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

We report the first experimental demonstration of an optical quantum controlled-NOT gate without any path interference, where two interacting interferometers original proposals (Phys. Rev. A {\bf 66}, 024308 (2001), Phys. 65}, 012314 (2002)) have been replaced by three partially polarizing beam splitters with suitable polarization dependent transmittances and reflectances. The performance device is evaluated using a recently proposed method Lett. 94}, 160504 (2005)), which process fidelity...

N00N states-maximally path-entangled states of N photons-exhibit spatial interference patterns sharper than any classical pattern. This is known as superresolution. However, even given perfectly efficient number-resolving detectors, the detection efficiency all previous measurements such would decrease exponentially with number photons in state, often leading to conclusion that are unsuitable for measurements. A technique "optical centroid measurement" has been proposed solve this and...

Infrared quantum absorption spectroscopy is one of the sensing techniques, by which infrared optical properties a sample can be estimated through visible or near photon detection without need for source detector, has been an obstacle higher sensitivity and spectrometer miniaturization. However, experimental demonstrations have limited to wavelengths shorter than 5 µm in terahertz region, not realized so-called fingerprint region 1500-500 cm-1 (6.6 20 µm), commonly used identify chemical...

Quantum information science addresses how uniquely quantum mechanical phenomena such as superposition and entanglement can enhance communication, processing precision measurement. Photons are appealing for their low noise, light-speed transmission ease of manipulation using conventional optical components. However, the lack highly efficient Kerr nonlinearities at single photon level was a major obstacle. In breakthrough, Knill, Laflamme Milburn (KLM) showed that an nonlinearity be achieved...

Quantum information technologies harness the intrinsic nature of quantum theory to beat limitations classical methods for processing and communication. Recently, application features metrology has attracted much attention. optical coherence tomography (QOCT), which utilizes two-photon interference between entangled photon pairs, is a promising approach overcome problem with (OCT): As resolution OCT becomes higher, degradation due dispersion within medium more critical. Here we report on...

Harnessing the quantum interference of pair generation processes, infrared spectroscopy, based on nonlinear interferometers with visible-infrared photon-pair sources, enables extraction optical properties a sample through visible photon detection without need for an source or detector. We develop theoretical framework Fourier-transform (QFTIR) spectroscopy. The proposed Fourier analysis method, which fully utilizes phase information in interferogram, allows us to determine complex...

Spectroscopy in the mid-infrared region is an indispensable tool for identifying molecular types various fields, including physics, chemistry, and medical sciences. However, conventional infrared light sources, detectors, noise from blackbody radiation have been obstacles to miniaturization higher sensitivity of spectrometers. Quantum spectroscopy, which uses visible photon pairs a quantum entangled state, has attracted attention as new sensing technology that enables spectroscopy with...

The ability to filter quantum states is a key capability in information science and technology, which one-qubit filters, or polarizers, have found wide application. Filtering on the basis of entanglement requires extension multi-qubit filters with qubit-qubit interactions. We demonstrated an optical that passes pair photons if they desired correlations their polarization. Such devices many important applications technologies.

The first experimental demonstration of an adaptive quantum state estimation (AQSE) is reported. strong consistency and asymptotic efficiency AQSE have been mathematically proven [A. Fujiwara, J. Phys. A 39, 12489 (2006)]. In this Letter, the angle linear polarization single photons, phase parameter between right left circularly polarization, estimated using AQSE, are experimentally verified. will provide a general useful method in both information processing metrology.

Abstract Quantum information science addresses how the processing and transmission of are affected by uniquely quantum mechanical phenomena. Combination two-qubit gates has been used to realize circuits, however, scalability is becoming a critical problem. The use three-qubit may simplify structure circuits dramatically. Among them, controlled-SWAP (Fredkin) essential since they can be directly applied important protocols, e.g., error correction, fingerprinting, optimal cloning. Here we...

Quantum entanglement of two photons created by spontaneous parametric downconversion (SPDC) can be used to probe quantum optical phenomena during a single cycle light. Harris [Phys. Rev. Lett. 98, 063602 (2007)] suggested using ultrabroad fluorescence generated from quasi-phase-matched (QPM) device whose poling period is chirped. In the Harris\' s original proposal, it assumed that are collinearly and then spatially separated frequency filtering. Here, we alternatively propose noncollinearly...

We theoretically and experimentally investigate the conditions necessary to realize highly indistinguishable single-photon sources using parametric down conversion.The visibilities of Hong-Ou-Mandel (HOM) interference between photons in different fluorescence pairs were measured a visibility 95.8 ± 2% was observed 0.7-mm-long beta barium borate crystal 2-nm bandpass filters, after compensating for reflectivity beam splitter.A theoretical model HOM is proposed that considers non-uniform...

Quantum metrology promises greater sensitivity for optical phase measurements than could ever be achieved classically. Here, we present a theory of the general case where detection probability is given by an N photon interference fringe. We find that has complicated dependence on both intrinsic efficiency η and fringe visibility V. Most importantly, gives maximum in not same as at which slope maximum, previously been assumed. determine parameter range quantum enhanced can achieved. In order...

Spatially formed two-photon interference fringes with fringe periods smaller than the diffraction limit are demonstrated.In experiment, a by NOON states wavelength λ=702.2nm is observed using specially developed near-field scanning optical microscope probe and detection setup.The period of 328.2 nm well below (351 = λ/2).Another experiment path-length difference larger coherent length photons confirms that due to interference.

We propose a novel method for generating broadband spontaneous parametric fluorescence by using set of bulk nonlinear crystals (NLCs).We also demonstrate this scheme experimentally.Our employs superposition spectra generated multiple NLCs.A typical bandwidth 160 nm (73 THz) with degenerate wavelength 808 was achieved two β -barium-borate (BBO) crystals, whereas 75 (34 realized single BBO crystal.We observed coincidence counts photon pairs in non-collinear configuration.The could be further...

The dispersion cancellation observed in Hong-Ou-Mandel (HOM) interference between frequency-entangled photon pairs has been the basis of quantum optical coherence tomography and clock synchronization. Here we explore effect phase on ultranarrow HOM dips. We show that higher-order dispersion, linewidth pump laser, spectral shape parametric fluorescence have a strong high-resolution regime with several experimental verifications. Perfect 3 $\ensuremath{\mu}$m is also demonstrated through 25 mm water.

We present a highly efficient photon pair source using chirped quasi-phase-matched (QPM) devices with ridge waveguide structure. developed QPM chirp rates of 3% and 6.7%. Spectrum measurements reveal that the generated photons have bandwidths 229 nm 325 in full width at half maximum (FWHM), alternatively, 418 428 base-to-base for 6.7% devices, respectively, which are much broader than bandwidth 16 FWHM observed non-chirp device. also evaluate generation efficiency pairs from coincidence two...

Heralded single-photon sources (HSPS) are widely used in experimental quantum science because they have negligibly small jitter and can therefore achieve high visibility for interference. However, it is necessary to decrease the photon generation rate suppress multi-photon components. To address this problem, two methods been proposed discussed: spatial (or temporal) source multiplexing photon-pair number discrimination. Here, we report realization of a HSPS combining these that two-photon...

We report an experimental demonstration of wavelength variable generation and detection photon pairs in the visible mid-infrared (MIR) regions over a wide spectral range 2–5 µm via spontaneous parametric downconversion. Despite recent increase interest such photon-pair source, there have been few detailed evaluations emitted photons generated downconversion process low gain regime, due to lack suitable single-photon detectors. By changing angle nonlinear crystal, we continuously tune...

Quantum optical coherence tomography (QOCT) is a promising approach to overcome the degradation of resolution in (OCT) due dispersion. Here, we report on an experimental demonstration QOCT imaging high-resolution regime. We achieved depth 2.5 μm, which highest value for imaging, best our knowledge. show that image dispersive material remains clear whereas OCT drastically degraded.

Infrared quantum absorption spectroscopy (IRQAS) enables the estimation of a sample's optical properties in infrared region, using only visible light source and detectors, which is technologically favorable. So far, spectral coverage IRQAS systems has been limited to less than 1 \textmu{}m. This work reports wavelength-tunable system an efficient measurement scheme achieve broadband short acquisition time. The successful demonstration rapid over wide midinfrared window (1.9--5.2 \textmu{}m)...