An optical nanoantenna and adjacent atomic systems are strongly coupled when an excitation is repeatedly exchanged between these subsystems prior to its eventual dissipation into the environment. It remains challenging to reach the strong-coupling regime but it is equally rewarding. Once they are achieved, promising applications such as signal processing at the nanoscale and at the single-photon level would immediately become available. Here, we study such hybrid configuration from different perspectives. The configuration we consider consists of two identical atomic systems, described in a two-level approximation, which are strongly coupled to an optical nanoantenna. First, we investigate when this hybrid system requires a fully quantum description, and we provide a simple analytical criterion. Second, a design for a nanoantenna is presented that enables the strong-coupling regime. In addition to a vivid time evolution, the strong coupling is documented in experimentally accessible quantities, such as the extinction spectra. The latter are shown to be strongly modified if the hybrid system is weakly driven and operates in the quantum regime. We find that the extinction spectra depend sensitively on the number of atomic systems coupled to the nanoantenna.
An optical nanoantenna and adjacent atomic systems are strongly coupled when an excitation is repeatedly exchanged between these subsystems prior to its eventual dissipation into the environment. It remains challenging to reach the strong-coupling regime but it is equally rewarding. Once they are achieved, promising applications such as signal processing at the nanoscale and at the single-photon level would immediately become available. Here, we study such hybrid configuration from different perspectives. The configuration we consider consists of two identical atomic systems, described in a two-level approximation, which are strongly coupled to an optical nanoantenna. First, we investigate when this hybrid system requires a fully quantum description, and we provide a simple analytical criterion. Second, a design for a nanoantenna is presented that enables the strong-coupling regime. In addition to a vivid time evolution, the strong coupling is documented in experimentally accessible quantities, such as the extinction spectra. The latter are shown to be strongly modified if the hybrid system is weakly driven and operates in the quantum regime. We find that the extinction spectra depend sensitively on the number of atomic systems coupled to the nanoantenna.
Attempting to implement quantum information related applications utilizing atoms and photons, as they naturally form quantum systems supporting superposition states, hybrid quantum plasmonic systems emerged in the past as a platform to study and engineer light-matter interaction. This platform combines the unrivaled electromagnetic field localization of surface plasmon polaritons, boosting the light-matter coupling rate, with the tremendous integration potential of truly nanoscale structures, and both the significant emission rates of nanoantennas and photonic transmission velocities. In this work, a classical description of surface plasmon polaritons is combined with a light-matter interaction model based on a cavity quantum electrodynamical formalism. The resulting composite semi-classical method, introduced and described in this thesis, provides efficient and versatile means to simulate the dynamical behavior of radiative atomic transitions coupled to plasmonic cavity modes in the weak incoherent coupling regime. Both the emission into the far field and various dissipation mechanisms are included by expanding the model to an open quantum system. The variety of light-matter interaction applications that can be modeled with the outlined method is indicated by the four different exemplary scenarios detailed in the application chapter of this thesis. The classical description of localized surface plasmon polaritons is benchmarked by reproducing the experimental measurements of the molecular fluorescence manipulation through optical nanoantennas in a collaborative effort with experimental partners. Furthermore, in the weak light-matter coupling regime, the potential of achieving a higher nanoantenna functionality and simultaneously realizing more elaborate quantum dynamics is revealed by the three remaining applications. Each pivotally involving a bimodal nanoantenna and demonstrating different quantum optical phenomena, the implementation of cavity radiation mode conversion, non-classical cavity emission statistics, and non-classical cavity emission properties is shown and described in the application chapter.
Resonance interaction between a molecular transition and a confined electromagnetic field can reach the coupling regime where coherent exchange of energy between light and matter becomes reversible. In this case, two new hybrid states separated in energy are formed instead of independent eigenstates, which is known as Rabi splitting. This modification of the energy spectra of the system offers new possibilities for controlled impact on various fundamental properties of coupled matter (such as the rate of chemical reactions and the conductivity of organic semiconductors). To date, the strong coupling regime has been demonstrated in many configurations under different ambient conditions. However, there is still no comprehensive approach to determining parameters for achieving the strong coupling regime for a wide range of practical applications. In this review, a detailed analysis of various systems and corresponding conditions for reaching strong coupling is carried out and their advantages and disadvantages, as well as the prospects for application, are considered. The review also summarizes recent experiments in which the strong coupling regime has led to new interesting results, such as the possibility of collective strong coupling between X-rays and matter excitation in a periodic array of Fe isotopes, which extends the applications of quantum optics; a strong amplification of the Raman scattering signal from a coupled system, which can be used in surface-enhanced and tip-enhanced Raman spectroscopy; and more efficient second-harmonic generation from the low polaritonic state, which is promising for nonlinear optics. The results reviewed demonstrate great potential for further practical applications of strong coupling in the fields of photonics (low-threshold lasers), quantum communications (switches), and biophysics (molecular fingerprinting).
We have studied a mathematical framework of higher-order multipole fields in the vicinity of optical nanoantennas. We have exemplified at suitably chosen Nanoantennas i.e. a Nano antenna which strongly enhances the quadruple field. The modification of excitation rates in quantum mechanical systems due to this quadrupolar enhancement was studied. The hybrid system consisting of an optical Nano antenna and a quantum mechanical three level system was studied in detail. A properly designed Nano-antenna can excite dipole for bidden transitions in three level systems due to the enhanced higher order multipole fields. The dynamics of the system is strongly altered by the presence of the nanoantenna and cannot be done by the quadrupolar enhancement alone. This can be achieved by enhancing higher order multipole fields near the antenna. A quadrupole transition as the dominant excitation channel in a three level system was considered. It was found that the enhancement of this transition significantly intensify subsequent emission processes with respect to altered emission characteristics. The effects depend on geometrical parameters; the properties of the optical nanoantenna can be tailored and hence allowed for direct implementations in spectroscopies schemes. The obtained results were found in good agreement with previously obtained results.
Highly integrated single-photon sources are key components in future quantum-optical circuits. Whereas the probabilistic generation of single photons can routinely be done by now, their triggered generation is a much greater challenge. Here, we describe the triggered generation of single photons in a hybrid plasmonic device. It consists of a lambda-type quantum emitter coupled to a multimode optical nanoantenna. For moderate interaction strengths between the subsystems, the description of the quantum optical evolution can be simplified by an adiabatic elimination of the electromagnetic fields of the nanoantenna modes. This leads to an insightful analysis of the emitter's dynamics, entails the opportunity to understand the physics of the device, and to identify parameter regimes for a desired operation. Even though the approach presented in this work is general, we consider a simple exemplary design of a plasmonic nanoantenna, made of two silver nanorods, suitable for triggered generation of single photons. The investigated device realizes single photons, triggered, potentially at high rates, and using low device volumes.
Optically controlled dipole-dipole interaction at submicrometers and subwavelength scales leads to many interesting phenomenon and remarkable potential applications in quantum optics, condensed matter physics, and today’s micro-devices. In this dissertation, we study the applications of quantum optical coherence to nano-optics in the following systems and aspects. On the one hand, chiral metamaterials has been previously reported as excellent candidates to realize both attractive and repulsive Casimir forces, where the existence of a repulsive Casimir force depends upon the strength of the chirality. On the other hand, nanoscale integration of metal nanoparticles and semiconductors is particularly interesting because the strengths of both materials are combined in such a hybrid system. In the first part of this work, we proposed a technical scheme to coherently control of the Casimir interaction energy with two identical chirality mediums. We took explicit caution regarding the requirements of passivity and causal response of the materials, since these requirements are essential for the application of the Lifshitz formula. The rare-earth metals’ atomic species, for instance, dysprosium, is proposed as an applicable medium for the forthcoming studies of possible experimental implementation of our technique. Secondly, we fully investigated the coherent control of the quantum optical properties of spontaneous emission spectra of a semiconductor quantum dot coupled to a metallic nanoparticle. The properties of the spontaneous emission spectra of such a system are studied in detail with and without involving the coherent field. The Rabi splitting effect in the spectrum emitted by the quantum dot under particular conditions is predicted for different sizes of the metal nanoparticles. We show that the spontaneous emission spectra of the transition coupled to surface plasmons may be further modified by adjusting the external coherent control on the adjacent transitions. In the third part, we propose a robust protocol to study the entanglement generation in a hybrid structure consisting of two quantum dots in the proximity of a metallic nanoshell. The entanglement arises impulsively due to common coupling to the plasmonic nanostructure, without demanding postselective measurement or mediating the dissipative environment. The long-lived entangled states can be created deterministically by optimizing the shell thickness as well as the ratio of the distances between the quantum dots and the surface of the shell. The loss of the system is greatly reduced even when the quantum dots are ultraclose to the shell, which signifies a slow decay rate of the coherence information and longtime entanglement preservation.
In nanostructures where confinement of a light wave is manifested, the conditions of strong light–matter interaction become feasible. In this case, the approach based on the environment-sensitive probability of quantum transitions is no longer applicable. Instead, joint states of light and matter should be considered and their time evolution explored. The content of the previous Chapters 13 and 14 can then be treated as a perturbative description of light–matter interactions with a limited range of applicability. In this chapter a few representative examples are given where joint light–matter states bring an unprecedented flavor of nanophotonic engineering to frozen excited states for quantum memory devices and single photon sources for quantum computing. Cavity quantum electrodynamics in the strong coupling regime The regime of strong coupling of a quantum system with an electromagnetic field can be performed in a cavity with very high Q-factor, where light can survive for a reasonable time until it either leaves the cavity or dies through being absorbed by cavity imperfections. In a simplified picture, a photon once emitted stays within the cavity so long that it is absorbed again by the emitter (an imaginary two-level system, an atom or a quantum dot). Thus spontaneous emission appears to become reversible. In a more accurate presentation, an “atom+field” state develops which evolves via oscillations between the state | E , 0〉 (“excited atom, depleted cavity”) to the state | G , 1〉 (“de-excited atom, a photon in the cavity”).