Controllable sources of correlated photons are key enabling technologies for quantum communication, computation, and sensing. By providing precise control over photon correlations and phase at the single- and few-photon level, this work advances scalable quantum networks, secure communication protocols, and photonic quantum devices. Beyond information processing, correlated photons enable quantum-enhanced spectroscopy and imaging with unprecedented sensitivity under ultra-low-light conditions. The proposed research establishes a versatile platform at the intersection of atomic physics and quantum photonics, supporting emerging quantum technologies while training a highly skilled quantum workforce. We consider a Lambda-type three-level atom in a QED cavity. One atomic transition is driven by a classical field and the other transition is driven by the ”vacuum” field. The vacuum field can be strongly modified by the cavity, and in particular, the ”vacuum” field can have a chirped frequency modulation that it can be a part of adiabatic rapid passage together with classical drive field. The action of the classical and ”vacuum” or quantum field can result in the generation of the quantum fields with controllable parameters. Such QED cavity can be used to generate strongly correlated quantum fields that can be of interest for quantum sensing, spectroscopy at the single photon level, quantum teleportation, and other applications for quantum information.
Controllable sources of correlated photons are key enabling technologies for quantum communication, computation, and sensing. By providing precise control over photon correlations and phase at the single- and few-photon level, this work advances scalable quantum networks, secure communication protocols, and photonic quantum devices. Beyond information processing, correlated photons enable quantum-enhanced spectroscopy and imaging with unprecedented sensitivity under ultra-low-light conditions. The proposed research establishes a versatile platform at the intersection of atomic physics and quantum photonics, supporting emerging quantum technologies while training a highly skilled quantum workforce. We consider a Lambda-type three-level atom in a QED cavity. One atomic transition is driven by a classical field and the other transition is driven by the ”vacuum” field. The vacuum field can be strongly modified by the cavity, and in particular, the ”vacuum” field can have a chirped frequency modulation that it can be a part of adiabatic rapid passage together with classical drive field. The action of the classical and ”vacuum” or quantum field can result in the generation of the quantum fields with controllable parameters. Such QED cavity can be used to generate strongly correlated quantum fields that can be of interest for quantum sensing, spectroscopy at the single photon level, quantum teleportation, and other applications for quantum information.
A sequence of single photons is emitted on demand from a single three-level atom strongly coupled to a high-finesse optical cavity. The photons are generated by an adiabatically driven stimulated Raman transition between two atomic ground states, with the vacuum field of the cavity stimulating one branch of the transition, and laser pulses deterministically driving the other branch. This process is unitary and therefore intrinsically reversible, which is essential for quantum communication and networking, and the photons should be appropriate for all-optical quantum information processing.
Summary form only given. In quantum information processing, a qubit is realised as a superposition of atomic or ionic eigenstates, or as a superposition of the states of a photon. A coupling between these different types of qubits is necessary to perform quantum operations or quantum transmissions, e.g. in a quantum network where single atoms or ions are entangled with individual photons. To generate such an entanglement in a controlled way, a triggered source for single photons, a photon pistol, will be needed. Our scheme will lead to the emission of one photon into a single, predetermined mode of the radiation field in response to a trigger event. This photon is emitted from an atom strongly coupled to a high-finesse optical cavity, and the trigger is a classical light pulse. The device combines cavity-QED with an adiabatic transfer technique. We consider a single lambda-type three-level atom being placed inside an empty cavity.
We propose a component-selective scheme for improving two-photon sources in a cavity-coupled two-atom system, where a single cavity mode interacts with two two-level atoms driven by phase-controlled classical fields of the same frequency. By controlling the atomic detunings and driving phase, the system can be tailored toward optimized cavity-field two-photon blockade or strongly correlated fluorescence photon-pair emission. When the two-cavity-photon component is enhanced, the cavity field exhibits optimized two-photon blockade with simultaneous suppression of unwanted one- and three-photon components at a comparable two-photon population. In another parameter regime, strongly correlated fluorescence photon pairs can also be generated from the two atoms by selecting the double-atomic-excitation component in the same two-excitation manifold. This approach provides a route toward high-quality and versatile two-photon sources, with potential applications in few-photon quantum optics and quantum information processing.
Strong coupling between light and matter has been demonstrated both in classical cavity quantum electrodynamics (QED) systems and in more recent circuit-QED experiments. This enables the generation of strong nonlinear photon-photon interactions at the single-photon level, which is of great interest for the observation of quantum nonlinear optical phenomena, the control of light quanta in quantum information protocols such as quantum networking, as well as the study of strongly correlated quantum many-body systems using light. Recently, strong coupling has also been realized in a variety of one-dimensional (1D) waveguide- QED experimental systems, which in turn makes them promising candidates for quantum information processing. Compared to cavity-QED systems, there are two new features in waveguide-QED: the existence of a continuum of states and the restricted 1D phase space, which together bring in new physical effects, such as the bound-state effects. This thesis consists of two parts: 1) understanding the fundamental interaction between local quantum objects, such as two-level systems and four-level systems, and photons confined in the waveguide; 2) exploring its implications in quantum information processing, in particular photonic quantum computation and quantum key distribution. First, we demonstrate that by coupling a two-level system (TLS) or three/fourlevel system to a 1D continuum, strongly-correlated photons can be generated inside the waveguide. Photon-photon bound states, which decay exponentially as a function of the relative coordinates of photons, appear in multiphoton scattering processes. As a result, photon bunching and antibunching can be observed in the photon-photon correlation function, and nonclassical light source can be generated on demand. In the case of an N-type four-level system, we show that the effective photon-photon interaction mediated by the four-level system, gives rise to a variety of nonlinear optical phenomena, including photon blockade, photon-induced tunneling, and creation of single-photon states and photon pairs with a high degree of spectral entanglement, all in the absence of a cavity. However, to enable greater quantum networking potential using waveguide- QED, it is important to study systems having more than just one TLS/qubit. We develop a numerical Green function method to study cooperative effects in a system of two qubits coupled to a 1D waveguide. Quantum beats emerge in photon-photon correlations, and persist to much longer time scales because of non-Markovian processes. In addition, this system can be used to generate a high-degree of long-distance entanglement when one of the two qubits is driven by an on-resonance laser, further paving the way toward waveguide-QED-based quantum networks. Furthermore, based on our study of light-matter interactions in waveguide- QED, we investigate its implications in quantum information processing. First, we study quantum key distribution using the sub-Possonian single photon source obtained by scattering a coherent state off a two-level system. The rate for key generation is found to be twice as large as for other sources. Second, we propose a new scheme for scalable quantum computation using flying qubits--propagating photons in a one-dimensional waveguide--interacting with matter qubits. Photonphoton interactions are mediated by the coupling to a three- or four-level system, based on which photon-photon -phase gates (Controlled-NOT) can be implemented for universal quantum computation. We show that high gate fidelity is possible given recent dramatic experimental progress in superconducting circuits and photonic-crystal waveguides. The proposed system can be an important building block for future on-chip quantum networks.
This thesis addresses challenges in the experimental realisation of optical quantum computing with atom-cavity platforms and develops techniques for experimental quantum control that generalise across a range of quantum modalities. Within the framework of cavity quantum electrodynamics (cQED), methods are developed and numerically validated for fast and precise control of single atoms to generate photonic states of interest. In particular, we consider the generation of high-repetition-rate n-photon bursts and time-bin entangled states. These photonic resources are essential for applications such as boson sampling, multi-photon interference, optical quantum computing, and quantum-enhanced metrology. Experimental improvements in coherent population transfer are demonstrated using adaptive pulse shaping with acousto-optic modulators. Beyond photon generation, the thesis introduces general-purpose pulse-level techniques, including pulse distortion correction, memory-efficient pulse compression, and machine learning-based optimisation. These methods are shown to be transferable to other platforms, such as neutral atom arrays and superconducting qubits. A particular contribution is the implementation of scalable pulse generation using fixed-point compressed pulse representations on FPGA hardware, achieving substantial memory savings while maintaining high fidelity in simulations of quantum operations. Additionally, reinforcement learning is presented as a powerful tool for optimising complex quantum dynamics, with state-of-the-art results demonstrated across various simulated systems. Throughout the thesis, theoretical developments are supported by numerical simulations and partial experimental validation, providing important insights for the development of future quantum technologies.
A recent experiment [H. S. Han et al., Phys. Rev. Lett. 127, 073604 (2021); see also accompanying online supplemental material] shows that when a three-level V-type atom with two closely lying upper states interacts with the same vacuum radiation field, its excited states enable vacuum-induced coupling (VIC) owing to the quantum interference between the spontaneous emission pathways. Here, we propose a feasible scheme for phase-engineered photon correlations in the presence of the VIC in an optical nanofiber (ONF) cavity quantum electrodynamics (QED) system. Specifically, we show that a phase-dependent strong photon antibunching with high brightness can be generated in the weak-coupling regime of light-atom interactions. This occurs because of the VIC, leading to both the destructive quantum interference between the different pathways for two-photon excitation and the total closed-loop coupling phase. Different types of purely quantum correlations, such as single- and two-photon blockades, can occur by properly tuning the total closed-loop coupling phase adhering on the VIC, and the switch from photon blockade to photon induced tunneling is revealed as well. On the other hand, the strong photon antibunching can be achieved in a broad driving frequency range, which relaxes the requirement for the driving frequency in the ONF cavity QED system. In addition, we compare the analytical and numerical results of the second- and third-order intensity correlation functions, and they are in good agreement. The present study may provide an alternative route to manipulate the few-photon states and have potential applications in single-photon sources and quantum communications.