The Quantum Lunch is regularly held on Thursdays in the Theoretical Division Conference Room, TA-3, Building 123, Room 121. For more information, contact Diego Dalvit.
February 23 , 2006
University of California
Entangled photons, solid-state cavity QED, and the quest for macroscopic quantum superpositions
Three sets of experiments will be addressed that are related to quantum information science and metrology. The first set of experiments studies the stimulated emission of entangled photons resulting in entanglement of two optical fields with each containing up to 50 photons. The second set, motivated by the desire to store optical qubits in solid-state qubits, presents the study of optically active quantum dots in microcavities. Initial experimental progress have led us to the unexpected observation of ultralow threshold lasing of a photonic crystal defect mode cavity embedded with only 1 to 3 InAs self-assembled quantum dots as gain medium. Photon correlation measurements confirm the transition from a thermal light source to a coherent light source. The final set of experiments has as long term aim the transfer of a superposition of a photon propagating in two directions into a superposition of two center-of-mass motions of a tiny mirror that is placed in one path of the beamsplitter. Based on current state-of-the-art experimental techniques a scheme is proposed that can lead to a quantum superposition about 10 orders of magnitude more massive than any superposition demonstrated to date. A crucial part of the proposed experiment is an optical cavity with one end mirror as small as 10 _m in diameter attached to a high Q mechanical cantilever. Such a tiny mirror attached to an atomic force microscope cantilever has been achieved. Aligning this mirror as part of a 25mm Fabry Perot cavity in vacuum resulted in an optical quality factor of 2.000 and a mechanical quality factor of 100.000. This provides an excellent interferometric position and motion measurement of the cantilever/mirror system. We use this readout to measure the thermal motion and to feed-back an optical force to counteract the thermal motion of the center-of-mass mode. Experimental results will be shown that demonstrate the optical cooling from room temperature to below 1 Kelvin.