Speaker
Description
Spectroscopy is routinely applied to measurement of photosensitive samples such as single molecules, quantum emitters (such as quantum dots), and perovskite solar cells. These samples are irreversibly altered when exposed to high optical powers, which necessitates the use of probe beams low photon fluxes. In this regime, measurement statistics are dominated by shot noise, which fundamentally limits the possible measurement precision. Recent advances in quantum optics have led to the use of heralded single photons for absorption spectroscopy, allowing for sub-shot noise sensitivity. At the same time, it is often desirable to measure the spectral phase imparted by the sample, which characterizes time-dependent processes.
Our group proposes, and has experimentally demonstrated, a new quantum spectroscopy technique allowing for simultaneous absorption and phase measurements at low photon fluxes. The technique relies on Hong-Ou-Mandel interference between a probe photon and a herald photon, which results in a phase-sensitive interference pattern. At the same time, heralding statistics can be measured through the number of coincidence and single detections. Theoretical calculations show that these heralding statistics can be used for a sub-shot noise absorption measurement, similar to previous techniques. Our method therefore allows one to obtain additional information about the phase shifts of a sample without sacrificing quantum-enhanced absorption sensitivity.
We report on a proof-of-principle experiment demonstrating this technique. Using a time-tagging biphoton spectrometer, we simultaneously measure the frequency of photons as well as their bunching statistics. This allows for a measurement of the spectrally-resolved Hong-Ou-Mandel interferogram, from which we estimate the absorption and phase spectra of a dye sample. Our experiment features a large 150 nm bandwidth and few-minute exposure times, making our technique a viable practical tool for low-flux spectroscopic measurements.
| Keyword-1 | Quantum metrology |
|---|---|
| Keyword-2 | Quantum spectroscopy |