Experimental Study Of The Optical Property Of Quantum Dot And Its Applications In Quantum Information

Quantum computation and quantum communication science, as a subject of appli-cations, is the extension of Von Neumann architecture of classical information which isvery popular today. This extension is necessary, because as the improvement of tech-nology people keep trying to challenge the limitation of speed and integration densityof the electronic chips, which makes the physical carrier of Von Neumann architecturehave almost reached the ceiling of progress. Quantum information shows to break thisrestriction of the physical carrier, and meanwhile, because of the proposal Shor algo-rithm, people see the power of quantum parallel algorithm. This makes people placehigh hopes for quantum information. Quantum information is a logical conception.If we want to realize it, we also need physical carriers. Self-assembled quantum dot(SAQD) with atomic character and photon are both good choices. Here we studiedthe spectra of SAQD and use it to make single photon source (SPS). Because of thethree-dimension spatial con?nement, SAQD has discrete energy levels and sharp spec-tral lines. The discreteness makes the energy states have limit lifetimes, then they canemit single photons. Using this single photons, we can perform some experiments ofquantum information on photon bit. Our primary works are as follow:1, We observed natural excitonic polaron in InAs/GaAs SAQD.This phenomenon shows the strong coupling between the exciton and longitudinaloptical phonon (LOP). We changed the temperature of the sample to make the shift ofenergy levels. When the level spacing is resonant with the energy of LOP, the energysplitting which is similar to the dressed states appears. These energy levels are levels ofpolaron. A distinctive sign is an anticrossing shown in the temperature-energy curve.2, We measured the energy lifetime of SAQD ensemble using a new methodof saturation.The saturation-method uses the character of saturation of SAQD to measure itsenergy lifetime. Comparing to the method of spontaneous parametric up conversion(SPUC), this method has the advantage of easy fabrication; and comparing to themethod of time correlation analyser (like picosecond time analyser, PTA), this methodhave more precision. Moreover, we also demonstrated that this method still works whenthe probe pulse is not fully saturated. Merely the error will get a little larger.3, We separated a single QD with both method of sparse QD sample and apertured mask, and obtained SPS.It is a necessary condition to isolate a single QD from the ensemble for manu-facturing a SPS. We compared the signal-noise ratio (SNR) under various conditions:exciting power intensity, size of pinhole in the beam path, dot density on the sampleand temperature. Finally we obtained the single-dot spectra with quite high SNR forsome certain parameters. We also made lithography for the samples, coated them with100 nm gold ?lm and etch holes of micrometers. We also obtained single-dot spectraand took Hanbury-Brown-Twiss test on the signal light.4, We tested the multiple-measurement time-domain Bell inequalities.The debate between classical physical reality and quantum mechanics (QM) isalways a hot topic. As one of the focal issues, Leggett-Garg inequality have manysimilarities with Bell inequality. It corresponds to the non-locality of QM in time,so it is also called time-domain Bell inequality. We explained in this thesis how toextend the equality and how to evaluate the extension methods when more than threemeasurements were taken, and experimentally tested them.5, We experimentally measured the non-Markovianity of a pure dephasingdynamical evolution.Non-Markovian processes have become the central interest in the study of openquantum systems. We experimentally measure the non-Markovianity of a pure dephas-ing dynamical process in which a photon emitted from a single quantum dot is sent toa 100 m polarization-maintaining optical ?ber. This measure is described by the totalinformation ?owing back to the system from the environment. The information is car-ried by the photon polarization states. Our results may be helpful to the understandingof non-Markovian processes and to the development of quantum memory and quantumcommunication.6, We prepared some initial states containing the system-environment corre-lations, and witness the correlations by using a delay setup.Multiple-system correlations, which include not only quantum entanglement, playan important role in quantum computation and quantum communication. In particular,system-environment correlations, which determine the (non-) Markovian character ofa dynamical process, attract much interest in the study of open quantum systems. Wesend photons emitted from a quantum dot sample into a 15 m polarization-maintainingoptical ?ber to generate different system-environment correlated states, and then wit-ness the correlations by observing the growth of trace distances. The ?owing of in-formation between the system and environment in our experiment is clearly described. This scheme of correlation witness based on the system-environment information ?ow-ing can also be used in other similar systems.