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."

Quantum coherent oscillations in a charge qubit Y. Nakamura, Yu.A. Pashkin, and J.S. Tsai. Nature, 398:786, 1999.

Tunable coupling scheme for flux qubits CREST-JST Niskanen, Nakamura and Tsai introduce a design for tunably coupling two flux qubits via a third high-frequency qubit, allowing the qubits to remain optimally-biased and shielded from harmful low-frequency flux noise. "The presented scheme is an experimentally realistic way of carrying out two-qubit gates, and should be easily extended to multiqubit systems."

Quantum phase slip junctions Kavli Institute Delft Quantum phase slip is the exact dual to Cooper pair tunneling in the Josephson junction. In cond-mat 0511535, Mooij and Nazarov propose coherent quantum phase slip junctions. If experimentally verified, these junctions could yield applications as resonators or in fundamental current standards.

Scalable controlled gate operations KU In a recent submission to Physical Review A, Han and Yang present a novel approach to realize scalable, controlled-U gate operations with superconducting qubits coupled to a microwave cavity or in atomic qubits within cavity QED. "The method operates essentially by creating a single photon through one of the control SQUIDs, and then performing an arbitrary unitary transformation on the target SQUID with the assistance of the cavity photon."

Decoherence and quantum measurement of Josephson qubits Stony Brook Doctoral dissertation, Kristian Rabenstein

Towards Fullerene-Based Quantum Computing Oxford In quant-ph 0511198, Benjamin 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.

Efficient evaluation of decoherence rates in complex Josephson circuits IBM Watson Theoretical analysis of the variables contributing to decoherence in Josephson flux qubits has led to order-of-magnitude extensions of coherence time in these circuits over recent years, assisting in both the design phase and control parameter optimization for increasingly-complex qubit circuitry. In cond-mat 0510843, DiVincenzo, Brito and Koch perform a complete quantitative analysis of the decoherence properties of a Josephson flux qubit, exploring relaxation and dephasing times from two different control circuits along an optimal line in the space of applied fluxes.

Quantum Time Machines: What, Why and How? Queensland/Tokyo Tim Ralph presents a Qulink seminar on closed timelike curves in context of quantum information processing. "Whether time travel into the past is possible is an undecided physical question. Recently it has been noted that certain models of time travel for quantum particles do not lead to the same difficult paradoxes that arise for classical particles. Furthermore the types of quantum evolutions predicted for these 'quantum time machines' could give rise to a 'super' quantum computer, able to solve problems thought to be intractable by any other means. In this talk I will discuss time machines in general, how quantum mechanics avoids the paradoxes and the unusual evolutions predicted. I will then argue that the requirements for realizing such machines are not as stringent as previously thought and I will propose "horizon technology" experiments which could test these ideas."

Theoretical and Experimental Exploration of Time Reversal Formalism Applied to Entanglement IQC, Waterloo In quant-ph/0510048, Laforest, Laflamme 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."

RSFQ Circuits with Selective Dissipation for Coherent Quantum Information Processing VTT, Finland RSFQ, or rapid single flux quantum logic serves as a central component of HTMT, hybrid technology multi-threaded computing and other prototype high-performance architectures. In cond-mat/0510189, Hassel et al. investigate frequency-dependent damping as a means to reduce dissipation and subsequent decoherence in Josephson junction RSFQ/qubit circuits. "We derive criteria for the stability of such an arrangement, and discuss the effect on decoherence and the optimisation issues. We also design a simple flux generator aimed at manipulating flux qubits."

Life, the Universe and The Complexity Zoo IQC Waterloo In Shtetl-Optimized, Scott Aaronson waxes poetic on complexity theory: "Why is it so hard to explain that we don't worry about [complexity classes] because we're eccentric anal-retentives, but because we want to know whether a never-ending cavalcade of machines, each richer and more complicated than the last, might possibly succeed at a task on which any one machine must inevitably flounder – namely, the task of outracing time itself, of simulating cosmic history in an eyeblink, of seeing in the unformed clumps of an embryonic universe the swirl of every galaxy and flight of every hummingbird billions of years hence, like Almighty God Himself?"

Workshop on Quantum and Classical Information Security ARDA/NSA/NSF/Caltech 15-18 December 2005 – "The workshop will bring together researchers from a variety of backgrounds who work on different aspects of classical and quantum information security. Participants will strive to identify issues and problems of common interest that can be effectively addressed by pooling their expertise."

Flux Qubits as Trapped Ions RIKEN In quant-ph 0509236, Liu, Wei, Tsai and Nori propose a scalable superconducting circuit in which the qubits act as 'trapped ions.' The qubits are coupled to a 'vibrating' mode provided by a superconducting inductor-capacitor circuit, and interqubit couplings are selectively controlled by modulating the frequencies of the applied time-dependent magnetic flux.

Parametric Coupling for Flux Qubits Delft Pashkin and McDermott have independently demonstrated entanglement between superconducting qubits using a fixed linear coupling scheme. In cond-mat 0509799, Bertet, Harmans and Mooij propose a scalable architecture for two superconducting charge or flux qubits biased at symmetry points with unequal energy splittings. "The fixed-coupling strategy would be difficult to scale to a large number of qubits, and it is desirable to investigate more sophisticated schemes. Modulating the coupling constant between two qubits at the sum or difference of their two frequencies allows to bring them into resonance in the rotating frame. Switching on and off the modulation amounts to switching on and off the coupling which can be realized at nanosecond speed. We discuss various physical implementations of this idea, and find that our scheme can lead to rapid operation of a two-qubit gate."

Post Quantum Cryptography PQCrypto2006 Via the Pontiff – The European Network of Excellence for Cryptology (ECRYPT) and its Asymmetric Techniques Virtual Lab (AZTEC) examine the future of cryptography in the quantum computer era: "Will large quantum computers be built? If so, what will they do to the cryptographic landscape? Anyone who can build a large quantum computer can break today's most popular public-key cryptosystems: e.g., RSA, DSA, and ECDSA. But there are several other cryptosystems that are conjectured to resist quantum computers: e.g., the Diffie-Lamport-Merkle signature system, the NTRU encryption system, the McEliece encryption system, and the HFE signature system. Exactly which of these systems are secure? How efficient are they, in theory and in practice? PQCrypto 2006, the International Workshop on Post-Quantum Cryptography, will look ahead to a possible future of quantum computers, and will begin preparing the cryptographic world for that future."

Quantum Interferometric Sensors LSU Quantum entanglement garners a number of advantages to metrology and remote sensing applications. Dowling, Kapale et al. have issued a recent summary of progress in quantum interferometric sensors, which harness quantum entanglement for improved measurement sensitivity approaching the Heisenberg limit.

Phase-Slip Flux Qubits TU Delft In a recent paper submitted to the New Journal of Physics special issue on solid-state quantum information processing, Mooij and Harmans introduce phase-slip flux qubits, which harness quantum tunnelling to realize a superconducting qubit without the use of Josephson junctions. Phase-slip qubits potentially hold two distinct advantages over traditional flux qubits: lower sensitivity to charge noise-based sources of decoherence, and well-defined separation of energy levels of more than 500 GHz, allowing for extremely rapid excitation of the qubit.



Energy Level Separation Energy levels as a function of applied flux for different fluxoid numbers. A phase-slip event changes the fluxoid number n. The arrow indicates the operating point at f= ½.

Macroscopic EPR Pairs in Superconducting Circuits RIKEN In quant-ph/0508027, Nori et al. propose an efficient approach for deterministic generation of entangled EPR pairs in coupled Josephson nanocicruits. Realization of the experiment would provide an effective means of testing Bell inequality violations, demonstrating nonlocality of quantum entanglement in macroscopic systems.

Delft Scientists Split Electron Pairs in Superconductors TU Delft "Scientists at Stichting FOM and Kavli Institute of Nanoscience Delft have demonstrated that electrons that normally travel through superconductors in pairs can be seperated while retaining their quantum mechanical kinship. The formation of electron pairs - so-called Cooper pairs - is such a fundamental property of current flow in superconductors that the Delft experiment is considered a breakthrough. It lays the foundation for the realization of a superconducting entangler capable of injecting pairs of entangled electrons into nanoelectronic circuits, an important building block of the quantum computer scientists have been dreaming of for years."

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."

Restoring Quantum Coherence Pavia, Italy Decoherence remains the foremost limiting factor on practical implementation of quantum information technologies. In quant-ph 0504195, Buscemi 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.

Measuring Decoherence in a three-level rf SQUID Qubit U Kansas In cond-mat 0507008, Han et al. perform direct and quantitative measurements of dissipation-induced relaxation in a three-level rf SQUID qubit. "Analysis of the system indicates that the dominant sources of qubit dissipation are the flux bias and magnetometer readout circuits. Since this kind of dissipation-induced qubit decoherence can be greatly suppressed with more sophisticated designs we believe it does not impose a fundamental limit to this type of qubit [...] We are developing advanced designs for qubit bias and readout circuits that are predicted to decrease their contributions to the qubit damping by several orders of magnitude."

Josephson Bifurcation Amplifier for Quantum Measurements Yale In cond-mat 0507248, Devoret et al. construct a new type of amplifier for superconducting qubit readout based on the transition of an rf driven Josephson junction between two distinct oscillation states near a dynamic bifurcation point: "The main advantages of this new amplifier are speed, high-sensitivity, low back-action, and the absence of on-chip dissipation. Using pulsed microwave techniques, we demonstrate bifurcation amplification in nanofabricated Al junctions and verify that the performance predicted by theory is attained."

Flux-Qubit Readout with Frequency Dependent Damping Berkeley, München "Recent experiments on superconducting flux qubits, consisting of a superconducting loop interrupted by Josephson junctions, have demonstrated quantum coherence between two different quantum states. The state of the qubit is measured with a superconducting quantum interference device. Such measurements require the SQUID to have high resolution while exerting minimal backaction on the qubit." In Phys. Rev. B 72, 024513 , Plourde, Wilhelm et al. employ a path-integral approach to analyze the Caldeira-Leggett model, calculating backaction of a shunted symmetric SQUID on a flux qubit. "To test the model, we fabricated a dc SQUID in which each junction is shunted with a thin-film interdigitated capacitor in series with a resistor, and measured the switching distribution as a function of temperature and applied magnetic flux. After accounting for the damping due to the SQUID leads, we found good agreement between the measured escape rates and the predictions of our model. "

arXiv Notables quant-ph Notable submissions to the arXiv this month include a comprehensive overview of solid-state qubits by Esteve and Vion [0505676], two papers by Nori 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], Wiesniak, Vedral 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].

Quantum-Classical Interface Sussex, Liverpool In cond-mat/0505390, Mark Everitt et al. explore nonlinear interaction of a quantum mechanical SQUID ring with its environment. Potential applications include large frequency ratio down-conversion between electromagnetic fields, such as in classical THz communications technologies. "With the now very serious interest being taken in the possibilities of creating quantum technologies such as quantum information processing and quantum computing, much attention is being focused on the application of Josephson effect devices, particularly the SQUID ring. The highly non-perturbative nature of the SQUID ring in the quantum regime means that the ring-environment interaction can be very non-linear, and may lead to unexpected results ..."

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 ..."

An n-qubit controlled phase gate with resonator-coupled SQUIDs U Kansas In quant-ph/0504188, Siyuan Han and Chui-Ping Yang propose a novel method to realize multiqubit controlled phase gates with SQUIDs. The scheme "operates essentially by exchanging a single photon between the controlled SQUIDs and the resonator mode before and after a phase shift performed on the target SQUID."

Transport of atoms in a quantum conveyor belt NIST Gaithersburg cond-mat/0504606 "An atomic-gas Bose-Einstein condensate (BEC) is a coherent source of matter waves – a collection of atoms, all in the same state, with an extremely narrow momentum spread ... We can easily control the velocity and acceleration of the atomic lattice structure as well as its strength, making it a variable 'quantum conveyor belt.' This allows us to explore situations that are difficult or impossible to achieve in solid state systems. The results are often remarkable and counterintuitive."

Signatures of quantum behavior in single-qubit weak measurements Penn State, UC Riverside quant-ph/0505094 "With the recent surge of interest in quantum computation, it has become very important to develop clear experimental tests for 'quantum behavior' in a system. This issue has been addressed in the past in the form of the inequalities due to Bell and those due to Leggett and Garg. These inequalities concern the results of ideal projective measurements, however, which are experimentally difficult to perform in many proposed qubit designs ... Here, we show that weak continuous measurements, which are often practical to implement experimentally, can yield particularly clear signatures of quantum coherence ..."

Full Protection of Superconducting Qubit Systems from Coupling Errors Munchen, Berkeley quant-ph/0407780 "Solid state qubits realized in superconducting circuits are potentially extremely scalable. However, strong decoherence may be transferred to the qubits by various elements of the circuits that couple individual qubits [...] We propose here an encoding that provides full protection against errors originating from these coupling elements ..."

Asymmetry and Decoherence in a Double-layer Persistent-current Qubit Kavli Institute Delft cond-mat/0405272 "We discuss a superconducting flux qubit design that exploits the symmetries of a circuit to protect the qubit from unwanted coupling to the noisy environment [...] Possibilities for prolonging the relaxation and decoherence times of the studied superconducting qubit are proposed on the basis of the obtained results."

Detection of Macroscopic Entanglement by Correlation of Local Observables University of Tokyo In quant-ph 0504086, Shimizu 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."

Spectroscopy on Two Coupled Superconducting Flux Qubits Kavli Institute Delft In PRL 94, 090501 (2005) Mooij et al. report on spectroscopy measurements of two coupled superconducting flux qubits: "The new results support the notion that superconducting flux qubits can be used to study entanglement in macroscopic quantum systems and for the development of nontrivial two-qubit gates [...] We demonstrate that two macroscopic flux qubits can be coupled to form a quantum mechanical four level system."

2005 Agilent Europhysics Prize Agilent Technologies The 2005 Agilent Technologies Europhysics Prize has been awarded to Awschalom, Dietl, and Ohno for their investigation of solid-state magnetic semiconductors and spin coherence. Spintronics is a promising candidate for scalable quantum computation. "We are proud to recognize these scientists for combining advanced materials engineering, insightful theoretical modeling, ingenious experimental techniques, and international collaboration to attain important breakthroughs in spintronics," said Jim Hollenhorst, director of molecular technology at Agilent Laboratories. Last year the award was shared by Mooij, Nakamura, Devoret and Esteve for their demonstration of superconducting circuits as qubits.

Nonlocal Measurements in Time-Symmetric Quantum Mechanics arXiv Vaidman and Nevo have 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 Effect Transistors PhysicsWeb Cardamone et al. propose a novel approach to single-molecule transistors, the quantum interference effect transistor, or QuIET. 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.


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" by Brassard et al, "Classical Rules in Quantum Games" by van Enk, "Quantum Strategies" by Meyer.