Frequency tuning of single photons from a whispering-gallery mode resonator to MHz-wide transitions

Abstract

Quantum repeaters rely on interfacing flying qubits with quantum memories. The most common implementations include a narrowband single photon matched in bandwidth and central frequency to an atomic system. Previously, we demonstrated the compatibility of our versatile source of heralded single photons, which is based on parametric down-conversion in a triply-resonant whisperinggallery mode resonator, with alkaline transitions [Schunk et al., Optica 2, 773 (2015)]. In this paper, we analyze our source in terms of phase matching, available wavelength-tuning mechanisms, and applications to narrow-band atomic systems. We resonantly address the D1 transitions of cesium and rubidium with this optical parametric oscillator pumped above its oscillation threshold. Below threshold, the efficient coupling of single photons to atomic transitions heralded by single telecom-band photons is demonstrated. Finally, we present an accurate analytical description of our observations. Providing the demonstrated flexibility in connecting various atomic transitions with telecom wavelengths, we show a promising approach to realize an essential building block for quantum repeaters.

Three‐wave mixing in whispering gallery resonators

“…waves [90] are still missing. These two strategies are of major importance for all devices based on quasi-phase matching since the domain pattern will hamper the tuning by applying an external electric field using simple surface electrodes.…”

“…Here, one has to take into account that the material might be photoconductive [110,111], i.e., the electric field generating the desired refractive index decreases with time while the characteristic decay rate increases with light power. Such a behavior has been observed in WGRs [90]. It considerably limits the tuning possibility with a static electric field.…”

“…There are several strategies for fine (mode-hop free) tuning the wavelengths of the generated light [90]: applying an external electric field, applying mechanical stress, or manipulating the evanescent fields of the circulating waves. Combining these strategies with the coarse tuning (wavelength jumps by changing the resonator temperature), it is possible to tune the output wavelengths in a controlled way until they meet MHz-wide resonances of alkali atoms [91].…”

Dielectric tuning and coupling of whispering gallery modes using an anisotropic prism

“…Practically, dielectric tuning is also achieved using an independent dielectric substrate [31,42], such that the excitation field does not contribute to the total field at the substrate interface. Accordingly we can safely neglect the contribution of E ir for our purposes (i.e.…”

“…So-called dielectric tuning, in which a dielectric substrate or prism (note we shall use the terms prism and substrate interchangeably throughout this text) is brought into close proximity to a WGM resonator, has also been proposed and demonstrated as a route to continuous fine tuning [16,31]. Several numerical and approximate analytic techniques have been developed to study the properties of WGMs in the presence of local dielectric or plasmonic perturbations [32][33][34][35] and to model cavitywaveguide coupling [36][37][38][39][40].…”