Superconducting qubits as artificial atoms

"The demonstrated resonance wave scattering indicates that superconducting quantum devices can be used as building blocks for controllable, quantum coherent, macroscopic artificial structures — in which a plethora of effects can be realized from quantum optics of atomic systems."

NEC 東京大学 This week's Qulink seminar by Yasunobu Nakamura (NEC) reports on recent developments in exploring the quantum optical properties of a superconducting flux qubit coupled to a 1d microwave transmission line. See also: Electromagnetically induced transparency on a single artificial atom (arXiv); Resonance fluorescence of a single artificial atom (Science); Ultimate on-chip quantum amplifier (Phys Rev Lett).

Quantum Zeno effect with a superconducting qubit NTT In arXiv 1006.2133, Matsuzaki and Semba provide detailed analysis of the Quantum Zeno effect in superconducting qubits: "Superconducting qubits are a promising system to observe the Quantum Zeno effect. We have studied how a sequence of projective measurements can alter the dephasing process, and suggest experimental requirements to observe the Quantum Zeno effect in existing superconducting qubits. It would be possible to demonstrate our prediction utilizing current technologies."

First quantum effects seen in visible object UCSB The first ever quantum superposition in an object visible to the naked eye has been observed (New Scientist) "The key was to connect the resonating strip to a superconducting qubit—the qubit acts as a bridge between the microscopic and the macroscopic worlds."

Quantum mechanics harnessed to control macroscopic mechanical system (Wired Science) "The goal of the experiment was to see if we could observe quantum mechanical effects in a large, mechanical object. It’s an exciting piece of work. People are interested in pushing the boundaries of quantum mechanics." The techniques harnessed to measure the effect are based upon research earlier reported in "Quantum Entanglement Visible to the Naked Eye" (Nature, Wired Science, BBC)

Room-temperature quantum coherence in photosynthesis (Wired News)"The Nature findings, made at room temperature in common marine algae, show that macroscopic biological coherence operates under everyday conditions. Moreover, similar results from an experiment on another, simpler light-harvesting structure, announced by Engel’s group last Thursday on the pre-publication online arXiv, suggest that photosynthetic coherence is routine. 'There’s every reason to believe this is a general phenomenon,' said Engel. Scholes’ finding is 'an extraordinary result that shows us a new way to use quantum effects at high temperatures.'"

Nature's hot green quantum computers revealed (New Scientist) "Exactly how these molecules remain coherent for so long, at such high temperatures and with relatively large gaps between them, is a mystery,' says Alexandra Olaya-Castro of University College London, who has been collaborating with Scholes to understand the underlying mechanisms and apply them elsewhere. She believes that the antenna's protein structure plays a crucial role. 'Coherence would not survive without it,' she says. 'The hope is that quantum coherence could be used to make solar cells more efficient. The work is going to change the way we think about photosynthesis and quantum computing, Engel says. 'It's an enormous result.'"

Long-lived quantum coherence in photosynthetic complexes at physiological temperature (arXiv) "We present the first evidence that quantum coherence survives at physiological temperature for at least 300 fs—long enough to perform a rudimentary quantum computational operation. This data proves that the wavelike energy transfer process discovered at 77K is directly relevant to biological function. Microscopically, we attribute this long coherence lifetime to correlated motions within the protein matrix encapsulating the chromophores, and we find that the degree of protection afforded by the protein appears constant between 77K and 277K. The protein shapes the energy landscape and mediates an efficient energy transfer despite thermal fluctuations. The persistence of quantum coherence in a dynamic, disordered system under these conditions suggests a new biomimetic strategy for designing dedicated quantum computational devices that can operate at high temperature."

Josephson junction neurons via physicsandcake Suzanne Gildert offers insights on a recent Phys. Rev. E preprint that proposes to model biologically realistic neurons using Josephson junction arrays. "These 'Josephson junction neurons' reproduce many characteristic behaviors of biological neurons such as action potentials, refractory periods, and firing thresholds, [and] would be orders of magnitude faster than both traditional computer simulations and biological neural networks." See also Quantum neural networks, backpropagation training, adaptive quantum networks.

Quantum Information Science—DARPA's New Frontier Collins offers this executive-level report on quantum information research at DARPA. "It's been almost a half-century since Intel founder Gordon Moore first observed that ever-shrinking circuitry on silicon chips leads to the doubling of the performance of these chips every 18 months or so. This has been instrumental in bringing rapid progress to the field of information processing. The era of Moore’s Law has been an interesting one, to say the least, but it is nearing its end: Within less than two decades, circuits will have shrunk to the atomic level."

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)

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?"

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."