# Research

The research in Raymer's group centers around quantum and classical optical phenomena in which statistical effects play a key role, including quantum information and nonlinear optics.

Raymer's group pioneered the Quantum State Tomography technique for experimentally determining the quantum wave function of a light field. From such measurements one candetermine photon-counting probabilities on picosecond time scales. This is applied in studies of the quantum dynamics of microcavity semiconductor lasers. Raymer's group studies quantum cryptography in a new form that uses intense light pulses. These are prepared using quantum noise reduction (squeezing) in nonlinear-optical processes such as parametric amplification. The security of information encoded on such pulses results from the use of two different polarization bases and the sensitivity of such fields to optical losses.

Another topic being studied is semiconductor quantum dots placed inside micro-optical cavities, for potential use as logic gates inquantum information processing. Strong coupling between the quantum dot and the cavity field is being engineered by the use of novel cavities.

Quantum information can be represented by the states of photons, as polarization, frequency, or spatial shape. Alternatively, quantum information can be stored in the macroscopic properties of a light beam, as amplitude and phase. Both cases are being studied in Raymer's lab. In either case, for quantum information technology to advance, stationary quantum memory devices are needed. The group is studying atomic vapors of rubidium atoms as a medium for such storage. By use of coherent Raman techniques, an incident light field, containing information, can be absorbed, leaving the atomic vapor in a coherent superposition of hyperfine atomic ground states. This collective, many-atom, state can persist for microseconds, after which it can be read out by anti-Stokes Raman scattering. Applications include long-range quantum communication and entanglement distribution

In the area of wave coherence the group uses a novel form of interferometry to characterize the properties of light that has passed through a random medium such as the atmosphere. The goals are to learn about the processes of classical or quantum decoherence of the light wave, which may contain single photons or correlated pairs of photons. These studies are relevant to the problem of distributing entangled quantum particles through noisy media.