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Physics Seminar - Shijie Chai

Monday, 11 March 2019

Physics Department

Shijie Chai

Department of Physics

University of Otago

"Measuring gravitational field with an atomic ruler"

Atom interferometry is a technique that underlines lots of precision measurements. It has tremendous applications ranging from very fundamental to highly practical. In this project, we developed a new method for implementing atomic interferometric measurement that was demonstrated as an atomic gravimeter. The scheme originates from the standard atom-optics delta-kicked rotor, where the laser-cooled atoms receive kicks from a standing-wave light beam (SW) at regular time intervals. The light forming the SW is tuned near an open atomic transition. The system is therefore dissipative since scattering of light from the SW causes the atoms to fall into a dark state where they are considered lost. So, the evolution is non-unitary and we measure the survival probability after the pulse sequence. Varying the pulse interval reveals a series of survival resonances when it is an integer multiple of half the Talbot time. These resonances can be understood through the matter-wave Talbot-Lau effect. A theoretical model agrees well with the experiments. We preformed a gravity measurement using the survival resonances and achieve a precision of 5 ppm with a drop distance of about 1 mm. The precision can be improved significantly by extending the drop time. The simple technical implementation of the system makes it a candidate for a compact atomic gravimeter. Actively feeding the atoms lost to the dark state back to their initial state can give them a second chance to survive the pulse and thereby enhance the resonant survival. We see an obvious improvement of the signal when recycle the lost atoms. This enhancement arises due to the atoms surviving pulses are “dark” to any laser field, which greatly boost the robustness of the system.

WHEN: Monday 11 March 2019
WHERE: Room 314, Science 3 Building
TIME: 3.00 pm–3.30 pm

All interested are welcome to attend

Light refreshments to follow in Common Room