Summary form only given. Light-matter interaction has been the subject of numerous investigations both in atomic and semiconductor physics. Experimentally, strong light-matter coupling regime can be achieved in a cavity. The photon is confined and in resonance with the electronic transition of the exciton or atom embedded in the cavity. As a result, photons emitted from the cavity (due to excitonic or atomic transition) will be reabsorbed and re-emitted a number of times before exiting the cavity. Direct spectroscopic measurements show two resonances split by the so-called vacuum Rabi splitting (VRS). This interaction can be modeled by a semiclassical model describing the electronic transition and the photon as two coupled Lorentzian oscillators. When in resonance their frequency is spit by the so-called vacuum Rabi splitting. In the present work we report for the first time to our knowledge, VRS of atoms in a monolithic Fabry-Perot cavity. The photon is confined in an Er/sub 2/O/sub 3/ layer embedded in a monolithic Si-SiO/sub 2/ Fabry-Perot cavity.
Summary form only given. Light-matter interaction has been the subject of numerous investigations both in atomic and semiconductor physics. Experimentally, strong light-matter coupling regime can be achieved in a cavity. The photon is confined and in resonance with the electronic transition of the exciton or atom embedded in the cavity. As a result, photons emitted from the cavity (due to excitonic or atomic transition) will be reabsorbed and re-emitted a number of times before exiting the cavity. Direct spectroscopic measurements show two resonances split by the so-called vacuum Rabi splitting (VRS). This interaction can be modeled by a semiclassical model describing the electronic transition and the photon as two coupled Lorentzian oscillators. When in resonance their frequency is spit by the so-called vacuum Rabi splitting. In the present work we report for the first time to our knowledge, VRS of atoms in a monolithic Fabry-Perot cavity. The photon is confined in an Er/sub 2/O/sub 3/ layer embedded in a monolithic Si-SiO/sub 2/ Fabry-Perot cavity.
Semiconductor quantum microcavities are interesting physical systems in which fundamental interactions between light and excitons can be explored. For example, in the weak - coupling limit, modified excitonic spontaneous emission can be observed. In the strong-coupling limit, the cavity field modes and the quantum well exciton modes become coupled; the normal modes of the system are "cavity-polaritons" [1,2]. For in-plane wavevectors k// near zero, the normal modes are split by the dipole coupling between the excitons and the cavity vacuum field. This splitting is often referred to as a vacuum-Rabi splitting (VRS), as it has the same physical origin as the VRS observed in the interactions of atoms with single-mode cavities. The physical system in this work consists of a λ planar microcavity formed by two distributed-Bragg reflectors, with five GaAs quantum wells situated in the center of the cavity. In all the experiments described here, the exciton and cavity modes are on resonance (the low-field VRS is 6 meV for this sample).
If an excited atom is put in between high-reflectance mirrors, the light emitted by the atom can be bounced back and be re-absorbed and be re-emitted, again and again until the light leaks out of the mirrors or is re-emitted into a wrong direction. This coherent oscillation between atom and light, called vacuum Rabi oscillation, results from interference between two superposition states of the atom and the photon, which have different energies or frequencies, or vacuum Rabi splitting. The vacuum Rabi oscillation and splitting demonstrate the quantum nature of light. They also provide single-photon non-linearity for photonic applications. In recent years, these effects have been considered particularly useful for quantum information processing [1] since the oscillation presents a natural mechanism for information exchange between a stationary quantum bit carried by the atom and a flying quantum bit carried by the photon, making scalable and distributed quantum computing possible. Realization of the vacuum Rabi oscillation and splitting, however, is highly non-trivial. It requires the so-called strong coupling condition, that is, the exchange between the atom and the photon must be faster than the photon leaks out of the space enclosed by the mirrors, i.e. the cavity, and faster than the atom emits the light into a wrong direction. The technique to realize the strong coupling condition is to make the cavity small so that the photon is bounced back more frequently to the atom and to make the mirrors more reflective so that the photon can be bounced more times. That means to decrease the cavity volume V and to increase the quality factor Q. Remarkable progresses have been made to make optical microcavities with small V and high Q, facilitating observation of vacuum Rabi oscillation and splitting in highly dissipative solid-state systems [2,3]. However, there is no systematic method to reduce V/Q—the key factor for realizing strong coupling (see Fig. 1a). The reason appears to be fundamental. When the size of a cavity is made as small as comparable to the light wavelength, small deformation of the cavity would result in large evanescent wave and hence photon leakage [4]. (a) An atom and a small cavity have strong coupling but the cavity leakage is also strong. A large cavity has small photon leakage but its coupling to the atom is small (so emission goes to free space). The atom and the large cavity can have strong coupling, with photons exchanged through but not occupying the small cavity—using the quantum tunneling effect. (b) In the classical world, two lower players have to provide sufficient energy to pass the ball through the higher player. (c) In the quantum world, the two lower players can pass balls through the wall via the higher players but with energy of the balls insufficient to reach the higher player. A recent proposal by [5] provides a general solution, using a divide-and-conquer strategy. A small cavity with relatively low Q is used to enhance the interaction between the emitter and the photon, while the photon stays in a large cavity with high Q. [5] demonstrate the strong coupling by showing Rabi splitting, Rabi oscillation, and single-photon non-linearity of the system. The scheme at the first sight does not seem to work since the emitter has no contact with the high-Q large cavity and if the photon enters the small cavity, it would leak out. The clever point of the scheme is: in the quantum mechanical world, the photon can interact with the emitter without occupying the small cavity! Similar to the ball game in Fig. 1b, a classical particle needs to have sufficient energy to pass a barrier. The small cavity is designed to have a frequency higher than those of the emitter and the large cavity, which would prevent the emitted photons entering the large cavity. However, quantum ball games allow tunneling of a barrier (Fig. 1c). So the emitter and the large cavity can indeed exchange photons. The small cavity would not be occupied since its frequency is not right, which prevents photon leakage. It looks the scheme applies generally to all types of photonic systems—photonic crystals, microspheres, microtoroids, etc. Considering the simplicity of the scheme, we expect applications be found soon.
Recently, several research groups have reported investigations of vacuum-field Rabi splittings (VRS) in the linear response of strongly coupled semiconductor microcavities [1-4]. We have previously reported on the dynamics of time-domain vacuum Rabi oscillations, which are most easily understood in the framework of cavity exciton-polaritons, in which the in-plane momentum k|| is conserved [2], so that at each k|| a single cavity mode interacts with only a single mode of the electromagnetic field (Jaynes-Cummings model). In high Q semiconductor microcavities, the strong coupling between two-dimensional excitons and planar distributed- Bragg-reflector cavity modes results in several-meV splittings observable in the reflectivity or absorption spectrum. In the low excitation regime, the VRS is independent of light intensity incident on the cavity, since the vacuum-Rabi frequency exceeds the externally-driven Rabi frequency (in which case the Jaynes-Cummings model is equivalent to the linear dispersion of the coupled exciton-cavity system). As the incident light intensity is increased, two different effects may be expected to contribute to the nonlinear response. First, as long as the excitonic absorption is equivalent to a two-level system, higher-lying states of the Jaynes-Cummings ladder might be observable. Second, at high intensity phase-space filling and Coulomb screening of the exciton states results in a reduced oscillator strength which leads to a reduced VRS; this effect has no analogue in the case of atom-cavity systems. In this paper, we apply several ultrafast nonlinear techniques to investigate the nonlinear response of semiconductor microcavities.
A single atom in a cavity is the model system of cavity quantum electrodynamics (CQED). The strong coupling regime between the atom and cavity-confined photon corresponds to the reversible exchange of energy between the two modes, and underpins a wide range of CQED phenomena with applications in quantum information science, including for example as quantum logic gates and as sources of entangled states. An important advance was achieved recently when strong coupling between excitons and cavity photons was reported for the first time for localized quantum dots (QDs) in micron-size solid state cavities. This has significance in terms of scalability and integration with other optical devices, and could lead to the emergence of "quantum optics on a chip" technology. However the results presented so far for quantum dots are in the linear regime, corresponding to coupling to the vacuum field (vacuum Rabi splitting); they are not a true QED effect and can equally well be described by classical physics as the coupling between two oscillators. In this paper, we present evidence for a purely quantum phenomenon for the QD/cavity photon system, namely the increase in splitting of the levels when the mean number of photons in the cavity is increased. This corresponds to non-linearities on the single-photon scale: the presence of a single excitation in the cavity changes the level structure, affecting the emission energies for a second photon. Such results are a first step in demonstrating the promise of quantum dots for CQED applications.
When an atom is strongly coupled to a cavity, the two systems can exchange a single photon through a coherent Rabi oscillation. This process enables precise quantum-state engineering and manipulation of atoms and photons in a cavity, which play a central role in quantum information and measurement. Recently, a new regime of cavity QED was reached experimentally where the strength of the interaction between light and artificial atoms (qubits) becomes comparable to the atomic transition frequency or the resonance frequency of the cavity mode. Here we show that this regime can strongly modify the concept of vacuum Rabi oscillations, enabling multiphoton exchanges between the qubit and the resonator. We find that experimental state-of-the-art circuit-QED systems can undergo two- and three-photon vacuum Rabi oscillations. These anomalous Rabi oscillations can be exploited for the realization of efficient Fock-state sources of light and complex entangled states of qubits.
Vacuum Rabi oscillations between a single photon and a single spin demonstrate the capability of harnessing light-matter interaction at the level of a single quantum of energy. Since the observation of strong spin-photon coupling in gate-defined quantum dots, probing this interaction in the time-domain has been a major objective. Here, we carefully engineer a device composed of two spatially separated double quantum dots hosting single electron spin qubits and a superconducting cavity to accommodate microwave photons. We observe multiple vacuum Rabi oscillations between each spin qubit and the cavity. By concatenating vacuum Rabi oscillations involving the two spins, an energy excitation in one qubit can be emitted as a photon and then transferred to the other qubit. When a single photon is emitted, the cavity is prepared in a Fock state, leading to an accelerated vacuum Rabi frequency. These results serve as building blocks not only in exploring light-matter interactions, but also in interfacing semiconductor spin qubits to photonic links.