve numerous measurements or for quantitative imaging based on FD maps