Laser-Induced Frequency Tuning of Fourier-Limited Single-Molecule Emitters

Abstract

The local interaction of charges and light in organic solids is the basis of distinct and fundamental effects. We here observe, at the single-molecule scale, how a focused laser beam can locally shift by hundreds of times their natural line width and, in a persistent way, the transition frequency of organic chromophores cooled at liquid helium temperature in different host matrices. Supported by quantum chemistry calculations, the results can be interpreted as effects of a photoionization cascade, leading to a stable electric field, which Stark-shifts the molecular electronic levels. The experimental observation is then applied to a common challenge in quantum photonics, i.e., the independent tuning and synchronization of close-by quantum emitters, which is desirable for multiphoton experiments. Five molecules that are spatially separated by about 50 μm and originally 20 GHz apart are brought into resonance within twice their line width. This tuning method, which does not require additional fabrication steps, is here independently applied to multiple emitters, with an emission line width that is only limited by the spontaneous decay and an inhomogeneous broadening limited to 1 nm. The system hence shows promise for photonic quantum technologies.

Real-time two-photon interference from distinct molecules on the same chip

“…We found raw visibilities of the order of 40% and post-selected values up to 97%. The tuning method is compatible with pre-structured samples, containing waveguides or cavities and was also demonstrated for multiple emitters simultaneously [56]. The addition of electrodes on a similar geometry could help stabilizing the charge-noise environment, while maintaining the local tuning by optical fields, hence allowing for a higher visibility.…”

“…Molecules are interrogated with a CW laser which can be scanned around the ZPL molecular resonance around 784 nm, and with a pulsed laser at 766 nm for the triggered non-resonant pumping. The experiment is made possible by the recently discovered effect of laser-induced charge-separated state formation in molecular matrices, giving rise to a local Stark shift for the DBT molecules therein embedded [56]. To this aim, an additional pump beam, called shift beam, is aligned to the optical path, with an intensity typically one order of magnitude higher than that of the trigger excitation laser.…”

Reverse Intersystem Crossing of Single Deuterated Perylene Molecules in a Dibenzothiophene Matrix

“…The ideal case of an uninterrupted stream of photons, caused by a very low triplet yield and/or a very short triplet lifetime, would act as a stable information source for probing local effects. Some of these proven concepts of single molecules as probes are high sensitivity to electric fields and charges by an electrically-or optically-induced Stark effect, [10][11][12] or single molecules as nano-microphones of mechanically induced strain. [13] Recently, single-molecule emitters have also received significant attention as stable and tunable singlephoton sources and non-linear elements in integrated photonic devices.…”

Single-molecule and -particle spectroscopy in Leiden: absorption, scattering and fluorescence

“…for example the detection of hopping of single electrons [11][12][13][14]. At room temperature, thermal fluctuations broaden the spectral linewidth, however single molecules can be spatially selected beyond the diffraction limit.…”