Single quantum states and defined wave packets

Edward A. Olszewski

Michael G. Raymer, Jaewoo Noh, Ian A. Walmsley +1 more

Pulsed spontaneous down conversion can be controlled by modifying the density of states of vacuum modes using cavity structures containing distributed Bragg gratings. It seems feasible to engineer the vacuum to create single-photon pairs in well defined coherent (pure-state) wave packets, thereby precluding the need for post-filtering.

V. K. Ignatovich

E. A. Shapiro, Michael Spanner, Misha Ivanov

We study control of wave packets with a finite accuracy, approaching it as quantum information processing. For a given control resolution, we define the analogs of several quantum bits within the shape of a single wave packet. These bits are based on wave packet symmetries. Analogs of one- and two-bit gates can be implemented using only free wave packet evolution and coordinate-dependent ac Stark shifts applied at the moments of fractional revivals. As in quantum computation, the gates form a logarithmically small set of basis operations which can be used to approximate any unitary transformation desired for quantum control of the wave packet dynamics. Numerical examples show the application of this approach to control vibrational wave packet revivals.

Ying Tang, Anders W. Sandvik

We develop a technique to directly study spinons (emergent spin S=1/2 particles) in quantum spin models in any number of dimensions. The size of a spinon wave packet and of a bound pair (a triplon) are defined in terms of wave-function overlaps that can be evaluated by quantum Monte Carlo simulations. We show that the same information is contained in the spin-spin correlation function as well. We illustrate the method in one dimension. We confirm that spinons are well-defined particles (have exponentially localized wave packet) in a valence-bond-solid state, are marginally defined (with power-law shaped wave packet) in the standard Heisenberg critical state, and are not well defined in an ordered Néel state (achieved in one dimension using long-range interactions).

J. Broeckhove, Luc Lathouwers, Piet Van Leuven