Quantum optical tomography based on time-resolved and mode-selective single-photon detection by femtosecond up-conversion.

We developed an optical time-of-flight measurement system using a time-resolved and mode-selective up-conversion single-photon detector for acquiring tomographic images of a mouse brain. The probe and pump pulses were spectrally carved from a 100-femtosecond mode-locked fiber laser at 1556 nm using 4f systems, so that their center wavelengths were situated at either side of the phase matching band separated by 30 nm. We demonstrated a sensitivity of 111 dB which is comparable to that of shot-noise-limited optical coherence tomography and an axial resolution of 57 µm (a refractive index of 1.37) with 380 femtosecond probe and pump pulses whose average powers were 1.5 mW and 30 µW, respectively. The proposed technique will open a new way of non-contact and non-invasive three-dimensional structural imaging of biological specimens with ultraweak optical irradiation.

Spin-dependent transient current in transistor-like nanostructures.

Transient current in transistor-like nanostructures has been studied by a model of a few electrons confined in a one-dimensional effective potential consisting of three quantum wells, 'source', 'gate', and 'drain'. The time-dependent Schrödinger equation for the electrons has been integrated relying on the symplectic integrator method and the transient current has been calculated as the flux of the probability density of electrons absorbed by the complex absorbing potential placed at the far edge of the drain region. The electrons are initially placed in the source domain as their lowest-energy state for a given spin multiplicity and the source-drain current has been calculated for different gate potential heights. The current for different spin configurations has shown strong emission at different values of the gate potential, suggesting use of the studied nanostructures for extracting current with a specific spin configuration from spin-unpolarized normal current. Dependence of the current emission on electron correlation has also been studied by changing the size of the source domain. The current has shown appreciable differences for different spin configurations for the medium and strong confinement regimes, while these differences become smaller for smaller confinement and tend to diminish in the weak limit of confinement. This observed trend has been rationalized on the basis of the formation of the Wigner lattice states.