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Entanglement is a fundamental feature of quantum mechanics, considered a key resource in quantum information processing. Measuring entanglement is an essential step in a wide range of applied and foundational quantum experiments. When a…
The wave-particle duality has been said to contain the entire mystery of quantum mechanics. Many delayed-choice experiments have been performed to further understand the wave-particle duality. Here, we reveal some flaws in the known…
Quantum entanglement is central to both the foundations of quantum mechanics and the development of new technologies in information processing, communication, and sensing. Entanglement has been realised in a variety of physical systems,…
One of the most striking quantum phenomena is photon bunching resulting from coincidently impinging two-indistinguishable photons on a beam splitter (BS) from two different input ports. Such a nonclassical feature has also been observed…
We study the impact of distinguishability and mixedness -- two fundamental properties of quantum states -- on quantum interference. We show that these can influence the interference of multiple particles in different ways, leading to…
Photon coincidence spectroscopy relies on detecting multiphoton emissions from the combined atom-cavity system in atomic beam cavity quantum electrodynamics experiments. These multiphoton emissions from the cavity are nearly simultaneous…
Interaction of atoms with twisted light is the subject of intense experimental and theoretical investigation. In almost all studies, the atom is viewed as a localized probe of the twisted light field. However, as argued in this paper,…
Quantum path interferences occur whenever multiple equivalent and coherent transitions result in a common final state. Such interferences strongly modify the probability of a particle to be found in that final state, a key concept of…
We apply our recently developed theory of frequency-filtered and time-resolved N-photon correlations to study the two-photon spectra of a variety of systems of increasing complexity: single mode emitters with two limiting statistics (one…
We apply input-output theory with quantum pulses [AH Kiilerich, K M\o lmer, Phys. Rev. Lett. {\bf 123}, 123604 (2019)] to a model of a new type of two-photon detector consisting of one molecule that can detect two photons arriving…
Scattering processes have played a crucial role in the development of quantum theory. In the field of optics, scattering phase shifts have been utilized to unveil interesting forms of light-matter interactions. Here, we investigate the…
We study the optical response of a binary system of identical atoms in which one of them is excited by an incoherent pump. %We study the properties of photon scattering, absorption and emission, together with the time evolution of the…
Quasi-elastic scattering processes have long been thought of providing the most promising signal for a first experimental detection of quantum vacuum nonlinearity. A prominent example of such a process is vacuum birefringence. However,…
The distinguishing of the multiphoton quantum interference effect from the classical one forms one of the most important issues in modern quantum mechanics and experimental quantum optics. For a long time, the two-photon interference (TPI)…
A single quantum emitter coupled to a one-dimensional photon field can perfectly trap a photon when placed close to a mirror. This occurs when the interference between the emitted and reflected light is completely destructive, leading to…
Photons, by nature, typically do not exhibit interactions with each other. Creating photon-photon interactions holds immense importance in both fundamental physics and quantum technologies. Currently, such interactions have only been…
A double-slit experiment with entangled photons is theoretically analyzed. It is shown that, under suitable conditions, two entangled photons of wavelength $\lambda$ can behave like a \emph{biphoton} of wavelength $\lambda/2$. The…
Young's double-slit interference experiment is central to quantum mechanics. While it has been demonstrated that an array of atoms can produce interference in light, it is a fundamental question to ask whether a single atom can act as a…
Photonic quantum technologies are on the verge of finding applications in everyday life with quantum cryptography and the quantum internet on the horizon. Extensive research has been carried out to determine suitable quantum emitters and…
Tremendous progress has been realized in quantum optics for engineering and detecting the quantum properties of light. Today, photon pairs are routinely created in entangled states. Entanglement is revealed using single-photon detectors in…