Observed Interference Fringes Research Articles

Sub-shot-noise-limited measurements with Bose-Einstein condensates

We discuss practical schemes for using entangled Bose-Einstein condensates to detect phase shifts with a resolution better than the shot-noise limit. We begin by outlining a procedure for demonstrating how squeezed matter waves can be used to make measurements by simply lowering and raising a potential barrier between two condensates. The phase shift is read out by a scheme which involves releasing the condensates and studying the collapses and revivals of the visibility of the observed interference fringes. Finally we show how this scheme could be extended to measurements of other quantities such as gravity. All the steps of this process are attainable with current technology and so may provide a practical route for achieving enhanced resolution measurements with matter waves.

Novel interferometer for cold neutrons using a pair of etalons

A new type of cold-neutron interferometer has been developed using a pair of etalons. We have observed interference fringes with the contrast of 60%. The air gap of the etalon is 10μm, which produces much larger separation between two paths in the interferometer. The present results have paved the way for the more high precision measurements and the new type of experiments.

Cold-neutron interferometer of the Jamin type

A cold-neutron interferometer using four independent multilayer mirrors is demonstrated. We have observed interference fringes with a contrast of 60%. The interferometer is based on a pair of devices using etalons with an air gap of $9.75\ensuremath{\mu}\mathrm{m}$ in spacing. The optical system is equivalent to the Jamin-type interferometer, which allows much larger spatial separation between the two coherent beams than the previous type of multilayer interferometer to broaden the applicability of neutron interferometry.

Experimental demonstration of complementarity with single photons

We demonstrate the principle of complementarity in quantum mechanics in a single-photon interference experiment. Single photons are provided by isolated, optically pumped nitrogen-vacancy centers in diamond, which can be easily addressed by confocal microscopy. In order to observe the particle-like behavior of photons, we perform an elementary Welcher-Weg measurement, detecting photons behind a beam splitter. In contrast, if we dispense with this Welcher-Weg information, we observe interference fringes with a visibility of about 96%, revealing the wave nature of the photon.

Coherent electron emission from carbon nanotubes.: Young's interference in the emission patterns

In field emission patterns of multi-walled carbon nanotubes, we have observed interference fringes of electrons emitted through different sites. Main features of the emission patterns are reproduced from Young's interference formula of optics. We point out reasons to observe clear Young's interference fringes in the electron emission patterns.

A simple experiment for discussion of quantum interference and which-way measurement

We have developed a which-way experiment using visible light that is completely analogous to a recent experiment involving which-way measurement in atom interference. This simple experiment, easily accessible to undergraduate students and the resources of undergraduate departments, facilitates the examination of the key elements of which-way measurement, quantum erasure, and related mysteries of quantum measurement. The experiment utilizes a Mach–Zehnder interferometer, and visually demonstrates the loss of interference fringes when a which-way measurement is imposed, and the restoration of that pattern when the which-way information is destroyed. This device is also sensitive enough to observe interference fringes arising from single photons. We present a simple analysis of the interference appropriate for the coherent classical field limit and the single photon limit at a level accessible to undergraduates. We also briefly mention related issues on the nature of the photon.

Young's interference of electrons in field emission patterns.

We have observed interference fringes of electrons in field emission patterns from multiwalled carbon nanotubes at 60 K. The observed fringe pattern is reproduced by calculations based on the formula of Young's interference of two beams. Three-beam interference has also been detected over short time periods. We discuss the reason why Young's interference appears in the electron emission pattern in accelerating fields.

Induction time and three-electrode current vs. voltage characteristics for electrical nucleation of concentrated solutions of sodium acetate trihydrate

The effect of NaOH concentration on the electrical nucleation of sodium acetate trihydrate crystals from solution was studied by measuring the current and voltage curves, and by observing interference fringes during the application of constant voltage. The interference fringes bent according to gradients of temperature and Ag + ion concentration. Adding NaOH to the supercooled solution shortened the induction time of the electrical nucleation. The applied voltage dependence of the induction time could be explained by the theory of Kashchiev. The system of Ag electrode in sodium acetate trihydrate solution exhibited the ion Peltier effect.

Superposition states at finite temperature

We describe a method to create superposition states from a mixed state of a harmonic oscillator. If the initial state is described by a thermal state, then the resulting superposition state will be a ``hot'' superposition state. Such a state can be distinguished from a statistical mixture by its coherence properties. Here we suggest how to demonstrate the coherence of the superposition state by observing interference fringes when the two parts of the wave packet are overlapped. In the case of the mixed superposition state, a partial overlap may not be sufficient to observe the presence of fringes. We introduce therefore the idea of a coherence length for the wave packet and demonstrate its relevance for interferometry of mixed states. We illustrate our ideas with the example of superposition states for the motion of a single trapped ion.

Interferometer for cold neutrons using multilayer mirrors.

We report a successful experimental test of an interferometer for cold neutrons using multilayer mirrors. Interference fringes that are analogous to the Brewster's fringes in classical optics have been clearly observed using the cold neutron beam with a wavelength of 12.6 \AA{} and a bandwidth of 3.5% at full width at half maximum. The observed interference fringes demonstrate the coherence of the reflection off the multilayer neutron mirror and confirm the feasibility of cold neutron interferometry using multilayer mirrors. \textcopyright{} 1996 The American Physical Society.

Observation of Nanometer-Level Structural Changes by the Trans−Cis Transition of an Azobenzene Derivative Monolayer with a Radioactive Tracer

We report direct observation of radioisotopically labeled molecular structural changes in these photochemical processes with the interference effect of electron-capture X-ray emitted by nuclear transformations in radioactive atoms. The azobenzene derivative molecules were specifically reacted with the radioactive atoms ( 111 In) by using ionic bonds between the carboxyl groups in the azobenzene derivatives and the radioactive atoms. The trans-cis isomerization of the monolayer on the substrate was distinctly reflected in the period of the observed interference fringes. We measured the trans-cis photoisomerizations on the same substrate during seven alternations by using UV-visible light irradiation. As a result, we observed irreversible photochromism in the monolayer of azobenzene derivatives on the substrate because of the close packing of chromophores.

Evaluation of the far-infrared dispersion properties of γ-irradiated polymer films

The optical dispersion of polaren-R (polyethylene base) films was determined from the transmission spectrum in the far-infrared region of the spectrum. The refractive indices of polaren-R films, with different macromolecular structures, were calculated from the observed interference fringes in transmission due to the internal multi-reflections. The refractive indices were calculated in the wavelength range 14–34 μm. The macromolecular structure of polaren-R films was varied by γ-ray irradiation with different doses. The variations in the polymer structure were detected by the measurement of density variations using a vibrational technique at resonance conditions. A new physical quantity describing the degree of anisotropy of a polymer has been suggested. This quantity is the magnitude of the shift in the polymer optical dispersion from the normal dispersion of the isotropic media. The authors also suggest a characteristic frequency for the lattice vibration which was found to be dependent on the lattice structure.

Large refractive index enhancement in PbTe/Pb1−xEuxTe multiquantum-well structures

Optical interband absorption between confined carrier states is studied in PbTe/Pb1−xEuxTe multiple quantum wells (MQWs). The frequency dependence of the refractive index is calculated by the Kramers–Kronig transformation of the absorption coefficient of the MQWs. It is shown that the observed interference fringes in mid-infrared transmission can only be accounted for if the enhancement of the refractive index η(ω) at the interband transition energies which follow from the Kramers–Kronig transformation are taken into account. These changes in η are as large as 19% (at T=77 K) and are thus relevant for the design and fabrication of mid-infrared QW lasers.

Electrical and Optical Characterization of InSb Grown on GaAs by MBE

AbstractInSb has been grown on semi-insulating GaAs substrates by molecular beam epitaxy. By growing an InSb buffer layer at 300 C prior to the main InSb layer growth at 420 C, the effect of the 14% lattice mismatch between GaAs and InSb was minimized. A typical 5 µrn InSb film had a room temperature carrier concentration and electron Hall mobility of 2 × 1016/cm3 and 6×104 cm2/Vs, respectively. At 77 K these values became 2 × 1015/cm3 and 1.1 ×105 cm2/Vs. Temperature dependent Hall measurements revealed a peak in the mobility at 85 K and 70 K for the 5 and 10 µm samples. Capacitance-voltage measurements using MIS capacitors produced 77 K carrier concentrations in agreement with the low fieldHall measurements. Carrier lifetimes were determined by photoconductive response measurements. Lifetimes of 20 ns and 50 ns were determined for the 5 and 10 µm films. For comparison, the carrier lifetime in bulk n-type InSb was found to be 200 ns. Optical characterization by room temperature IR transmission spectroscopy showed a broad absorption edge, with an absorption coefficient of 1.4 × 103/cm at a wavelength of 6 µm. Epilayer thickness was determined from observed interference fringes. Raman spectroscopy showed that each epitaxial layer had a spectrum equivalent to that of bulk InSb.

Optical fiber Fabry-Perot sensors

A new optical fiber Fabry-Perot (F.P.) temperature sensor is proposed and demonstrated. In particular, it can discern the temperature rise from the temperature drop. With this sensor, the temperature change and the direction of temperature change can be determined as a function of time. The basic concept has been verified experimentally. The results of fiber F.P. sensor measurement compare well with an independent thermocouple measurement. To provide further insight, details of the experimentally observed interference fringes have also been compared to a computer simulation. Possible real-time implementations with highspeed electronics are suggested.

X-ray scattering from a single-quantum-well heterostructure

The authors have observed interference fringes in x-ray scattering from a single-quantum-well structure of InGaAs, 230 AA thick, in InP. The interference fringe pattern is amenable to a straightforward physical interpretation and contains information on the lattice parameter strain, the thickness and interface roughness of the quantum well. The latter two parameters can be measured with an accuracy of several angstroms. The sensitivity of the experiment is enhanced by the use of glancing-incidence scattering geometry and a triple-crystal x-ray diffractometer.

Direct interferometric measurement of streaming birefringence

The two refractive indices in the flow of a colloidal birefringent liquid are measured separately by means of a Mach-Zehnder interferometer. For a quantitative evaluation of the resulting interferograms it is not necessary to linearize the respective equations relating the refractive index distribution to the deformation velocity in the flow. Therefore it becomes possible to perform velocity measurements in the non-Newtonian flow range. An additional measurement of the mean flow rate enables one to determine the velocity field without the need of a calibration of the observed interference fringes.

Eye Deformation Measurement by Laser Interferometry

Using low-power laser illumination of the human eye in vivo, it is possible to observe interference fringes produced by light reflected from different optical interfaces within the eye, in particular from the front surface of the cornea and from the retina. Real-time changes in these fringes have also been observed, reflecting deformation of the eye in response to the subject's heart-beat. Some experimental results are presented. Possible applications of this technique include its use as an ophthalmological diagnostic tool in the measurement of such parameters as eye rigidity and intra-ocular pressure.

Measurement of flow velocity distribution by means of double-exposure holographic interferometry

A method for measuring flow velocity distribution in the interior of a transparent fluid is proposed. The method utilizes a thin sheet of laser light, which illuminates fluid containing small scattering particles. A double-exposure hologram is made with the scattered light as a signal wave. In the reconstructed image we can observe interference fringes which correspond to the distribution of particle displacements between the two exposures and consequently to the distribution of flow velocity. Simple experiments were performed that confirmed the usefulness of the method. A discussion of the relation of this method to laser Doppler velocimetry shows that the two methods utilize different aspects of the same phenomenon.

Resonance cone and Bernstein wave interference patterns in a magnetoplasma

General dispersion relations for a hot magnetoplasma are used to explain the interference observed between electrostatic waves and the electromagnetic field in an afterglow plasma. Observations are made near both oblique resonance cones (connected with whistler and Z‐propagation modes) and in the frequency region corresponding to “Bernstein” waves. Independent measurements of the lower (whistler) and upper (Z‐mode) resonance cones, for a particular case, lead to the same isotropic temperature in the late afterglow, namely 540 K. Independent measurements of the lower resonance cone and of Bernstein waves in the early afterglow also lead to consistent isotropic temperatures. As the real and imaginary components of the wave number increase, a point of inflection is reached on the various dispersion curves for homogeneous plane waves beyond which these curves can no longer be used to explain the observed interference fringes. For homogeneous waves with a wave number smaller than that corresponding to the inflection point, reasonable values of Landau damping are obtained which agree roughly with observed damping.