| Sources of single photons and entangled photons are needed for proposed applications in the field of quantum information, such as quantum cryptography and linear-optical quantum computation. Most experiments in quantum information have used spontaneous parametric downconversion, which produces a random number of entangled photon pairs. Recently, however, single-photon sources based on molecules, color centers, and quantum dots have advanced significantly. A single-photon source ideally emits a series of pulses that each contain one photon. An actual source is characterized by the degree of two-photon suppression, the efficiency, and whether photons in consecutive pulses are quantum-mechanically indistinguishable.; This work focuses on the development of nonclassical light sources based on single InAs quantum dots. Quantum dots are tiny regions of a smaller-bandgap semiconductor embedded in a larger-bandgap semiconductor. Electrons and holes confined in these structures have discrete energy levels, as in an atom. Quantum dots have large dipole moments, can be isolated, and are conveniently integrated into fabricated structures, such as optical cavities. Our single-photon source uses an optically excited quantum dot, placed in a microcavity to improve its spontaneous emission properties. By optimizing the excitation conditions and applying a spectral filter to the emission, we obtain a two-photon suppression factor (compared to a Poisson distribution) as large as 40, as observed in photon correlation measurements. Through a two-photon interference experiment, we show that photons in consecutive pulses can be nearly indistinguishable. We also investigate the polarization correlation properties of photon pairs emitted through biexciton decay, with the goal of realizing a source of single pairs of polarization-entangled photons. |
