713 research outputs found
Physics and Applications of Laser Diode Chaos
An overview of chaos in laser diodes is provided which surveys experimental
achievements in the area and explains the theory behind the phenomenon. The
fundamental physics underpinning this behaviour and also the opportunities for
harnessing laser diode chaos for potential applications are discussed. The
availability and ease of operation of laser diodes, in a wide range of
configurations, make them a convenient test-bed for exploring basic aspects of
nonlinear and chaotic dynamics. It also makes them attractive for practical
tasks, such as chaos-based secure communications and random number generation.
Avenues for future research and development of chaotic laser diodes are also
identified.Comment: Published in Nature Photonic
Deterministic polarization chaos from a laser diode
Fifty years after the invention of the laser diode and fourty years after the
report of the butterfly effect - i.e. the unpredictability of deterministic
chaos, it is said that a laser diode behaves like a damped nonlinear
oscillator. Hence no chaos can be generated unless with additional forcing or
parameter modulation. Here we report the first counter-example of a
free-running laser diode generating chaos. The underlying physics is a
nonlinear coupling between two elliptically polarized modes in a
vertical-cavity surface-emitting laser. We identify chaos in experimental
time-series and show theoretically the bifurcations leading to single- and
double-scroll attractors with characteristics similar to Lorenz chaos. The
reported polarization chaos resembles at first sight a noise-driven mode
hopping but shows opposite statistical properties. Our findings open up new
research areas that combine the high speed performances of microcavity lasers
with controllable and integrated sources of optical chaos.Comment: 13 pages, 5 figure
Continuous time crystal in an electron-nuclear spin system: stability and melting of periodic auto-oscillations
Crystals spontaneously break the continuous translation symmetry in space,
despite the invariance of the underlying energy function. This has triggered
suggestions of time crystals analogously lifting translational invariance in
time. Originally suggested for closed thermodynamic systems in equilibrium,
no-go theorems prevent the existence of time crystals. Proposals for open
systems out of equilibrium led to the observation of discrete time crystals
subject to external periodic driving to which they respond with a sub-harmonic
response. A continuous time crystal is an autonomous system that develops
periodic auto-oscillations when exposed to a continuous, time-independent
driving, as recently demonstrated for the density in an atomic Bose-Einstein
condensate with a crystal lifetime of a few ms. Here we demonstrate an
ultra-robust continuous time crystal in the nonlinear electron-nuclear spin
system of a tailored semiconductor with a coherence time exceeding hours.
Varying the experimental parameters reveals huge stability ranges of this time
crystal, but allows one also to enter chaotic regimes, where aperiodic behavior
appears corresponding to melting of the crystal. This novel phase of matter
opens the possibility to study systems with nonlinear interactions in an
unprecedented way.Comment: 12 figures, 17 page
Hybrid quantum-classical modeling of quantum dot devices
The design of electrically driven quantum dot devices for quantum optical
applications asks for modeling approaches combining classical device physics
with quantum mechanics. We connect the well-established fields of
semi-classical semiconductor transport theory and the theory of open quantum
systems to meet this requirement. By coupling the van Roosbroeck system with a
quantum master equation in Lindblad form, we introduce a new hybrid
quantum-classical modeling approach, which provides a comprehensive description
of quantum dot devices on multiple scales: It enables the calculation of
quantum optical figures of merit and the spatially resolved simulation of the
current flow in realistic semiconductor device geometries in a unified way. We
construct the interface between both theories in such a way, that the resulting
hybrid system obeys the fundamental axioms of (non-)equilibrium thermodynamics.
We show that our approach guarantees the conservation of charge, consistency
with the thermodynamic equilibrium and the second law of thermodynamics. The
feasibility of the approach is demonstrated by numerical simulations of an
electrically driven single-photon source based on a single quantum dot in the
stationary and transient operation regime
Spintronic reservoir computing without driving current or magnetic field
Recent studies have shown that nonlinear magnetization dynamics excited in
nanostructured ferromagnets are applicable to brain-inspired computing such as
physical reservoir computing. The previous works have utilized the
magnetization dynamics driven by electric current and/or magnetic field. This
work proposes a method to apply the magnetization dynamics driven by voltage
control of magnetic anisotropy to physical reservoir computing, which will be
preferable from the viewpoint of low-power consumption. The computational
capabilities of benchmark tasks in single MTJ are evaluated by numerical
simulation of the magnetization dynamics and found to be comparable to those of
echo-state networks with more than 10 nodes.Comment: 13 pages, 5 figure
Stochastic Effects in Physical Systems
A tutorial review is given of some developments and applications of
stochastic processes from the point of view of the practicioner physicist. The
index is the following: 1.- Introduction 2.- Stochastic Processes 3.- Transient
Stochastic Dynamics 4.- Noise in Dynamical Systems 5.- Noise Effects in
Spatially Extended Systems 6.- Fluctuations, Phase Transitions and
Noise-Induced Transitions.Comment: 93 pages, 36 figures, LaTeX. To appear in Instabilities and
Nonequilibrium Structures VI, E. Tirapegui and W. Zeller,eds. Kluwer Academi
Criticality and phase classification for quadratic open quantum many-body systems
We study the steady states of translation-invariant open quantum many-body
systems governed by Lindblad master equations, where the Hamiltonian is
quadratic in the ladder operators, and the Lindblad operators are either linear
or quadratic and Hermitian. These systems are called quasi-free and quadratic,
respectively. We find that steady states of one-dimensional systems with
finite-range interactions necessarily have exponentially decaying Green's
functions. For the quasi-free case without quadratic Lindblad operators, we
show that fermionic systems with finite-range interactions are non-critical for
any number of spatial dimensions and provide bounds on the correlation lengths.
Quasi-free bosonic systems can be critical in dimensions. Lastly, we
address the question of phase transitions in quadratic systems and find that,
without symmetry constraints beyond invariance under single-particle basis and
particle-hole transformations, all gapped Liouvillians belong to the same
phase.Comment: 13 pages, 2 figures; the employed methods for the solution of
quasi-free and quadratic open systems are described in arXiv:2112.0834
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