71 research outputs found
Multi-plasmon absorption in graphene
We show that graphene possesses a strong nonlinear optical response in the
form of multi-plasmon absorption, with exciting implications in classical and
quantum nonlinear optics. Specifically, we predict that graphene nano-ribbons
can be used as saturable absorbers with low saturation intensity in the
far-infrared and terahertz spectrum. Moreover, we predict that two-plasmon
absorption and extreme localization of plasmon fields in graphene nano-disks
can lead to a plasmon blockade effect, in which a single quantized plasmon
strongly suppresses the possibility of exciting a second plasmon
Theory of self-induced back-action optical trapping in nanophotonic systems
Optical trapping is an indispensable tool in physics and the life sciences.
However, there is a clear trade off between the size of a particle to be
trapped, its spatial confinement, and the intensities required. This is due to
the decrease in optical response of smaller particles and the diffraction limit
that governs the spatial variation of optical fields. It is thus highly
desirable to find techniques that surpass these bounds. Recently, a number of
experiments using nanophotonic cavities have observed a qualitatively different
trapping mechanism described as "self-induced back-action trapping" (SIBA). In
these systems, the particle motion couples to the resonance frequency of the
cavity, which results in a strong interplay between the intra-cavity field
intensity and the forces exerted. Here, we provide a theoretical description
that for the first time captures the remarkable range of consequences. In
particular, we show that SIBA can be exploited to yield dynamic reshaping of
trap potentials, strongly sub-wavelength trap features, and significant
reduction of intensities seen by the particle, which should have important
implications for future trapping technologiesComment: 7 pages, 5 figure
Non-equilibrium diagrammatic approach to strongly interacting photons
We develop a non-equilibrium field-theoretical approach based on a systematic
diagrammatic expansion for strongly interacting photons in optically dense
atomic media. We consider the case where the characteristic photon-propagation
range is much larger than the interatomic spacing and where the
density of atomic excitations is low enough to neglect saturation effects. In
the highly polarizable medium the photons experience nonlinearities through the
interactions they inherit from the atoms. If the atom-atom interaction range
is also large compared to , we show that the subclass of diagrams
describing scattering processes with momentum transfer between photons is
suppressed by a factor . We are then able to perform a self-consistent
resummation of a specific (Hartree-like) diagram subclass and obtain
quantitative results in the highly non-perturbative regime of large single-atom
cooperativity. Here we find important, conceptually new collective phenomena
emerging due to the dissipative nature of the interactions, which even give
rise to novel phase transitions. The robustness of these is investigated by
inclusion of the leading corrections in . We consider specific
applications to photons propagating under EIT conditions along waveguides near
atomic arrays as well as within Rydberg ensembles.Comment: 72 pages, 36 figure
Optical properties of an atomic ensemble coupled to a band edge of a photonic crystal waveguide
We study the optical properties of an ensemble of two-level atoms coupled to
a 1D photonic crystal waveguide (PCW), which mediates long-range coherent
dipole-dipole interactions between the atoms. We show that the long-range
interactions can dramatically alter the linear and nonlinear optical behavior,
as compared to a typical atomic ensemble. In particular, in the linear regime,
we find that the transmission spectrum reveals multiple transmission dips,
whose properties we show how to characterize. In the many-photon regime the
system response can be highly non-linear, and under certain circumstances the
ensemble can behave like a single two-level system, which is only capable of
absorbing and emitting a single excitation at a time. Our results are of direct
relevance to atom-PCW experiments that should soon be realizable
Photon molecules in atomic gases trapped near photonic crystal waveguides
Realizing systems that support robust, controlled interactions between
individual photons is an exciting frontier of nonlinear optics. To this end,
one approach that has emerged recently is to leverage atomic interactions to
create strong and spatially non-local interactions between photons. In
particular, effective interactions have been successfully created via
interactions between atoms excited to Rydberg levels. Here, we investigate an
alternative approach, in which atomic interactions arise via their common
coupling to photonic crystal waveguides. This technique takes advantage of the
ability to separately tailor the strength and range of interactions via the
dispersion engineering of the structure itself, which can lead to qualitatively
new types of phenomena. As an example, we discuss the formation of correlated
transparency windows, in which photonic states of a certain number and shape
selectively propagate through the system. Through this technique, we show in
particular that one can create molecular-like potentials that lead to molecular
bound states of photon pairs
Multi-photon Scattering Theory and Generalized Master Equations
We develop a scattering theory to investigate the multi-photon transmission
in a one-dimensional waveguide in the presence of quantum emitters. It is based
on a path integral formalism, uses displacement transformations, and does not
require the Markov approximation. We obtain the full time-evolution of the
global system, including the emitters and the photonic field. Our theory allows
us to compute the transition amplitude between arbitrary initial and final
states, as well as the S-matrix of the asymptotic in- and out- states. For the
case of few incident photons in the waveguide, we also re-derive a generalized
master equation in the Markov limit. We compare the predictions of the
developed scattering theory and that with the Markov approximation. We
illustrate our methods with five examples of few-photon scattering: (i) by a
two-level emitter, (ii) in the Jaynes-Cummings model; (iii) by an array of
two-level emitters; (iv) by a two-level emitter in the half-end waveguide; (v)
by an array of atoms coupled to Rydberg levels. In the first two, we show the
application of the scattering theory in the photon scattering by a single
emitter, and examine the correctness of our theory with the well-known results.
In the third example, we analyze the condition of the Markov approximation for
the photon scattering in the array of emitters. In the forth one, we show how a
quantum emitter can generate entanglement of out-going photons. Finally, we
highlight the interplay between the phenomenon of electromagnetic-induced
transparency and the Rydberg interaction, and show how this results in a rich
variety of possibilities in the quantum statistics of the scattering photons.Comment: 21 pages,10 figure
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