Beating in electronic transport through quantum dot based devices

Electronic transport through a two-level system driven by external electric field and coupled to (magnetic or non-magnetic) electron reservoirs is considered theoretically. The basic transport characteristics such as current and tunnel magnetoresistance (TMR) are calculated in the weak coupling approximation by the use of rate equation connected with Green function formalism and slave-boson approach. The time dependent phenomenon is considered in the gradient expansion approximation. The results show that coherent beats pattern can be observed both in current and TMR. The proposed system consisting of two quantum dots attached to external leads, in which the dots' levels can be tuned independently, can be realized experimentally to test this well known physical phenomenon. Finally, we also indicate possible practical applications of such device.Comment: 9 pages, 9 figure

Kondo-Dicke resonances in electronic transport through triple quantum dots

Electronic transport through a triple quantum dot system, with only a single dot coupled directly to external leads, is considered theoretically. The model includes Coulomb correlations in the central dot, while such correlations in the two side-coupled dots are omitted. The infinite-U mean-field slave-boson approach is used to obtain basic transport characteristics in the Kondo regime. When tuning position of the side-coupled dots' levels, transition from subradiant to superradiant like mode (and vice versa) has been found in the spectral function, in analogy to the Dicke effect in atomic physics. Bias dependence of the differential conductance and zero frequency shot noise is also analysed.Comment: 8 pages, 10 figure

Analysis of Kerr comb generation in silicon microresonators under the influence of two-photon absorption and free-carrier absorption

Kerr frequency comb generation relies on dedicated waveguide platforms that are optimized towards ultralow loss while offering comparatively limited functionality restricted to passive building blocks. In contrast to that, the silicon-photonic platform offers a highly developed portfolio of high-performance devices, but is deemed to be inherently unsuited for Kerr comb generation at near-infrared (NIR) telecommunication wavelengths due to strong two-photon absorption (TPA) and subsequent free-carrier absorption (FCA). Here we present a theoretical investigation that quantifies the impact of TPA and FCA on Kerr comb formation and that is based on a modified version of the Lugiato-Lefever equation (LLE). We find that silicon microresonators may be used for Kerr comb generation in the NIR, provided that the dwell time of the TPA-generated free-carriers in the waveguide core is reduced by a reverse-biased p-i-njunction and that the pump parameters are chosen appropriately. We validate our analytical predictions with time integrations of the LLE, and we present a specific design of a silicon microresonator that may even support formation of dissipative Kerr soliton combs.Comment: 26 pages, 6 figures. Submitted to Physical Review

Analysis of Kerr comb generation in silicon microresonators under the influence of two-photon absorption and fast free-carrier dynamics

Kerr frequency comb generation relies on dedicated waveguide platforms that are optimized toward ultralow loss while offering comparatively limited functionality restricted to passive building blocks. In contrast to that, the silicon-photonic platform offers a highly developed portfolio of high-performance devices, but suffers from strong two-photon absorption (TPA) and subsequent free-carrier absorption (FCA) at near-infrared telecommunication wavelengths, thereby rendering Kerr comb generation a challenge. Here we present a model to investigate the impact of TPA and FCA on Kerr comb formation. Our model combines a modified version of the Lugiato-Lefever equation with a refined relation to precisely describe the fast space and time dependence of the free-carrier concentration along the circumference of the microresonator. Using this refined model, we derive conditions for modulation instability, in particular for necessary pump powers depending on TPA parameters and free-carrier lifetimes. We validate our analytical predictions by time integration and study the impact of fast free-carrier dynamics on Kerr comb formation. We find that silicon microresonators may be suitable for Kerr comb generation in the NIR, provided that the dwell time of the TPA-generated free carriers in the waveguide core is reduced by a reverse-biased p-i-n-junction and that the pump parameters are chosen appropriately

HLA-Associated viral mutations are common in human immunodeficiency virus type 1 elite controllers

Elite controllers (EC) of human immunodeficiency virus type 1 (HTV-1) maintain viremia below the limit of detection without antiretroviral treatment. Virus-specific cytotoxic CD8+ T lymphocytes are believed to play a crucial role in viral containment, but the degree of immune imprinting and compensatory mutations in EC is unclear. We obtained plasma gag, pol, and nef sequences from HLA-diverse subjects and found that 30 to 40% of the predefined HLA-associated polymorphic sites show evidence of immune selection pressure in EC., compared to approximately 50% of the sites in chronic progressors. These data indicate ongoing viral replication and escape from cytotoxic T lymphocytes are present even in strictly controlled HTV-1 infection

Ultrafast optical ranging using microresonator soliton frequency combs

Light detection and ranging (LIDAR) is critical to many fields in science and industry. Over the last decade, optical frequency combs were shown to offer unique advantages in optical ranging, in particular when it comes to fast distance acquisition with high accuracy. However, current comb-based concepts are not suited for emerging high-volume applications such as drone navigation or autonomous driving. These applications critically rely on LIDAR systems that are not only accurate and fast, but also compact, robust, and amenable to cost-efficient mass-production. Here we show that integrated dissipative Kerr-soliton (DKS) comb sources provide a route to chip-scale LIDAR systems that combine sub-wavelength accuracy and unprecedented acquisition speed with the opportunity to exploit advanced photonic integration concepts for wafer-scale mass production. In our experiments, we use a pair of free-running DKS combs, each providing more than 100 carriers for massively parallel synthetic-wavelength interferometry. We demonstrate dual-comb distance measurements with record-low Allan deviations down to 12 nm at averaging times of 14 $\mu$s as well as ultrafast ranging at unprecedented measurement rates of up to 100 MHz. We prove the viability of our technique by sampling the naturally scattering surface of air-gun projectiles flying at 150 m/s (Mach 0.47). Combining integrated dual-comb LIDAR engines with chip-scale nanophotonic phased arrays, the approach could allow widespread use of compact ultrafast ranging systems in emerging mass applications.Comment: 9 pages, 3 figures, Supplementary information is attached in 'Ancillary files

50 Tbit/s Massively ParallelWDMTransmission in C and L Band Using Interleaved Cavity-Soliton Kerr Combs

Interleaving two soliton Kerr combs we generate 179 carriers for WDM transmission and demonstrate transmission of a data stream of 50 Tbit/s over 75 km. This is the highest data rate achieved with a chip-scale comb source

Microresonator solitons for massively parallel coherent optical communications

Optical solitons are waveforms that preserve their shape while propagating, relying on a balance of dispersion and nonlinearity. Soliton-based data transmission schemes were investigated in the 1980s, promising to overcome the limitations imposed by dispersion of optical fibers. These approaches, however, were eventually abandoned in favor of wavelength-division multiplexing (WDM) schemes that are easier to implement and offer improved scalability to higher data rates. Here, we show that solitons may experience a comeback in optical communications, this time not as a competitor, but as a key element of massively parallel WDM. Instead of encoding data on the soliton itself, we exploit continuously circulating dissipative Kerr solitons (DKS) in a microresonator. DKS are generated in an integrated silicon nitride microresonator by four-photon interactions mediated by Kerr nonlinearity, leading to low-noise, spectrally smooth and broadband optical frequency combs. In our experiments, we use two interleaved soliton Kerr combs to transmit a data stream of more than 50Tbit/s on a total of 179 individual optical carriers that span the entire telecommunication C and L bands. Equally important, we demonstrate coherent detection of a WDM data stream by using a pair of microresonator Kerr soliton combs - one as a multi-wavelength light source at the transmitter, and another one as a corresponding local oscillator (LO) at the receiver. This approach exploits the scalability advantages of microresonator soliton comb sources for massively parallel optical communications both at the transmitter and receiver side. Taken together, the results prove the significant potential of these sources to replace arrays of continuous-wave lasers in high-speed communications.Comment: 10 pages, 3 figure