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Keiji Sasaki

Publications and source records attributed to Keiji Sasaki.

8 recordsLinked to original sources
PubMed2006

Spectrally-resolved atomic-scale length variations of gold nanorods.

Functionality of gold nanorod structures as ultra-sensitive optical rulers is demonstrated. Arrays of gold nanorods were fabricated by electron beam lithography and lift-off techniques with high accuracy and uniformity. Their longitudinal plasmon scattering spectra were found to exhibit extreme sensitivity to the length of the nanorods. This phenomenon enables optical detection of the nanorod length variations comparable to the thickness of a few atomic layers of gold.

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PubMed2005

Demonstration of an optical quantum controlled-NOT gate without path interference.

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gate without any path interference, where the two interacting path interferometers of the original proposals have been replaced by three partially polarizing beam splitters with suitable polarization dependent transmittance and reflectance.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.

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PubMed2005

Enhancement of Förster energy transfer within a microspherical cavity.

Energy transfer from pyrene to perylene molecules co-doped within a poly(methyl methacrylate) latex microsphere was drastically accelerated relative to free space. Fluorescence spectra of the microspheres showed that the relative emission intensities of pyrene and perylene changed with the sphere diameter. Analyses of emission decay profiles clarified that Förster-type energy-transfer processes were induced and that the transfer rates increased within the microspherical cavity. This enhancement can be ascribed not only to the quantum electrodynamic effects on the pyrene emission rate, but also the cavity effect of increasing the overlapping factor between donor emission and acceptor absorption spectra.

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PubMed2005

Optical properties of nanoengineered gold blocks.

We report on control over the extinction spectrum of tetragonal gold nanoblocks by changing their lateral aspect ratio. Nanoblocks were patterned on a glass substrate by electron-beam lithography and were 40-400 nm in lateral dimensions and spanned from 1 to 9 in aspect ratio. This allowed us to tune the localized surface plasmon bands from 700 nm to 1.5 microm (longitudinal mode) and from 700 to 550 nm (transverse mode). Unprecedented polarization selectivity of the transverse and longitudinal plasmon bands was achieved via alignment and 3D control of the dimensions of the nanoblocks.

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PubMed2005

Ultrabright femtosecond source of biphotons based on a spatial mode inverter.

A method of enhancing the efficiency of entangled biphoton sources based on a type II femtosecond spontaneous parametric downconversion (SPDC) process is proposed and implemented experimentally. Enhancement is obtained by mode inversion of one of the SPDC output beams, which allows the beams to overlap completely, thus maximizing the number of SPDC photon pairs with optimum spatiotemporal overlap. By use of this method, biphoton count rates as high as 16 kHz from a single 0.5-mm-long beta-barium borate crystal pumped by second-harmonic radiation from a Ti:sapphire laser were obtained.

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PubMed2004

High-yield single-photon source using gated spontaneous parametric downconversion.

The construction of a single-photon source by use of gated parametric fluorescence is reported with the measurement results of the photon number distribution. A beamlike twin-photon method is used in order to achieve high-collection efficiency. The estimated probability P(1) to find a single photon in a collimated output pulse is 26.5% at a repetition rate of 10 kHz when the effective quantum efficiency of 27.4% in the detection setup is compensated.

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PubMed2004

Distinguishing genuine entangled two-photon-polarization sfrom independently generated pairs of entangled photons.

A scheme to distinguish entangled two-photon-polarization (ETP) states from two independent entangled one-photon-polarization (EOP) states is proposed. Using this scheme, the experimental generation of ETP by parametric down-conversion is confirmed through the anticorrelations among three orthogonal two-photon-polarization states. The estimated fraction of ETP among the correlated photon pairs is 37% in the present experimental setup.

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