We demonstrate coupling and entangling of quantum states in a pair vertically aligned, self-assembled dots by studying the emission an interacting electron-hole (exciton) single dot molecule as function separation between dots. An interaction-induced energy splitting exciton is observed that exceeds 30 millielectron volts for layer 4 nanometers. The results are interpreted mapping tunneling particle double to problem spin. complex shown be equivalent entangled two spins.

A new temperature performance record of 199.5 K for terahertz quantum cascade lasers is achieved by optimizing the lasing transition oscillator strength resonant phonon based three-well design.The optimum 0.58 was found to be larger than that previous (0.41) Kumar et al. [Appl.Phys.Lett.94, 131105 (2009)].The choice tunneling barrier thicknesses determined with a simplified density matrix model, which converged towards higher coupling strengths previously explored and nearly perfect...

Transport measurements are presented on a class of electrostatically defined lateral dots within high mobility two-dimensional electron gas (2DEG). The design allows Coulomb blockade (CB) to be performed single dot containing 0, 1 over 50 electrons. CB enhanced by the spin polarized injection from and into 2DEG magnetic edge states. This combines measurement charge with through spin-blockade spectroscopy. results spectroscopy for first 45 electrons enable us construct addition spectrum...

The direction of emission photoexcited electrons in semiconductors is controlled by adjusting the relative phase difference between a midinfrared radiation and its second harmonic. This achieved using quantum interference produced with one- two-photon bound-to-free intersubband transitions AlGaAs/GaAs well superlattices.

Self-assembled strained semiconductor nanostructures have been grown on GaAs substrates to fabricate quantum dot infrared photodetectors. State-filling photoluminescence experiments used probe the zero-dimensional states and revealed four atomic-like shells (s,p,d,f) with an excitonic intersublevel energy spacing which was adjusted ∼60 meV. The lower electronic were populated carriers by n doping heterostructure, transitions from occupied wetting layer or continuum resulted in...

Nontrivial capacitance behavior, including a negative (NC) effect, observed in variety of semiconductor devices, is discussed emphasizing the physical mechanism and theoretical interpretation experimental data. The correct NC can be based on analysis time-domain transient current response to small voltage step or impulse, involving self-consistent treatment all relevant effects (carrier transport, injection, recharging etc.). appears case non-monotonic positive-valued behavior...

We present results of room temperature photoluminescence (PL) emission from a 0-dimensional system in the ∼1.4 to ∼1.7 μm spectral region. Molecular beam epitaxy was used grow InAs self-assembled quantum dots AlInAs on an InP substrate. Preliminary characterizations have been performed using PL and transmission electron microscopy. The low temperatures spectra also display excited state filling as excitation intensity is increased.

We report the unequivocal demonstration of mid-infrared mode-locked pulses from a semiconductor laser. The train short was generated by actively modulating current and hence optical gain in small section an edge-emitting quantum cascade laser (QCL). Pulses with pulse duration at full-width-at-half-maximum about 3 ps energy 0.5 pJ were characterized using second-order interferometric autocorrelation technique based on nonlinear well infrared photodetector. mode-locking dynamics QCLs modelled...

The authors report on a design of terahertz quantum-cascade lasers based three-well active modules. Each module consists two tunnel-coupled wells for the lasing states and another well both resonant-phonon depopulation carrier injection. This is simplest so far among various published working devices. test device has frequency 3.4THz maximum operating temperature 142K.

Artificial atoms with up to five well-defined electronic shells are fabricated using self-assembled quantum dots (QD's) grown by molecular-beam epitaxy. State-filling spectroscopy of the zero-dimensional transitions between confined electrons and holes demonstrates that energy levels readily tunable. One levels, an interlevel spacing 25 90 meV, obtained adjusting growth temperature or post annealings. The uniformity reproducibility InAs/GaAs QD's optimized parameters affecting evolution...

Conductance fluctuations have been studied in a soft wall stadium and Sinai billiard defined by electrostatic gates on high mobility semiconductor heterojunction. These reproducible magnetoconductance are found to be fractal confirming recent theoretical predictions of quantum signatures classically mixed (regular chaotic) systems. The character the provides direct evidence for hierarchical phase space structure at boundary between regular chaotic motion.

We report terahertz quantum-well photodetectors with background-limited infrared performance (BLIP). The device dark current characteristics were improved by employing thick barriers to reduce interwell tunneling. BLIP operations observed for all samples (three in total) designed different wavelengths. temperatures of 17, 13, and 12K achieved peak detection frequencies at 9.7THz (31μm), 5.4THz (56μm), 3.2THz (93μm), respectively.

We have studied the origin of switching (telegraph) noise at low temperature in lateral quantum structures defined electrostatically GaAs/AlGaAs heterostructures by surface gates. The was measured monitoring conductance fluctuations around $e^2/h$ on first step a point contact 1.2 K. Cooling with positive bias gates dramatically reduces this noise, while an asymmetric exacerbates it. propose model which originates from leakage current electrons that tunnel through Schottky barrier under gate...

Using GaAs based quantum well infrared photodetectors (QWIPs) with either or InGaAs wells, we experimentally investigate the accuracy of polarization selection rule for conduction band intersubband transitions. We employ a device structure and light coupling geometry where parasitic scattering is negligible. The experiments imply that followed to an 0.2% 8.1 μm QWIP wells; this degrades 3% 4.6 In0.1Ga0.9As wells.

Performing optical spectroscopy of highly homogeneous quantum dot arrays in ultrahigh magnetic fields, an unprecedently well resolved Fock-Darwin spectrum is observed. The existence up to four degenerate electronic shells demonstrated where the field lifts initial degeneracies, which reappear when levels with different angular momenta come into resonance. resulting level shifting and crossing pattern also show evidence many-body effects such as mixing configurations exciton condensation at...

We have measured the exciton dephasing time in InAs/GaAs quantum dot molecules having different interdot barrier thicknesses temperature range from 5 to 60 K, using a highly sensitive four-wave mixing heterodyne technique. At K times of several hundred picoseconds are found. Moreover, systematic dependence dynamics on thickness is observed. These results show how quantum-mechanical coupling electronic wave functions affects both radiative lifetime and exciton-acoustic phonon interaction.

We investigate the transition to a Sinai geometry by introducing circular pattern at center of square mesoscopic billiard defined in high quality AlGaAs/GaAs crystal. The induces novel quantum interference structure magnetoresistance with characteristic field scale over an order magnitude smaller than previously reported billiards. A systematic comparison fine and coarse structures, which differ scale, demonstrates first observation geometry-induced ``self-similarity'' semiconductor system.

We explore the high-frequency capability of quantum-well infrared photodetectors using a microwave-rectification technique. characterize variety devices with barrier thicknesses from 234 to 466 /spl Aring/ and number wells 4 32. Our packaged detectors have relatively flat frequency response up about 30 GHz. These experiments indicate that intrinsic photoconductive lifetime for these in high-biasing field regime is range 5-6 ps.

Dopant segregation in the well region of a multiple quantum intersubband photodetector can cause an asymmetry observed forward and reverse current-voltage characteristics. We compensate for by shifting position Si δ doping model effect with good agreement range shift values. For samples grown at substrate temperature 605 °C, we find that behavior is best described assuming δ-doping profile smears growth direction resulting asymmetric broadening about 27 Å.

The frequency dependence of microwave-induced resistance oscillations (MIROs) has been studied experimentally in high-mobility electron $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ structures to explore the limits at which these can be observed. It is found that dc transport experiments frequencies above $120\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$, MIROs start quench, while $230\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$, they completely disappear. results will need understood...

We measure a triple quantum dot in the regime where three addition lines, corresponding to of an electron each dots, pass through other. In particular, we probe interplay between transport and three-dimensional nature stability diagram. choose most pertinent for spin qubit applications. find that at low bias circuit is only possible six quadruple point locations. The results are consistent with equivalent model.