Quantum dots coupled to high-Q cavities can induce optical transparency that provides photon switching capabilities. However, the optical access to such cavities can be inefficient due to their restrictive optical modes. Here, we observe optical transparency of ∼ 80% induced by a quantum dot coupled to a cavity with an efficient optical access, the low-Q bullseye cavity, due to the destructive interference of reflected light. Together with optical lifetimes of quantum dots as short as 80 ps, and the coherent manipulation capabilities of their spin, the transparency induced by coupling these dots to bullseye cavities makes them promising for quantum technologies.
Quantum dots coupled to high-Q cavities can induce optical transparency that provides photon switching capabilities. However, the optical access to such cavities can be inefficient due to their restrictive optical modes. Here, we observe optical transparency of ∼ 80% induced by a quantum dot coupled to a cavity with an efficient optical access, the low-Q bullseye cavity, due to the destructive interference of reflected light. Together with optical lifetimes of quantum dots as short as 80 ps, and the coherent manipulation capabilities of their spin, the transparency induced by coupling these dots to bullseye cavities makes them promising for quantum technologies.
ABSTRACT Bidirectional coherent control between photonic and matter qubits in solid‐state quantum networks demand a tailored photon‐emitter interface that can operate at the few‐photon level. Cavity‐coupled quantum dots with high input coupling efficiency provides a viable path toward such interface. However, reflection from the bare cavity can contaminate, or even overwhelm, the desired output photons that have interacted with the emitter. To overcome this problem, we implement a low‐reflectivity ( 1%) quantum dot‐micropillar cavity system with 97% input coupling efficiency. We achieve an optical nonlinearity threshold of 5.6 incident photons per pulse while maintaining high antibunching fidelity ( 0.2), measured at a pulse duration of twice the quantum dot exciton lifetime. Furthermore, we observe quantum dot transition inversion at 9 photons when the pulse duration is reduced to roughly match the quantum dot lifetime. This highly efficient photon‐emitter interface paves the way for key quantum photonic resources and functionalities.
In 1946, E. M. Purcell predicted that the radiative lifetime of an emitter is not an intrinsic property but can be modified by structuring the surrounding electromagnetic field [36]. By inserting a semiconductor quantum dot (QD) in an optical cavity, one can accelerate or inhibit its spontaneous emission. In the present article, we show that the QD spontaneous emission can be deterministically controlled to fabricate bright sources of quantum light. QDs in cavities: basics, motivation, first demonstrations Light-matter coupling We note f the ground state of the QD and e its excited state. For a cavity mode close to resonance with the QD optical transition, we consider only the states with 0 or 1 photon in the cavity mode. The states ∣ e, 0〉 and ∣ f, 1〉 are coupled through light–matter interaction, with a constant g , where h g = ∣〈 e, 0∣ Ed ∣ f, 1∣, with d the dipole of the optical transition e → f and E the electric field at the QD position. Each of the states ∣ e, 0 > and ∣ f, 1 > are also coupled to continua of states: continuum of the free-space optical mode, phonons of the semiconductor matrix, etc. [4]. Here, we consider only the coupling to the continuum of the free-space optical mode, related to the cavity losses, with a constant γ c . When g << γ c , the photon emitted by the recombination of an exciton efficiently escapes outside the cavity. The QD optical transition radiative recombination rate can be accelerated (Purcell effect) or inhibited.
We coherently probe a quantum dot that is strongly coupled to a photonic crystal nano-cavity by scattering of a resonant laser beam. The coupled system's response is highly nonlinear as the quantum dot saturates with nearly one photon per cavity lifetime. This system enables large amplitude and phase shifts of a signal beam via a control beam, both at single photon levels. We demonstrate photon-photon interactions with short pulses in a system that is promising for ultra-low power switches and two-qubit quantum gates.
By embedding a single quantum emitter inside a nanoresonator that strongly localizes optical field, it is possible to achieve a very strong light-matter interaction. The strength of this interaction is characterized by the coherent emitter-field coupling strength (g), which increases with reduction in the optical mode volume and which also sets the limit on the operational speed of such a system. With InAs quantum dots inside GaAs photonic crystal cavities, coupling strengths of 40 GHz can be reached (much greater than the record values in atom-cavity QED systems), while nanometallic cavities could increase them over 100 GHz, as a result of the further reduction in the mode volume. Such a quantum dot-nanocavity platform is of interest for various quantum technologies, as well as in optical switching/computing.
A bright source of on-demand entangled photons is needed for quantum networks. A single quantum dot in a site-selected nanowire waveguide is a promising candidate for realizing such sources. However, such sources are associated with poor single-photon indistinguishability, limiting their applicability in quantum networks. A common approach for enhancing the single-photon indistinguishability in quantum dot-based entangled photon sources is to implement a broadband optical cavity. Achieving a high-Purcell cavity while retaining the advantages of the nanowire, such as directional emission, a broad operational bandwidth, and high light extraction efficiency, has been a significant challenge. Here, we propose a nanowire cavity based on quasi-bound states in the continuum formed by the strong coupling of two resonant optical modes. We numerically predict this design to support a cavity mode with 4 nm bandwidth and a Purcell enhancement of $\sim$17. This cavity mode enables a directional far-field emission profile (88% overlap with a Gaussian) with a light extraction efficiency of $\sim$74%. Our solution opens up a route for generating entangled photon pairs with enhanced extraction efficiency and single-photon indistinguishability for the practical realization of quantum networks.
The interaction of light with matter is at the heart of quantum optics, which itself enables insight into the fundamental aspects of quantum mechanics. First experimental access to this research field has been realized by coupling atoms to light. Here, the transition between discrete energy states of the atom is associated with the absorption and emission of a photon, a single quantum of the electromagnetic field. As a central aspect of quantum optics, the light-emitter interaction can be significantly enhanced by placing the emitter in optical cavity that is on resonance with the emitter. In recent years, this has led to a rapidly evolving research field known as cavity quantum electrodynamics (CQED). In CQED two different regimes are distinguished: the strong and the weak coupling regimes. In the strong coupling regime, the emitted photon is reflected from the cavity mirrors and eventually reabsorbed by the emitter. In contrast, the weak coupling regime describes the irreversible emission, where the photon leaks out of the cavity before it can be reabsorbed. Both the weak and strong coupling regimes enabled fundamental experiments for a better understanding of quantum optical phenomena. \n \n \n \nCQED grants access to the quantum world and hence offers potentially revolutionizing applications, particularly in the field of quantum information processing. A central aspect for the successful implementation of quantum applications is the system's scalability. Unfortunately, placing atoms deterministically inside a cavity remains technologically elaborate and hence minimizes the prospect of scaling a atom-CQED system. \n \nA possibility to address this issue is to implement CQED in the solid state, where sophisticated fabrication strategies allow miniaturization and scalability of the system. Particularly the development of self-assembled quantum dots (QD) in semiconductors represent a promising route. QDs can be considered as artificial atoms that mimic the atomic two-level system. These structures interact strongly with light and therefore have the potential for replacing atoms in CQED. As a central advantage, QDs are naturally trapped, which greatly simplifies the deterministic incorporation into the cavity. \n \nIn recent years, many efforts have been made to couple self-assembled QDs to microcavities. Generally, the successful implementation of CQED requires a cavity with a high quality factor Q and a low mode volume. In a majority of the approaches, the high Q/small mode volume cavities were monolithically defined around the QD, embedding the QD at a fixed position inside the cavity. Both the weak and strong coupling regimes have been reached with these systems. However, for future applications they suffer from several disadvantages. The fixed position of the QD inside the cavity minimizes the prospects for spectral tunability and spatial positioning the QD inside the cavity. Furthermore, prospects for further increasing of the cavity Q-factor and minimization of the mode volume remain limited in these systems. \n \nIn this thesis the mentioned disadvantages are addressed by developing a fully tunable miniaturized Fabry-Pérot microcavity with low mode volume. The design enables both spatial positioning of the emitter inside the cavity and spectral tunability. Successful coupling of a single QD to the microcavity is demonstrated including the strong coupling regime. Further a new approach to decrease the cavity mode volume is presented, where we demonstrate weak coupling is achieved