Quantum Control of Qubits and Atomic Motion Using Ultrafast Laser Pulses

Pulsed lasers offer significant advantages over CW lasers in the coherent control of qubits. Here we review the theoretical and experimental aspects of controlling the internal and external states of individual trapped atoms with pulse trains. Two distinct regimes of laser intensity are identified. When the pulses are sufficiently weak that the Rabi frequency $\Omega$ is much smaller than the trap frequency \otrap, sideband transitions can be addressed and atom-atom entanglement can be accomplished in much the same way as with CW lasers. By contrast, if the pulses are very strong (\Omega \gg \otrap), impulsive spin-dependent kicks can be combined to create entangling gates which are much faster than a trap period. These fast entangling gates should work outside of the Lamb-Dicke regime and be insensitive to thermal atomic motion.Comment: 16 pages, 15 figure

Collisional Semiclassical Aproximations in Phase-Space Representation

The Gaussian Wave-Packet phase-space representation is used to show that the expansion in powers of $\hbar$ of the quantum Liouville propagator leads, in the zeroth order term, to results close to those obtained in the statistical quasiclassical method of Lee and Scully in the Weyl-Wigner picture. It is also verified that propagating the Wigner distribution along the classical trajectories the amount of error is less than that coming from propagating the Gaussian distribution along classical trajectories.Comment: 20 pages, REVTEX, no figures, 3 tables include

Entanglement of Atomic Qubits using an Optical Frequency Comb

We demonstrate the use of an optical frequency comb to coherently control and entangle atomic qubits. A train of off-resonant ultrafast laser pulses is used to efficiently and coherently transfer population between electronic and vibrational states of trapped atomic ions and implement an entangling quantum logic gate with high fidelity. This technique can be extended to the high field regime where operations can be performed faster than the trap frequency. This general approach can be applied to more complex quantum systems, such as large collections of interacting atoms or molecules.Comment: 4 pages, 5 figure

Parent perceptions of their child’s and their own physical activity after treatment for childhood cancer

Purpose: Parents are important facilitators of physical activity for children, yet little is known about the perceptions of parents of childhood cancer survivors. We investigated parent perceptions of their own and their child’s physical activity levels after cancer treatment and examined associations with clinical, demographic, and psychosocial factors. Methods: We conducted a cross-sectional survey among 125 parents and 125 survivors. Parents reported on the perceived importance of their child being physically active and concerns regarding exercising after cancer treatment. Results: Parents and survivors self-reported median (range) of 127.5 (0–1260) and 220 (0–1470) min/week of moderate-to-vigorous physical activity. Most parents (n = 109, 98%) believed that physical activity was highly important for their child. Some parents (n = 19, 17%) reported concerns, most commonly regarding exercise safety (n = 7, 22%). Parents were more likely to perceive that their child should increase physical activity if their child was an adolescent and had high body fat percentage. Conclusions: Physical activity levels varied widely among survivors, reflecting factors including parents’ lifestyles, limited understanding of exercise benefits and perceptions of risk. Given survivors’ insufficient physical activity levels and sedentary behaviour among families, embedding physical activity promotion into health systems and follow-up support could benefit the entire family unit

Self alignment and instability of waveguides induced by optical forces

We introduce a new fundamental property of waveguides induced by the forces of the guided light, namely, the ability to self align or be in instability. A nanoscale waveguide broken by an offset and a gap may tend to self align to form a continuous waveguide. Conversely, depending on the geometry and light polarization, the two parts of the waveguide may be deflected away from each other, thus being in an unstable state. These effects are unique as they rely on the presence of both the guided mode and the scattered light. Strong self alignment forces may be facilitated by near field interaction with polarization surface charges

Nonadiabatic geometric phase induced by a counterpart of the Stark shift

We analyse the geometric phase due to the Stark shift in a system composed of a bosonic field, driven by time-dependent linear amplification, interacting dispersively with a two-level (fermionic) system. We show that a geometric phase factor in the joint state of the system, which depends on the fermionic state (resulting form the Stark shift), is introduced by the amplification process. A clear geometrical interpretation of this phenomenon is provided. We also show how to measure this effect in an interferometric experiment and to generate geometric "Schrodinger cat"-like states. Finally, considering the currently available technology, we discuss a feasible scheme to control and measure such geometric phases in the context of cavity quantum electrodynamics