Ph.D Student | Hayat Alex |
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Subject | Applications of Multi-Photon Processes for Semiconductor Quantum Photonics |

Department | Department of Electrical Engineering |

Supervisor | Professor Meir Orenstein |

Full Thesis text |

Miniaturizing quantum photonics is a rapidly growing field. Semiconductors are promising materials due to their strong optical nonlinearities and compatibility with the existing photonic technology allowing high-scale integration and miniaturization. Moreover, in contrast to insulating nonlinear crystals, semiconductors allow manipulation of free charge-carriers, and therefore, more efficient low-order resonant nonlinear processes can be used in semiconductor devices involving generation and recombination of charge-carriers.

In two-photon emission, electron transitions occur by simultaneous emission of a pair of photons. This phenomenon is important for astrophysics, and atomic physics due to the dependence of the spectrum on the entire level structure. However, two-photon emission in semiconductors (or any solids) has not been observed, nor has it been analyzed theoretically before. We demonstrated experimentally the first observation of two-photon emission in semiconductors. Spontaneous and singly-stimulated two-photon emission in bulk GaAs and in electrically-driven quantum wells were observed at room temperature, and a divergence-free theoretical model was developed.

We proposed the phenomenon of semiconductor two-photon emission as an electrically-driven room-temperature source of energy-entangled photons, much more efficient than down-conversion schemes, and without the need for phasematching. We also proposed a hyper-entanglement source emitting photon pairs entangled in both energy and polarization. A theoretical formalism was derived for the calculation of photon pair generation spectra and rates. We also proposed two-photon absorption for infrared photon detection in wide-gap semiconductors and for interferometric characterization of energy qubits including complete Bell state analysis.

Two-photon gain, in which photons are amplified in pairs, was proposed for development of alternative kinds of quantum oscillators with unique properties including squeezing and ultrafast pulse generation. Previously, it was demonstrated in atomic systems in maser-like configurations with very low output efficiencies and optical pumping. Achieving two-photon gain in solids, and in particular semiconductors, is similar to the transition from the maser to the laser diode, with the benefit of higher efficiencies, miniaturization, and electrical pumping. First observations of electrically-induced two-photon transparency and two-photon gain in semiconductor waveguides are demonstrated here experimentally, and employed for ultrafast pulse compression.

A scheme for
a femtosecond-scale g^{(4)} coherence measurement is implemented. The
scheme is realized by a Michelson interferometer and second harmonic generation
in a semiconductor quantum well AlGaAs/GaAs waveguide followed by a Hanbury
Brown-Twiss setup. The measurement of the fourth-order coherence function, g^{(4)}, allows definitive characterization of
photon pair statistics, important in quantum information processing and
nonlinear quantum optics.