Generating quantum entanglement in large systems on time scales much shorter than the coherence time is key to powerful quantum simulation and computation. Trapped ions are among the most accurately controlled and best isolated quantum systems [1] with low-error entanglement gates operated via the vibrational motion of a few-ion crystal within tens of microseconds [2]. To exceed the level of complexity tractable by classical computers the main challenge is to realise fast entanglement operations in large ion crystals [3,4]. The strong dipole-dipole interactions in polar molecule [5] and Rydberg atom [6,7] systems allow much faster entangling gates, yet stable state-independent confinement comparable with trapped ions needs to be demonstrated in these systems [8]. Here, we combine the benefits of these approaches: we report a 700 ns two-ion entangling gate which utilises the strong dipolar interaction between trapped Rydberg ions and produce a Bell state with 78% fidelity. The sources of gate error are identified and a total error below 0.2% is predicted for experimentally-achievable parameters. Furthermore, we predict that residual coupling to motional modes contributes ∼ 10 −4 gate error in a large ion crystal of 100 ions. This provides a new avenue to significantly speed up and scale up trapped ion quantum computers and simulators. Trapped atomic ions are one of the most promising architectures for realizing a universal quantum computer [1]. The fundamental single-and two-qubit quantum gates have been demonstrated with errors less than 0.1% [2], sufficiently low for fault-tolerant quantum errorcorrection schemes [10]. Nevertheless, a scalable quantum computer requires a large number of qubits and a large number of gate operations to be conducted within the coherence time.Most established gate schemes using a common motional mode are slow (typical gate times are between 40 and 100 µs) and difficult to scale up since the motional spectrum becomes more dense with increasing ion number. Many new schemes have been proposed [11][12][13][14], with the fastest experimentally-achieved gate being 1.6 µs (99.8% fidelity) and 480 ns (60% fidelity) [15], realised by driving multiple motional modes simultaneously. Although the gate speed is not limited by the trap frequencies, the gate protocol requires the phase-space trajectories of all modes to close simultaneously at the end of the pulse sequence [15]. In long ion strings with a large number of vibrational modes, it becomes increasingly challenging to find and implement laser pulse parameters that execute this gate with a low error. Thus, a slow-down of gate speed appears inevitable.Two-qubit entangling gates in Rydberg atom systems are substantially faster, owing to strong dipole-dipole interactions. The gate fidelities in recent experiments using neutral atoms are fairly high [16,17]. However, the atom traps need to be turned off during Rydberg excitation. This can cause unwanted coupling between qubits and atom motion as well as atom loss [8,18]. Employing blue-detune...

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The efficiency of energy transfer in hybrid organic/inorganic nanocomposites based on conjugated polymers and semiconductor nanocrystals is strongly dependent on both the energy transfer rate and the rate of the nonradiative recombination of the polymer. We demonstrate that the polymer nonradiative recombination can be reduced by the suppression of exciton diffusion via proper morphology engineering of a hybrid structure. In the layer-by-layer assembled nanocomposite of a conjugated polymer and CdTe nanocrystals the latter have a dual role: first, they are efficient exciton acceptors and, second, they reduce nonradiative recombination in the polymer by suppressing exciton diffusion across the layers. © 2010 American Institute of Physics. ͓doi:10.1063/1.3319838͔The development of hybrid organic/inorganic nanocomposite materials is a promising strategy to create new functional materials with tunable optical and electronic properties not accessible in any of the individual components. In particular, composites of conjugated polymers and semiconductor nanocrystals ͑NCs͒ have recently attracted significant attention because of their potential applications in lightemitting and photovoltaic devices. 1,2 In comparison to organic emitters, semiconductor NCs possess a number of advantages such as high photostability, broad spectral range of light absorption and narrow emission line widths. 3 On the other hand the conduction properties of closely packed NC films are poor, 4 making the electrical pumping of NCs inefficient. An evident approach to overcome this difficulty is designing a composite material where the NCs provide their advantageous luminescent properties and a conducting polymer provides efficient charge conduction. 5 Designing such nanocomposite materials requires a deep and detailed understanding of the energy transfer ͑ET͒ process from the organic to the inorganic component, which is still a subject of extensive research. Efficient ET has been reported 6-9 and the importance of the exciton diffusion has been verified 10 in the blended films of conjugated polymers and semiconductor NCs. Recently we've revealed that ET occurs rather via the Förster than the Dexter mechanism due to the nanoscale geometry of the system. 11 However, although a considerable understanding of the ET process has been achieved, the influence of morphology of such hybrid structures on the optoelectronic properties of the conjugated polymers and as a consequence on the ET process has not been understood and/or analyzed yet. In this work we explore by means of temperature dependent photoluminescence ͑PL͒ measurements the role of the morphology in the ET process in hybrid layer-by-layer ͑LbL͒ nanocomposites. We find that semiconductor NCs have a dual function in LbL structures. First, they are very efficient energy acceptors and, second, they reduce nonradiative recombination of the polymer.Following reported procedures we synthesized the water-soluble conjugated polymer poly͓9,9-bis͑3Ј-͓͑N,Ndimethyl͒ -N-ethylammonium͔-propyl͒ -2,7-fluore...

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