7 research outputs found
Universal Superfluid Transition and Transport Properties of Two-Dimensional Dirty Bosons
We study the phase diagram of two-dimensional, interacting bosons in the
presence of a correlated disorder in continuous space, using large-scale finite
temperature quantum Monte Carlo simulations. We show that the superfluid
transition is strongly protected against disorder. It remains of the
Berezinskii-Kosterlitz-Thouless type up to disorder strengths comparable to the
chemical potential. Moreover, we study the transport properties in the strong
disorder regime where a zero-temperature Bose-glass phase is expected. We show
that the conductance exhibits a thermally activated behavior vanishing only at
zero temperature. Our results point towards the existence of Bose bad-metal
phase as a precursor of the Bose-glass phase
Online Trajectory Planning Through Combined Trajectory Optimization and Function Approximation: Application to the Exoskeleton Atalante
Autonomous robots require online trajectory planning capability to operate in
the real world. Efficient offline trajectory planning methods already exist,
but are computationally demanding, preventing their use online. In this paper,
we present a novel algorithm called Guided Trajectory Learning that learns a
function approximation of solutions computed through trajectory optimization
while ensuring accurate and reliable predictions. This function approximation
is then used online to generate trajectories. This algorithm is designed to be
easy to implement, and practical since it does not require massive computing
power. It is readily applicable to any robotics systems and effortless to set
up on real hardware since robust control strategies are usually already
available. We demonstrate the computational performance of our algorithm on
flat-foot walking with the self-balanced exoskeleton Atalante
Reactive Stepping for Humanoid Robots using Reinforcement Learning: Application to Standing Push Recovery on the Exoskeleton Atalante
State-of-the-art reinforcement learning is now able to learn versatile
locomotion, balancing and push-recovery capabilities for bipedal robots in
simulation. Yet, the reality gap has mostly been overlooked and the simulated
results hardly transfer to real hardware. Either it is unsuccessful in practice
because the physics is over-simplified and hardware limitations are ignored, or
regularity is not guaranteed, and unexpected hazardous motions can occur. This
paper presents a reinforcement learning framework capable of learning robust
standing push recovery for bipedal robots that smoothly transfer to reality,
providing only instantaneous proprioceptive observations. By combining original
termination conditions and policy smoothness conditioning, we achieve stable
learning, sim-to-real transfer and safety using a policy without memory nor
explicit history. Reward engineering is then used to give insights into how to
keep balance. We demonstrate its performance in reality on the lower-limb
medical exoskeleton Atalante
Tailoring Chirp in Spin-Lasers
The usefulness of semiconductor lasers is often limited by the undesired
frequency modulation, or chirp, a direct consequence of the intensity
modulation and carrier dependence of the refractive index in the gain medium.
In spin-lasers, realized by injecting, optically or electrically,
spin-polarized carriers, we elucidate paths to tailoring chirp. We provide a
generalized expression for chirp in spin-lasers and introduce modulation
schemes that could simultaneously eliminate chirp and enhance the bandwidth, as
compared to the conventional (spin-unpolarized) lasers.Comment: 4 pages, 3 figure
Universal Superfluid Transition and Transport Properties of Two-Dimensional Dirty Bosons (Orale)
conferenc
Universal Superfuid Transition and Transport Properties of Two-Dimensional Dirty Bosons
Séminaire au LPMMC (Laboratoire de Physique et Modélisation des Milieux Condensés) de Grenoble, 8 novembre 201