Quantum cascaded systems offer the possibility to manipulate a target system with the quantum state of a source system. Here, we study in detail the differences between a direct quantum cascade and coherent or incoherent driving for the case of two coupled cavity-QED systems. We discuss qualitative differences between these excitations scenarios, which are particularly strong for higher-order photon-photon correlations: ${g}^{(n)}(0)$ with $n>2$. Quantum cascaded systems show a behavior differing from the idealized cases of individual coherent or incoherent driving and allow one to produce qualitatively different quantum statistics. Furthermore, the quantum cascaded driving exhibits an interesting mixture of quantum coherent and incoherent excitation dynamics. We develop a measure where the two regimes intermix and quantify these differences via experimentally accessible higher-order photon correlations.
Quantum cascaded systems offer the possibility to manipulate a target system with the quantum state of a source system. Here, we study in detail the differences between a direct quantum cascade and coherent or incoherent driving for the case of two coupled cavity-QED systems. We discuss qualitative differences between these excitations scenarios, which are particularly strong for higher-order photon-photon correlations: g(n)(0) with n>2. Quantum cascaded systems show a behavior differing from the idealized cases of individual coherent or incoherent driving and allow one to produce qualitatively different quantum statistics. Furthermore, the quantum cascaded driving exhibits an interesting mixture of quantum coherent and incoherent excitation dynamics. We develop a measure where the two regimes intermix and quantify these differences via experimentally accessible higher-order photon correlations.
We study the dissipative dynamics and the formation of entangled states in driven cascaded quantum networks, where multiple systems are coupled to a common unidirectional bath. Specifically, we identify the conditions under which emission and coherent reabsorption of radiation drives the whole network into a pure stationary state with non-trivial quantum correlations between the individual nodes. We illustrate this effect in more detail for the example of cascaded two-level systems, where we present an explicit preparation scheme that allows one to tune the whole network through 'bright' and 'dark' states associated with different multi-partite entanglement patterns. In a complementary setting consisting of cascaded nonlinear cavities, we find that two cavity modes can be driven into a non-Gaussian entangled dark state. Potential realizations of such cascaded networks with optical and microwave photons are discussed.
We propose a possibility to study the quantum light excitation of atomic systems. To confine our study, we limit the configuration to two and four level emitters as target systems. Source and target are coupled via unidirectional waveguide. We numerically implement the cascaded formalism and use the source-target approach. Herein, we focus on continuous excitation scenarios where the source system is excited by continuous incoherent or coherent pumping. We demonstrate that, to a certain extent, one can control the target system's photon statistics via the source system pumping mechanism. Additionally, different coupling regimes in both cavities can change the output of the target system. In addition, we show that via tuning the cavity’s parameters one can produce an exotic type of quasi-probability distributions, a flat Fock state distributions. We also discuss the different obtained photon statistics for different coupling regimes. The used quantum light source, driven by spontaneous emission, can be categorized as a single photon source or two photon source. Therefore, the thesis is divided also according to these types of quantum light sources into two parts: In the first part of the thesis, after review of the theoretical methods, which are applied in the thesis , we specifically study coupled cavities. The first cavity, pumped incoherently, performs effectively as a single photon source. We consider system-bath interaction in the coupling waveguide, i.e boson-boson interaction, for the photon occurring in the system .We demonstrate that even for a simple scenario , where thermal bath modes couple to the system, the photon statistics of the source is not completely mapped to the target system. This suggest that the environment for such a coupled systems influence the photon statistics of the source while transferring it into the target system. In the case of direct coupling of emitters to the waveguide the influence of the environment, as a dissipator, on the photon statistics can be seen in photon number distribution. Additionally, higher order correlation functions for the target system deviate drastically from the source system and show a mixture of quantum coherent and incoherent dynamics. For the case of indirect coupling of emitters to the waveguide, when the modes of two cavities are coupled, the mediating environment also influences the photon statistics of the target system. This phenomenon manifests itself in the second-order correlation function of the source and target, wherein, while the source behaves in the anti-bunched regime, the target system shows highly bunched pattern. In the second part of thesis, we study the production of two photons in nonlinear optics. As an example, we propose an optical setup where we can produce entangled pairs of photons through the dynamical Casimir effect(DCE). By applying the laser on a superconducting surface of a metal dielectric we induce a surface plasmon polariton (SPP). SPP give rise to the enhancement of DCE such as the efficiency of two photon production exceed the common nonlinear optical processes for instance parametric down conversion. We show that the resonant enhancement of the emission of two photons happens when the excitation wavelength coincides with the amplitude of the laser light. Another even more efficient source for the two photon emission is a biexciton excitation of a quantum dot. We provide a formalism for a cascaded biexciton which can be used to show how the source biexciton, pumped coherently or incoherently, influences the target biexciton through a unidirectional waveguide, modeled as a thermal bath.
We investigate theoretically the model of a cavity-quantum-electrodynamics (QED) system that consists of two two-level atoms coupled to a single-mode cavity in the weak coupling regime, where the system is driven by quantum light. The dynamics behavior of the entire system is tackled in the framework of a cascaded quantum system. We find that the two-photon blockade with two-photon bunching and three-photon antibunching can be obtained even when the strong system dissipation is included. This result shows that our work has potential for realizing entangled photon pairs in a weakly coupled cavity. Moreover, we also analyze the photon statistics of the system in the case of out-of-resonance coupling between cavity and two nonidentical atoms. Here, an unconventional photon blockade effect with suppression of two-photon correlation and enhancement of three-photon correlation can be realized, which shows many quantum statistical characteristics of a cavity QED system in weak coupling.
The output incoherent spectrum and the photon blockade for the two-photon near-resonant excitation are numerically investigated by using the modified theories which are valid for an arbitrary degree of the qubit-cavity interaction. Owing to the effects of strong coupling of the system, the relaxation coefficients of the system are very sensitive to the coupling strength between the qubit and the cavity mode, which results in the redistribution of the populations and the appearance of the population inversion between the ground state and the first excited state, and it is demonstrated by the intensity of the output incoherent spectrum. The redistribution of the populations leads to one cascaded decay channel being weakened and the other possibly being enhanced significantly. Moreover, by adjusting the detuning between the qubit and the cavity mode, the phenomenon of the intercrossing in the energy levels appears. Through choosing the proper two-photon near-resonant excitation of the external classical driving field, the strong-coupling qubit-cavity system effectively causes one cascaded decay channel to realize the two-photon blockade. It is shown that the two-photon blockade can be further enhanced by one cascaded decay channel.
In the strong coupling regime of cavity QED where the characteristic damping rates are orders of magnitude below the coherent coupling, resolved multi-photon resonances can be observed for strong enough driving strength. In a certain frequency range, the external coherent drive field hits multi-photon resonances which correspond to very high order transitions that cannot be excited at the given power of the driving field. We found that in this range the cavity field evolves into a robust semiclassical solution which is the mixture of the vacuum and an excited quasi-classical state. The system is reminiscent of optical bistability, however, here a single atom produces a telegraph signal for the outgoing intensity by switching between two states with large photon number difference. We calculate this behavior also for the Tavis-Cummings model representing three qubits in an existing circuit QED experimental setting.
We consider a laser-driven and dissipative system of two coupled cavities with Jaynes-Cummings nonlinearity. In particular, we investigate both incoherent and coherent laser driving, corresponding to different experimental situations. We employ Arnoldi time evolution as a numerical tool to solve exactly the many-body master equation describing the nonequilibrium quantum system. We evaluate the fluorescence spectrum and the spectrum of the second-order correlation function of the emitted light field. Finally, we relate the measured spectra of the dissipative quantum system to excitations of the corresponding nondissipative quantum system. Our results demonstrate how to interpret spectra obtained from dissipative quantum systems and specify what information is contained therein.