Two-photon interference is an indispensable resource in quantum photonics, but it is not straightforward to achieve. The cascaded generation of photon pairs contains intrinsic temporal correlations that negatively affect the ability of such sources to perform two-photon interference, thus hindering applications. We report on how such correlation interplays with decoherence and temporal postselection, and under which conditions temporal postselection could improve two-photon interference visibility. Our study identifies crucial parameters and points the way to a source with optimal performance.

Quantum non-Gaussian states of light have fundamental properties that are essential for a multitude of applications in quantum technology. However, many of these features are difficult to detect using standard criteria due to optical losses and detector inefficiency. As the statistics of light are unknown, the loss correction on the data is unreliable, despite the fact that the losses can be precisely measured. To address this issue, we employ a loss-mitigated verification technique utilizing quantum non-Gaussian witnesses, which incorporate the known optical losses and detector inefficiency into their derivation. This approach allows us to address the considerable challenge of experimentally demonstrating unheralded quantum non-Gaussian states of single photons and photon pairs.

Quantum non-Gaussianity is a stricter criterion and the next step after non-classicality in the classification of quantum states. We will present our experimental results on the certification of quantum non-Gaussian coincidences through a noisy channel.

This work analyzes two of the most common sources of entangled photon pairs. In the two manuscripts, we focused on the study of various properties of the emission coming from a semiconductor quantum dot. In particular, we first investigated and subsequently attempted to reduce the effect of the time correlation of the photon pair on Hong-Ou-Mandel interference visibility. Furthermore, we analyze the photon statistic of the quantum dot emission and use it to test a novel criterion for the certification of quantum non-Gaussianity capable of incorporating some amount of known losses. The last part is instead dedicated to the construction and characterization process of a source of entangled photon pairs based on spontaneous parametric down-conversion in a Sagnac configuration. Throughout this work, we compare the source types' relative strengths and weaknesses, highlighting their suitability for different applications.

Detta arbete analyserar två av de vanligaste källorna till sammanflätade fotonpar. I de två manuskripten fokuserade vi på att studera olika egenskaper hos den emission som kommer från en halvledarkvantpunkt. I synnerhet undersökte vi först och försökte sedan minska effekten av fotonparets tidskorrelation på Hong-Ou-Mandel-interferenssynlighet. Dessutom analyserar vi fotonstatistiken för kvantpunktens emission och använder den för att testa ett nytt kriterium för certifiering av kvantnegaussianitet som kan införliva en viss mängd kända förluster. Den sista delen ägnas istället åt konstruktionen och karakteriseringsprocessen av en källa för sammanflätade fotonpar baserad på spontan parametrisk nedkonvertering i en Sagnac-konfiguration.Genom hela arbetet jämför vi källtypernas relativa styrkor och svagheter och belyser deras lämplighet för olika tillämpningar.

Quantum dots are promising semiconductor sources of nonclassical light. Quantum dots can be used to, on-demand, generate single photons [1] and photon pairs [2]. They can generate pairs of photons entangled in polarization [3] and time bin [4]. Furthermore, the photons emitted by a quantum dot can be employed in a broad range of applications including optical quantum computation, long-distance quantum communication, and protocols like quantum state teleportation. In particular, the possibility to excite the quantum dots resonantly is one of the most important assets of this system. The resonant excitation is the process responsible for the high photon generation efficiency. In combination with photonic structures that enables high photon extraction efficiency, quantum dots can lay the basis for accomplishing very high efficiency sources of quantum light [5].

The Hong-Ou-Mandel (HOM) effect is a direct consequence of the bosonic nature of photons [1], as such, it occurs maximally in the presence of truly indistinguishable photons. Measuring the magnitude of the HOM effect is required to determine the reliability with which a photon source is able to produce indistinguishable photons. Using this method, single photon sources have shown the ability to provide photons with remarkable levels of indistinguishability [2].

Quantum non-Gaussian states of light have fundamental properties that are essential for a multitude of applications in quantum technology. However, many of these features are difficult to detect using standard criteria due to optical losses and detector inefficiency. As the statistics of light are unknown, the loss correction on the data is unreliable, despite the fact that the losses can be precisely measured. To address this issue, we employ a loss-mitigated verification technique utilising quantum non-Gaussian witnesses, which incorporate the known optical losses and detector inefficiency into their derivation. This approach allows us to address the considerable challenge of experimentally demonstrating unheralded quantum non-Gaussian states of single photons and photon pairs.