Optical Ramsey spectroscopy on a single molecule

Abstract

Organic chemistry offers the potential to synthesize individual molecules for specific tasks in quantum information processing. One of their striking properties is the emission of single photons with nearly ideal coherence. Here, we implement Ramsey spectroscopy to measure the electronic state coherence of a single molecule. Conventionally, the emitter’s coherence is characterized by saturation or intensity auto-correlation measurements. However, both methods are under the steady influence of continuous interaction with the excitation laser. This influence can be eliminated by using a pump–probe sequence of two optical pulses to observe the decoherence. We have measured a near-transform-limited decoherence time of 17.6 ns, while the radiative lifetime is 10.1 ns. We also perform frequency-detuned excitation, gaining richer insights into the dephasing behavior of the molecule. The experiments exhibit that optical Ramsey spectroscopy is a promising tool for measuring the emitter’s coherence properties.