G. A. Garrett

Ultrafast optical excitation of a combined coherent-squeezed phonon field in SrTiO 3

We have simultaneously excited a coherent and a squeezed phonon field in SrTiO3 using femtosecond laser pulses and stimulated Raman scattering. The frequency of the coherent state (a 1.3 THz) is that of the A1g-component of the soft mode responsible for the cubic-tetragonal phase transformation at approximately 110 K. The squeezed field involves a continuum of transverse acoustic phonons dominated by a narrow peak in the density of states at a 6.9 THz.

Many-spin quantum entanglement induced by femtosecond pulses

Summary form only given. Femtosecond pulses were used to generate long-lived (/spl tau/>0.1 ns) quantum-entangled states involving the spins of many individual Mn/sup 2+/ ions in Cd/sub 1-x/Mn/sub x/Te. The experiments were performed on a single crystal of Cd/sub 0.98/Mn/sub 0.02/Te with a standard pump-probe setup in the Voigt reflection geometry. We used a mode-locked Ti:sapphire laser which provided /spl sim/ 95 fs pulses at a repetition rate of 85 MHz an average-power of 80 mW and focused to a 80-/spl mu/m-diameter spot. The intensity of the reflected probe pulse measures changes in the optical constants that depend on the expectation value of the total spin for the particular entangled state /spl Psi/ created by the pump. The signature for an entanglement between states |j) and |l) is the observation of oscillations of frequency n/spl Omega//sub 0/ where n=(n/sub j/-n/sub l/). We notice that the highest harmonic of /spl Omega//sub 0/ provides a lower bound for the number of magnetic ions N that are entangled. The entanglement process, relying on coupling to localized excitons, holds promise for quantum-gate operations.

Generation of coherent and squeezed phonon fields using femtosecond laser pulses

Squeezed phonon fields in KTaO3 and SrTiO3 are generated using femtosecond laser techniques. Coherent, first-order, phonon oscillations were observed in SrTiO3 at temperatures below its cubic-tetragonal phase transition at ≈ 110K. Time-domain data are compared with measurements of spontaneous Raman scattering.