Stockholms universitet logo, länk till startsida

Entangled source for quantum information

torsdag 18 mars 2021 14.00 – 14.14

Plats: C5:1007

Licentiate thesis defense by Alban Seguinard

Arrangör/Organiser: Fysikum, Stockhockholm University
Kontakt/Contact: Alban Seguinard
Ingen föranmälan krävs/No registration required

A spontaneous parametric down conversion based source which produces 780 nm and 1550
nm polarization-entangled photon pairs has been developed and characterized in order to
implement quantum communication experiments. These two wavelengths are of great
importance from experimental point of view. The780 nm wavelength corresponds to D2
optical transition for rubidium-87 atom which is used for building quantum memories, and
the 1550 nm wavelength corresponds to the low-loss telecom window well adapted to long
distance optical communications.

The entangled photons were produced by pumping a 15 mm long periodicallypoled
Potassium Titanyl Phosphate crystal (ppKTP) with a 518.9 nm stabilizedlaser diode inside a
Sagnac interferometric configuration.

The source produces two-qubit maximally entangled state with high fidelity of 96.95%. We
have tested the violation of Bell inequality and obtained a violation of 2.765 > 2. In addition,
we also developed a characterization setup for testing single photon detectors based on
nanowires superconductors (SSPD) to determine and calibrate their quantum efficiency,
dark counts and time jitter.