Quantum Coherence, Noise and Decoherence in Nanostructures Max-Planck Institute "The modern field of nanoelectronics has brought about novel physical phenomena and created new challenges for their interpretation within quantum theory. Among the most fundamental concepts are quantum coherence and interference effects. An improved understanding of these phenomena is needed both from a fundamental point of view as well as for a variety of potential applications – ranging from highly sensitive detectors to quantum information devices and single-electron logic circuits operating at room temperature. The goal of this meeting is to bring together leading scientists from different subfields of condensed matter physics in order to advance the understanding of decoherence in nanostructures."

Constructive Role of Noise in Complex Systems Max-Planck Institute "Noise is inevitably present in any dissipative systems, and all living organisms operate in the noisy environment. Understanding the role of noise is crucial both in fundamental research in nonlinear physics, and in many applications in engineering, biology and medicine. Recent developments in statistical physics and nonlinear dynamics have shed light on a new, sometimes counterintuitive role which noise plays in nonlinear systems: in a wide range of systems, random forces may bring a system to a more ordered state. This meeting will focus on recent developments in the field of noise and fluctuations in complex nonlinear systems, as well as on applications of new noise-mediated phenomena and theoretical methodologies in experimental physics, biological physics, neuroscience and medicine."

Macroscopic Quantum Coherence and Computing MQC² Workshop "The aim of the workshop is to report on the recent theoretical and experimental results on the macroscopic quantum coherence of mesoscopic systems, as well as on solid state realization of qubits and quantum gates. Particular attention will be given to coherence effects in Josephson devices. Other physical systems, including quantum dots, optical, atomic, and molecular devices, exhibiting macroscopic quantum coherence, will also be discussed."

Quantum Communications in Telecom Networks IEEE "Quantum Cryptography, which carries a promise of fundamentally secure communications, has reached a point of relative maturity and first commercial offerings. Its broad deployment, however, is impeded by many technical challenges. This conference will bring together researchers from universities, industry and government labs, commercial QC system manufacturers, service providers, and funding agencies to discuss the novel physics of single-photon sources, interactions between photonic and material qubits, distant entanglement, single photon detection, fundamental physical constraints on the performance of QC links and networks, and resulting trade-offs among key rate, distance and cryptographic security."

Entanglement Distribution Revealed by Macroscopic Observations Vienna "Observation of quantum entanglement between increasingly larger macroscopic objects is one of the most promising avenues of experimental quantum physics. Eventually, all these developments will lead to a complete understanding of the simultaneous coexistence of a macroscopic classical world and an underlying quantum realm." In quant-ph 0603208, Kofler and Brukner compute multipartite entanglement measures to reveal quantum correlations in the collective properties of two separated objects – "The present work demonstrates that macroscopic properties can reveal entanglement between two or more macroscopic samples. On the fundamental side, our method demonstrates that there is no principal reason why purely quantum correlations could not have an effect on the global properties of objects."

Macroscopic Einstein-Podolsky-Rosen Pairs in Superconducting Circuits RIKEN In quant-ph 0508027, Wei et al. introduce an efficient method of creating EPR pairs in capacitively-coupled Josephson nanocircuits: "A possible application of the deterministically generated EPR pairs is to test Bell's Inequality at the macroscopic level. The approach proposed can be easily modified to engineer quantum entanglement in other fixed-interaction solid-state systems."

Quantum Computing with Superconducting Qubits NATO ASI Geller, Wilhelm et al. provide a concise overview of research efforts currently underway to develop scalable superconducting quantum circuits in Superconducting Qubits I: Architectures and Superconducting Qubits II: Decoherence – "Josephson junctions have demonstrated enormous potential as qubits for scalable quantum computing architectures. Here we discuss the current approaches for making multi-qubit circuits and for performing quantum information processing with them."

Defense and Security Applications of Quantum Information SPIE Applied technologies that compute, store, and distribute information based upon quantum mechanical entanglement, superposition, and interference phenomena are currently being pursued and realized in multiple parallel architectures, with high-impact assessment in the fields of cryptography, communications, computation and metrology. The SPIE Defense and Security Symposium, the largest unclassified international meeting of its kind, was held from 17-21 April, 2006.

Entanglement as a function of effective coupling between light and mirror (k) and effective duration of coupling (x-axis). Maximal entanglement is shown in red.

High-Temperature Macroscopic Entanglement PRL Via Raitio – Aires Ferreira, Ariel Guerreiro, and Vlatko Vedral have published novel results on high-temperature macroscopic entanglement in Phys. Rev. Lett. 96, 060407 [arXiv, physicsweb]. "Can entanglement and the quantum behavior in physical systems survive at arbitrary high temperatures? In this Letter we show that this is the case for a electromagnetic field mode in an optical cavity with a movable mirror in a thermal state [...] Entanglement between a macroscopic mirror and a cavity mode field can arise due to radiation pressure at arbitrarily high temperatures as the system evolves in time. This is very surprising because it is commonly believed that high temperature completely destroys entanglement."

Tunable flux qubit. (A) Double SQUID with two control coils. (B) Potential of the double SQUID in the symmetric case, relative energy levels. (C) Potential in the asymmetric case. Chiarello, cond-mat 0602464.

Tunable flux qubit manipulated by fast pulses MQC Group Chiarello evaluates the physical parameters for operation of a tunable flux qubit, calculating dissipation and decoherence factors, and discussing the potential for employment of integrated rapid single flux quantum (RSFQ) logic for qubit control.

High fidelity state tomography of capacitively shunted phase qubits UCSB Steffen et al. introduce a novel design concept for superconducting qubits – separating the capacitive element from the Josephson junction for improved qubit performance. Environmental coupling to the qubit is reduced by an order of magnitude; measurement fidelity improves to 90%. "This improved design enables the first demonstration of quantum state tomography with superconducting qubits using single shot measurements."

High-contrast dispersive readout of a superconducting flux qubit Delft Lupascu et al. demonstrate high-contrast state detection of a superconducting flux qubit by probing the microwave transmission of a nonlinear resonator based on a SQUID. "Measured contrast of Rabi oscillations is as high as 87%; of the missing 13%, only 3% is unaccounted for. Experiments involving two consecutive detection pulses are consistent with preparation of the qubit state by the first measurement."

Feedback control for communication with non-orthogonal states LSU Kurt Jacobs examines continuous implementation of optimal measurement for distinguishing between two non-orthogonal states. "Feedback control can be used during measurement to increase the rate at which the information regarding the initial preparation is obtained. Enhancement in the rate of information gain is achieved at the expense of reducing the total information which the measurement can extract in the long-time limit."

Frontiers in Quantum Nanoscience Queensland/PiTP "Within a few years the lives of most people will be touched by the quantum revolution – a change as profound as cars, flight, antibiotics or the Internet. Most people have heard of nanotechnology as the building of new materials at the molecular or atomic scale. That's the stone-axe age compared to what's coming." Nanoscience and nanotechnology receive much attention in the media today. However almost all current work concentrates on very small scale classical devices. This conference looks ahead to the far more revolutionary developments expected once nanoscience 'goes quantum', and begins to use the full potential of quantum mechanical superposition, phase coherence, and entanglement. Conference resources include public surveys on classical and quantum nanoscience.

Frequency dependence of multiphoton interference fringes in a superconducting qubit. Qubit switching probability plotted as a function of frequency and flux detuning in the limit of (A) strong driving and (B) weak driving signals. Symmetric patterns in peaks and valleys due to quantum interference are clearly observable. Oliver et al. Science 310.

Superconducting circuits and quantum information RIKEN You and Nori discuss recent advances in quantum information processing with superconducting circuits in the charge, flux and phase regimes. "The device can test Bell inequalities, produce Schrödinger cat states, and simulate the Einstein-Podolsky-Rosen experiment. Quantum engineering of macroscopic entangled states will surely play a central role in several future technologies."

Mach-Zehnder interferometry in a strongly driven superconducting qubit Lincoln Lab In Science 310 and cond-mat 0512691, Oliver et al. demonstrate Mach-Zehnder interferometry in a flux qubit. "The development of artificial atoms with lithographically defined superconducting circuits presents a new paradigm of quantum solid state physics, allowing the realization and exploration of new macroscopic quantum phenomena, and holding promise for applications in quantum computing [...] The generalization of optical Mach-Zehnder interferometry, performed in qubit phase space, provides an alternative means to manipulate and characterize the qubit in the strongly driven regime."

Dephasing of a superconducting qubit induced by photon noise Delft In PRL 95, 257002, Bertet et al. evaluate photon noise-induced dephasing in a superconducting flux qubit coupled to a harmonic oscillator. "Retaining quantum coherence is a central requirement in quantum information processing. Solid-state qubits, including superconducting ones, couple to environmental degrees of freedom that potentially lead to dephasing [...] By careful tuning of flux and current bias, long coherence times can be achieved with flux qubits."

Heisenberg limited measurements with superconducting circuits JPL Guillaume and Dowling describe an assembly of superconducting qubits in a single-mode cavity. Performing collective manipulations of the assembly to generate maximally entangled states, "this method can thus enable Heisenberg limited sensor technology with electric charge or magnetic field superconducting devices."