One aspect of solid-state photonic devices that distinguishes them from their atomic counterparts is the unavoidable interaction between system excitations and lattice vibrations of the host material. This coupling may lead to surprising departures in emission properties between solid-state and atomic systems. Here we predict a striking and important example of such an effect. We show that in solid-state cavity quantum electrodynamics, interactions with the host vibrational environment can generate quantum cavity-emitter correlations in regimes that are semiclassical for atomic systems. This behaviour, which can be probed experimentally through the cavity emission properties, heralds a failure of the semiclassical approach in the solid-state, and challenges the notion that coupling to a thermal bath supports a more classical description of the system. Furthermore, it does not rely on the spectral details of the host environment under consideration and is robust to changes in temperature. It should thus be of relevance to a wide variety of photonic devices.
One aspect of solid-state photonic devices that distinguishes them from their atomic counterparts is the unavoidable interaction between system excitations and lattice vibrations of the host material. This coupling may lead to surprising departures in emission properties between solid-state and atomic systems. Here we predict a striking and important example of such an effect. We show that in solid-state cavity quantum electrodynamics, interactions with the host vibrational environment can generate quantum cavity-emitter correlations in regimes that are semiclassical for atomic systems. This behaviour, which can be probed experimentally through the cavity emission properties, heralds a failure of the semiclassical approach in the solid-state, and challenges the notion that coupling to a thermal bath supports a more classical description of the system. Furthermore, it does not rely on the spectral details of the host environment under consideration and is robust to changes in temperature. It should thus be of relevance to a wide variety of photonic devices.
Strong coupling between a quantum system and its many-body environment is becoming an increasingly important topic for many branches of physics. Numerous systems of experimental and technological relevance demonstrate strong system-environment coupling, leading to complex dynamical behaviour. This thesis is concerned with two particular examples of such systems, namely quantum dots (QDs) and excitonic energy transfer (EET) in molecular systems. Traditional quantum optics treatments are often insufficient to describe the transient, steady state, and optical properties of QDs due to system-environment correlations. In contrast, we present a modified theory of quantum optics capable of capturing the influence of a thermal environment on the behaviour of QDs. Using this framework we demonstrate a striking departure of the emission spectra and photon measurement statistics of a classically driven QD when compared to an analogous atomic system. Furthermore, in contradiction to accepted notions of decoherence and dissipation, we show that the interaction between a QD and its thermal environment induces non-classical light-matter correlations in an otherwise semi-classical regime of cavity quantum electrodynamics. Away from QDs, we develop the reaction coordinate (RC) formalism to describe the dynamics of a system coupled to a low frequency environment — a regime important to EET systems. We do so by identifying and incorporating important environmental degrees of freedom into an enlarged system Hamiltonian. Uniquely, this approach gives insight directly into the dynamical evolution of the environment and correlations accumulated between the system and environment. Furthermore, it is demonstrated that these corre- lations persist into the steady state, generating non-canonical equilibrium states of the system and environment. We then apply the RC model to describe EET in a molecular dimer, highlighting the effect that under- and over-damped environments have on the excitation dynamics. In doing so, we show interactions between the dimer and a structured environment can significantly enhance the energy transfer rate.
Suitability of solid-state platforms as sources of N-photon bundles
N-photon bundles constitute a class of highly nonclassical quantum states of light. They are a specific type of photon emission, where light quanta are released from a cavity only in groups of N particles with a characteristic photon number statistics that may be taken as their fingerprint. We consider two solid-state cavity quantum electrodynamics (cQED) systems in terms of their suitability as emitters of N-photon bundles. As one example, we consider a semiconductor quantum-dot--microcavity system coupled to longitudinal acoustic phonons. There, we find the environmental influence to be detrimental to the emission of N-photon bundles. The other example is a superconducting qubit inside a microwave resonator. In these systems, pure dephasing is not important and an experimentally feasible parameter regime is found, where bundle emission can be observed.
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”).
Solid state-based light emitters such as semiconductor quantum dots (QDs) have been demonstrated to be versatile candidates to study the fundamentals of light–matter interaction. In contrast to optics with isolated atomic systems, in the solid-state dissipative processes are induced by the inherent coupling to the environment and are typically perceived as a major obstacle toward stable performances in experiments and applications. In this theoretical model study we show that this is not necessarily the case. In fact, in certain parameter regimes, the memory of the solid-state environment can enhance coherent quantum optical effects. In particular, we demonstrate that the non-Markovian coupling to an incoherent phonon bath can exhibit a stabilizing effect on the coherent QD cavity-quantum electrodynamics by inhibiting irregular oscillations and allowing for regular collapse and revival patterns. For self-assembled GaAs/InAs QDs at low photon numbers we predict dynamics that deviate dramatically from the well-known atomic Jaynes–Cummings model. Even if the required sample parameters are not yet available in recent experimental achievements, we believe our proposal opens the way to a systematic and deliberate design of photon quantum effects via specifically engineered solid-state environments.
Light is often characterized only by its classical properties, like intensity or coherence. When looking at its quantum properties, described by photon correlations, new information about the state of the matter generating the radiation can be revealed. In particular the difference between independent and entangled emitters, which is at the heart of quantum mechanics, can be made visible in the photon statistics of the emitted light. The well-studied phenomenon of superradiance occurs when quantum-mechanical correlations between the emitters are present. Notwithstanding, superradiance was previously demonstrated only in terms of classical light properties. Here, we provide the missing link between quantum correlations of the active material and photon correlations in the emitted radiation. We use the superradiance of quantum dots in a cavity-quantum electrodynamics laser to show a direct connection between superradiant pulse emission and distinctive changes in the photon correlation function. This directly demonstrates the importance of quantum-mechanical correlations and their transfer between carriers and photons in novel optoelectronic devices.
Strong quantum correlations in matter are responsible for some of the most extraordinary properties of materials, from magnetism to high-temperature superconductivity, but their integration in quantum devices requires a strong, coherent coupling with photons, which still represents a formidable technical challenge in solid state systems. In cavity quantum electrodynamics, quantum gases such as Bose-Einstein condensates or lattice gases have been strongly coupled with light. However, neither Fermionic quantum matter, comparable to electrons in solids, nor atomic systems with controlled interactions, have thus far been strongly coupled with photons. Here we report on the strong coupling of a quantum-degenerate unitary Fermi gas with light in a high finesse cavity. We map out the spectrum of the coupled system and observe well resolved dressed states, resulting from the strong coupling of cavity photons with each spin component of the gas. We investigate spin-balanced and spin-polarized gases and find quantitative agreement with ab initio calculation describing light-matter interaction. Our system offers complete and simultaneous control of atom-atom and atom-photon interactions in the quantum degenerate regime, opening a wide range of perspectives for quantum simulation.