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Application fields of light emitting diodes (LEDs) are expanding in various fields. Development of LED-based single photon sources is expected to open a new possibility to expand the applications to quantum information communication and processing. The authors have proposed a photon-emitting LED combined with superconducting electrodes, which is expected to be an on-demand entangled photon pair source. The main mechanism is based on the coherent spatial extension of the Cooper-pair states to the photon emitting layer, which is expected to enhance the oscillator strength of the radiative recombination processes by the Cooper-pair superradiance effect. The preliminary operation was demonstrated with InGaAs quantum well (QW) LEDs and about 20-times enhancement of the electroluminescence (EL) was observed under the low-injection current regime. This is the demonstration of the improved internal quantum efficiency (QE) under the low internal QE operation of the LED. In this paper, the enhancement of the radiative recombination processes with the superconducting (SC) effect is demonstrated by the lifetime measurements under the operation with high (~100%) internal quantum efficiency (QE).

To demonstrate the contribution of Cooper pairs to radiative recombination in a semiconductor, a n-InGaAs/p-InP light emitting diode with superconducting Nb electrodes was fabricated. Electroluminescence as well as photoluminescence from the n-InGaAs into which electron Cooper pairs were expected to penetrate from the superconducting Nb electrodes by the proximity effect was drastically enhanced at the temperature lower than the superconducting transition temperature. This is the experimental evidence that Cooper pairs enhance radiative recombinations by the superradiance effect.

We report on observations of supercurrents through multi-walled carbon nanotubes (MWNTs) in a diffusive carrier transport regime, which possesses weak localization, in niobium (Nb)/diffusive MWNTs/aluminum(Al) junction systems. We successfully find proximity-induced superconductivity and supercurrents at T=0.6 K Some of these behaviors are very similar to those in single-walled carbon nanotubes, but we also find many drastic differences, such as the critical magnetic field anomalously 35-times larger than that of Nb electrodes. This implies strong spin coherence and entanglement in the MWNTs, resulting in realization of spin quantum bit and teleportation.

We give a detailed analysis based on Shubnikov-de Haas measurement of the effective mass of 2DEG in an InAs-inserted-channel InAlAs/InGaAs modulation-doped structure. The measured effective mass of the InAs-inserted-channel inverted MD structure was found to be 0.044 m/sub 0/, when n/sub s/=2.08/spl times/10/sup 12/ cm/sup -2/. The results indicate that almost all of the 2DEG forms in the strained InAs quantum well. They show that the InAs-inserted-channel MD structure improves the electron confinement, since the 2DEG is confined in the InAs quantum well with the thickness of 4 nm. Therefore, it is possible to utilize the excellent transport properties of InAs by the InAs-inserted-channel MD structure.