Seminars
Polarization Entangled Photon Pairs from a Single Molecule


Ilja Gerhardt
March 20th, 2018 ILJA GERHARDT Max Planck Institute for Solid State Researches

Single molecules |the _rst ever detected single quantum emitter in the solid state -allow for the generation of single photons in the entire visible spectrum. Unlike as for other emitters the photon collectione_ciency can approach unity, and under cryogenic conditions their spectral linewidth can be truly Fourier limited. We observe more than 1 Mio raw clicks per second on a silicon avalanche photo diode (APD). At the same time the emitted photons show a spectral linewidth of less than 20 MHz.

In the past years, we have learned to utilize the spectral superposition of the molecule’s emission with alkali atoms. This allowed us to observe slow light in a hot atomic vapor, to _lter the emitted photons from background contributions, and to perform atomic spectroscopy with a stream of single photons. The combination of an atomic _lter with single molecule studies allows to achieve a pure single photon stream on the sodium D2 line.

A next hybridization step aims towards a utilization of these photons in all-optical quantum operations, such as in all-optical gates. A _rst step to this goal is an e_cient Hong-Ou-Mandel interference [5], as the basic building block of linear optics quantum operations. A Hong-Ou-Mandel visibility of 94% is observed. In a slightly modi_ed Hong-Ou-Mandel experiment, we can prove the ideal Fourier limited nature of the emitted photons.

A closely related experiment is the preparation of the incoming photons in orthogonal polarization states. This is known as Shih-Alley con_guration. It does not only allows for the implementation of a quantum eraser, but also for the observation of a Hong-Ou-Mandel peak instead of the commonly observed dip. Most importantly, this experiment allows for the generation of photonic entanglement. Coincidence clicks on both sides of the beam splitter are polarization-entangled. We are able to disprove the locality-reality principle with a Bell-parameter of S =2.260.06. Unlike for many other emitters, the violation of Bell’s inequality is observed with the raw coincidence clicks.


Seminar, March 20, 2018, 15:00. ICFO’s Seminar Room

Hosted by Prof. Morgan Mitchell

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