Typical Weekly Events:

Seminars:  May 2012

• Thu 5/10, 3:30PM in Room 190                   print event

  Stephen M. Carr, Sandia National Laboratory, Albuquerque, NM
  Resolved Sideband Emission of Quantum Dots Strained by Surface Acoustic Waves

  Remarkable and relentless progress has recently been realized in the pursuit of the cooling of mesoscopic mechanical systems toward the quantum ground state. For certain optomechanical and electromechanical cooling schemes, a key technical requirement is the attainment of the resolved sideband regime, where the mesoscopic mechanical mode frequency exceeds the linewidth of the central resonance. A particularly intriguing theoretical proposal [1] is based on resonant laser excitation of a phonon sideband of a quantum dot embedded in a mesoscopic mechanical resonator. In this seminar I will describe my previous experimental work, performed at the National Institute of Standards and Technology (NIST), on self-assembled quantum dots strained by surface acoustic waves, which was motivated in part by the aforementioned theoretical proposal [1]. A cryogenic experimental apparatus was designed, constructed, and implemented to enable precision optical measurements and radio-frequency electrical transmission to a semiconductor chip at low temperature. Surface acoustic waves in the GHz range were generated on-chip using nanofabricated interdigital transducers, resulting in the controlled inducement of phonon sidebands in the quantum dot emission spectrum. The resolved sideband regime and optical frequency conversion were experimentally demonstrated [2] using resonant spectroscopy. Finally, I will briefly describe my current work at Sandia National Laboratory on the experimental investigation of adiabatic and non-adiabatic qubit evolution and encoding using semiconductor devices, including electrostatically-defined quantum dots. [1] Physical Review Letters 92, 075507 (2004). [2] Physical Review Letters 105, 037401 (2010).

• Thu 5/3, 3:30PM in Room 190                   print event

  James Chin-wen Chou, National Institute of Standards and Technology, Boulder, CO. Current address: Sandia National Laboratories, Albuquerque, NM.
  Al+ optical clocks for fundamental physics and geodesy

  Laser‐cooled trapped atoms have long been recognized as potentially very accurate frequency standards for clocks. Ultimate accuracies of 10^‐18 to 10^‐19 appear possible, limited by the time‐dilation of trapped ions that move at laser‐cooled velocities. The Al+ ion is an attractive candidate for high accuracy, owing to its narrow electronic transition in the optical regime and low sensitivity to ambient field perturbations. Precision spectroscopy on Al+ is enabled by quantum information techniques. With Al+ “quantum‐logic” clocks, the current accuracy of 8.6 ×10^‐18 has enabled a geo‐potential‐difference measurement that detected a height change of 37±17 cm due to the gravitational red‐shift. We have also observed quantum coherence between two Al+ ions with a record Q‐factor of 3.4×10^16, and compared the Al+ resonance frequency to that of a single Hg+ ion to place limits on the temporal variation of the fine‐structure constant. This work is done in collaboration with D. B. Hume, M. J. Thorpe, D. J. Wineland, and T. Rosenband.