Very strong light-matter interaction and optical nolinearity at the level of few photons is achieved by employing optical nanocavities (e.g., in GaAs, GaP, SiC) with embedded quantum emitters, such as quantum dots and color centers.
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.
Building quantum networks requires efficient coupling of solid-state quantum emitters to photonic devices. Tinvacancy center (SnV) has attracted much interest for having long spin coherence times at temperatures above 1 K. Employing SnV as an optically addressable qubit requires integration with photonic structures to both route the emitted photons and enhance the light-matter interaction. We present incorporation of high-quality SnV centers with narrow linewidths in suspended diamond waveguides. Furthermore, we fabricate photonic crystal cavities in diamond with embedded SnV centers. We observe strong intensity enhancement of the photon emission when the cavity is resonant with the color center. Time-resolved photoluminescence measurements confirm that this effect is due to radiative Purcell enhancement of the spontaneous emission. Finally, we demonstrate Stark tuning of transition frequency of SnV centers, essential for multiemitter applications. These results are a significant step toward color-center-based quantum information processing applications without the need for dilution refrigerators.
Optically active color centers in nanodiamonds offer unique opportunities for generating and manipulating quantum states of light. These mechanically, chemically, and optically robust emitters can be produced in mass quantities, deterministically manipulated, and integrated with a variety of quantum device geometries and photonic material platforms. Nanodiamonds with deeply sub-wavelength sizes coupled to nanophotonic structures feature a giant enhancement of light-matter interaction, promising high bitrates in quantum photonic systems. We review the recent advances in controlled techniques for synthesizing, selecting, and manipulating nanodiamond-based color centers for their integration with quantum nanophotonic devices.