Electrical control of polariton coupling in intersubband microcavities

We demonstrate the external control of the coupling between the intersubband transition and the photonic mode of a GaAs/AlGaAs microcavity with multiple quantum wells embedded. By electrical gating, the charge density in the wells can be lowered, thereby quenching the intersubband polaritons and reverting the system to uncoupled excitations. The angle-dependent reflectance measurements are in good agreement with theoretical calculations performed in the transfer matrix formalism. The experiment shows the prospects offered by intersubband microcavities through manipulation of the system ground state

Tunnel-assisted manipulation of intersubband polaritons in asymmetric coupled quantum wells

The authors report the external control of the polariton ground state by manipulating the coupling between the intersubband transition and the photonic mode of a GaAs∕AlGaAs microcavity. The vacuum-field Rabi splitting is varied by means of charge transfer between the energetically-aligned ground subbands of asymmetric tunnel-coupled quantum wells. The authors propose the use of this structure concept for implementing ultrafast modulation of intersubband polaritons

Charge transport studies on Si nanopillars for photodetectors fabricated using vapor phase metal-assisted chemical etching.

Si nanopillars (SiNPLs) were fabricated using a novel vapor phase metal-assisted chemical etching (V-Mace) and nanosphere lithography. The temperature dependent current–voltage (I–V) characteristics have been studied over a broad temperature range 170–360 K. The SiNPLs show a Schottky diode-like behavior at a temperature below 300 K and the rectification (about two orders of magnitude) is more prominent at temperature < 210 K. The electrical properties are discussed in detail using Cheung’s and Norde methods, and the Schottky diode parameters, such as barrier height, ideality factor, series resistance, are carefully figured out and compared with different methods. Moreover, the light sensitivity of the SiNPLs has been studied using I–V characteristics in dark and under the illumination of white light and UV light. The SiNPLs show fast response to the white light and UV light (response time of 0.18 and 0.26 s) under reverse bias condition and the mechanism explained using band diagram. The ratio of photo-to-dark current shows a peak value of 9.8 and 6.9 for white light and UV light, respectively. The Si nanopillars exhibit reflectance < 4% over the wavelength region 250–800 nm with a minimum reflectance of 2.13% for the optimized sample. The superior light absorption of the SiNPLs induced fast response in the I–V characteristics under UV light and white light. The work function of the SiNPLs in dark and under illumination has been also studied using Kelvin probe to confirm the light sensitivity

Light-matter excitations in the ultra-strong coupling regime

In a microcavity, light-matter coupling is quantified by the vacuum Rabi frequency $\Omega_R$. When $\Omega_R$ is larger than radiative and non-radiative loss rates, the system eigenstates (polaritons) are linear superposition of photonic and electronic excitations, a condition actively investigated in diverse physical implementations. Recently, a quantum electrodynamic regime (ultra-strong coupling) was predicted when $\Omega_R$ becomes comparable to the transition frequency. Here we report unambiguous signatures of this regime in a quantum-well intersubband microcavity. Measuring the cavity-polariton dispersion in a room-temperature linear optical experiment, we directly observe the anti-resonant light-matter coupling and the photon-energy renormalization of the vacuum field

Coupling of THz radiation with intervalence band transitions in microcavities

The strong coupling of THz radiation and material excitations can improve the quantum efficiency of THz emitters. In this paper, we investigate THz polaritons and antipolaritons based on valence band transitions, which allow TE coupling in a simple configuration. The approach can improve the quantum efficiency of THz based devices based on TE mode in the strong coupling regime of THz radiations and intervalence bands transitions in a GaAs/AlGaAs quantum wells. A Nonequilibrium Many Body Approach for the optical response beyond the Hartree-Fock approximation is used as input to the effective dielectric function formalism for the polariton/antipolariton problem. The energy dispersion relations in the THz range are obtained by adjusting the full numerical solutions to simple analytical expressions, which can be used for non specialists in a wide number of new structures and material systems. The combination of manybody and nonparabolicity at high densities leads to dramatic changes in the polariton spectra in a nonequilibrium configuration, which is only possible for intervalence band transitions

Switching ultrastrong light–matter coupling on a subcycle scale

Intersubband cavitypolaritons in a quantum wellwaveguide structure are optically generated within less than one cycle of light by a 12-femtosecond near-infrared pulse. Mid-infrared probe transients trace the nonadiabatic switch-on of ultrastrong light-matter coupling and the conversion of bare photons into cavitypolaritons directly in the time domain. Future perspectives of room-temperature subcycle control of ultrastrong electron–photon interaction are discussed

Beyond the Jaynes-Cummings model: circuit QED in the ultrastrong coupling regime

In cavity quantum electrodynamics (QED), light-matter interaction is probed at its most fundamental level, where individual atoms are coupled to single photons stored in three-dimensional cavities. This unique possibility to experimentally explore the foundations of quantum physics has greatly evolved with the advent of circuit QED, where on-chip superconducting qubits and oscillators play the roles of two-level atoms and cavities, respectively. In the strong coupling limit, atom and cavity can exchange a photon frequently before coherence is lost. This important regime has been reached both in cavity and circuit QED, but the design flexibility and engineering potential of the latter allowed for increasing the ratio between the atom-cavity coupling rate and the cavity transition frequency above the percent level. While these experiments are well described by the renowned Jaynes-Cummings model, novel physics is expected in the ultrastrong coupling limit. Here, we report on the first experimental realization of a superconducting circuit QED system in the ultrastrong coupling limit and present direct evidence for the breakdown of the Jaynes-Cummings model.Comment: 5 pages, 3 figure

Influence of defects on electrical properties of electrodeposited Co-doped ZnO nanocoatings

We present a systematic investigation of the electrical properties of undoped and Co-doped ZnO nanostructures at room temperature as an extensive study of the role of defects in ZnO. The ZnO nanostructures were fabricated by the electrodeposition method at low bath temperature (80 °C) and the Co concentration was varied from 0.01 to 0.2 mM. Electrical properties of the undoped and Co-doped ZnO nanostructures were studied in detail. The carrier concentration increases while the mobility reduces with increase in Co-concentration. The resistivity increases with an increase in Co-concentration and the reason is correlated with the defects in ZnO. In order to understand more details of the role of defects in the present I–V characteristic behavior of the Co-doped ZnO, high temperature vacuum annealing of ZnO sample was carried out. Electrical, optical and magnetic properties of the high temperature vacuum annealed ZnO were studied in detail. Photoluminescence spectroscopy (PL) results revealed more information of the defect levels which act as scattering centers for the carriers. Co-doping as well as annealing at high temperature in vacuum environment tunes the defects in ZnO and which influence the optical, magnetic and electrical behavior of the ZnO nanostructures

Electrical control of polariton coupling in intersubband microcavities

We demonstrate the external control of the coupling between the intersubband transition and the photonic mode of a GaAs/AlGaAs microcavity with multiple quantum wells embedded. By electrical gating, the charge density in the wells can be lowered, thereby quenching the intersubband polaritons and reverting the system to uncoupled excitations. The angle-dependent reflectance measurements are in good agreement with theoretical calculations performed in the transfer matrix formalism. The experiment shows the prospects offered by intersubband microcavities through manipulation of the system ground state

Tailoring light-matter interaction in intersubband microcavities

The strong coupling of bound-to-quasi-bound intersubband transitions with the confined mode of a semiconductor microcavity, resulting in the formation of intersubband polaritons, has been observed. The quasi-bound state above the barrier is formed by growing electron Bragg mirrors on both sides of the quantum well. With the application of an electric field, the oscillator strength of the transition is redistributed between the quasi-bound state and the above-barrier miniband formed by the Bragg superlattice, which deteriorates the intersubband absorption intensity, leading to a decrease in the intersubband polariton coupling. The paper reports the preliminary results in the quantum interference control of intersubband polariton coupling. (C) 2007 Elsevier B.V. All rights reserved