61 research outputs found
Polaritonic states in a dielectric nanoguide: localization and strong coupling
Propagation of light through dielectrics lies at the heart of optics.
However, this ubiquitous process is commonly described using phenomenological
dielectric function and magnetic permeability , i.e. without
addressing the quantum graininess of the dielectric matter. Here, we present a
theoretical study where we consider a one-dimensional ensemble of atoms in a
subwavelength waveguide (nanoguide) as fundamental building blocks of a model
dielectric. By exploring the roles of the atom-waveguide coupling efficiency,
density, disorder, and dephasing, we establish connections among various
features of polaritonic light-matter states such as localization, super and
subradiance, and strong coupling. In particular, we show that coherent multiple
scattering of light among atoms that are coupled via a single propagating mode
can gives rise to Rabi splitting. These results provide important insight into
the underlying physics of strong coupling reported by recent room-temperature
experiments with microcavities and surface plasmons.Comment: 10 pages, 6 figure
Gain-tunable optomechanical cooling in a laser cavity
We study the optical cooling of the resonator mirror in a
cavity-optomechanical system that contains an optical gain medium. We find that
the optical damping rate is vanishingly small for an incoherently pumped laser
above threshold. In the presence of an external coherent drive however, the
optical damping rate can be enhanced substantially with respect to that of a
passive cavity. We show that the strength of the incoherent pump provides a
conduit to tune the damping rate and the minimum attainable phonon number with
the same radiation pressure force, and the latter can be lowered from that of a
passive cavity if the thermal contribution is nonnegligible. We also show that
the system can undergo a transition from the weak optomechanical coupling
regime to the strong optomechanical coupling regime as the incoherent pump
strength is varied.Comment: 7 pages, 5 figure
Optical tracing of multiple charges in single-electron devices
Single molecules that exhibit narrow optical transitions at cryogenic
temperatures can be used as local electric-field sensors. We derive the single
charge sensitivity of aromatic organic dye molecules, based on first
principles. Through numerical modeling, we demonstrate that by using currently
available technologies it is possible to optically detect charging events in a
granular network with a sensitivity better than
and track positions of multiple electrons, simultaneously, with nanometer
spatial resolution. Our results pave the way for minimally-invasive optical
inspection of electronic and spintronic nanodevices and building hybrid
optoelectronic interfaces that function at both single-photon and
single-electron levels.Comment: 7 pages, submitted to Physical Revie
Sensing force and charge at the nanoscale with a single-molecule tether
Measuring the electrophoretic mobility of molecules is a powerful
experimental approach for investigating biomolecular processes. A frequent
challenge in the context of single-particle measurements is throughput,
limiting the obtainable statistics. Here, we present a molecular force sensor
and charge detector based on parallelised imaging and tracking of tethered
double-stranded DNA functionalised with charged nanoparticles interacting with
an externally applied electric field. Tracking the position of the tethered
particle with simultaneous nanometre precision and microsecond temporal
resolution allows us to detect and quantify electrophoretic forces down to the
sub-piconewton scale. Furthermore, we demonstrate that this approach is capable
of detecting changes to the particle charge state, as induced by the addition
of charged biomolecules or changes to pH. Our approach provides an alternative
route to studying structural and charge dynamics at the single-molecule level.Comment: 23 pages, 7 figure
Coherent Interaction of Light and Single Molecules in a Dielectric Nanoguide
We present a new scheme for performing optical spectroscopy on single
molecules. A glass capillary with a diameter of 600 nm filled with an organic
crystal tightly guides the excitation light and provides a maximum spontaneous
emission coupling factor () of 18% for the dye molecules doped in the
organic crystal. Combination of extinction, fluorescence excitation and
resonance fluorescence spectroscopy with microscopy provides high-resolution
spatio-spectral access to a very large number of single molecules in a linear
geometry. We discuss strategies for exploring a range of quantum optical
phenomena, including coherent cooperative interactions in a mesoscopic ensemble
of molecules mediated by a single mode of propagating photons.Comment: 5 pages, 5 figure
Varying the effective refractive index to measure optical transport in random media
We introduce a new approach for measuring both the effective medium and the
transport properties of light propagation in heterogeneous media. Our method
utilizes the conceptual equivalence of frequency variation with a change in the
effective index of refraction. Experimentally, we measure intensity
correlations via spectrally resolved refractive index tuning, controlling the
latter via changes in the ambient pressure. Our experimental results perfectly
match a generalized transport theory that incorporates the effective medium and
predicts a precise value for the diffusion constant. Thus, we directly confirm
the applicability of the effective medium concept in strongly scattering
materials.Comment: 5 pages, 5 figure
Design and synthesis of aromatic molecules for probing electric-fields at the nanoscale
We propose using halogenated organic dyes as nanoprobes for electric field
and show their greatly enhanced Stark coefficients using density functional
theory (DFT) calculations. We analyse halogenated variants of three molecules
that have been of interest for cryogenic single molecule spectroscopy,
perylene, terrylene, and dibenzoterrylene, with the zero-phonon optical
transitions at blue, red, and near infrared. Out of all the combinations of
halides and binding sites that are calculated, we have found that fluorination
of the optimum binding site induces a dipole difference between ground and
excited states larger than 0.5 D for all three molecules with the highest value
of 0.69 D for fluoroperylene. We also report on synthesis of 3-fluoroterrylene
and bulk spectroscopy of this compound in liquid and solid organic
environments.Comment: Article presented in Faraday Discussions on September 201
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