4,968 research outputs found
Roadmap to Majorana surface codes
Surface codes offer a very promising avenue towards fault-tolerant quantum
computation. We argue that two-dimensional interacting networks of Majorana
bound states in topological superconductor/semiconductor heterostructures hold
several distinct advantages in that direction, both concerning the hardware
realization and the actual operation of the code. We here discuss how
topologically protected logical qubits in this Majorana surface code
architecture can be defined, initialized, manipulated, and read out. All
physical ingredients needed to implement these operations are routinely used in
topologically trivial quantum devices. In particular, we show that by means of
quantum interference terms in linear conductance measurements, composite
single-electron pumping protocols, and gate-tunable tunnel barriers, the full
set of quantum gates required for universal quantum computation can be
implemented.Comment: 23 pages, 8 figure
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.Comment: 5 pages, 1 p. suppl.mat, PRL in pres
Critical Workforce Skills for Bachelor-Level Geoscientists: An Analysis of Geoscience Job Advertisements
Understanding the skills bachelor-level geoscientists need to enter the workforce is critical to their success. The goal of this study was to identify the workforce skills that are most requested from a broad range of geoscience employers. We collected 3668 job advertisements for bachelor-level geoscientists and used a case-insensitive, code-matching function in Matlab to determine the skills geoscience employers seek. Written communication (67%), field skills (63%), planning (53%), and driving (51%) were most frequently requested. Field skills and data collection were frequently found together in the ads. Written communication skills were common regardless of occupation. Quantitative skills were requested less frequently (23%) but were usually mentioned several times in the ads that did request them, signaling their importance for certain jobs. Some geoscience-specific skills were rarely found, such as temporal understanding (5%) and systems thinking (0%). We also subdivided field skills into individual tasks and ranked them by employer demand. Site assessments and evaluations, unspecified field tasks, and monitoring were the most frequently requested field skills. This study presents the geoscience community with a picture of the skills sought by employers of bachelor-level geoscientists and provides departments and programs with data they can use to assess their curricula for workforce preparation
Diamagnetism of doped two-leg ladders and probing the nature of their commensurate phases
We study the magnetic orbital effect of a doped two-leg ladder in the
presence of a magnetic field component perpendicular to the ladder plane.
Combining both low-energy approach (bosonization) and numerical simulations
(density-matrix renormalization group) on the strong coupling limit (t-J
model), a rich phase diagram is established as a function of hole doping and
magnetic flux. Above a critical flux, the spin gap is destroyed and a Luttinger
liquid phase is stabilized. Above a second critical flux, a reentrance of the
spin gap at high magnetic flux is found. Interestingly, the phase transitions
are associated with a change of sign of the orbital susceptibility. Focusing on
the small magnetic field regime, the spin-gapped superconducting phase is
robust but immediately acquires algebraic transverse (i.e. along rungs) current
correlations which are commensurate with the 4k_F density correlations. In
addition, we have computed the zero-field orbital susceptibility for a large
range of doping and interactions ratio J/t : we found strong anomalies at low
J/t only in the vicinity of the commensurate fillings corresponding to delta =
1/4 and 1/2. Furthermore, the behavior of the orbital susceptibility reveals
that the nature of these insulating phases is different: while for delta = 1/4
a 4k_F charge density wave is confirmed, the delta = 1/2 phase is shown to be a
bond order wave.Comment: 15 pages, 17 figure
Spin-orbit coupling and electron spin resonance for interacting electrons in carbon nanotubes
We review the theoretical description of spin-orbit scattering and electron
spin resonance in carbon nanotubes. Particular emphasis is laid on the effects
of electron-electron interactions. The spin-orbit coupling is derived, and the
resulting ESR spectrum is analyzed both using the effective low-energy field
theory and numerical studies of finite-size Hubbard chains and two-leg Hubbard
ladders. For single-wall tubes, the field theoretical description predicts a
double peak spectrum linked to the existence of spin-charge separation. The
numerical analysis basically confirms this picture, but also predicts
additional features in finite-size samples.Comment: 19 pages, 4 figures, invited review article for special issue in J.
Phys. Cond. Mat., published versio
Current bistability and hysteresis in strongly correlated quantum wires
Nonequilibrium transport properties are determined exactly for an
adiabatically connected single channel quantum wire containing one impurity.
Employing the Luttinger liquid model with interaction parameter , for very
strong interactions g\lapx 0.2, and sufficiently low temperatures, we find an
S-shaped current-voltage relation. The unstable branch with negative
differential conductance gives rise to current oscillations and hysteretic
effects. These non perturbative and non linear features appear only out of
equilibrium.Comment: 4 pages, 1 figur
Tomonaga-Luttinger liquid parameters of magnetic waveguides in graphene
Electronic waveguides in graphene formed by counterpropagating snake states in suitable inhomogeneous magnetic fields are shown to constitute a realization of a Tomonaga-Luttinger liquid. Due to the spatial separation of the right- and left-moving snake states, this non-Fermi liquid state induced by electron-electron interactions is essentially unaffected by disorder. We calculate the interaction parameters accounting for the absence of Galilei invariance in this system, and thereby demonstrate that non-Fermi liquid effects are significant and tunable in realistic geometries
Rashba spin-orbit coupling and spin precession in carbon nanotubes
The Rashba spin-orbit coupling in carbon nanotubes and its effect on
spin-dependent transport properties are analyzed theoretically. We focus on
clean non-interacting nanotubes with tunable number of subbands . The
peculiar band structure is shown to allow in principle for Datta-Das
oscillatory behavior in the tunneling magnetoresistance as a function of gate
voltage, despite the presence of multiple bands. We discuss the conditions for
observing Datta-Das oscillations in carbon nanotubes.Comment: 12 pages, published versio
- …