Wednesday, June 23, 2010

Towards high-speed optical quantum memories

K. F. Reim, J. Nunn, V. O. Lorenz, B. J. Sussman, K. C. Lee, N. K. Langford, D. Jaksc & I. A. Walmsley

Quantum memories, capable of controllably storing and releasing a photon, are a crucial component for quantum computers1 and quantum communications2. To date, quantum memories3, 4, 5, 6 have operated with bandwidths that limit data rates to megahertz. Here we report the coherent storage and retrieval of sub-nanosecond low-intensity light pulses with spectral bandwidths exceeding 1 GHz in caesium vapour. The novel memory interaction takes place through a far off-resonant two-photon transition in which the memory bandwidth is dynamically generated by a strong control field7, 8. This should allow data rates more than 100 times greater than those of existing quantum memories. The memory works with a total efficiency of 15%, and its coherence is demonstrated through direct interference of the stored and retrieved pulses. Coherence times in hot atomic vapours are on the order of microseconds9, the expected storage time limit for this memory.

Ground State Laser Cooling with Electromagnetically Induced Transparency

C. F. Roos*, D. Leibfried, A. Mundt, F. Schmidt-Kaler, J. Eschner, and R. Blatt

Ground state laser cooling of a single trapped Ca+ ion is achieved with a technique which tailors the absorption profile for the cooling laser by exploiting electromagnetically induced transparency. Using the Zeeman structure of the S1/2 to P1/2 dipole transition we achieve up to 90% ground state probability. The new method is robust, easy to implement, and proves particularly useful for cooling several motional degrees of freedom simultaneously, which is of great practical importance for the implementation of quantum logic schemes with trapped ions.

Suppression of Density Fluctuations in a Quantum Degenerate Fermi Gas

Christian Sanner, Edward J. Su, Aviv Keshet, Ralf Gommers, Yong-il Shin, Wujie Huang, Wolfgang Ketterle

We study density profiles of an ideal Fermi gas and observe Pauli suppression of density fluctuations (atom shot noise) for cold clouds deep in the quantum degenerate regime. Strong suppression is observed for probe volumes containing more than 10,000 atoms. Measuring the level of suppression provides sensitive thermometry at low temperatures. After this method of sensitive noise measurements has been validated with an ideal Fermi gas, it can now be applied to characterize phase transitions in strongly correlated many-body systems.

**Groupmeeting by Dylan Jervis, June 2nd, 2010**