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International Conference on Information and Communication Technology Convergence (ICTC)

Delayed-choice quantum erasure using Poisson-distributed photons

Sang-Bae Kim, Byoung Seung HAM

Published Oct 11, 2023• 0 citations
Publisher

Abstract

Quantum superposition lies at the core of quantum mechanics and has been applied to various quantum technologies. Over the past few decades, Wheeler’s delayed-choice thought experiment has been extensively examined to explore the wave-particle duality of the complementary nature of quantum mechanics. The essence of the delayed-choice quantum eraser lies in the contradictory quantum property that violates the cause-effect relationship in classical physics. Our experiments present empirical evidence of the quantum eraser using coherent photon pairs provided in a noninteracting Mach-Zehnder interferometer for the polarization-basis control of output photons. The observed interference fringe is the direct proof of the quantum eraser, where the violation of the cause-effect relationship is due to the selective choices of the measurement events.

DOI
10.1109/ictc58733.2023.10392711

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Quantum superposition lies at the core of quantum mechanics and has been applied to various quantum technologies. Over the past few decades, Wheeler’s delayed-choice thought experiment has been extensively examined to explore the wave-particle duality of the complementary nature of quantum mechanics. The essence of the delayed-choice quantum eraser lies in the contradictory quantum property that violates the cause-effect relationship in classical physics. Our experiments present empirical evidence of the quantum eraser using coherent photon pairs provided in a noninteracting Mach-Zehnder interferometer for the polarization-basis control of output photons. The observed interference fringe is the direct proof of the quantum eraser, where the violation of the cause-effect relationship is due to the selective choices of the measurement events.
Quantum superposition is the cornerstone of quantum mechanics, where interference fringes originate in the self-interference of a single photon via indistinguishable photon characteristics. Wheeler's delayed-choice experiments have been extensively studied for the wave-particle duality over the last several decades to understand the complementarity theory of quantum mechanics. The heart of the delayed-choice quantum eraser is in the mutually exclusive quantum feature violating the cause-effect relation. Here, we experimentally demonstrate the quantum eraser using coherent photon pairs by the delayed choice of a polarizer placed out of the interferometer. Coherence solutions of the observed quantum eraser are derived from a typical Mach-Zehnder interferometer, where the violation of the cause-effect relation is due to selective measurements of basis choice.
The delayed-choice thought experiment proposed by Wheeler has been demonstrated over the last several decades for the wave-particle duality of a single photon. The delayed-choice quantum eraser proposed by Scully and Druhl has also been intensively studied for the violation of the cause-effect relation of a single photon as well as a pair of entangled photons in an interferometric system. Here, a coherence interpretation is conducted for the nonlocal realism of the space-like separated photons observed in Phys. Rev. Lett. 84, 1 (2000). As a result, coherence solutions of the observed nonlocal fringes are deterministically derived from coincidence detection-caused selective measurements, where the resulting product-basis superposition becomes the origin of the otherwise quantum mystery of the nonlocal fringes. For this, a fixed sum-phase relation between entangled photons is a prerequisite, which cannot be explained by conventional particle nature-based quantum mechanics.
Quantum eraser is known as one of the mysterious quantum features, where the action of the delayed choice retrospectively determines the photon’s nature. Over the last decades, various photon characteristics have been used to demonstrate the quantum eraser, especially for violating the cause-effect relation. In this manuscript, recent observations of the quantum eraser based on a Mach-Zehnder interferometer (MZI) using an attenuated laser are speculated as the origin of the quantum mystery, where the delayed choice is conducted for the MZI output photons via polarization projection measurements. For this, the wave nature of a photon is taken for the present pure coherence optics-based analysis. By the definition of group velocity-based information, the violation of the cause-effect relation in the quantum eraser should be related to the ensemble coherence of measured photons, but not to individual photon’s coherence, where the ensemble coherence is dramatically decreased as the spectral bandwidth of the photon ensemble increases.
Wheeler's delayed-choice experiment demonstrates wave-particle duality of particles using different experimental configurations of a Mach-Zehnder interferometer. In a quantum version of this experiment, the wave-particle behavior of photons can be observed by controlling presence or absence of the second beam splitter. Here, we implement a delayed-choice experiment with dual selections based on entangled photons, experimentally controlling both of two beam splitters in the Mach-Zehnder interferometer, where the presence and absence of the second beam splitter are simultaneously controlled through path encoding. Our experiment reveals the wave-particle behavior of single photons under different configurations of two beam splitters. We further discuss the scenario when two beam splitters are in a quantum superposition of being present and absent, photons will be in a wave-particle quantum superposition state.
The heart of quantum mechanics is quantum superposition between orthogonal bases of a single particle. In the particle nature of quantum mechanics, quantum superposition is represented by probability amplitudes between mutually exclusive natures such as orthogonal polarization bases. The delayed-choice quantum eraser is for the post-determination of the photon nature, raising the cause-effect relation issue. Over the last several decades, quantum erasers have been intensively studied using nearly all kinds of photons. Here, the macroscopic delayed-choice quantum eraser is experimentally demonstrated using a continuous wave laser and discussed for quantum superposition in a macroscopic regime. For this, a noninterfering Mach-Zehnder interferometer composed of two polarizing beam splitters is chosen to manipulate polarization bases of lights and to measure them in a delayed-choice manner via polarization-basis projection.
Ever since the proposal of delayed choice quantum erasure and subsequent realization in the experiment by Kim et al., the interpretation and implications of delayed-choice experiments have remained a subject of intense foundational debate. This paper resolves the apparent paradox attached to the experiment using standard quantum mechanics. Using an extended Mach-Zehnder interferometer which captures every operational feature of the original experiment, we show that choosing between which-path and erasure detectors is simply a choice of measurement bases, which does not rewrite a photon's past. Furthermore, by mapping the experiment to a two-way Stern-Gerlach framework, we prove that quantum erasure is an expected result of measuring entangled states, not a physical anomaly. Ultimately, through a pedagogical game, we illustrate that the illusion of retrocausality arises from asking illegitimate questions, and that a forward-in-time description is entirely sufficient to explain the logic.