410 research outputs found
Angular Schmidt Modes in Spontaneous Parametric Down-Conversion
We report a proof-of-principle experiment demonstrating that appropriately
chosen set of Hermite-Gaussian modes constitutes a Schmidt decomposition for
transverse momentum states of biphotons generated in the process of spontaneous
parametric down conversion. We experimentally realize projective measurements
in Schmidt basis and observe correlations between appropriate pairs of modes.
We perform tomographical state reconstruction in the Schmidt basis, by direct
measurement of single-photon density matrix eigenvalues.Comment: 5 pages, 4 figure
Self-calibrating Tomography for Angular Schmidt Modes in Spontaneous Parametric Down-Conversion
We report an experimental self-calibrating tomography scheme for entanglement
characterization in high-dimensional quantum systems using Schmidt
decomposition techniques. The self-tomography technique based on maximal
likelihood estimation was developed for characterizing non-ideal measurements
in Schmidt basis allowing us to infer both Schmidt eigenvalues and detecting
efficiencies.Comment: 10 pages, 11 figure
Pulse area theorem in a single mode waveguide and its application to photon echo and optical memory in Tm3+:Y3Al5O12
We derive the area theorem for light pulses interacting with inhomogeneously
broadened ensemble of two-level atoms in a single-mode optical waveguide and
present its analytical solution for Gaussian-type modes, which demonstrates the
significant difference from the formation of pulses by plane waves. We
generalize this theorem to the description of photon echo and apply it to the
two-pulse (primary) echo and the revival of silenced echo (ROSE) protocol of
photon echo quantum memory. For the first time, we implemented ROSE protocol in
a single-mode laser-written waveguide made of an optically thin crystal
. The experimental data obtained are satisfactorily
explained by the developed theory. Finally, we discuss the obtained
experimental results and possible applications of the derived pulse area
approach
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
Observation of charge asymmetry dependence of pion elliptic flow and the possible chiral magnetic wave in heavy-ion collisions
We present measurements of and elliptic flow, , at
midrapidity in Au+Au collisions at 200, 62.4, 39, 27,
19.6, 11.5 and 7.7 GeV, as a function of event-by-event charge asymmetry,
, based on data from the STAR experiment at RHIC. We find that
() elliptic flow linearly increases (decreases) with charge asymmetry
for most centrality bins at and higher.
At , the slope of the difference of
between and as a function of exhibits a
centrality dependence, which is qualitatively similar to calculations that
incorporate a chiral magnetic wave effect. Similar centrality dependence is
also observed at lower energies.Comment: 6 pages, 4 figure
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