Precision measurements are important across all fields of science. In particular, optical phase measurements can be used to measure distance, position, displacement, acceleration, and optical path length. Quantum entanglement enables higher precision than would otherwise be possible. We demonstrated an optical phase measurement with an entangled four-photon interference visibility greater than the threshold to beat the standard quantum limit-the limit attainable without entanglement. These results open the way for new high-precision measurement applications.

We demonstrate the possibility to achieve optical triggering of photochemical reactions via two-photon absorption using incoherent light sources. This is accomplished by the use of arrays of gold nanoparticles, specially tailored with high precision to obtain high near-field intensity enhancement.

Strong coupling between plasmons and optical modes, such as waveguide or resonator modes, gives rise to a splitting in the plasmon absorption band. As a result, two new hybrid modes are formed that exhibit near-field enhancement effects. These hybrid modes have been exploited to improve light absorption in a number of systems. Here we show that this modal strong coupling between a Fabry-Pérot nanocavity mode and a localized surface plasmon resonance (LSPR) facilitates water splitting reactions. We use a gold nanoparticle (Au-NP)/TiO/Au-film structure as a photoanode. This structure exhibits modal strong coupling between the Fabry-Pérot nanocavity modes of the TiO thin film/Au film and LSPR of the Au NPs. Electronic excitation of the Au NPs is promoted by the optical hybrid modes across a broad range of wavelengths, followed by a hot electron transfer to TiO. A key feature of our structure is that the Au NPs are partially inlaid in the TiO layer, which results in an enhancement of the coupling strength and water-oxidation efficiency. We observe an 11-fold increase in the incident photon-to-current conversion efficiency with respect to a photoanode structure with no Au film. Also, the internal quantum efficiency is enhanced 1.5 times under a strong coupling over that under uncoupled conditions.

We report the first experimental demonstration of an optical quantum controlled-NOT gate without any path interference, where the two interacting path interferometers of the original proposals have been replaced by three partially polarizing beam splitters with suitable polarization dependent transmittance and reflectance. The performance of the device is evaluated using a recently proposed method, by which the quantum process fidelity and the entanglement capability can be estimated from the 32 measurement results of two classical truth tables, significantly less than the 256 measurement results required for full quantum tomography.

Modification of optical properties of materials by nanoengineering is one of the current trends in the materials science. Periodic dielectric and metallo-dielectric nanostructures show great potential for the control of light emission, propagation and absorption via photonic band-gap effect. [1,2] Nanoengineered particles of noble metals exhibit intense optical nearfield due to localized surface plasmon (LSP) resonance and promise novel applications in nonlinear optics and spectroscopy, [3,4] optical sensing, [5][6][7][8][9] and metrology. [10,11] Although metals are typically perceived as poor light emitters, silver and gold nanoparticles exhibit intense photoluminescence (PL) under near-infrared excitation via two-photon absorption (TPA) assisted by the strong LSP near-field.[12] Thus, structurally tailored metal nanoparticles can be regarded as an alternative to chemically tailored [13][14][15] organic molecules optimized for high TPA (and PL) rates for applications in highresolution three-dimensional fluorescence imaging [16] and single-molecule fluorescence-quenching spectroscopy.[17]However, such structural tailoring requires control of the nanoparticles' size, shape and orientation with nanometric accuracy. Although fabrication techniques having an adequate resolution have been available in semiconductor nanotechnology, most of the earlier studies focused on nanoparticles fabricated by chemical techniques. This approach produces ensembles of nanoparticles having significant variations of size, shape, and orientation, which may have deteriorating effect on the ensemble-averaged optical and near-field characteristics. Here we describe large, homogeneous clusters of gold nanoblocks, fabricated using electron-beam lithography (EBL) and vacuum deposition techniques, whose high degree of homogeneity allows observation of strong PL excited via TPA at near-infrared wavelengths. The key feature of our structures is intense near-field existing in few nanometer-wide nanogaps between the nanoblocks, and associated with collective LSP modes of the cluster. The degree of localization of these modes, and correspondingly, the PL intensity can be tuned by fine adjustment of the nanogap width. Thus, gold nanoengineering by a top-down technology allows one to obtain metallic systems capable of light emission, and having controllable TPA and PL properties.Photoluminescence from gold is due to radiative recombination following interband electronic transitions between the d and sp electronic bands. [12,18,19] Gold nanoparticles and rough surfaces exhibit PL quantum yields over a million times larger than the bulk gold [20] due to local enhancement of the LSP near-field [21] by orders of magnitude, compared to the incident radiation. Closely-spaced nanoparticles usually exhibit collective LSP modes whose field enhancement is even higher than that of non-interacting nanoparticles, and increases with decreasing interparticle separation. [22] Maximizing the PL yield will likely require gaps between the particles smaller than 20 nm ...

A novel micromanipulation technique is proposed for aligning fine particles on micrometer-scale spatial patterns and for moving the particles continuously along the formed patterns. This technique is based on the repetitive scanning of a focused trapping laser beam. The velocity of the particle flow can be controlled by scan speed and laser power. The origin of the driving force is considered theoretically and experimentally.

Phase transitions in aqueous solutions of poly(N-isopropylacrylamide) (PNIPAM) with a molecular weight (M h w) of 63 000 were achieved by irradiating the solutions (0.2-3.6 wt %) with an IR laser beam (1064 nm) through an optical microscope. First, a microparticle with the size of the focused laser beam was formed (=1.5 µm). This microparticle continuously grew and after prolonged irradiation (up to 10 min), a microparticle with a maximum size of 25 µm was obtained. Upon further irradiation, the microparticle became unstable and finally disappeared. The importance of the optical alignment of the microscope/laser system is discussed. Particle formation was also found in D 2O solutions of PNIPAM. These experimental results indicate that, besides a photothermal effect (heating up of the solution due to absorption of water at 1064 nm), there is influence of the "radiation force" upon particle formation and conformation properties of the polymer. The observations mentioned above are discussed in connection with the theory of the single beam gradient force optical trap for dielectric particles.

We show that a nonlinear phase shift of π can be obtained by using a single two level atom in a one sided cavity with negligible losses. This result implies that the use of a one sided cavity can significantly improve the π/18 phase shift previously observed by Turchette et al. [Phys. Rev. Lett. 75, 4710 (1995)].One of the most significant achievements in the field of quantum optics is the realization of strong nonlinear effects by enhancing the coupling between single atoms and the light field. In particular, the possibility of obtaining large conditional phase shifts has attracted much attention because of its potential usefulness in the realization of phase gates for optical quantum computation and similar manipulations of quantum states at the few photon level [1,2,3,4,5,6]. In order to optimize controlled phase shifts, it is desirable to avoid losses while moving close to the resonance of the two level atom causing the nonlinear phase shift. In the experiment by Turchette et al. [2], the nonlinearity of the atom was observed in the phase change of the light transmitted through the atom-cavity system. However, the transmission of a two sided cavity at the atomic resonance is very low, so the experiment was conducted at frequencies significantly detuned from this resonance. As a result, the phase shift observed was limited to only about π/18. In order to improve this phase shift, it is necessary to move closer to resonance while avoiding dissipative losses. In this paper, we therefore propose the use of a one sided cavity with negligible losses to non-cavity modes. In such a geometry, the total reflection is always close to one and all dissipation is suppressed. The nonlinearity then has the maximal effect on the phase of the light field while leaving the intensity unchanged. This makes it possible to realize a nonlinear phase shift of π at the atomic resonance. Figure 1 shows an illustration of this dissipation free setup. Effectively, the cavity confines the light field interacting with the two level atom to a single beam with a well defined transversal profile. The suppression of losses to non-cavity modes can be achieved by covering a large solid angle of emission with the confocal cavity mirrors. Further improvements may be possible by using dielectric materials, e.g. in a photonic crystal geometry.The most simple case of this dissipation free setup is obtained in the bad cavity regime, where the cavity lifetime is so short that the cavity field can be adiabatically eliminated. In terms of the conventional cavity quantum electrodynamics parameters this regime is characterized by κ ≫ g, where κ is the cavity damping rate and g is the dipole coupling between the atom and the cavity. The effective dipole damping rate caused by emissions through the cavity