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European Journal of Physics

A time-energy delayed-choice interference experiment for the undergraduate laboratory

Jhonny Castrillón, Enrique J. Galvez, Boris A. Rodríguez, Omar Calderón-Losada

Published Jun 19, 2019• 10 citations
Publisher

Abstract

Abstract Laboratory experiments that illustrate the fundamentals of quantum physics are powerful teaching instruments because they re-enact thought experiments, allowing students to think deeper about the quantum-mechanical principles involved. Interference, wave–particle duality and entanglement are among the most important predictions of quantum mechanics. They are abstract and counter-intuitive. More recent concepts that help illustrate these subtleties include quantum erasure and delayed choice. In this article we present an experiment for the undergraduate laboratory that involves all of these issues or concepts. The experiment entails only minor modifications to a well-known setup for doing single-photon interference. In this article we present the experiment, its results and a theoretical description.

DOI
10.1088/1361-6404/ab2afc

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Abstract Laboratory experiments that illustrate the fundamentals of quantum physics are powerful teaching instruments because they re-enact thought experiments, allowing students to think deeper about the quantum-mechanical principles involved. Interference, wave–particle duality and entanglement are among the most important predictions of quantum mechanics. They are abstract and counter-intuitive. More recent concepts that help illustrate these subtleties include quantum erasure and delayed choice. In this article we present an experiment for the undergraduate laboratory that involves all of these issues or concepts. The experiment entails only minor modifications to a well-known setup for doing single-photon interference. In this article we present the experiment, its results and a theoretical description.
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Wave-particle duality lies at the root of quantum mechanics and is central in the description of interferences observed with elementary objects. In a delayed-choice experiment, the decision to observe the particle or wave character of a quantum system is delayed with respect to the time at which the system enters the interferometer. This paper reviews the history of the delayed-choice idea, introduced as a challenge to a realistic explanation of the wave-particle duality. It also describes recent experimental realizations of this idea and discusses intriguing extensions, such as the duality between separability and entanglement in multiple quantum systems.
Abstract Wave–particle duality is a counterintuitive nature of quantum physics that challenges many common-sense assumptions, and Young’s double-slit interference is a prototypical example. While most quantum erasure experiments emphasized the choice of erasing or marking the which-path information of one quantum system, we use frequency entanglement to report a nonlocal temporal double-slit interferometer such that the which-time information determines the wave-like or particle-like behaviors. Since frequency-entangled photons are created simultaneously by using spontaneous parametric down conversion, the mark of temporal distinguishability is readily prepared by delaying one of the entangled photons, and its quantum eraser is implemented by using spectrally resolved detection with a tunable delayed choice. These results may provide an alternative aspect and insight into the role of the temporal degree in quantum-light complementarity and photon interference.
The wave-particle duality has been said to contain the entire mystery of quantum mechanics. Many delayed-choice experiments have been performed to further understand the wave-particle duality. Here, we reveal some flaws in the known interference theories by comparing the theoretical predictions with the experimental facts and show that the presence of media is a necessary condition for interference of single photons, a photon interferes with other photon via microscopic particles in the interface of media, and the wave-like property of a photon originates from interaction between the photon and media; the particle property is the inherent characteristic of a photon, and the wave-like behavior of a photon always accompanies the particle behavior; the coherent time of single photons cannot be longer than the lifetime of the polarized states of the microscopic particles. Interference of single photons is interpreted properly, and the conundrum of the wave-particle duality is well solved.
We have developed a series of undergraduate teaching laboratories that explore some of the fundamentals of quantum mechanics. All of the experiments involve performing measurements on individual photons or entangled-photon pairs. The experiments include: "Proving" that light consists of photons, single-photon interference, and tests of local realism. We will describe the experiments, placing an emphasis on an experiment which measures the quantum-mechanical polarization state of a photon. This experiment explicitly demonstrates that measurements performed on one member of an entangled-photon pair effect the results of measurements of the other photon. We will also describe how we have integrated the experiments with our upper-level undergraduate quantum mechanics course.