1,108 research outputs found
Quantum Electrodynamic Control of Matter: Cavity-Enhanced Ferroelectric Phase Transition
The light-matter interaction can be utilized to qualitatively alter physical properties of materials. Recent theoretical and experimental studies have explored this possibility of controlling matter by light based on driving many-body systems via strong classical electromagnetic radiation, leading to a time-dependent Hamiltonian for electronic or lattice degrees of freedom. To avoid inevitable heating, pump-probe setups with ultrashort laser pulses have so far been used to study transient light-induced modifications in materials. Here, we pursue yet another direction of controlling quantum matter by modifying quantum fluctuations of its electromagnetic environment. In contrast to earlier proposals on light-enhanced electron-electron interactions, we consider a dipolar quantum many-body system embedded in a cavity composed of metal mirrors and formulate a theoretical framework to manipulate its equilibrium properties on the basis of quantum light-matter interaction. We analyze hybridization of different types of the fundamental excitations, including dipolar phonons, cavity photons, and plasmons in metal mirrors, arising from the cavity confinement in the regime of strong light-matter interaction. This hybridization qualitatively alters the nature of the collective excitations and can be used to selectively control energy-level structures in a wide range of platforms. Most notably, in quantum paraelectrics, we show that the cavity-induced softening of infrared optical phonons enhances the ferroelectric phase in comparison with the bulk materials. Our findings suggest an intriguing possibility of inducing a superradiant-type transition via the light-matter coupling without external pumping. We also discuss possible applications of the cavity-induced modifications in collective excitations to molecular materials and excitonic devices
Room-temperature transverse-electric polarized intersubband electroluminescence from InAs/AlInAs quantum dashes
We report the observation of transverse electric polarized
electroluminescence from InAs/AlInAs quantum dash quantum cascade structures up
to room temperature. The emission is attributed to the electric field confined
along the shortest lateral dimension of the dashes, as confirmed by its
dependence on crystallographic orientation both in absorption measurements on a
dedicated sample and from electroluminescence itself. From the absorption we
estimate a dipole moment for the observed transition of =1.7 nm. The
electroluminescence is peaked at around 110 meV and increases with applied
bias. Its temperature dependence shows a decrease at higher temperatures
limited by optical phonon emission.Comment: 15 pages, 4 figures, submitted to Applied Physics Letter
Highly tunable hybrid metamaterials employing split-ring resonators strongly coupled to graphene surface plasmons
Metamaterials and plasmonics are powerful tools for unconventional
manipulation and harnessing of light. Metamaterials can be engineered to
possess intriguing properties lacking in natural materials, such as negative
refractive index. Plasmonics offers capabilities to confine light in
subwavelength dimensions and to enhance light-matter interactions.
Recently,graphene-based plasmonics has revealed emerging technological
potential as it features large tunability, higher field-confinement and lower
loss compared to metal-based plasmonics. Here,we introduce hybrid structures
comprising graphene plasmonic resonators efficiently coupled to conventional
split-ring resonators, thus demonstrating a type of highly tunable
metamaterial, where the interaction between the two resonances reaches the
strong-coupling regime. Such hybrid metamaterials are employed as high-speed
THz modulators, exhibiting over 60% transmission modulation and operating speed
in excess of 40 MHz. This device concept also provides a platform for exploring
cavity-enhanced light-matter interactions and optical processes in graphene
plasmonic structures for applications including sensing, photo-detection and
nonlinear frequency generation
Gain and Loss in Quantum Cascade Lasers
We report gain calculations for a quantum cascade laser using a fully
self-consistent quantum mechanical approach based on the theory of
nonequilibrium Green functions. Both the absolute value of the gain as well as
the spectral position at threshold are in excellent agreement with experimental
findings for T=77 K. The gain strongly decreases with temperature.Comment: 7 pages, 3 figures directly include
Quantum vacuum properties of the intersubband cavity polariton field
We present a quantum description of a planar microcavity photon mode strongly
coupled to a semiconductor intersubband transition in presence of a
two-dimensional electron gas. We show that, in this kind of system, the vacuum
Rabi frequency can be a significant fraction of the intersubband
transition frequency . This regime of ultra-strong light-matter
coupling is enhanced for long wavelength transitions, because for a given
doping density, effective mass and number of quantum wells, the ratio
increases as the square root of the intersubband
emission wavelength. We characterize the quantum properties of the ground state
(a two-mode squeezed vacuum), which can be tuned {\it in-situ} by changing the
value of , e.g., through an electrostatic gate. We finally point out
how the tunability of the polariton quantum vacuum can be exploited to generate
correlated photon pairs out of the vacuum via quantum electrodynamics phenomena
reminiscent of the dynamic Casimir effect.Comment: Final version accepted in PR
Intersubband gain in a Bloch oscillator and Quantum cascade laser
The link between the inversion gain of quantum cascade structures and the
Bloch gain in periodic superlattices is presented. The proposed theoretical
model based on the density matrix formalism is able to treat the gain mechanism
of the Bloch oscillator and Quantum cascade laser on the same footing by taking
into account in-plane momentum relaxation. The model predicts a dispersive
contribution in addition to the (usual) population-inversion-dependent
intersubband gain in quantum cascade structures and - in the absence of
inversion - provides the quantum mechanical description for the dispersive gain
in superlattices. It corroborates the predictions of the semi-classical
miniband picture, according to which gain is predicted for photon energies
lower than the Bloch oscillation frequency, whereas net absorption is expected
at higher photon energies, as a description which is valid in the
high-temperature limit. A red-shift of the amplified emission with respect to
the resonant transition energy results from the dispersive gain contribution in
any intersubband transition, for which the population inversion is small.Comment: 10 pages, 6 figure
High-Power Directional Emission from Microlasers with Chaotic Resonators
High-power and highly directional semiconductor cylinder-lasers based on an
optical resonator with deformed cross section are reported. In the favorable
directions of the far-field, a power increase of up to three orders of
magnitude over the conventional circularly symmetric lasers was obtained. A
"bow-tie"-shaped resonance is responsible for the improved performance of the
lasers in the higher range of deformations, in contrast to
"whispering-gallery"-type modes of circular and weakly deformed lasers. This
resonator design, although demonstrated here in midinfrared quantum-cascade
lasers, should be applicable to any laser based on semiconductors or other
high-refractive index materials.Comment: Removed minor discrepancies with published version in the text and in
Fig.
Positive Cross Correlations in a Normal-Conducting Fermionic Beam Splitter
We investigate a beam splitter experiment implemented in a normal conducting
fermionic electron gas in the quantum Hall regime. The cross-correlations
between the current fluctuations in the two exit leads of the three terminal
device are found to be negative, zero or even positive depending on the
scattering mechanism within the device. Reversal of the cross-correlations sign
occurs due to interaction between different edge-states and does not reflect
the statistics of the fermionic particles which `antibunch'.Comment: 4 pages, 4 figure
Investigation of the Chromatic Dispersion in Two-Section InAs/GaAs Quantum-Dot Lasers
We present the measurements of the dispersion of InAs/GaAs quantum-dot lasers emitting at 1230 nm (ground state) and 1160 nm (excited state) from the analysis of their subthreshold emission spectra. Measurements from devices with various lengths allow us to deduce that the group velocity dispersion is as high as 2270 fs2mmâ1 and is mainly due to the dispersion of bulk GaAs. The gain-induced dispersion varies with the injected current at a rate of ââ2 fs2 mAâ1mmâ1, whereas the effect of a saturable absorber on the dispersion is found to be negligible. These results suggest that the implementation of integrated dispersion compensation could significantly reduce the pulse duration of these lasers in mode-locked regime and lead to an enhancement of the formation of optical frequency combs in these devices
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