Recent progress towards achieving quantum storage in solid state devices, manipulating single‑electron spins in quantum dots, and laser cooling of mechanical oscillators were among the highlights of the 2008 meeting of the APS Division of Atomic, Molecular and Optical Physics (DAMOP), held 27‑31 May in State College, Pennsylvania.
Quantum Memory. Quantum memories are likely to be critical components in any future long‑range communications network, and several talks at the DAMOP meeting focused on various methods and approaches to achieving a viable quantum memory. Matthew Sellars of the University of Otago described a method for storing light that operates by controlling the local group velocity of light in a crystal, using an applied electric field. He maintains that unlike other proposals for quantum memories, his method requires no optical control pulses, thereby simplifying the operation of the memory and improving its signal to noise.
Hugues de Riedmatten of the University of Geneva is developing atomic ensembles to realize a quantum storage device for single photons in a solid state environment. His ensembles employ rare‑earth ions–a “frozen gas of atoms”–doped into dielectric crystals, which can in principle store single photos and recall them with high efficiency using a modified photon echo approach. Different wavelengths of absorption can be achieved depending on the choice of rare‑earth ions employed. De Riedmatten finds that erbium-doped solids are an especially attractive candidate for a quantum memory at telecommunication wavelengths.
The “holy grail” of research into quantum memory is a system that would allow high‑fidelity storage and retrieval of an arbitrary optical state. Alexander Lvovsky of the University of Calgary reported on the potential for storage of squeezed light to serve as a step towards a universal quantum memory. He presented results from a functioning testbed for such a system, bringing together the quantum state, the memory cell, and full characterization of both the input and the retrieved state in a single apparatus.
Quantum Dots. David Awschalom of the University of California, Santa Barbara’s Center for Spintronics and Quantum Computation reported that his research group has demonstrated the non‑destructive detection of a single electron spin in a quantum dot. The ability to sequentially initialize, manipulate and read out the state of a qubit, such as an electron spin in a quantum dot, is necessary for virtually any scheme for quantum information processing. The dot in this case is formed by interface fluctuations of a gallium arsenide quantum well, and embedded in a diode structure, positioned within a vertical optical cavity to enhance the small single spin signal. Awschalom’s group has also recently developed a scheme for high‑speed all‑optical manipulation of the spin state that enables multiple operations.
Cool Runnings. Laser cooling of macroscopic mechanical oscillators has applications in high‑precision measurements, gravitational wave detectors, and exploration of the classical‑quantum transition, according to MIT’s Nergis Mavalvaya. She described a series of cooling experiments–inspired by gravitational wave detectors–to trap and cool gram‑scale mirror oscillators. To achieve this, her team had to use a variety of cooling techniques that employ frictionless forces. Such forces are created from either radiation pressure in a detuned optical resonator, or from electronic feedback forces in an active servo. They predict that as the experiments approach the quantum regime, an assortment of non‑classical behavior and effects become evident, such as quantum radiation pressure noise, and squeezing and entanglement of the light and mirror states. With upgrades to their current apparatus, Mavalvaya hopes to observe these effects in the near future.
Runaway Electrons. In 2005, the Reuven Ramaty High Energy Solar Spectroscopic Imager recorded gamma‑ray flashes of atmospheric origin, thereby revealing the presence of relativistic electrons in Earth’s mesosphere, with energies up to 40 MeV. E.E. Kunhardt of Polytechnic University in New York examined the origin of these bursts in runaway electrons, which are not, on average, in dynamical equilibrium with the background gas, and move progressively towards higher energies. A collisional avalanche mechanism seems likely, but would have to overcome the fact that the peak ambient electric fields in the mesosphere are too low, even during thunderstorms, for electrons to overcome collisional losses and accelerate to such high energies.
Magnetic Sensing. Paola Cappellaro of the Harvard‑Smithsonian Center for Astrophysics reported on development of a novel magnetic sensor that can operate at room temperature ambient conditions and could provide an “unprecedented combination of ultra‑high sensitivity and spatial resolution.” Among other applications, the new sensor could enable sensing of nanotesla magnetic fields with resolution below 50 nm–allowing for the detection of a single nuclear spin’s precession within one second. Cappellaro’s team took advantage of recently developed techniques for coherent control of solid‑state electronic spin quantum bits, specifically, the use of spins associated with nitrogen‑vacancy centers in diamond.
Biomolecule Precursors in Space. It is a topic of intense debate to what extent biomolecule precursors have been synthesized on planetary surfaces or in the interstellar medium. Advanced biomolecules such as amino acids are unlikely to survive the strong YV field present under disc and planetary formation, but precursor molecules like nitriles are present abundantly in the interstellar medium, and could possibly be delivered to planets by comets or meteorites, according to Wolf Geppert of Stockholm University. He presented recent measurements on the rate constants and branching ratios of several protonated nitriles gleaned from a storage ring experiment. In planetary atmospheres, nitriles can polymerize to tholines, which can form amino acids and nucleobases. Furthermore, the Cassini‑Huygens mission revealed that protonated nitriles are abundant in Titan’s atmosphere, which may resemble that of early Earth.