2,429 research outputs found
Sub-nanosecond signal propagation in anisotropy engineered nanomagnetic logic chains
Energy efficient nanomagnetic logic (NML) computing architectures propagate
and process binary information by relying on dipolar field coupling to reorient
closely-spaced nanoscale magnets. Signal propagation in nanomagnet chains of
various sizes, shapes, and magnetic orientations has been previously
characterized by static magnetic imaging experiments with low-speed adiabatic
operation; however the mechanisms which determine the final state and their
reproducibility over millions of cycles in high-speed operation (sub-ns time
scale) have yet to be experimentally investigated. Monitoring NML operation at
its ultimate intrinsic speed reveals features undetectable by conventional
static imaging including individual nanomagnetic switching events and
systematic error nucleation during signal propagation. Here, we present a new
study of NML operation in a high speed regime at fast repetition rates. We
perform direct imaging of digital signal propagation in permalloy nanomagnet
chains with varying degrees of shape-engineered biaxial anisotropy using
full-field magnetic soft x-ray transmission microscopy after applying single
nanosecond magnetic field pulses. Further, we use time-resolved magnetic
photo-emission electron microscopy to evaluate the sub-nanosecond dipolar
coupling signal propagation dynamics in optimized chains with 100 ps time
resolution as they are cycled with nanosecond field pulses at a rate of 3 MHz.
An intrinsic switching time of 100 ps per magnet is observed. These
experiments, and accompanying macro-spin and micromagnetic simulations, reveal
the underlying physics of NML architectures repetitively operated on nanosecond
timescales and identify relevant engineering parameters to optimize performance
and reliability.Comment: Main article (22 pages, 4 figures), Supplementary info (11 pages, 5
sections
Extended particle-in-cell schemes for physics in ultrastrong laser fields: Review and developments.
We review common extensions of particle-in-cell (PIC) schemes which account for strong field phenomena in laser-plasma interactions. After describing the physical processes of interest and their numerical implementation, we provide solutions for several associated methodological and algorithmic problems. We propose a modified event generator that precisely models the entire spectrum of incoherent particle emission without any low-energy cutoff, and which imposes close to the weakest possible demands on the numerical time step. Based on this, we also develop an adaptive event generator that subdivides the time step for locally resolving QED events, allowing for efficient simulation of cascades. Further, we present a unified technical interface for including the processes of interest in different PIC implementations. Two PIC codes which support this interface, PICADOR and ELMIS, are also briefly reviewed
Towards quantum simulation with circular Rydberg atoms
The main objective of quantum simulation is an in-depth understanding of
many-body physics. It is important for fundamental issues (quantum phase
transitions, transport, . . . ) and for the development of innovative
materials. Analytic approaches to many-body systems are limited and the huge
size of their Hilbert space makes numerical simulations on classical computers
intractable. A quantum simulator avoids these limitations by transcribing the
system of interest into another, with the same dynamics but with interaction
parameters under control and with experimental access to all relevant
observables. Quantum simulation of spin systems is being explored with trapped
ions, neutral atoms and superconducting devices. We propose here a new paradigm
for quantum simulation of spin-1/2 arrays providing unprecedented flexibility
and allowing one to explore domains beyond the reach of other platforms. It is
based on laser-trapped circular Rydberg atoms. Their long intrinsic lifetimes
combined with the inhibition of their microwave spontaneous emission and their
low sensitivity to collisions and photoionization make trapping lifetimes in
the minute range realistic with state-of-the-art techniques. Ultra-cold
defect-free circular atom chains can be prepared by a variant of the
evaporative cooling method. This method also leads to the individual detection
of arbitrary spin observables. The proposed simulator realizes an XXZ spin-1/2
Hamiltonian with nearest-neighbor couplings ranging from a few to tens of kHz.
All the model parameters can be tuned at will, making a large range of
simulations accessible. The system evolution can be followed over times in the
range of seconds, long enough to be relevant for ground-state adiabatic
preparation and for the study of thermalization, disorder or Floquet time
crystals. This platform presents unrivaled features for quantum simulation
Linear circuit models for on-chip quantum electrodynamics
We present equivalent circuits that model the interaction of microwave
resonators and quantum systems. The circuit models are derived from a general
interaction Hamiltonian. Quantitative agreement between the simulated resonator
transmission frequency, qubit Lamb shift and experimental data will be shown.
We demonstrate that simple circuit models, using only linear passive elements,
can be very useful in understanding systems where a small quantum system is
coupled to a classical microwave apparatus
- …