We study a minimal model of collective light emission from an incoherently driven ensemble of atoms where incoherent drive is applied to only a subset of the atoms and show that both the linewidth and the photon statistics can be controlled within a single framework. In this setting, collective dissipation induces correlations between the pumped and unpumped parts of the system, leading to interference between their emission contributions. By introducing a relative phase between these contributions and tuning the pump rate, we demonstrate that the properties of the emitted light can be varied over a broad range. In particular, the linewidth can be made either independent of system size or scale extensively with it, while the photon statistics can be tuned from antibunched or quantum to bunched. We further show that the role of the relative phase in controlling the interference can alternatively be played by the coherent interaction. By tuning the interaction strength together with the pump rate, one can access the same regimes as in the dissipation-only model. In addition, coherent interactions stabilize regimes of coherent emission with narrow linewidth, reminiscent of superradiant lasing. Our results illustrate how interference in partially driven collective systems provides a flexible mechanism for tailoring both spectral and statistical properties of light.
We study a minimal model of collective light emission from an incoherently driven ensemble of atoms where incoherent drive is applied to only a subset of the atoms and show that both the linewidth and the photon statistics can be controlled within a single framework. In this setting, collective dissipation induces correlations between the pumped and unpumped parts of the system, leading to interference between their emission contributions. By introducing a relative phase between these contributions and tuning the pump rate, we demonstrate that the properties of the emitted light can be varied over a broad range. In particular, the linewidth can be made either independent of system size or scale extensively with it, while the photon statistics can be tuned from antibunched or quantum to bunched. We further show that the role of the relative phase in controlling the interference can alternatively be played by the coherent interaction. By tuning the interaction strength together with the pump rate, one can access the same regimes as in the dissipation-only model. In addition, coherent interactions stabilize regimes of coherent emission with narrow linewidth, reminiscent of superradiant lasing. Our results illustrate how interference in partially driven collective systems provides a flexible mechanism for tailoring both spectral and statistical properties of light.
Controlling the photon statistics of light is paramount for quantum science and technologies. Recently, we demonstrated that transmitting resonant laser light past an ensemble of two-level emitters can result in a stream of single photons or excess photon pairs. This transformation is due to quantum interference between the transmitted laser light and the incoherently scattered photon pairs [Prasad et al., Nat. Photonics 14, 719 (2020)NPAHBY1749-488510.1038/s41566-020-0692-z]. Here, using the dispersion of the atomic medium, we actively control the relative quantum phase between these two components. We thereby realize a tunable two-photon interferometer and observe interference fringes in the normalized photon coincidence rate. When tuning the relative phase, the coincidence rate varies periodically, giving rise to a continuous modification of the photon statistics from antibunching to bunching. Beyond the fundamental insight that there exists a tunable quantum phase between incoherent and coherent light that dictates the photon statistics, our results lend themselves to the development of novel quantum light sources.
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 the photon statistics of an ensemble of coherently driven non-interacting two-level atoms in the weak driving regime. As it turns out, the system displays unique emission characteristics that are strongly in contrast to the emission of classical oscillating dipoles. By deriving the second-order autocorrelation function, we show that extraordinary two-photon correlations are obtained, ranging from strong antibunching to superbunching. These features are enhanced by disorder in the emitter positions, and the control parameter is the number of excitations in the system. We observe the appearance of bunching and antibunching when the light is scattered by the atoms predominantly coherently, i.e., mimicking classical Rayleigh scattering, whereas thermal photon statistics is obtained when the light is scattered via spontaneous decay, a well-known quantum effect. The underlying mechanism is the interplay between coherent scattering, which exhibits spatial fluctuations due to interference, and dissipation in the form of isotropic spontaneous decay.
Superradiant lasers promise continuous, narrow-linewidth coherent emission at the bare atomic transition frequency, enabling frequency references of exceptional precision. Recent experiments have advanced the field, but achieving truly continuous operation remains technically challenging. Here we propose an alternative route to an active optical frequency reference with fewer emitters using all-to-all dipole-dipole interactions mediated by a nanophotonic waveguide. We show that selectively pumping only a sub-ensemble of emitters, rather than the full ensemble, substantially improves emission characteristics. The collective interactions with unpumped emitters provide narrowband frequency selection and establish an effective feedback mechanism analogous to the role of a macroscopic cavity. We find directional superradiant emission with strongly phase-synchronized emitter correlations and a narrow output spectrum close to the bare emitter resonance. Our results demonstrate a strong metrological gain from selective partial pumping of quantum emitters with the second-order intensity correlation g(2)(0)≃1, indicating reduced equal-time intensity fluctuations, and open a route to waveguide-based optical frequency references using small clock-atom ensembles for chip-scale precision metrology.
We report nonclassical aspects of the collective behavior of two atoms in a cavity by investigating the photon statistics and photon distribution over a very broad domain of parameters. Starting with the dynamics of two atoms radiating in phase into the cavity, we study the photon statistics for arbitrary interatomic phases as revealed by the second-order intensity correlation function at zero time, g(2)(0), and the Mandel Q parameter. We find that the light field can be tuned from antibunched to (super-)bunched as well as nonclassical to classical behavior by merely modifying the atomic position. The highest nonclassicality in the sense of the smallest Q parameter is found when spontaneous emission, cavity decay, coherent pumping, and atom-cavity coupling are of comparable magnitude. We introduce a quantum version of the negative binomial distribution with its parameters directly related to Q and g(2)(0) and discuss its range of applicability. We also examine the Klyshko parameter, which highlights the nonclassicality of the photon distribution.
Superradiant (SR) lasers store optical coherence in the atomic medium rather than the cavity field, but the incoherent drive that sustains inversion imposes a trade-off: local pumping yields coherent light at a rate that grows linearly with the atom number N, heating the medium through photon recoil, whereas fully collective pumping removes this scaling but limits the emission to partial coherence. We interpolate between these limits employing a spatially correlated pump on a chain of N two-level atoms, with rates decaying with distance between atoms as a power law of exponent α. To study systems beyond the reach of exact solutions, we employ the Truncated Wigner Approximation (TWA), whose independent trajectories are ideally suited to GPU parallelism. Harnessing this, we perform a full scan of the steady-state observables for up to 104 atoms at a computational cost that is practical. Our findings indicate that ultra-narrow emission persists for all α, while the coherence improves as the pump becomes shorter ranged, with g(2)→1 surviving at least down to α≈1, indicating that fully coherent light thus does not require local pumping. The drive strength needed for lasing is reduced by a factor N1−α for α<1, and by logN as α→1, parametrically suppressing recoil heating; notably, α=1 matches the far-field envelope of dissipative couplings in free space. The correlation range of the pump thus acts as a knob trading drive intensity, and the heating it causes, against optical coherence.