The interaction between free electrons and light stands at the base of both classical and quantum physics, with applications in free-electron acceleration, radiation sources, and electron microscopy. Yet to this day, all experiments involving free-electron–light interactions are fully explained by describing the light as a classical wave. We observed quantum statistics effects of photons on free-electron–light interactions. We demonstrate interactions that pass continuously from Poissonian to super-Poissonian and up to thermal statistics, revealing a transition from quantum walk to classical random walk on the free-electron energy ladder. The electron walker serves as the probe in nondestructive quantum detection, measuring the second-order photon-correlation g(2)(0) and higher-orders g(n)(0). Unlike conventional quantum-optical detectors, the electron can perform both quantum weak measurements and projective measurements by evolving into an entangled joint state with the photons. These findings inspire hitherto inaccessible concepts in quantum optics, including free-electron–based ultrafast quantum tomography of light.

We report temperature-dependent current-voltage (I - V - T) and output light power-voltage or current (P - V - T) or (P - I - T) characteristics of 1550 nm tunneling injection quantum dot (TI QD) laser diodes. Experimental data is accompanied by physical models that distinguish between different current flow and light emission mechanisms for different applied voltages and temperature ranges. Three exponential regimes in the I - V characteristics were identified for low bias levels where no optical radiation takes place. At the lowest bias levels, the diffusion-recombination mechanism based on the classical Shockley-Reid-Hall theory dominates. This is followed, at low and near room temperature, by a combination of weak tunneling and generation-recombination, respectively. In the third exponential region, for all temperatures carrier transport is dictated by strong tunneling, which is characterized by a temperature-independent slope of the I - V curves and a variable ideality factor. The I - V results were compared to a conventional QD laser in which the current flow mechanisms of the first and third types are absent, which clearly demonstrates the key role played by the TI layer. In the post-exponential voltage range, when the diodes are in the high injection regime, the characteristics of the two types of diodes are identical. The typical behavior at the threshold current, where the output power increases fast has a clear signature in the I - V characteristics. Finally, an analytical quantitative relationship is established between the light output power and the applied voltage and current as well as the carrier density participating in radiative recombination.

We demonstrate the hallmark concept of periodic collapse and revival of coherence in a room-temperature ensemble of quantum dots (QDs) in the form of a 1.5-mm-long optical amplifier. Femtosecond excitation pulses induce coherent interactions with a number of discrete homogeneous QD subgroups within an inhomogeneously broadened ensemble, which interfere constructively to induce coherent revival (CR). The amplitude decay of CR is dictated by the QD homogeneous linewidth, thus enabling its extraction in a double-pulse Ramsey-type experiment. The more common photon echo technique is also invoked and yields the same linewidth provided that both experiments use the same bias. A dephasing time T₂ longer than 5 ps is extracted. This is a record long T₂ for a room-temperature QD ensemble and testifies to the high quality of the InAs/InP QDs used in the experiments. Measured electrical bias and temperature dependencies of the transverse relaxation times (T₂ and T^*₂) enable the determination of the two main decoherence mechanisms: carrier-carrier and carrier-phonon scatterings.

Using quantum dot (QD) structures as active material for optoelectronics was already in focus before the development of quantum well (QW) lasers and before semiconductor lasers occupied an important place in the market. The big step in reducing laser threshold conditions by substituting bulk gain materials with QWs should find a logical continuation by further reducing the dimensionality toward full 3D carrier confinement by QDs. This was predicted by theoretical considerations at the beginning of the 1980s [1], [2]. However, no practical technologies were available at that time. Top-down approaches, as originally addressed, to produce nanoscale species on very large surfaces and interface areas resulted in the accumulation of a large defect density within the active region and the domination of nonradiative carrier recombination mechanisms. Only during the early 1990s was a major breakthrough achieved with the introduction of the bottom-up approach of strain-driven, self-organized epitaxial QD growth. The first lasers were obtained in the gallium arsenide (GaAs)-based material system [3].

We present a planar three terminal device fabricated on a silicon-on-insulator substrate. The device is based on a two-layer dielectric stack comprising SiO₂ tunneling and HfO₂ layers. A so-called gate electrode is placed between two other contacts, of the source and drain, all deposited on the insulator stack. In the dark as well as under illumination, the current–voltage characteristic can be shifted in an ideal linear manner with changes in a positive gate voltage with the shift being somewhat larger under illumination. The reason for the change of shift is the ability of high-density oxygen vacancies, arranged in the filament regions within an HfO₂ sublayer that was voltage stress. Namely, holes or electrons are trapped in the HfO₂ sublayer, respectively, from the inverted or accumulated Si layer. This process is controlled by the gate and drain bias levels. Moreover, under illumination and at negative gate and drain voltages, the device exhibits negative differential resistance caused by capture of photo-generated minority carriers induced in the depletion region of the Si after they tunnel through the SiO₂ layer by negative oxygen vacancies that migrate to the SiO₂/HfO₂ interface through the filament regions. Finally, the low level of saturation current in the dark and the ability to precisely control its value by illumination intensity, together with a large sensitivity of 80–85 A/W and 25 A/W, at 490 nm and 365 nm, respectively, allow additional applications that cannot be achieved with conventional MIS devices.

We present amplitude and phase characterization of short optical pulses using dual-comb spectroscopy, where one comb is a well-characterized stable-frequency comb and the second is the pulse source to be measured. We demonstrate that the technique is suitable for truly arbitrary repetition rates of the two combs. Moreover, the system is highly sensitive and is shown to enable measurements of low-intensity pulses. In one experiment we use relatively long (80-ps) pulses generated by an actively mode-locked semiconductor laser at a repetition rate that is slightly different from that of the reference laser. In a second experiment, we employ 2-ps pulses generated by a fiber laser whose repetition rate differs significantly from that of the reference laser. We benchmark the method by comparison with conventional methods of pulse characterization. Furthermore, limitations due to fluctuations of the carrier-envelope offset and the repetition rate, are addressed and overcome by implementing computational nonuniform sampling of measured interferograms.