Quantum logic at a distance

Quantum computers could revolutionize how specific computational problems are solved that remain untractable even for the world’s best supercomputers. However, although the basic elements of a quantum computer—realizing a register of qubits that preserve superposition states, controlling and reading out qubits individually, and performing quantum gates between them—have been scaled to a few dozen qubits, millions are needed to attack problems such as integer factorization. One approach for scaling up quantum computers is to “divide and conquer”—keep individual processing units smaller and connect many of them together. This approach leaves local processing nodes tractable but requires generation of entanglement and performance of quantum gates on qubits located at distant nodes to keep the advantages of quantum processing. On page 614 of this issue, Daiss et al. (1) made substantial progress toward this goal by performing quantum-logic operations on two distant qubits in an elementary network

Photothermal effects in ultra-precisely stabilized tunable microcavities

We study the mechanical stability of a tunable high-finesse microcavity under ambient conditions and investigate light-induced effects that can both suppress and excite mechanical fluctuations. As an enabling step, we demonstrate the ultra-precise electronic stabilization of a microcavity. We then show that photothermal mirror expansion can provide high-bandwidth feedback and improve cavity stability by almost two orders of magnitude. At high intracavity power, we observe self-oscillations of mechanical resonances of the cavity. We explain the observations by a dynamic photothermal instability, leading to parametric driving of mechanical motion. For an optimized combination of electronic and photothermal stabilization, we achieve a feedback bandwidth of $500\,$kHz and a noise level of $1.1 \times 10^{-13}\,$m rms

Strong atom-field coupling for Bose-Einstein condensates in an optical cavity on a chip

An optical cavity enhances the interaction between atoms and light, and the rate of coherent atom-photon coupling can be made larger than all decoherence rates of the system. For single atoms, this strong coupling regime of cavity quantum electrodynamics (cQED) has been the subject of spectacular experimental advances, and great efforts have been made to control the coupling rate by trapping and cooling the atom towards the motional ground state, which has been achieved in one dimension so far. For N atoms, the three-dimensional ground state of motion is routinely achieved in atomic Bose-Einstein condensates (BECs), but although first experiments combining BECs and optical cavities have been reported recently, coupling BECs to strong-coupling cavities has remained an elusive goal. Here we report such an experiment, which is made possible by combining a new type of fibre-based cavity with atom chip technology. This allows single-atom cQED experiments with a simplified setup and realizes the new situation of N atoms in a cavity each of which is identically and strongly coupled to the cavity mode. Moreover, the BEC can be positioned deterministically anywhere within the cavity and localized entirely within a single antinode of the standing-wave cavity field. This gives rise to a controlled, tunable coupling rate, as we confirm experimentally. We study the heating rate caused by a cavity transmission measurement as a function of the coupling rate and find no measurable heating for strongly coupled BECs. The spectrum of the coupled atoms-cavity system, which we map out over a wide range of atom numbers and cavity-atom detunings, shows vacuum Rabi splittings exceeding 20 gigahertz, as well as an unpredicted additional splitting which we attribute to the atomic hyperfine structure.Comment: 20 pages. Revised version following referees' comments. Detailed notes adde

Bose-Einstein condensate coupled to a nanomechanical resonator on an atom chip

We theoretically study the coupling of Bose-Einstein condensed atoms to the mechanical oscillations of a nanoscale cantilever with a magnetic tip. This is an experimentally viable hybrid quantum system which allows one to explore the interface of quantum optics and condensed matter physics. We propose an experiment where easily detectable atomic spin-flips are induced by the cantilever motion. This can be used to probe thermal oscillations of the cantilever with the atoms. At low cantilever temperatures, as realized in recent experiments, the backaction of the atoms onto the cantilever is significant and the system represents a mechanical analog of cavity quantum electrodynamics. With high but realistic cantilever quality factors, the strong coupling regime can be reached, either with single atoms or collectively with Bose-Einstein condensates. We discuss an implementation on an atom chip.Comment: published version (5 pages, 3 figures

Fiber Fabry-Perot cavity with high finesse

We have realized a fiber-based Fabry-Perot cavity with CO2 laser-machined mirrors. It combines very small size, high finesse F>=130000, small waist and mode volume, and good mode matching between the fiber and cavity modes. This combination of features is a major advance for cavity quantum electrodynamics (CQED), as shown in recent CQED experiments with Bose-Einstein condensates enabled by this cavity [Y. Colombe et al., Nature 450, 272 (2007)]. It should also be suitable for a wide range of other applications, including coupling to solid-state emitters, gas detection at the single-particle level, fiber-coupled single-photon sources and high-resolution optical filters with large stopband.Comment: Submitted to New J. Phys

Cavity-enhanced Raman Microscopy of Individual Carbon Nanotubes

Raman spectroscopy reveals chemically specific information and provides label-free insight into the molecular world. However, the signals are intrinsically weak and call for enhancement techniques. Here, we demonstrate Purcell enhancement of Raman scattering in a tunable high-finesse microcavity, and utilize it for molecular diagnostics by combined Raman and absorption imaging. Studying individual single-wall carbon nanotubes, we identify crucial structural parameters such as nanotube radius, electronic structure and extinction cross-section. We observe a 320-times enhanced Raman scattering spectral density and an effective Purcell factor of 6.2, together with a collection efficiency of 60%. Potential for significantly higher enhancement, quantitative signals, inherent spectral filtering and absence of intrinsic background in cavity-vacuum stimulated Raman scattering render the technique a promising tool for molecular imaging. Furthermore, cavity-enhanced Raman transitions involving localized excitons could potentially be used for gaining quantum control over nanomechanical motion and open a route for molecular cavity optomechanics

Concepts in Strategic Management and Business Policy: Achieving Sustainability -12/E.

This edition introduce a new theme that runs throughout all 12 chapter: environmental sustainability. This new theme complements the existing global issues theme carried forward from past editions. Environmental sustainability has become a strategic issues and one that will become even more important in the year ahead, as all of you struggle to deal with the consequence of climate change, global warming, and energy availability. Feature new in this edition: • Each chapter contains a boxed insert dealing with an issues in environmental sustainability. • Each chapter and with Eco Bits, interesting tidbits of ecological information, such as the number of plastic bags added to landfills each year. • Each part end with a short case dealing with topic and issues from that part’s chapter on companies ranging from Chiquita Bananas to Boeing and Airbus. • Special section on sustainability have been added to chapter 1 and 3. • A section on the natural environment has been added to the societal and task environments in chapter 4. • A section on managing strategic alliances has been added to chapter 7. • Off shoring has been added to the outsourcing section in chapter 8

Spectroscopy of mechanical dissipation in micro-mechanical membranes

We measure the frequency dependence of the mechanical quality factor (Q) of SiN membrane oscillators and observe a resonant variation of Q by more than two orders of magnitude. The frequency of the fundamental mechanical mode is tuned reversibly by up to 40% through local heating with a laser. Several distinct resonances in Q are observed that can be explained by coupling to membrane frame modes. Away from the resonances, the background Q is independent of frequency and temperature in the measured range.Comment: 4 pages, 5 figure