Two-photon Interference Experiment Research Articles

Generation of time-bin entangled photon pairs by cascaded second-order nonlinearity in a single periodically poled LiNbO_3 waveguide

Entangled photon pairs are one of the most important resources for the development of quantum communication technologies. In order to produce pulsed photon pairs in the telecommunication band from 1.5 mum pump light, most of the previous experiments used two successive periodically poled lithium niobate (PPLN) waveguides. We report what we believe to be a new method using cascaded second-order nonlinearity in a single PPLN waveguide to produce high-purity time-bin entangled photon pairs. We confirmed the generation of entanglement through a two-photon interference experiment showing a coincidence fringe with a visibility of up to 97%.

High-visibility two-photon interference at a telecom wavelength using picosecond-regime separated sources

We report on a two-photon interference experiment in a quantum relay configuration using two picosecond regime PPLN waveguide based sources emitting paired photons at 1550 nm. The results show that the picosecond regime associated with a guided-wave scheme should have important repercussions for quantum relay implementations in real conditions, essential for improving both the working distance and the efficiency of quantum cryptography and networking systems. In contrast to already reported regimes, namely femtosecond and CW, it allows achieving a 99% net visibility two-photon interference while maintaining a high effective photon pair rate using only standard telecom components and detectors.

High-flux and broadband biphoton sources with controlled frequency entanglement

We report the high-flux and broadband generation of biphotons with controlled frequency entanglement. For the generation of the entangled state consisting of frequency-anticorrelated photons, we use PPMgSLT pumped by a continuous-wave (cw) laser. Meanwhile, the state consisting of frequency-correlated photons is produced from PPKTP under the extended phase-matching condition. Both states exhibited interference patterns with over 90% visibilities in two-photon interference experiments.

Fiber-based source of photon pairs at telecom band with high temporal coherence and brightness for quantum information processing

We experimentally demonstrate a bright pulsed source of correlated photon pairs at the 1550 nm telecom band by pumping 300 m dispersion-shifted fiber with a 4 ps pulse train. We investigate the coherence property of the source by measuring the second-order intensity correlation function g(2) of individual signal (idler) photons. A preliminary Hong-Ou-Mandel-type two-photon interference experiment with two such sources confirms the high temporal and spatial coherence of the source. The source is suitable for multiphoton quantum interference of independent sources, which is required in quantum information processing.

Temporal coherence and indistinguishability in two-photon interference effects

We show that temporal two-photon interference effects involving the signal and idler photons created by parametric down-conversion can be fully characterized in terms of the variations of two length parameters---called the biphoton path-length difference and the biphoton path-asymmetry-length difference---which we construct using the six different length parameters that a general two-photon interference experiment involves. We perform an experiment in which the effects of the variations of these two parameters can be independently controlled and studied. In our experimental setup, which does not involve mixing of signal and idler photons at a beam splitter, we further report observations of Hong-Ou-Mandel- (HOM-)like effects both in coincidence and in one-photon count rates. As an important consequence, we argue that the HOM and the HOM-like effects are best described as observations of how two-photon coherence changes as a function of the biphoton path-asymmetry-length difference.

Generation of energy-time entangled photon pairs in 15-μm band with periodically poled lithium niobate waveguide

We report the generation of 1.5-mm-band energy-time entangled photon pairs using a periodically poled lithium niobate (PPLN) waveguide. We performed a two-photon interference experiment and obtained coincidence fringes with 77.3% visibilities without subtracting accidental coincidences.

Two-photon quantum interference in the 1.5 μm telecommunication band

We report on two-photon quantum interference experiments in the standard telecommunication band. Two identical photons in the 1.5 mm wavelength band were generated in spatially separated modes by a type-I spontaneous parametric down-conversion process, and injected into a fiber-optic Hong-Ou-Mandel interferometer. Two-photon interference patterns of dip and spatial beating in the coincidence counting rate were observed by varying the difference in optical path lengths. The visibilities obtained in the net coincidences were close to the theoretical value of 100%. The raw visibilities were also well above the classical limit.

Long-distance distribution of time-bin entangled photon pairs over 100 km using frequency up-conversion detectors

We report an experimental demonstration of the distribution of time-bin entangled photon pairs over 100 km of optical fiber. In our experiment, 1.5-mum non-degenerated time-bin entangled photon pairs were generated with a periodically poled lithium niobate (PPLN) waveguide by using the parametric down conversion process. Combining this approach with ultra-low-loss filters to eliminate the pump light and separate signal and idler photons, we obtained an efficient entangled photon pair source. To detect the photons, we used single-photon detectors based on frequency up-conversion. These detectors operated in a non-gated mode so that we could use a pulse stream of time correlated entangled photon pairs at a high repetition frequency (1 GHz). Using these elements, we distributed time-bin entangled photon pairs over 100 km of dispersion shifted fiber and performed a two-photon interference experiment. We obtained a coincidence fringe of 81.6% visibility without subtracting any background noise, such as accidental coincidence or dark count, which was good enough to violate Bell's inequality. Thus, we successfully distributed time-bin entangled photon pairs over 100 km.

A High-Brightness Source of Narrowband, Identical-Photon Pairs

We generated narrowband pairs of nearly identical photons at a rate of 5 x 10(4) pairs per second from a laser-cooled atomic ensemble inside an optical cavity. A two-photon interference experiment demonstrated that the photons could be made 90% indistinguishable, a key requirement for quantum information-processing protocols. Used as a conditional single-photon source, the system operated near the fundamental limits on recovery efficiency (57%), Fourier transform-limited bandwidth, and pair-generation-rate-limited suppression of two-photon events (factor of 33 below the Poisson limit). Each photon had a spectral width of 1.1 megahertz, ideal for interacting with atomic ensembles that form the basis of proposed quantum memories and logic.

Quantum diffraction and interference of spatially correlated photon pairs and its Fourier-optical analysis

We present one- and two-photon diffraction and interference experiments involving parametric down-converted photon pairs. By controlling the divergence of the pump beam in parametric down-conversion, the diffraction-interference pattern produced by an object changes from a quantum (perfectly correlated) case to a classical (uncorrelated) one. The observed diffraction and interference patterns are accurately reproduced by Fourier-optical analysis taking into account the quantum spatial correlation. We show that the relation between the spatial correlation and the object size plays a crucial role in the formation of both one- and two-photon diffraction-interference patterns.

QUANTIZED DETECTOR REPRESENTATION OF QUANTUM OPTICAL NETWORKS

We present a unified and algorithmic approach to the calculation of final state amplitudes for quantum optical networks of arbitrary size and complexity. We discuss networks consisting of coupled Mach-Zender interferometers, experiments conventionally described by the POVM approach, and two-photon interference experiments.

Generation of correlated photon pairs in the 1550‐nm band using a periodically poled lithium niobate waveguide

AbstractLong‐distance communication is important for practical quantum key distribution. From the viewpoint of transmission distance, generation of single photons at 1550 nm is desirable for fiber transmission. Making use of parametric down‐conversion (signal and idler photons) as a single photon source for quantum key distribution can obtain communication distance longer than using a conventional weak coherent pulse. The reason for this is that the arrival time of the idler photon can be known by the detection of signal photon and therefore the dark count probability can be reduced by operating Bob's detector for a very short time around the photon arrival. In this paper, we report on the generation of the correlated photon pairs in the 1550‐nm band using a periodically poled lithium niobate waveguide which has a high conversion efficiency. Our measurements are in agreement with a Poissonian photon‐pair distribution. We have deduced that the probability of multi‐photon‐pair generation is sufficiently reduced when the pump is lower than 5 µW with a repetition rate of 800 kHz. We also demonstrated a two‐photon interference experiment using a Mach‐Zehnder interferometer to confirm the quantum‐mechanical nature of the correlated photon pairs. We found that that visibility was decreased when the pump power was increased due to the multi‐photon‐pair contribution. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(11): 28–36, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20130

Quantum interference with distinguishable photons through indistinguishable pathways

We report a two-photon quantum interference experiment in which the detected individual photons have quite different properties. The interference is observed even when no effort is made to mask the distinguishing features before the photons are detected. The results can be explained only in terms of indistinguishable two-photon amplitudes.

Theory of two-photon interference in an electromagnetically induced transparency system

We examine the possibility of storing and retrieving a single photon using electromagnetically induced transparency. We consider the theory of a proof-of-principle two-photon interference experiment, in which an atomic vapor cell is placed in one arm of a two-photon interferometer. Since the two-photon state is entangled, we can examine the degree to which entanglement survives. We show that while the experiment might be difficult, it should be possible to perform. We also show that the two-photon interference pattern has oscillatory behavior.

Tailoring photonic entanglement in high-dimensional Hilbert spaces

We present an experiment where two photonic systems of arbitrary dimensions can be entangled. The method is based on spontaneous parametric down-conversion with trains of $d$ pump pulses with a fixed phase relation, generated by a mode-locked laser. This leads to a photon pair created in a coherent superposition of $d$ discrete emission times, given by the successive laser pulses. Entanglement is shown by performing a two-photon interference experiment and by observing the visibility of the interference fringes increasing as a function of the dimension $d$. Factors limiting the visibility, such as the presence of multiple pairs in one train, are discussed.

광자쌍의 뭉침현상이 단일계수에 미치는 영향

Hong-Ou-Handel 간섭계를 이용한 광자쌍의 4차 간섭실험에서 두 광자의 뭉침이 단일계수에 미치는 영향을 조사하였다. 검출기의 단일광자 시간 분해능보다 짧은 시간간격으로 두 광자가 검출기에 입사할 때 하나의 검출기에서 측정되는 단일계수가 현저하게 줄어드는 변화를 확인하였다. We report an effect of photon pairs on single-photon detection rates, while Hong-Ou-Handel's two-photon interference experiment is performed with photons produced in noncollinear type-I parametric down-conversion. Photon pairing behavior or spatial bunching is measured and shown to cause a decrease in the single photon counting rate. Such a dip is found to result from the fact that the single-photon timing resolution of photodetectors is much longer compared to the time interval between the two photons incident on the single-photon detector.

Two-Photon Interference Experiment in a Mach-Zehnder Interferometer

A two-photon interference experiment is presented in which an entangled pair of photons generated from a parametric down-conversion was incident on two input ports of a Mach-Zehnder interferometer. The experiment was carried out using two photon coincidence detection with two detectors at the two output ports of the interferometer. The measured coincidence counts exhibit an interference effect with visibility of 0.75 at simultaneous inputs and 0.38 at inputs with different arrival times according to the degree of photon number entanglement.

Quantum diffraction and interference of spatially correlated photon pairs generated by spontaneous parametric down-conversion

We demonstrate one- and two-photon diffraction and interference experiments utilizing parametric down-converted photon pairs (biphotons) and a transmission grating. With two-photon detection, the biphoton exhibits a diffraction-interference pattern equivalent to that of an effective single particle that is associated with half the wavelength of the constituent photons. With one-photon detection, however no diffraction-interference pattern is observed. We show that these phenomena originate from the spatial quantum correlation between the down-converted photons.

Generation of polarisation-entangled photon pairs at 1550 nm using two PPLN waveguides

Generation of polarisation-entangled photon pairs at 1550 nm is demonstrated using two periodically poled lithium niobate (PPLN) waveguides. In two-photon interference experiments, the coincidence detection rate was 0.53 kHz with a visibility of /spl sim/94% (after subtraction of accidental coincidences). The ratio of single-photon to coincidence detection rate is /spl sim/50.

광자쌍을 이용한 Hanbury Brown-Twiss 실험

매개하향변환과정에서 발생한 광자쌍과 Hong-Ou-Handel 간섭계를 이용한 4차 간섭실험에서 두 광자가 빔분할기에 동시에 입사할 때 빔분할기의 한 쪽 출구로만 두 광자가 쌍을 이루어 빠져나가는 두-광자의 공간적인 뭉침 효과를 관측하였다. 또한 검출기의 단일광자 시간 분해능보다 짧은 시간에 두 광자가 쌍으로 입사할 때 하나의 검출기에 의한 단일계수와 비교하였다. We present experimental observations of two-photon spatial bunching effect in a two-photon interference experiment by using the photon pairs produced by parametric down-conversion and the Hong-Ou-Mandel interferometer. We show that this pairing behavior is observed by coincidence detection, but gives a negligible effect for a single count.