126 research outputs found
Eigenvalue distributions of large Euclidean random matrices for waves in random media
We study probability distributions of eigenvalues of Hermitian and
non-Hermitian Euclidean random matrices that are typically encountered in the
problems of wave propagation in random media.Comment: 29 pages, 10 figure
Transmission of quantum entanglement through a random medium
We study the high-dimensional entanglement of a photon pair transmitted
through a random medium. We show that multiple scattering in combination with
the subsequent selection of only a fraction of outgoing modes reduces the
average entanglement of an initially maximally entangled two-photon state.
Entanglement corresponding to a random pure state is obtained when the number
of modes accessible in transmission is much less than the number of modes in
the incident light. An amount of entanglement approaching that of the incident
light can be recovered by accessing a larger number of transmitted modes. In
contrast, a pair of photons in a separable state does not gain any entanglement
when transmitted through a random medium.Comment: 6 pages, 2 figures. Text slightly revise
Mutual information between reflected and transmitted speckle images
We study theoretically the mutual information between reflected and
transmitted speckle patterns produced by wave scattering from disordered media.
The mutual information between the two speckle images recorded on an array of N
detection points (pixels) takes the form of long-range intensity correlation
loops, that we evaluate explicitly as a function of the disorder strength and
the Thouless number g. Our analysis, supported by extensive numerical
simulations, reveals a competing effect of cross-sample and surface spatial
correlations. An optimal distance between pixels is proven to exist, that
enhances the mutual information by a factor Ng compared to the single-pixel
scenario.Comment: 5 pages, 4 figures, + S
Non-Hermitian Euclidean random matrix theory
We develop a theory for the eigenvalue density of arbitrary non-Hermitian
Euclidean matrices. Closed equations for the resolvent and the eigenvector
correlator are derived. The theory is applied to the random Green's matrix
relevant to wave propagation in an ensemble of point-like scattering centers.
This opens a new perspective in the study of wave diffusion, Anderson
localization, and random lasing.Comment: 11 pages, 9 figure
Correlations between reflected and transmitted intensity patterns emerging from opaque disordered media
The propagation of monochromatic light through a scattering medium produces
speckle patterns in reflection and transmission, and the apparent randomness of
these patterns prevents direct imaging through thick turbid media. Yet, since
elastic multiple scattering is fundamentally a linear and deterministic
process, information is not lost but distributed among many degrees of freedom
that can be resolved and manipulated. Here we demonstrate experimentally that
the reflected and transmitted speckle patterns are correlated, even for opaque
media with thickness much larger than the transport mean free path, proving
that information survives the multiple scattering process and can be recovered.
The existence of mutual information between the two sides of a scattering
medium opens up new possibilities for the control of transmitted light without
any feedback from the target side, but using only information gathered from the
reflected speckle.Comment: 6 pages, 4 figure
Coherent control of photocurrent in a strongly scattering photoelectrochemical system
A fundamental issue that limits the efficiency of many photoelectrochemical
systems is that the photon absorption length is typically much longer than the
electron diffusion length. Various photon management schemes have been
developed to enhance light absorption; one simple approach is to use randomly
scattering media to enable broadband and wide-angle enhancement. However, such
systems are often opaque, making it difficult to probe photo-induced processes.
Here we use wave interference effects to modify the spatial distribution of
light inside a highly-scattering dye-sensitized solar cell to control photon
absorption in a space-dependent manner. By shaping the incident wavefront of a
laser beam, we enhance or suppress photocurrent by increasing or decreasing
light concentration on the front side of the mesoporous photoanode where the
collection efficiency of photoelectrons is maximal. Enhanced light absorption
is achieved by reducing reflection through the open boundary of the photoanode
via destructive interference, leading to a factor of two increase in
photocurrent. This approach opens the door to probing and manipulating
photoelectrochemical processes in specific regions inside nominally opaque
media.Comment: 21 pages, 4 figures, in submission. The first two authors contributed
equally to this paper, and should be regarded as co-first author
Euclidean matrix theory of random lasing in a cloud of cold atoms
We develop an ab initio analytic theory of random lasing in an ensemble of
atoms that both scatter and amplify light. The theory applies all the way from
low to high density of atoms. The properties of the random laser are controlled
by an Euclidean matrix with elements equal to the Green's function of the
Helmholtz equation between pairs of atoms in the system. Lasing threshold and
the intensity of laser emission are calculated in the semiclassical
approximation. The results are compared to the outcome of the diffusion theory
of random lasing.Comment: 6 pages, 4 figure
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