41 research outputs found
Coherent and compatible information: a basis to information analysis of quantum systems
Relevance of key quantum information measures for analysis of quantum systems
is discussed. It is argued that possible ways of measuring quantum information
are based on compatibility/incompatibility of the quantum states of a quantum
system, resulting in the coherent information and introduced here the
compatible information measures, respectively. A sketch of an information
optimization of a quantum experimental setup is proposed.Comment: 10 pages, 5 figures, submitted to the Procs of 17th Int'l Conf. on
Coherent and Nonlinear Optics (ICONO-2001), June 26-July 1, 2001, Minsk,
Belaru
Physical implementation of entangling quantum measurements
We clarify the microscopic structure of the entangling quantum measurement
superoperators and examine their possible physical realization in a simple
three-qubit model, which implements the entangling quantum measurement with an
arbitrary degree of entanglement.Comment: 6 pages, 2 fihure
Macroscopic Zeno effect in Su-Schrieffer-Heeger photonic topological insulator
The quantum Zeno effect refers to slowing down of the decay of a quantum
system that is affected by frequent measurements. Nowadays, the significance of
this paradigm is extended far beyond quantum systems, where it was introduced,
finding physical and mathematical analogies in such phenomena as the
suppression of output beam decay by sufficiently strong absorption introduced
in guiding optical systems. In the latter case, the effect is often termed as
macroscopic Zeno effect. Recent studies in optics, where enhanced transparency
of the entire system was observed upon the increase of the absorption, were
largely focused on the systems obeying parity-time symmetry, hence, the
observed effect was attributed to the symmetry breaking. While manifesting
certain similarities in the behavior of the transparency of the system with the
mentioned studies, the macroscopic Zeno phenomenon reported here in topological
photonic system is far more general in nature. In particular, we show that it
does not require the existence of exceptional points, and that it is based on
the suppression of decay for only a subspace of modes that can propagate in the
system, alike the quantum Zeno dynamics. By introducing controlled losses in
one of the arms of a topological insulator comprising two closely positioned
Su-Schrieffer-Heeger arrays, we demonstrate the macroscopic Zeno effect, which
manifests itself in an increase of the transparency of the system with respect
to the topological modes created at the interface between two arrays. The
phenomenon remains robust against disorder in the non-Hermitian topological
regime. In contrast, coupling a topological array with a non-topological one
results in a monotonic decrease in output power with increasing absorption
Observation of nonlinearity-controlled switching of topological edge states
We report the experimental observation of the periodic switching of
topological edge states between two dimerized fs-laser written waveguide
arrays. Switching occurs due to the overlap of the modal fields of the edge
states from topological forbidden gap, when they are simultaneously present in
two arrays brought into close proximity. We found that the phenomenon occurs
for both strongly and weakly localized edge states and that switching rate
increases with decreasing spacing between the topological arrays. When
topological arrays are brought in contact with nontopological ones, switching
in topological gap does not occur, while one observes either the formation of
nearly stationary topological interface mode or strongly asymmetric diffraction
into the nontopological array depending on the position of the initial
excitation. Switching between topological arrays can be controlled and even
completely arrested by increasing the peak power of the input signal, as we
observed with different array spacings.Comment: 8 pages, 6 figure
Observation of nonlinear disclination states
Introduction of controllable deformations into periodic materials that lead
to disclinations in their structure opens novel routes for construction of
higher-order topological insulators hosting topological states at
disclinations. Appearance of these topological states is consistent with the
bulk-disclination correspondence principle, and is due to the filling anomaly
that results in fractional charges to the boundary unit cells. So far,
topological disclination states were observed only in the linear regime, while
the interplay between nonlinearity and topology in the systems with
disclinations has been never studied experimentally. We report here bon the
experimental observation of the nonlinear photonic disclination states in
waveguide arrays with pentagonal or heptagonal disclination cores inscribed in
transparent optical medium using the fs-laser writing technique. The transition
between nontopological and topological phases in such structures is controlled
by the Kekul\'e distortion coefficient with topological phase hosting
simultaneously disclination states at the inner disclination core and spatially
separated from them corner, zero-energy, and extended edge states at the outer
edge of the structure. We show that the robust nonlinear disclination states
bifurcate from their linear counterparts and that location of their propagation
constants in the gap and, hence, their spatial localization can be controlled
by their power. Nonlinear disclination states can be efficiently excited by
Gaussian input beams, but only if they are focused into the waveguides
belonging to the disclination core, where such topological states reside.Comment: 11 pages, 6 figure
Entanglement transfer between bipartite systems
The problem of a controlled transfer of an entanglement initially encoded
into two two-level atoms that are successively sent through two single-mode
cavities is investigated. The atoms and the cavity modes form a four qubit
system and we demonstrate under which conditions the initial entanglement
encoded into the atoms can be completely transferred to other pairs of qubits.
We find that in the case of a nonzero detuning between the atomic transition
frequencies and the cavity mode frequencies, no complete transfer of the
initial entanglement is possible to any of the other pairs of qubits. In the
case of exact resonance and equal coupling strengths of the atoms to the cavity
modes, an initial maximally entangled state of the atoms can be completely
transferred to the cavity modes. The complete transfer of the entanglement is
restricted to the cavity modes only with the transfer to the other pairs being
limited to up to 50%. We have found that the complete transfer of an initial
entanglement to other pairs of qubits may take place if the initial state is
not the maximally entangled state and the atoms couple to the cavity modes with
unequal strengths. Depending on the ratio between the coupling strengths, the
optimal entanglement can be created between the atoms and one of the cavity
modes.Comment: 3 figures. Oral talk presented in CEWQO 18, Madrid 201
Observation of solitons in oscillating waveguide arrays
Floquet systems with periodically varying in time parameters enable
realization of unconventional topological phases that do not exist in static
systems with constant parameters and that are frequently accompanied by
appearance of novel types of the topological states. Among such Floquet systems
are the Su-Schrieffer-Heeger lattices with periodically-modulated couplings
that can support at their edges anomalous modes of topological origin
despite the fact that the lattice spends only half of the evolution period in
topologically nontrivial phase, while during other half-period it is
topologically trivial. Here, using Su-Schrieffer-Heeger arrays composed from
periodically oscillating waveguides inscribed in transparent nonlinear optical
medium, we report experimental observation of photonic anomalous modes
residing at the edge or in the corner of the one- or two-dimensional arrays,
respectively, and demonstrate a new class of topological solitons
bifurcating from such modes in the topological gap of the Floquet spectrum at
high powers. solitons reported here are strongly oscillating nonlinear
Floquet states exactly reproducing their profiles after each longitudinal
period of the structure. They can be dynamically stable in both one- and
two-dimensional oscillating waveguide arrays, the latter ones representing the
first realization of the Floquet photonic higher-order topological insulator,
while localization properties of such solitons are determined by their
power.Comment: 10 pages, 6 figures, to appear in Science Bulleti
Observation of nonlinear fractal higher-order topological insulator
Higher-order topological insulators (HOTIs) are unique materials hosting
topologically protected states, whose dimensionality is at least by a factor of
2 lower than that of the bulk. Topological states in such insulators may be
strongly confined in their corners that leads to considerable enhancement of
nonlinear processes involving such states. However, all nonlinear HOTIs
demonstrated so far were built on periodic bulk lattice materials. Here we
demonstrate first \textit{nonlinear photonic} HOTI with the fractal origin.
Despite their fractional effective dimensionality, the HOTIs constructed here
on two different types of the Sierpi\'nski gasket waveguide arrays, may support
topological corner states for unexpectedly wide range of coupling strengths,
even in parameter regions where conventional HOTIs become trivial. We
demonstrate thresholdless solitons bifurcating from corner states in nonlinear
fractal HOTIs and show that their localization can be efficiently controlled by
the input beam power. We observe sharp differences in nonlinear light
localization on outer and multiple inner corners and edges representative for
these fractal materials. Our findings not only represent a new paradigm for
nonlinear topological insulators, but also open new avenues for potential
applications of fractal materials to control the light flow.Comment: 10 pages, 5 figure