We propose and investigate a scheme for the steady-state emission of quantum-correlated, telecom-band light from a single multilevel atom. By appropriately tuning the frequency of a pair of lasers, a two-photon transition is continually driven to an atomic excited state that emits photons at the desired wavelength. We show that resonantly coupling a cavity mode to the telecom transition can enhance the rate of emission while retaining the antibunched counting statistics that are characteristic of atomic light sources. We also explore coupling a second, independent cavity mode to the atom, which increases the telecom emission rate and introduces quantum correlations between the cavity modes. A model for the hyperfine structure of a single cesium atom is then described and numerically integrated to demonstrate the viability of implementing the scheme with a modern cavity QED system.
We propose and investigate a scheme for the steady-state emission of quantum-correlated, telecom-band light from a single multilevel atom. By appropriately tuning the frequency of a pair of lasers, a two-photon transition is continually driven to an atomic excited state that emits photons at the desired wavelength. We show that resonantly coupling a cavity mode to the telecom transition can enhance the rate of emission while retaining the antibunched counting statistics that are characteristic of atomic light sources. We also explore coupling a second, independent cavity mode to the atom, which increases the telecom emission rate and introduces quantum correlations between the cavity modes. A model for the hyperfine structure of a single cesium atom is then described and numerically integrated to demonstrate the viability of implementing the scheme with a modern cavity QED system.
We propose schemes for steady-state emission of quadrature-squeezed light from a single-atom cavity quantum electrodynamics system. Two effective atom-cavity interaction models are suggested, motivated by correlated photon-pair emissions and multiphoton coherences that manifest themselves as squeezing of light emitted from the cavity. We consider idealized models to examine the mechanisms and optimal regimes for generating squeezed light. We also demonstrate realizations of these models based on both single 87Rb and 133Cs atoms, using combinations of laser- and laser-plus-cavity-driven Raman transitions between magnetic sublevels in a single ground hyperfine state. We show that these systems can in principle produce a much stronger level of squeezing than has previously been possible from a single-atom source.
The steady-state transmission spectrum of a cavity with two modes of orthogonal polarization strongly coupled to a single atom with multiple Zeeman states is computed. Effects due to cavity birefringence and atomic ac-Stark shifts are included. The transmission spectrum is compared to experimental results for a single Cesium atom trapped via an intracavity FORT in a Fabry-Perot cavity. The excellent agreement of the theory with the data is used to infer the distribution of the position of the trapped atom.
The intensity correlation function of this system is also calculated, and found to be strongly antibunched and sub-Poissonian. This effect is explained in terms of photon blockade, based on the structure of the lowest energy eigenvalues. Experimental results confirm the strong nonlinearity at the single-photon level.
We present theoretical predictions of the weak field spectra of microtoroid and photonic bandgap cavities strongly coupled to the D2 transition of single Cesium atoms. These calculations include all hyperfine and Zeeman states of the transition and model the cavity as a single-mode, linearly polarized resonator.
Finally, we outline a technique for using multiple hyperfine and Zeeman levels of a single atom in a strongly coupled atom-cavity system to generate polarized single photons on demand in a well-defined temporal mode via adiabatic passage. The technique is insensitive to cavity birefringence and only weakly sensitive to atomic position. Variations of this technique for generating entanglement of photon polarization and atomic Zeeman state are also discussed.
Quantum information technology strongly relies on coupling of optical photons with narrowband quantum systems, such as quantum dots, color centers, and atomic systems. This coupling requires matching the optical wavelength and bandwidth to the desired system, which presents a considerable problem for most available sources of quantum light. Here we demonstrate coupling of alkali dipole transitions with a tunable source of photon pairs. Our source is based on spontaneous parametric down-conversion in a triply-resonant whispering-gallery mode resonator. For this, we have developed novel wavelength tuning mechanisms, which allow for a coarse tuning to either cesium or rubidium wavelength with subsequent continuous fine-tuning to the desired transition. As a demonstration of the functionality of the source, we performed a heralded single photon measurement of the atomic decay. We present a major advance in controlling the spontaneous down-conversion process, which makes our bright source of single photons now compatible with a plethora of narrow-band resonant systems.
Quantum repeaters rely on an interfacing of flying qubits with quantum memories. The most common implementations include a narrowband single photon matched in bandwidth and central frequency to an atomic system. Previously, we demonstrated the compatibility of our versatile source of heralded single photons, which is based on parametric down-conversion in a triply-resonant whispering-gallery mode resonator, with alkaline transitions [Schunk et al., Optica 2, 773 (2015)]. In this paper, we analyze our source in terms of phase matching, available wavelength-tuning mechanisms, and applications to narrow-band atomic systems. We resonantly address the D1 transitions of cesium and rubidium with this optical parametric oscillator pumped above its oscillation threshold. Below threshold, the efficient coupling of single photons to atomic transitions heralded by single telecom-band photons is demonstrated. Finally, we present an accurate analytical description of our observations. Providing the demonstrated flexibility in connecting various atomic transitions with telecom wavelengths, we show a promising approach to realize an essential building block for quantum repeaters.
Alkali atoms are a workhorse in quantum optics, owing to the relative simplicity of their elec- tronic structure, which affords remarkable and reliable control over their behaviour. In particular, the ability to probe and manipulate alkali atoms with electromagnetic fields provides an important resource for studying and harnessing their fundamental properties. This thesis explores interac- tions between alkali atoms and light, to uncover ways of exploiting their properties for a variety of purposes. The main results of the thesis are divided into three main parts, as we detail below. Firstly, we develop theoretical models of effective interactions between alkali atoms in cavity quantum electrodynamics (cavity QED) systems, building on previous work in this area. The models are based on Raman transitions between the Zeeman sublevels of hyperfine ground states in an alkali atom. We show that by coupling light to both D-lines of the atom simultaneously, a versatile effective Hamiltonian can be realised with terms that can be manipulated independently. Additionally, we show that, with careful arrangement of the fields, the effective interactions can persistinsteadystate, continuouslyoutputtinglightthatcarriessignaturesoftheinteraction. These models reveal novel mechanisms for generating nonclassical states of light, with the potential for producing Wigner-negative and quadrature-squeezed light from single-atom sources. We simulate full hyperfine structure models of the interactions, using parameters inspired by modern cavity QED architectures, to demonstrate the robustness of their implementation in a real atom. Secondly, we explore nonclassical photon statistics through specific configurations of single- atom nanofibre cavity QED systems. By coupling an alkali atom to nanofibre cavity modes, we demonstrate antibunching and strong two-mode correlations, showcasing the versatility of these systems for generating nonclassical photon statistics. We consider two schemes for their photon correlations, each based on coupling two cavity modes to a single atom. First, the generation of nonclassical light at telecom-band wavelengths is studied, using cascaded transitions within a caesium atom. The atomic states are chosen such that one of the cavity modes is resonant at a telecom-band frequency. Second, we explore the coupling an adjacent pair of resonances of a long cavity to a strongly-driven atom. The characteristic emission spectrum is matched to the free spectral range of the cavity. In both cases, we consider simplified models to understand the critical behaviour of the systems, and then use full hyperfine structure models to examine the viability of implementing them in modern nanofibre cavity QED systems. Finally, we present a model for the interaction of light with a thermal cloud of Rydberg atoms. The random thermal motion of a room-temperature gas necessitates ensemble averaging in order to predict the absorption spectrum for a probe beam. The effective model that we develop accurately predicts the absorption profile of electromagnetically-induced transparency in the atomic cloud, offering insights for experiments in atom-based sensing of microwave-frequency electromagnetic fields. Overall, this thesis enhances the fundamental understanding of alkali atom-light interactions and adds to the ever-growing quantum-optical toolbox.