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A wafer-scale graphene circuit was demonstrated in which all circuit components, including graphene field-effect transistor and inductors, were monolithically integrated on a single silicon carbide wafer. The integrated circuit operates as a broadband radio-frequency mixer at frequencies up to 10 gigahertz. These graphene circuits exhibit outstanding thermal stability with little reduction in performance (less than 1 decibel) between 300 and 400 kelvin. These results open up possibilities of achieving practical graphene technology with more complex functionality and performance.

The realization of an all-optical transistor, in which one \"gate\" photon controls a \"source\" light beam, is a long-standing goal in optics. By stopping a light pulse in an atomic ensemble contained inside an optical resonator, we realized a device in which one stored gate photon controls the resonator transmission of subsequently applied source photons. A weak gate pulse induces bimodal transmission distribution, corresponding to zero and one gate photons. One stored gate photon produces fivefold source attenuation and can be retrieved from the atomic ensemble after switching more than one source photon. Without retrieval, one stored gate photon can switch several hundred source photons. With improved storage and retrieval efficiency, our work may enable various new applications, including photonic quantum gates and deterministic multiphoton entanglement.

Closer to an exotic goal Placing a macroscopic object in its quantum-mechanical ground state of motion is an exciting experimental prospect. If achieved, it should reveal counter-intuitive physical behaviour — such as the existence of the system in two locations simultaneously. Rocheleau et al . come tantalizingly close to this goal. They have cooled a nanomechanical resonator to a point where the probability of it residing in its motional ground state is 0.21 (which in itself should be sufficient to enable direct measurement of some anticipated quantum phenomena), and have identified the experimental hurdles that need to be overcome to push the system more fully into this exotic quantum regime. Placing a macroscopic object in its quantum-mechanical ground state of motion is an exciting experimental target that should reveal counterintuitive physical behaviour — such as the existence of states in which the mechanical system is located in two places simultaneously. A nanomechanical resonator is now cooled to a point where the probability of its residing in the quantum ground state of motion is 0.21; this level of cooling should allow a series of fundamental quantum mechanical observations. Cold, macroscopic mechanical systems are expected to behave contrary to our usual classical understanding of reality; the most striking and counterintuitive predictions involve the existence of states in which the mechanical system is located in two places simultaneously. Various schemes have been proposed to generate and detect such states 1 , 2 , and all require starting from mechanical states that are close to the lowest energy eigenstate, the mechanical ground state. Here we report the cooling of the motion of a radio-frequency nanomechanical resonator by parametric coupling to a driven, microwave-frequency superconducting resonator. Starting from a thermal occupation of 480 quanta, we have observed occupation factors as low as 3.8 ± 1.3 and expect the mechanical resonator to be found with probability 0.21 in the quantum ground state of motion. Further cooling is limited by random excitation of the microwave resonator and heating of the dissipative mechanical bath. This level of cooling is expected to make possible a series of fundamental quantum mechanical observations including direct measurement of the Heisenberg uncertainty principle and quantum entanglement with qubits.

Cavity quantum electrodynamics: Fock states represent quantum purity In cavity quantum electrodynamics (QED), light–matter interactions between a single emitter (an atom or an atom-like system with discrete energy levels) and a resonant optical cavity are investigated at a fundamental level. Recent advances in solid-state implementations, which offer great design flexibility, have given this field considerable momentum. An outstanding important question has been which features in such a system show true quantum behaviour and cannot be explained with classical models. Hofheinz et al . study a 'circuit' QED system where a superconducting qubit acts as an atom-like two-energy level system and is embedded in a microwave transmission circuit, acting as the optical cavity. They demonstrate in this system the creation of pure quantum states, known as Fock states, which give specific numbers of energy quanta, in this case photons. Fock states with up to six photons are prepared and analysed. The results are important because cavity QED is expected to play a crucial role in the development of quantum information processing and communication applications. A 'circuit' quantum electrodynamics system where a superconducting qubit acts as an atom-like two-energy level system and is embedded in a microwave transmission circuit (acting as the optical cavity) is studied. In this system, it is demonstrated that the creation of pure quantum states, known as Fock states, which give specific numbers of energy quanta, in this case photons. Fock states with up to six photons are prepared and analysed. Spin systems and harmonic oscillators comprise two archetypes in quantum mechanics 1 . The spin-1/2 system, with two quantum energy levels, is essentially the most nonlinear system found in nature, whereas the harmonic oscillator represents the most linear, with an infinite number of evenly spaced quantum levels. A significant difference between these systems is that a two-level spin can be prepared in an arbitrary quantum state using classical excitations, whereas classical excitations applied to an oscillator generate a coherent state, nearly indistinguishable from a classical state 2 . Quantum behaviour in an oscillator is most obvious in Fock states, which are states with specific numbers of energy quanta, but such states are hard to create 3 , 4 , 5 , 6 , 7 . Here we demonstrate the controlled generation of multi-photon Fock states in a solid-state system. We use a superconducting phase qubit 8 , which is a close approximation to a two-level spin system, coupled to a microwave resonator, which acts as a harmonic oscillator, to prepare and analyse pure Fock states with up to six photons. We contrast the Fock states with coherent states generated using classical pulses applied directly to the resonator.

Although universal quantum computers ideally solve problems such as factoring integers exponentially more efficiently than classical machines, the formidable challenges in building such devices motivate the demonstration of simpler, problem-specific algorithms that still promise a quantum speedup. We constructed a quantum boson-sampling machine (QBSM) to sample the output distribution resulting from the nonclassical interference of photons in an integrated photonic circuit, a problem thought to be exponentially hard to solve classically. Unlike universal quantum computation, boson sampling merely requires indistinguishable photons, linear state evolution, and detectors. We benchmarked our QBSM with three and four photons and analyzed sources of sampling inaccuracy. Scaling up to larger devices could offer the first definitive quantum-enhanced computation.

A passive optical diode effect would be useful for on-chip optical information processing but has been difficult to achieve. Using a method based on optical nonlinearity, we demonstrate a forward-backward transmission ratio of up to 28 decibels within telecommunication wavelengths. Our device, which uses two silicon rings 5 micrometers in radius, is passive yet maintains optical nonreciprocity for a broad range of input power levels, and it performs equally well even if the backward input power is higher than the forward input. The silicon optical diode is ultracompact and is compatible with current complementary metal-oxide semiconductor processing.

Emerging applications based on optical beams carrying orbital angular momentum (OAM) will probably require photonic integrated devices and circuits for miniaturization, improved performance, and enhanced functionality. We demonstrate silicon-integrated optical vortex emitters, using angular gratings to extract light confined in whispering gallery modes with high OAM into free-space beams with well-controlled amounts of OAM. The smallest device has a radius of 3.9 micrometers. Experimental characterization confirms the theoretical prediction that the emitted beams carry exactly defined and adjustable OAM. Fabrication of integrated arrays and demonstration of simultaneous emission of multiple identical optical vortices provide the potential for large-scale integration of optical vortex emitters on complementary metal-oxide-semiconductor compatible silicon chips for wide-ranging applications.

Internet data traffic capadty is rapidly reaching limits imposed by optical fiber nonlinear effects. Having almost exhausted available degrees of freedom to orthogonally multiplex data, the possibility is now being explored of using spatial modes of fibers to enhance data capadty. We demonstrate the viability of using the orbital angular momentum (OAM) of light to create orthogonal, spatially distinct streams of data-transmitting channels that are multiplexed in a single fiber. Over 1.1 kilometers of a specially designed optical fiber that minimizes mode coupling, we achieved 400-gigabits-per-second data transmission using four angular momentum modes at a single wavelength, and 1.6 terabits per second using two OAM modes over 10 wavelengths. These demonstrations suggest that OAM could provide an additional degree of freedom for data multiplexing in future fiber networks.

Quantum computers are unnecessary for exponentially efficient computation or simulation if the Extended Church-Turing thesis is correct. The thesis would be strongly contradicted by physical devices that efficiently perform tasks believed to be intractable for classical computers. Such a task is boson sampling: sampling the output distributions of n bosons scattered by some passive, linear unitary process. We tested the central premise of boson sampling, experimentally verifying that three-photon scattering amplitudes are given by the permanents of submatrices generated from a unitary describing a six-mode integrated optical circuit. We find the protocol to be robust, working even with the unavoidable effects of photon loss, non-ideal sources, and imperfect detection. Scaling this to large numbers of photons should be a much simpler task than building a universal quantum computer.

Flexible nanotube circuits Integrated circuits formed on flexible plastic sheets can be lighter and tougher than those made from conventional materials, as well as being usefully bendy. Semiconductors made from organic small molecules and polymers have shown promise in such applications, but a new carbon-based nanomaterial described in this issue — its creators say — promises higher performance in electronic applications than the currently available options. Cao et al . have developed small- to medium-scale integrated digital circuits consisting of random networks of single-walled carbon nanotubes on plastic substrates. The layouts enable both high mobilities and high on/off ratios and the resulting devices and circuits (consisting of up to 100 transistors) show excellent electronic properties. These new films should be of use for a wide range of applications such as unusual consumer electronic devices, biological sensing and optoelectronics. The ability to form integrated circuits on flexible sheets of plastic enables attributes (for example conformal and flexible formats and lightweight and shock resistant construction) in electronic devices that are difficult or impossible to achieve with technologies that use semiconductor wafers or glass plates as substrates 1 . Organic small-molecule and polymer-based materials represent the most widely explored types of semiconductors for such flexible circuitry 2 . Although these materials and those that use films or nanostructures of inorganics have promise for certain applications, existing demonstrations of them in circuits on plastic indicate modest performance characteristics that might restrict the application possibilities. Here we report implementations of a comparatively high-performance carbon-based semiconductor consisting of sub-monolayer, random networks of single-walled carbon nanotubes to yield small- to medium-scale integrated digital circuits, composed of up to nearly 100 transistors on plastic substrates. Transistors in these integrated circuits have excellent properties: mobilities as high as 80 cm 2  V -1  s -1 , subthreshold slopes as low as 140 m V dec -1 , operating voltages less than 5 V together with deterministic control over the threshold voltages, on/off ratios as high as 10 5 , switching speeds in the kilohertz range even for coarse (∼100-μm) device geometries, and good mechanical flexibility—all with levels of uniformity and reproducibility that enable high-yield fabrication of integrated circuits. Theoretical calculations, in contexts ranging from heterogeneous percolative transport through the networks to compact models for the transistors to circuit level simulations, provide quantitative and predictive understanding of these systems. Taken together, these results suggest that sub-monolayer films of single-walled carbon nanotubes are attractive materials for flexible integrated circuits, with many potential areas of application in consumer and other areas of electronics.