Kavli Colloquium — From the foundations of quantum mechanics to quantum information Delft Friday, 05 June 2009, "Quantum in Delft" (Leo Kouwenhoven), "Is there quantum in bio?" (Nynke Dekker), "Is ψ real?" (Yuli Nazarov), "From the foundations of quantum mechanics to quantum information" (Anton Zeilinger)

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Multi-Qubit Quantum Coherent Operations College Park "The purpose of this meeting is to identify – on a technology-specific basis – the primary difficulties that are likely to be encountered as qubit systems beyond typical current experiments with one, two, or three qubits are pursued. Topics of interest include, but are not limited to: controllable qubit interactions, miniaturization and integration to increase qubit density, new physics arising from the assembly of many-qubit systems, and process and state validation for larger systems. The workshop aims to address the following questions:

Given a particular qubit technology that has already demonstrated full single qubit control, what are the challenges facing this system as it grows into the multiple qubit regime? In a system with multiple qubits, what will be the mechanism(s) through which these qubits interact? How can these interactions be well enough controlled to achieve reliable, scalable logic gates? Do they contribute to decoherent processes?

What new physics must be taken into account for the benefit of, or hindrance to, many qubit operations? Are there any fundamental results that will inform the community of possible roadblocks that may be encountered when growing systems to the multiple qubit regime?

How can cross-talk from the control/readout channel for one qubit, to a bystander qubit, be reduced to a satisfactory level? What are the specific technologies required to ensure that a robust multi-qubit information processing system can be realized?

As systems grow larger, quantum state and, and even more so, process tomography will become impractical. What other measures will be effective for validating the operations of these systems?"

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National Workshop on Quantum Information Science OSTP|NTSC Via John Preskill, Dave Bacon, Ian Durham and Scott Aaronson — NSTC has announced a workshop in response to the recent Federal Vision for Quantum Information Science: "In January 2009, the United States National Science and Technology Council issued the report A Federal Vision for Quantum Information Science. The report proposes that

“The United States … create a scientific foundation for controlling, manipulating, and exploiting the behavior of quantum matter, and for identifying the physical, mathematical, and computational capabilities and limitations of quantum information processing systems in order to build a knowledge base for this 21st century technology.”

This Workshop on Quantum Information Science (QIS) has been organized in response to the NSTC report. It brings together leading theorists and experimenters drawn from physical science, computer science, mathematics, and engineering who will assess recent progress in QIS and identify major goals and challenges for future research."

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Adaptive quantum networks – We introduce a robust, error-tolerant adaptive training algorithm for generalized learning in high-dimensional, superposed quantum networks, or adaptive quantum networks. The formalized procedure applies standard backpropagation training to a coherent ensemble of discrete topological configurations of individual neural networks, each of which is formally merged under linear superposition. Quantum parallelism facilitates simultaneous training and revision within this coherent state space, resulting in accelerated convergence to optima. The protocol provides quantitative, numerical indicators for optimization of both single-neuron activation functions and reconfiguration of global network topology.

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Entanglement made Visible Genève In arXiv 0902.2896 and arXivblog summary, Gisin et al. show that macroscopic entanglement – and Bell inequality violations – can be made directly visible to the human retina. "We have shown that quantum experiments with human eyes as detectors appear possible, based on a realistic model of the eye as a photon detector. Entanglement, in principle, can be seen."

The Case for a National Investment: A Policy Essay for the Obama Transition Office In a recent CCC white paper, Aaronson and Bacon present the case for quantum computing as a national mandate. "First, quantum computing must be considered a national security issue. Since quantum computers break the codes used ubiquitously to protect transactions over the Internet, any country obtaining a scalable quantum computer would have the ability to disrupt electronic communication. Second, quantum information science research will help to maintain the US's scientific and technological advantages. Third, quantum computing is the study of the fundamental limits of computing and, as such, offers the potential to revolutionize our understanding of computation itself."

Pentagon explores quantum biology DARPA/DSO has launched a research initiative to investigate quantum mechanical effects in biological systems [initial Wired announcement, Sep. 2008]. "Scientists have recently discovered that quantum energy transfers allow plants and cynobacteria to convert sunlight into chemical energy nearly instantly, and with almost 100 percent efficiency. As energy passes between molecules involved in photosynthesis, a newly-observed 'wavelike characteristic' allows the energy to 'simultaneously sample all the potential energy pathways and choose the most efficient one.' DARPA says there are other biological examples of quantum effects — including an explanation, perhaps, for how birds are able to navigate along the Earth's magnetic fields."
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Quantum effects in biosystems Discover Magazine In Discover (February 2009), Mark Anderson reviews contemporary experiments in biophysics that explore the influence of quantum effects in living systems: "Could quantum mechanisms be driving some of the most elegant and inexplicable processes of life? For years experts doubted it: Quantum phenomena typically reveal themselves only in lab settings, in vacuum chambers chilled to near absolute zero. Biological systems are warm and wet. Most researchers thought the thermal noise of life would drown out any quantum weirdness that might rear its head. Yet new experiments keep finding quan­­tum processes at play in biological systems, says Christopher Altman, [alumnus researcher from European futurist think-tank Starlab, now pursuing applied physics and quantum information science at Kavli Institute of Nanoscience in Delft, The Netherlands]. With the advent of powerful new tools like femtosecond [10^-15 second] lasers and nanoscale-precision positioning, life’s quantum dance is finally coming into view."
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Convergence⁰⁸  Mountain View  " From 15-16 November 2008 – the world's most dangerous ideas will collide in Mountain View, California. Convergence⁰⁸ examines the world-changing possibilities of nanotechnology and the life-changing promises of biotechnology. It is the premier forum for debate and exploration of cognitive technology ethics – and ground zero of the past and future information technology revolution. Convergence⁰⁸ is an innovative, lively 'unconference' – the first and only unclassified forum dedicated solely to the convergence of NBIC – nano-, bio-, information and cognitive – technology developments." 
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Time in Quantum Mechanics Perimeter Institute The Clock and the Quantum focuses on conceptual and technical issues concerning the role of time in quantum theory – including quantum correlations in time, histories approaches, pre- and post-selected ensembles, time and quantum measurement, and causality under the framework of quantum theory. 
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From Qubits to Black Holes Technion | Macquarie University "Asher Peres (1934-2005), was an Israeli scientist who is widely considered to be one of the pioneering founders of quantum information science. A student of Nathan Rosen, (the “R” of EPR), Asher codiscovered quantum teleportation, a time-reversal test for quantum entanglement, and published numerous works on the foundations of quantum science. His research legacy continues through his many research collaborators, students, textbooks and research papers."

The Technion (Israel), and Macquarie University (Australia), will host the inaugural Asher Peres International Physics School 2008, for senior undergraduates and junior postgraduates in a series of lectures ranging from quantum mechanics, theory and experiments, through to quantum gravity. Held over five days, from November 17-22 (2008), in the historic environs at Chowder Bay on Sydney Harbor, the School will feature lectures from leading scientists from around the world, including Sir Peter Knight, Artur Ekert, Christian Kurtsiefer, Chris Fuchs, Bei Lok Hu, Jason Twamley, Daniel Terno, Gavin Brennen, Alexei Gilchrist, James Rabeau, and James Cresser.

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Progress in Quantum Computing IQSA | LT₂₅ | Lorentz Center – I've recently returned from a series of international conferences and workshops on superconductivity, quantum computation, entanglement and quantum coherence. In Sopot, Poland at the International Conference on Quantum Structures, much of the week was spent in long walks on the shores of the Baltic Sea, holding intense discussions on quantum information theory with Lev Levitin, who will be hosting the IQSA meeting at MIT in two years. We also continued ongoing research with Roman Zapatrin (Starlab) to advance the development of adaptive quantum networks for applications in fault-tolerant quantum computation, associative processing and pattern recognition.

Following IQSA, I moved on to the 25^th triennial International Conference on Low-temperature Condensed Matter Physics, where I met with Keith Schwab following presentation of his group's recent experiments with nanomechanical resonators to probe the boundaries of quantum and classical regimes, as well as discussing present and upcoming experiments in superconducting flux qubit systems with Yasu Nakamura, John Clarke, Robert Schoelkopf, and John Martinis.

Upon conclusion of LT₂₅, a satellite conference on Quantum Decoherence in Quantum Information Systems was held at the Lorentz Center, where I met with Vlatko Vedral to discuss long-term research initiatives in multipartite and macroscopic entanglement in condensed matter systems. Jasper van Wezel presented a review of the limits to quantum behavior related to spontaneous symmetry breaking – summarizing recent results on the quantum to classical transition, and future experiments which may elucidate the process of wavefunction collapse. Dirk Bouwmeester was generous enough to offer a tour of the experimental laboratory setup for the MiniGRAIL gravitational wave detector, which has just undergone several modifications, including improvements to the antenna, cryogenic cool-down systems, improved shielding, redesign of the capacitive transducer and fabrication of a new two-stage SQUID module for more stable operation at low temperatures.

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The Reality Tests Vienna In Seed (June 2008), the Vienna experimental group discusses physical and philosophical implications of new correlations between entangled photons, which violate an inequality proposed by Leggett for nonlocal realistic theories. This new series of experiments invalidates macrorealism in quantum mechanics by more than 80 orders of magnitude. Preliminary coverage of the experimental results was first presented in Nature 446 (871) and PhysicsWorld, 20 April 2007. According to Časlav Brukner: "Quantum mechanics does not always wash itself out – but to observe its effects for larger and larger objects, we would need more and more accurate measurement devices. We just do not have the sensitivity to observe the quantum effects around us. In essence, we do create the classical world we perceive. There could be other classical worlds completely different from ours."





Quantum networks: Entanglement of distant atoms by projective measurement University of Barcelona | ICFO | Spain Quantum cryptography is rapidly developing into a mature and robust technology for secure data transactions in financial, government and military sector applications. In arXiv 0806.1052, Zippilli et al. quantify the role of photon detector efficiency in quantum repeaters, which will be necessary to scale beyond the point-to-point networks currently employed for secure communications.

Presently, state-of-the-art systems employ atom-photon interaction to generate entanglement between distant nodes across a quantum network through projective measurement. "We assess proposals for entangling two distant atoms by measurement of emitted photons, analyzing how their performance depends on the photon detection efficiency – we believe that these concepts are generally applicable to all systems that may be considered for the creation of distant entanglement, including atomic-ensemble, photonic, and solid state implementations."

The groups's objectives are to quantify the importance of detector efficiency as applied to generating remote entanglement across quantum networks. With minor modifications, these results can be extended to the efficiency of quantum teleportation protocols that are also based on projective quantum measurement. "In all such systems, the detection efficiency will have a similar, important role for the use of the entanglement as a resource in quantum technologies."


Space-QUEST: Experiments with quantum entanglement in space Vienna | ESA | ISS In a recent submission to the arXiv,  Zeilinger's group at University of Vienna, Austria has proposed an experiment – Space-QUEST, Quantum Entanglement Science and Technology – for space-to-ground, entangled-photon Bell Inequality violation measurements to verify quantum nonlocality at distances over thousands of kilometers, in a joint operation between the International Space Station and a ground observatory in the European Union.
 
Entanglement and nonlocality have been pivotal controversies since the birth of quantum mechanics – Einstein's "spooky action at a distance" implies simultaneous, nonlocal correlations between separate entangled particles. J. S. Bell was the first to confirm the phenomenon experimentally in 1964.

Further refinements and increasing precision in succeeding experiments have consistently shown quantum mechanics to be an explicitly nonlocal theory – the outcome Einstein was most averse to accept. However, long-distance relativistic experiments, such as between orbiting satellites, have been technologically cost-prohibitive to date. The paper will be presented at the 2008 IAC Microgravity Sciences and Processes Symposium, under a proposed joint initiative between the European Space Agency and the International Space Station. 
 
"Testing quantum correlations over distances achievable with systems placed in the Earth orbit, or even beyond, would allow to verify both the validity of quantum physics and the preservation of entanglement over distances impossible to achieve on the ground. Using the large relative velocity of two orbiting satellites, one can perform experiments on entanglement where – due to special relativity – both observers can claim that they have performed the measurement on their system prior to the measurement of the other observer. In such an experiment, it is not possible anymore to think of any local realistic mechanisms that potentially influence one measurement outcome according to the other one."

Zeilinger's group has previously conducted proof-of-principle experiments in the Canary Islands with a 144 km free-space link, using an ESA receiver telescope to receive single entangled photons [Nature Physics, 3:481-486 (2007)]. A more recent experiment in Italy has demonstrated single-photon downlink communications viability from a near-earth orbit satellite [New Journal of Physics, 10:033038 (2008)].
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Superconducting Qubits RIKEN | UBC | Sherbrooke – In arXiv 0805.0164, Zagoskin and Blais provide a broad and accessible introduction to quantum information processing with superconducting qubits. "From a physicist's standpoint, the most interesting part of quantum computing research may well be the possibility to probe the boundary between the quantum and the classical worlds. The more macroscopic are the structures involved, the better. So far, the most "macroscopic" qubit prototypes that have been studied in the laboratory are certain kinds of superconducting qubits. To get a feeling for how macroscopic these systems can be, the states of flux qubits which are brought in a quantum superposition corresponds to currents composed of as much as 10⁵ - 10⁶ electrons flowing in opposite directions in a superconducting loop."

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Efficient pulsed gates for an oscillator stabilized Josephson qubit IBM Watson In arXiv 0709.1478 and New J. Phys. 10 033027 (2008), Koch, DiVincenzo, Brito and Steffen derive operational specifications for high-fidelity one and two-qubit pulsed gates for a superconducting flux qubit, calculating the Hamiltonian with tunable interaction from initialization to readout.

"The quantitative fact that the values of gate infidelity are at the 1% level – and below – is the major result of this paper."

So, can a "debugged" IBM qubit be used soon for universal quantum computation?

"The short answer is, in our opinion, ultimately yes."

"The answer would certainly be no if the noise threshold for fault-tolerant quantum computation were in the neighborhood of the oft-quoted value of 10⁻⁵. It is not inconceivable for the experiment to get to these values someday, since we find that the infidelities decrease much faster than linearly with the assumed noise levels."

"To get to 10⁻⁵, we would need to get to the very daunting levels of 100nΦ₀ at 1Hz for the 1/f noise amplitudes and 100 f s for timing accuracies; there is optimism that both of these numbers are ultimately attainable. Fortunately, while 10⁻⁵ was the threshold as it was understood ten years ago, much recent work shows that with good designs, much higher thresholds are possible. According to Terhal and Burkard – 1% is, in fact, on the high end of the noise levels for which fault tolerance may be possible."

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Photon transmission through sub-wavelength diameter apertures Delft | Optica In Optics Express 16, 10 (abstract, full article) and concurrent TU Delft summary, Photonics review, Adam, Planken et al. report on high time-resolution terahertz mapping of photon transmission through sub-wavelength diameter apertures:

"According to the laws of physics, it is particularly difficult to pass light through a hole smaller than half the wavelength of the light used." The Delft group conducted experiments using extremely high time-resolution measurements in the terahertz (THz) frequency range. The group discovered that even if the hole is up to fifty times smaller than the wavelength used, sufficient light can pass through to allow measurements near the hole – an extremely difficult task using other methods. "Improving the sharpness of THz microscopes, coupled with more sensitive detectors, will improve the viability of creating images of biological cells using this type of measurement."

Prior experiments at Leiden University (Nature 418, 304-306) have also studied photon transmission through sub-wavelength metal films and shown entanglement conservation to be much more robust than expected – surviving the conversion process from surface-plasmon waves, which tunnel through the barrier, before reradiating as photons on the opposite side of the film. "It's a good omen, because it's saying quantum entanglement can survive when you might not expect it to," says Bill Barnes, a photonics expert at the University of Exeter. "If they can survive this, what else can they survive?"

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