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Strong ties Achieving coherent quantum control over massive mechanical resonators via coupling to electrons or photons is a current research goal. Here Gröblacher et al . report clear evidence for coupling of cavity photons to a mechanical resonator in the strong regime, which is essential for the preparation of mechanical quantum states and applications in quantum information processing. Achieving coherent quantum control over massive mechanical resonators via coupling to electrons or photons is a current research goal. Here, unambiguous evidence for strong coupling of cavity photons to a mechanical resonator is reported, paving the way for full quantum optical control of nano- and micromechanical devices. Achieving coherent quantum control over massive mechanical resonators is a current research goal. Nano- and micromechanical devices can be coupled to a variety of systems, for example to single electrons by electrostatic 1 , 2 or magnetic coupling 3 , 4 , and to photons by radiation pressure 5 , 6 , 7 , 8 , 9 or optical dipole forces 10 , 11 . So far, all such experiments have operated in a regime of weak coupling, in which reversible energy exchange between the mechanical device and its coupled partner is suppressed by fast decoherence of the individual systems to their local environments. Controlled quantum experiments are in principle not possible in such a regime, but instead require strong coupling. So far, this has been demonstrated only between microscopic quantum systems, such as atoms and photons (in the context of cavity quantum electrodynamics 12 ) or solid state qubits and photons 13 , 14 . Strong coupling is an essential requirement for the preparation of mechanical quantum states, such as squeezed or entangled states 15 , 16 , 17 , 18 , and also for using mechanical resonators in the context of quantum information processing, for example, as quantum transducers. Here we report the observation of optomechanical normal mode splitting 19 , 20 , which provides unambiguous evidence for strong coupling of cavity photons to a mechanical resonator. This paves the way towards full quantum optical control of nano- and micromechanical devices.

An ideal Q -factor Interest in the properties of surface plasmon polaritons is intense because of their relevance to plasmonics and nanophotonics. They are electron density waves excited at the interface between metals and dielectric materials and interact strongly with light at a subwavelength-scale. A good starting point for useful applications would be a plasmonic micro- or nanocavity with a high figure of merit, or Q -value; a high Q factor means that the plasmons are strongly confined and bounce around many times inside the cavity before escaping, resulting in a rich range of physical properties. Until now the Q -factor for plasmonic resonant cavities has been limited to values less than one hundred for visible and near-infrared wavelengths. Now Min et al . demonstrate a high- Q 'whispering gallery' microcavity for surface plasmons that is fabricated by coating the surface of high- Q silica microresonator with a thin layer of noble metal. This structure enables room-temperature operation with a Q -factor of around 1,380 in the near infrared for surface plasmon modes — a nearly ideal value. The work also includes a coupling scheme where a tapered optical fibre is in near-contact with the cavity, which provides a convenient way for selectively exciting and probing confined plasmon modes. This paper demonstrates a high-Q microcavity for surface plasmons that is fabricated by coating the surface of high-Q silica microresonator with a thin layer of noble metal. This structure enables room-temperature operation with a Q-factor of around 1380 in the near infrared for surface plasmon modes. The work also includes a coupling scheme where a tapered optical fibre is in near-contact with the cavity, which provides a convenient way for selectively exciting and probing confined plasmon modes. Surface plasmon polaritons (SPPs) are electron density waves excited at the interfaces between metals and dielectric materials 1 . Owing to their highly localized electromagnetic fields, they may be used for the transport and manipulation of photons on subwavelength scales 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 . In particular, plasmonic resonant cavities represent an application that could exploit this field compression to create ultrasmall-mode-volume devices. A key figure of merit in this regard is the ratio of cavity quality factor, Q (related to the dissipation rate of photons confined to the cavity), to cavity mode volume, V (refs 10 , 11 ). However, plasmonic cavity Q factors have so far been limited to values less than 100 both for visible and near-infrared wavelengths 12 , 13 , 14 , 15 , 16 . Significantly, such values are far below the theoretically achievable Q factors for plasmonic resonant structures. Here we demonstrate a high- Q SPP whispering-gallery microcavity that is made by coating the surface of a high- Q silica microresonator with a thin layer of a noble metal. Using this structure, Q factors of 1,376 ± 65 can be achieved in the near infrared for surface-plasmonic whispering-gallery modes at room temperature. This nearly ideal value, which is close to the theoretical metal-loss-limited Q factor, is attributed to the suppression and minimization of radiation and scattering losses that are made possible by the geometrical structure and the fabrication method. The SPP eigenmodes, as well as the dielectric eigenmodes, are confined within the whispering-gallery microcavity and accessed evanescently using a single strand of low-loss, tapered optical waveguide 17 , 18 . This coupling scheme provides a convenient way of selectively exciting and probing confined SPP eigenmodes. Up to 49.7 per cent of input power is coupled by phase-matching control between the microcavity SPP and the tapered fibre eigenmodes.

Ultrabroad-bandwidth radiofrequency pulses offer significant applications potential, such as increased data transmission rate and multipath tolerance in wireless communications. Such ultrabroad-bandwidth pulses are inherently difficult to generate with chip-based electronics due to limits in digital-to-analog converter technology and high timing jitter. Photonic means of radiofrequency waveform generation, for example, by spectral shaping and frequency–time mapping, can overcome the bandwidth limit in electronic generation. However, previous bulk optic systems for radiofrequency arbitrary waveform generation do not offer the integration advantage of electronics. Here, we report a chip-scale, fully programmable spectral shaper consisting of cascaded multiple-channel microring resonators, on a silicon photonics platform that is compatible with electronic integrated circuit technology. Using such a spectral shaper, we demonstrate the generation of burst radiofrequency waveforms with programmable time-dependent amplitude, frequency and phase profiles, for frequencies up to 60 GHz. Our demonstration suggests potential for chip-scale photonic generation of ultrabroad-bandwidth arbitrary radiofrequency waveforms. Ultrabroad-bandwidth radiofrequency pulses that increase data transmission rate and allow multipath tolerance in wireless communications are difficult to generate using chip-based electronics. Now, a chip-scale fully programmable spectral shaper consisting of cascaded multichannel micro-ring resonators is demonstrated as a solution.

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.

The circulation of light within dielectric volumes enables storage of optical power near specific resonant frequencies and is important in a wide range of fields including cavity quantum electrodynamics 1 , 2 , photonics 3 , 4 , biosensing 5 , 6 and nonlinear optics 7 , 8 , 9 . Optical trajectories occur near the interface of the volume with its surroundings, making their performance strongly dependent upon interface quality. With a nearly atomic-scale surface finish, surface-tension-induced microcavities such as liquid droplets or spheres 10 , 11 , 12 , 13 are superior to all other dielectric microresonant structures when comparing photon lifetime or, equivalently, cavity Q factor. Despite these advantageous properties, the physical characteristics of such systems are not easily controlled during fabrication. It is known that wafer-based processing 14 of resonators can achieve parallel processing and control, as well as integration with other functions. However, such resonators-on-a-chip suffer from Q factors that are many orders of magnitude lower than for surface-tension-induced microcavities, making them unsuitable for ultra-high- Q experiments. Here we demonstrate a process for producing silica toroid-shaped microresonators-on-a-chip with Q factors in excess of 100 million using a combination of lithography, dry etching and a selective reflow process. Such a high Q value was previously attainable only by droplets or microspheres and represents an improvement of nearly four orders of magnitude over previous chip-based resonators.

Inkjet-printing is a very promising technology for the development of microwave circuits and components. Inkjet-printing technology of conductive silver nanoparticles on an organic flexible paper substrate is introduced in this study. The paper substrate is characterised using the T-resonator method. A variety of microwave passive and active devices, as well as complete circuits inkjet-printed on paper substrates are introduced. This work includes inkjet-printed artificial magnetic conductor structures, a substrate integrated waveguide, solar-powered beacon oscillator for wireless power transfer and localisation, energy harvesting circuits and nanocarbon-based gas-sensing materials such as carbon nanotubes and graphene. This study presents an overview of recent advances of inkjet-printed electronics on paper substrate.