New Scientist: Nature's hot green quantum computers revealed

Room temperature quantum coherence in pi resonance chains

(Thanks to Professor Robin Carter)

Biological quantum coherence in photosynthesis Nature 446:782-786, April 12, 2007 

Can one see entanglement?

Is DNA a quantum computer?

Birds do it!

Quantum Zeno Effect Underpinning the Radical-Ion-Pair Mechanism of Avian Magnetoreception

I. K. Kominis

The spooky world of quantum biology

Room temperature quantum Hall effect in graphene

Diamonds at room temperature

Is the world a hologram?

Fermilab 'holometer' to test reality

 

Thanks to Chris Altman, Mark Anderson and others

The following is from Chris Altman's http://superconducting.blogspot.com/ 

Christopher Altman <altman@casimirinstitute.net>:

Unusual decoherence in qubit measurements with a BEC
http://arxiv.org/abs/0807.4440

Decoherence is present for any microscopic system interacting with a macroscopic device, characterised by a large number of degrees of freedom and a dense distribution of energy levels. As a result, an initial state of a qubit is expected to be rapidly (exponentially in time) converted into a statistical mixture, so that the information stored in the qubit is erased."

In contrast to conventional expectations, in arXiv (0807.4440), Sokolovski and Gurvitz have obtained unusually extended coherence times when measuring qubits with Bose Einstein condensates as opposed to classical detectors – BEC detection of qubit state is correlated with extremely slow decoherence rates – 1/sqrt(t) – as opposed to exponential time decay under classical detection measurement. In the strong interaction limit, the researchers further expect to find radically different time evolution of the quantum Zeno effect.

One remarkable feature of a Markovian environment is that the qubit’s evolution under such frequent observations is practicall indistinguishable from its unitary observation-free evolution. For a qubit-BEC hybrid system whose behavior is explicitly non-Markovian, we expect the two types of evolution to be drastically different."

Detection of hidden entanglement by photon anti-bunching
http://arxiv.org/abs/0807.4437
Zeilinger's group has reported detection of hidden entanglement via two-photon anti-bunching at a beamsplitter – a direct indication of entanglement in a variable which might not be directly accessible in an experiment, since the total state of two photons must be symmetric. This may facilitate observation of entanglement in other systems, such as atomic ensembles or BECs. The analogue in fermionic systems would be to observe bunching.


Schrodinger's Kittens Mohanty Group In Physical Review Letters, the Mohanty Group at Boston University reports evidence of center-of-mass displacement quantum nanomechanical oscillations in silicon antennae of ~50 billion atoms, making this the largest observation of quantum mechanical behavior to date.  " It's a truly macroscopic quantum system, "  says Alexei Gaidarzhy, the paper's lead author and a graduate student in the BU College of Engineering's Department of Aerospace and Mechanical Engineering.  " When it's a new phenomenon, it's best not to be guided by expectations based on conventional wisdom. The philosophy here is to let the data speak for itself. "  


.......
Robust Entanglement Innsbruck  " It is common belief among physicists that entangled states of quantum systems lose their coherence rather quickly. The reason is that any interaction with the environment which distinguishes between the entangled sub-systems collapses the quantum state. Here we investigate entangled states of two trapped Ca+ ions and observe robust entanglement lasting for more than 20 seconds. " 
.......
Quantum entanglement stronger than suspected: A recent New Scientist article outlines work at Leiden University showing quantum entanglement to be much more robust than traditionally expected. See link and homepage for physics research at Leiden University, The Netherlands. Plasmon assisted transmission of quantum entanglement ,Quantum Optics and Information Laboratory, University of Leiden
.......
Entanglement Extraction from a Solid NEST-INFM, Leeds, Vienna quant-ph/0505107  " It has been a common belief that entanglement cannot exist on a macroscopic scale. This is because decoherence effects from many-particle interaction would destroy all quantum correlations. However, it has been predicted that macroscopic entanglement can exist in solids in the thermodynamical limit – even at high temperature – and it is related to critical phenomena. Here we propose an experimental setup to demonstrate entanglement extraction with present-day technology using optical lattices. This demonstrates that entanglement not only exists in solids, but can even be used for quantum information processing or to violate Bell’s inequalities ...
.......
High-Temperature Macroscopic Entanglement PRL Via Raitio – Aires FerreiraAriel Guerreiro, and Vlatko Vedral have published novel results on high-temperature macroscopic entanglement in Phys. Rev. Lett. 96, 060407 – arXivphysicsweb .  " 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. " 
.......
Signatures for generalized macroscopic superpositions Queensland In quant-ph 0701204 and Phys. Rev. Lett. 97Cavalcanti and Reid develop signature detection criteria for macroscopic quantum coherence in situations which are not limited to only two macrosopically distinct measurement outcomes.  "  The criteria provide a means to distinguish a single macroscopic quantum state from one based on a mixture of several microscopic superpositions of pointer-measurement eigenstates. "  Calculations are provided for the case of Gaussian-squeezed and spin-entangled states.
.......
Adaptive Quantum Networks quantum topology, neural networks Our most recent paper (Altman, Pykacz, Zaptatrin) on adaptive quantum neural networks appears in this month's International Journal of Theoretical Physics. We introduce a novel model of superposed, adaptive quantum networks, with considerations for high-dimensional dissipative quantum systems in both quantum computation and molecular biology. A preprint of the article is available via quant-ph 0311016
.......
Quantum Game Theory arXiv Nash equilibria and game theory profoundly affected the outcome of the 20th Century – preventing escalation of Cold War conflict between the US and USSR, for example. Quantum game theoretic approaches similarly hold the potential to influence strategic developments in the coming century. Quantum communications networks are already operating in research laboratories across the globe. With the recent birth of the DARPA/BBN quantum internet, quantum game theory has left the realm of academia and entered the world of practical applications, showing promise to transform politics, economics, conflict and warfare in the decades to come. In a recent PhD thesis,Iqbal reviews the current state of the field. See also  " Quantum Pseudo-Telepathy "  byBrassard et al,  " Classical Rules in Quantum Games "  by van Enk,  " Quantum Strategies "  by Meyer

.......
Restoring Quantum Coherence Pavia, Italy Decoherence remains the foremost limiting factor on practical implementation of quantum information technologies. In quant-ph0504195Buscemi et al. show that for qubit and qutrit systems it is always possible to recover quantum coherence by performing controlled measurements upon the environment, and that the minimal information required to invert qubit decoherence is equivalent to the von Neumann entropy exchange of the system. 
.......
Transfer of Nonclassical Properties from Microscopic Superpositions to Macroscopic Thermal States H. Jeong ,T.C. Ralph Abstract quant-ph 0410210  " We have studied a more reasonable analogy of Schrodinger’s cat paradox where the virtual cat is a significantly mixed thermal state. Our discussion was motivated by the observation that a truly classical system cannot be in a pure quantum state. We have found that non-classical properties of microscopic quantum superpositions can be transferred to thermal states of large average photon numbers. The resulting states show strong quantum coherence and entanglement between severely mixed thermal states. Our examples are feasible in real physical systems and may be realized for some moderate cases using current technology. Finally, it will be an interesting future work to explore the possibility of quantum information processing using the thermal-state “superpositions” and entanglement studied in this paper. " 
.......
Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems Berkeley Lab In Nature 446, 782-786, Fleming et al. report on coherent electron transfer in photosynthetic complexes.  "  We have obtained the first direct evidence that remarkably long-lived wavelike electronic quantum coherence plays an important part in energy transfer processes during photosynthesis. This wavelike characteristic can explain the extreme efficiency of the energy transfer, because it enables the system to simultaneously sample all the potential energy pathways and choose the most efficient one.  "  Covered also in Scientific AmericanWiredPhysicsWeb,rose.blog.
.......
Tunneling and green tea  J Am Chem Soc 129 (18) pp 5846 - 5854  "  Tunneling is a ubiquitous phenomenon in nature [...] We had a problem understanding how polyphenols work at such low concentrations. This paper gives theoretical credence to a large amount of experimental evidence of polyphenols as in vitro and in vivo antioxidants. " 
.......
Quantum Interference Effect Transistors PhysicsWeb Cardamone et al. propose a novel approach to single-molecule transistors, the quantum interference effect transistor, orQuIET. Each transistor consists of two electrodes attached to an organic ring molecule in one of two configurations: the presence or absence of quantum interference in the ring determines the state of the transistor.  " One potential advantage of the QuIET approach is that it could work in aqueous environments, such as those inside living organisms, because it is made of organic molecules. "  


Schematic diagrams of two types of QuIET In each, base voltage modulates the coherent suppression of current between emitter (E) and collector (C) leads. In (a), base voltage controls the distance x between the benzene ring and base lead (B), for example an STM tip. This in turn controls the coupling of the ring to the base lead. In (b), a base complex is introduced between the ring and base lead. The electrostatic effect of the base lead's bias on this molecule alters its coupling to the benzene ring.



.......
Room-temperature Bose-Einstein condensation? Hideyo OKUSHI, AIST Tsukuba Diamond Research Center, Japan The AIST Tsukuba Diamond Research Center has observed extremely sharp 235-nm exciton emission in fabricated single-crystal diamond film semiconductors at 300K. If the exciton lifetimes are long enough it is possible that Bose-Einstein condensation can occur in these diamond films, even at room temperature. 



.......
Refuting Nonlocal Realism In Nature 446 (871 - 875) and concurrent arXiv preprintZeilinger et al. refute nonlocal quantum realism in experiments with entangled photon pairs.  "  We measure previously untested correlations between two entangled photons, and show that these correlations violate an inequality proposed by Leggett for nonlocal realistic theories. Our result suggests that giving up the concept of locality is not sufficient to be consistent with quantum experimentsunless certain intuitive features of realism are abandoned "  Via Nature, Scientific AmericanQuantum Quandaries.
.......
Entangled Quantum Networks ICFO|ICREA|Max-Planck Institute In Nature Physics advance publication10.1038/nphys549Acin et al. draw upon the classical percolation methods of statistical mechanics to optimize entanglement distribution through quantum networks.  "  We argue that there exists an entanglement phase transition in quantum networks which may be exploited to obtain very efficient protocols. This work opens a new set of problems in quantum information theory, which are related to statistical physics, but pose completely new challenges in these fields [...] The work leads to a novel type of critical phenomenon, an entanglement phase transition that we call entanglement percolation.  " 




Maximizing entanglement in quantum networks. Each node is connected by a state consisting of two copies of the same two-qubit state. The nodes marked in (a) make the optimal measurement for the one-repeater configuration on pairs of qubits belonging to different connections. (b) A triangular lattice is obtained where the maximally entangled state for each connection is the same as for the two-qubit state. Acin et al., Nature Physics, 25 February 2007.

.......
Teleportation of massive particles without shared entanglement Queensland|Canberra arXiv quant-ph 0706.0062.  "  We propose a method for quantum state transfer from one atom laser beam to another via an intermediate optical field, using Raman incoupling and outcoupling techniques. Our proposal utilises existing experimental technologies to teleport macroscopic matter waves over potentially large distances without shared entanglement.  " 
.......
Proton Tunneling in Molecular Biophysics Rensselaer RPI researchers have employed the SCOREC supercomputing cluster to conduct advanced modeling of protein folding dynamics which incorporates quantum mechanical effects to study the influence of proton tunneling in enzyme catalysis. The group's initial study of intein's role in C-termini protein folding will be used to develop nanoscale switches for applications ranging from drug delivery to novel sensors.

.......
Measuring the Size of a Schrödinger Cat State München  " We propose a measure for the  " size "  of a Schrödinger cat state, i.e. a quantum superposition of two many-body states with macroscopically distinct properties, by counting how many single-particle operations are needed to map one state onto the other. This definition gives sensible results for simple, analytically tractable cases and is consistent with a previous definition restricted to Greenberger-Horne-Zeilinger-like states. We apply our measure to the experimentally relevant, nontrivial example of a superconducting three-junction flux qubit put into a superposition of left- and right-circulating supercurrent states and find this Schrödinger cat to be surprisingly small. " 
.......
Single-atom Macroscopic Entanglement Resource Texas A&M  " We discuss the generation of a macroscopic entangled state in a single atom cavity-QED system. The three-level atom in a cascade configuration interacts dispersively with two classical coherent fields inside a doubly resonant cavity. We show that a macroscopic entangled state between these two cavity modes can be generated under large detuning conditions. The entanglement persists even under the presence of cavity losses. " 
.......
Local Extraction of EPR Entanglement from Classical Systems Leeds|NUS Kaszlikowskiand Vedral outline a novel method of entanglement extraction using independent probes that locally interact with two subsets of a macroscopic system.  " Coherent states with large amplitudes are traditionally thought of as the best quantum mechanical approximation of classical behavior. Here we argue that, far from being classical, coherent states are in fact highly entangled. We demonstrate this by showing that a general system of indistinguishable bosons in a coherent state can be used to entangle, by local interactions, two spatially separated and distinguishable non-interacting quantum systems. Entanglement can also be extracted in the same way from number states or any other nontrivial superpositions of them [...] It may well be that nature already uses a phonon-to-electron entanglement transfer scheme similar to this to achieve some sort of coherent macroscopic behavior. " 
.......
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. " 



.......
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 0603208Kofler 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. " 



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.

.......
Towards Fullerene-Based Quantum Computing Oxford In quant-ph 0511198Benjamin et al. report on recent investigation of C60 arrays as a potential architecture for coherent quantum information processing.  " Molecular structures appear to be natural candidates for a quantum technology: individual atoms can support quantum superpositions for long periods, and such atoms can in principle be embedded in a permanent molecular scaffolding to form an array [...] Here we report our efforts, both experimental and theoretical, to create such a technology based on endohedral fullerenes or ‘buckyballs’. We describe our successes with respect to these criteria, along with the obstacles we are currently facing and the questions that remain to be addressed. " 



Fullerene Molecules Left: A model of N@C60, illustrating that the nitrogen atom sits at the centre of the fullerene cage. Its electron wavefunction lies almost entirely inside, extending on the cage with only a 2% overlap. Right: The ‘peapod’ nanotube contains fullerenes packed in a pseudo-helical phase.

.......
Theoretical and Experimental Exploration of Time Reversal Formalism Applied to Entanglement IQC, Waterloo In quant-ph/0510048, LaforestLaflamme and Baugh investigate time reversal of the Schrodinger equation in the context of teleportation. Experimental results are consistent with the interpretation that information can be seen as flowing backward in time through entanglement.  " In this paper, we analyze whether the acausal flow of information in a teleportation protocol can actually be physical, or should only consist of a mathematical model. Using an NMR spectrometer, we have demonstrated /experimental results faithful with the interpretation that, conditionally and in principle, entanglement seems like it can break the causality of time. "  
.......
Macroscopic entanglement measures quant-ph Notable submissions to the arXiv this month include a comprehensive overview of solid-state qubits by Esteve and Vion [0505676], two papers byNori et al. on macroscopic cat states [0506011] and testing Bell inequalities in Josephson qubits [0408089], Wilhelm and Kack present an efficient readout scheme for flux qubits at the degeneracy point [0505537], Greenberger and Svozil derive a quantum information theoretic analysis of time travel [0506027], WiesniakVedral and Brukner on macroscopic entanglement measures [0503037], Brassard et al. on quantum game theory and pseudo-telepathy [0408052], and a novel quantum storage and information transfer method in superconducting qubits by Wang et al. [0506144].
.......
Detection of Macroscopic Entanglement by Correlation of Local Observables University of Tokyo In quant-ph 0504086Shimizu and Morimae propose a macroscopic entanglement index for unknown and mixed states.  " We propose a correlation of local observables on many sites in macroscopic quantum systems. By measuring the correlation one can detect, if any, 'superposition of macroscopically distinct states,' which we call macroscopic entanglement, in arbitrary quantum states that are (effectively) homogeneous. Using this property, we also propose an index of macroscopic entanglement. " 
.......
Nonlocal Measurements in Time-Symmetric Quantum Mechanics arXiv Vaidman and Nevohave posted a preprint on nonlocal demolition measurement of backward evolving quantum states which allows for the introduction of novel types of nonlocal variables. The work builds upon upon Aharonov's time-symmetric formalism, which contains the quantum state evolving backward in time from complete measurement performed in the future relative to the time in question.  " Demolition measurements of nonlocal backward evolving quantum states require remarkably small resources. This is so because the combined operation of time reversal and teleportation of a local backward evolving quantum state requires only a single quantum channel and no transmission of classical information. " 
.......
Quantum Interference in Time arXiv Paulus has posted a preprint of the recent temporal quantum interference experiments, widely reported earlier this month:  " The conceptually most important interference experiment is the double-slit scheme, which has played a pivotal role in the development of optics and quantum mechanics. [...] We have realized an intriguing implementation of the double slit in the time domain. The observation of interference and its absence at the same time for the same electron is a beautiful demonstration of the principles of quantum mechanics. " 
.......
Macromolecular Quantum Interference Vienna ArndtHornberger and Zeilinger provide a summary of recent progress in matter-wave interferometry, outlining near-term experimental objectives as well as theoretical developments towards understanding the mechanisms of decoherence.  " In our view, matter-wave interferometry should be feasible for large objects such as proteins, small viruses and nanocrystals with atomic masses of up to 10^6 units. Extrapolating our results to bigger masses and higher temperatures, we believe that neither collisions nor thermal decoherence will be a problem in these cases. No fundamental limit of quantum interference is yet in sight, but much work still has to be done to prepare and manipulate coherent beams of supermassive particles. Carrying out such experiments will be a fascinating challenge. "  
.......
Energy-time entanglement preservation in plasmon-assisted light transmission  quant-ph0410064  " ...the only soliton particle quantum state compatible with [our] results is a superposition of a single soliton particle existing at two different moments in time separated one from the other by a duration of thousands of times longer than its own lifetime. At a macroscopic level this would lead to a  " Schrodinger cat "  living at two epochs that differ by much more than a cat's lifetime. " 
.......

NATO / Army Research Office – Advanced Research Workshop on Quantum Chaos Como, Italy I recently presented on superconducting quantum computing at the NATO ARO Advanced Research Workshop on Quantum Chaos at Lake Como, Italy. " The Workshop was organized to assess the state of the art in an authoritative and unprecedented way - to set the goals of the new frontiers of quantum chaos, the dynamics of complex systems, the feasibility of quantum computing, the development of new photonic devices, and to bring to light the seeds of new perspectives. " 
.......
Quantum entanglement by classical computer: a crucial experiment  Luigi Accardi, Centro V. Volterra, Roma A simple experiment is described in which two experimenters, by performing independent, local, binary choices on a common classical, deterministic, macroscopic source of randomness (in fact a generator of random points in the unit disk in the plane) and computing the empirical correlations among their results, arrive to a violation of Bell's inequalities. The local binary choices satisfy all the standard conditions of the EPR experiment: singlet, equiprobability, rotation invariance, etc. In addition the experiment suggests a new interpretation of the usual EPR experiment, more natural and appealing from the physical point of view than the usual one and totally in line with the  " chameleon effect "  which is at the basis of the quantum probabilistic approach to the theory of quantum measurement. A mathematical formulation of the  " chameleon effect "  will be discussed and illustrated with the mathematical model used to write the computer programme used in the experiment. The result of the present experiment, which for a long time has been considered to be impossible by the majority of physicists, fully confirms the point of view advocated, starting from the late 70's, by quantum probability in absolute isolation and strongly opposed by the majority of physicists who, following the interpretation due to Bell, were relating the violation of Bell's inequality to a non locality effect. In particular the experiment proves that: (i) it is possible to produce non-Kolmogorovian correlations by local realistic classical deterministic macroscopic systems (ii) it is possible to produce quantum entanglement by classicalcomputer. This opens the way to a series of new possibilities, for example the possibility of implementing quantum cryptography by classical computer. The experiment will be described and performed during the talk and the public will have the possibility to check the procedure by choosing the parameters of the measurements. An earlier version of the experiment is available at the Volterra Institute.
.......