Spontaanse parameetrilise allamuundamise võimendamine pinnaplasmonite ja dielektriliste pinnalainetega

Väitekirja elektrooniline versioon ei sisalda publikatsiooneKvantpõimitust loetakse kvantmaailma üheks suurimaks „veidruseks“. Üheks näiteks on põimitud valguskvantide (footonite) paarid – ühe footoni mõõtmistulemusest sõltub hetkeliselt ka teise footoni mõõtmistulemus hoolimata paariliste vahelisest kaugusest. Einstein võttis nähtuse kokku sõnadega „tontlik kaugmõju“ (inglise keeles „spooky action at a distance“) ja pidas seda liiga veidraks, et olla tõsi. Tänaseks päevaks vaadeldakse seda „veidrust“ kui kvantmaailma olulisimat omadust, seda toetavad ka paljud kvantpõimitust demonstreerivad Belli katsed, ja on asutud looma kvantpõimitusel põhinevaid rakendusi: kvantkrüptograafia, kvantarvutid, jne. Kõikide nende tulevikurakenduste eelduseks on efektiivne kvantpõimitud osakeste allikas. Põhiline meetod põimitud footonpaaride genereerimiseks on spontaanne parameetriline allamuundamine mittelineaarsetes kristallides. See seisneb valguse väikseima osakese, footoni, „poolitamisel“ kaheks madalama energiaga footoniks. Kahjuks on see meetod väga ebaefektiivne. Antud doktoritöö eesmärgiks on põimitud footonpaaride allika efektiivsuse tõstmine kasutades spetsiaalseid pinnalaineid, mis on seotud vabade elektrilangute võnkumisega metalli pinnal. Optiliste protsesside võimendamist pinnalainetega on uuritud palju ning efekti on korduvalt eksperimentaalselt demonstreeritud. Sellest hoolimata pole meile teadaolevalt uuritud pinnalainete kasutamist spontaanse parameetrilise allamuundamise võimendamiseks. Käesoleva doktoritöö raames töötati välja uued arvutusmeetodid, millega uuriti pinnalainete mõju spontaansele parameetrilisele allamuundamisele. Töö käigus võrreldi kolme eri tüüpi pinnalaineid ja kaardistati võimendustegurid, nõudmised objektile ning võimalikud protsessi takistavad tegurid. Töö eksperimentaalses osas disainiti ja ehitati goniomeetriline mõõtesüsteem spontaanse parameetrilise allamuundamise uurimiseks ning viidi läbi esialgsed mõõtmised. Doktoritöö käigus valminud arvutusmeetodeid saab ka edaspidi kasutada uut tüüpi objektide disainimeseks, modelleerimiseks ning optimeerimiseks. Töös esitatud arvutustulemused ja mõõtesüsteemi kirjeldus on oluliseks sisendiks edasisele eksperimentaalsele tööle.Quantum entanglement is considered to be one of the biggest “quirks” of quantum mechanics. One example is entangled pairs of photons – the measurement of one photon instantaneously influences the measurement outcome of the other photon despite the distance between them. Einstein considered it too strange to be true and called the phenomenon as “spooky action at a distance”. Today, this “quirk”, proved in several Bell test experiments, is considered to be the most important property of quantum mechanics and development of several applications based on it is in-progress: quantum cryptography, quantum computing, etc. The prerequisite for all of those future applications is an effective source of entangled particles. The most common source of pairs of entangled photons is spontaneous parametric down-conversion in nonlinear crystals. Essentially, the smallest quanta of light, photon, is split into two photons with a smaller energy due to a nonlinear interaction with matter. Unfortunately, this method is highly inefficient. The goal of this thesis is to enhance the efficiency of the entangled photon pair source by surface waves at the interface of a metal film. The enhancement of optical processes by surface waves is well established and experimentally verified. Despite it, the enhancement of spontaneous parametric down-conversion by surface waves is virtually unstudied to best of our knowledge. In this thesis, new computational methods were developed in order to study the enhancement of photon pair generation by surface waves. New methods were used to compare the effect of three different types of surface waves. In the experimental part of the thesis, a goniometric measurement setup was designed and built for investigating the enhancement of entangled pair generation and initial measurements were conducted. In conclusion, the computational methods developed in this work could be used in future to design, model and optimize a new type of objects. Moreover, the theoretical results and the description of the measurement setup is an important input to the future experimental work

Spontaanse kiirguse võimendamine plasmonefektide abil

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