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Journal of Optics B Quantum and Semiclassical Optics

Time-resolved Young$rquot$s interference and decoherence

Igor Saveliev, Mikel Sanz, N. Garcı́a

Published Aug 1, 2002• 8 citations
Publisher

Abstract

We present a two-slit time-resolved Young's interference experiment. We use a streak camera, with 2 ps resolution, to measure the arrival time as well as the location of the photons into the detector from an infrared femtosecond pulsed laser. The interfering photons can have the same or different energies as selected from a monochromator. We show that the interference fringes tilt in x – t space and disappear as the difference in energy and the resolution time set in the streak camera increase. The results show deviations from classical interference formulae and a possible interpretation in terms of decoherence may be adequate.

DOI
10.1088/1464-4266/4/4/343

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Time-resolved diffraction and interference: Young's interference with photons of different energy as revealed by time resolution

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Annual Meeting Optical Society of America•Jan 1, 1987•0 citations
Time-resolved Youngrquotrquotrquots interference and decoherence
We present a two-slit time-resolved Young's interference experiment. We use a streak camera, with 2 ps resolution, to measure the arrival time as well as the location of the photons into the detector from an infrared femtosecond pulsed laser. The interfering photons can have the same or different energies as selected from a monochromator. We show that the interference fringes tilt in x – t space and disappear as the difference in energy and the resolution time set in the streak camera increase. The results show deviations from classical interference formulae and a possible interpretation in terms of decoherence may be adequate.
We present time-resolved diffraction and two-slit interference experiments using a streak camera as a detector for femtosecond pulses of photons. These experiments show how the diffraction pattern is built by adding frames of a few photons to each frame. It is estimated that after 300 photons the diffraction pattern emerges. With time resolution we can check the speed of light and put an upper limit of 2 ps at our resolution to the time for wave function collapse in the quantum measurement process. We then produce interference experiments with photons of different energies impinging on the slits, i.e. we know which photon impinges on each slit. We show that for poor time resolution, no interference is observed, but for high time resolution, we have interference that is revealed as beats of 100 GHz frequency. The condition for interference is that the two pulses should overlap spatially at the detector, even if the pulses have different energies but are generated from the same pulse of the laser. The interference seems to be in agreement with classical theory at first sight. However, closer study and analysis of the data show deviations in the visibility of the interference fringes and of their phase. These experiments are discussed in connection with quantum mechanics and it may be concluded that the time resolution provides new data for understanding the longstanding and continuing arguments on wave-particle duality initiated by Newton, Young, Fresnel, Planck and others. A thought experiment is presented in the appendix to try to distinguish the photons at the detector by making it sensitive to colour.
A photoelectron forced to pass through two atomic energy levels before receding from the residual ion shows interference fringes in its angular distribution as a manifestation of a two-slit-type interference experiment in wave-vector space. This scenario was experimentally realized by irradiating a rubidium atom by two low-intensity continuous-wave lasers [Pursehouse et al., Phys. Rev. Lett. 122, 053204 (2019)]. In a one-photon process, the first laser excites the 5p5p5p level whereas the second uncorrelated photon elevates the excited population to the continuum. This same continuum state can also be reached when the second laser excites the 6p6p6p state, and the first photon then triggers the ionization. As the two lasers are weak and their relative phases uncorrelated, the coherence needed for generating the interference stems from the atom itself. Increasing the intensity or shortening the laser pulses enhances the probability that two photons from both lasers act at the same time, and hence, the coherence properties of the applied lasers are expected to affect the interference fringes. Here, this aspect is investigated in detail, and it is shown how tuning the temporal shapes of the laser pulses allows for tracing the time dependence of the interference fringes. We also study the influence of applying a third laser field with a random amplitude, resulting in a random fluctuation of one of the ionization amplitudes and discuss how the interference fringes are affected.
We report an experiment of observation of classical double-slit interference fringes of two-photon interference. In the experiment, a commercial continuous-wave multi-mode F-P laser diode without either mode-locked or frequency-locked is used as the light source, the density of photons is far more than the single-photon level, and the path difference of the long and short paths is far more than the longitudinal coherence length of the laser diode. The temporal stable and clearly visible spatial-distributed pattern, i.e. first-order interference fringes, was observed .Contradict to the prediction of single-photon interference mechanism, the interference happened far beyond the coherence length, the occurrence possibility and time duration of the interference fringes decrease with the reduction of mode number of the LD, and the time difference between the fringes disappearance and the light vanish is equal to the time difference of the two paths. After discussion, we came to the conclusion that the observed phenomena can be understood in time-resolved two-photon interference mechanism. We reveal a new method to perform two-photon first-order interference, and this help to understand the nature of two-photon interference and also can be useful for quantum information science.
In classical optics, Young's double-slit experiment with colored coherent light gives rise to individual interference fringes for each light frequency, referring to single-photon interference. However, two-photon double-slit interference has been widely studied only for wavelength-degenerate biphoton, known as subwavelength quantum lithography. In this work, we report double-slit interference experiments with two-color biphoton. Different from the degenerate case, the experimental results depend on the measurement methods. From a two-axis coincidence measurement pattern we can extract complete interference information about two colors. The conceptual model provides an intuitional picture of the in-phase and out-of-phase photon correlations and a complete quantum understanding about the which-path information of two colored photons.
When a frequency stabilized dye laser (linewidth ~1 MHz) is passed through a 15.25-MHz Bragg cell, a Doppler-shifted beam emerges at a small angle. Lenses are used to cross this beam with the unshifted beam to form moving interference fringes at the photocathode of a streak camera. By using a large gain of the streak camera intensifier and an intensified low-background readout of the phosphor, single photons are detectable at the photocathode. This forms a novel Young’s experiment conducted with two resolvable frequency beams passing through one known pinhole each. If the photocathode could discriminate the frequency of the detected photon, and hence which beam it came from, or if either beam were blocked, zero visibility results. The experiment gives a direct measurement of the first-order cross-coherence at single-photon detection levels of two-frequency resolvable beams. By contrast, in quantum beat experiments only the photon probability intensity vs time is measured, and the beats are then attributed to a first-order cross-coherence of the quantum pathways. The question of the frequency spectrum and cross-spectral density of each detected photon is addressed with reference to a time-dependent physical spectrum of light.1