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Optical and Quantum Sensing and Precision Metrology II

Coherence analysis of the observed delayed-choice quantum eraser using coherent photons

Byoung Seung HAM

Published Mar 13, 2024• 0 citations
Publisher

Abstract

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.

DOI
10.1117/12.3011033

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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.
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.
Quantum entanglement is known as a unique feature of quantum mechanics, which cannot be obtained from classical physics. Recently, a coherence interpretation has been conducted for the delayed-choice quantum eraser using coherent photon pairs, where phase-locked symmetric frequency detuning between paired photons plays an essential role for selective measurement-caused nonlocal correlation. Here, a macroscopic version of the nonlocal correlation is presented using orthogonally polarized optical fields in a continuous wave quantum eraser scheme in a Mach-Zehnder interferometer (MZI). The resulting polarization projection of each MZI output fields onto a rotated polarizer satisfies the violation of the cause-effect relation. Based on this macroscopic quantum eraser, the intensity product between two projected output fields satisfies the inseparable joint-parameter relation if the intensity product is selectively measured through a low pass filter to block beating signals between them.
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.
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.
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.
Abstract The delayed-choice quantum eraser has long been a subject of controversy, and has been looked at as being incomprehensible to having retro-causal effect in time. Here the delayed-choice quantum eraser is theoretically analyzed using standard quantum mechanics. Employing a Mach–Zehnder interferometer, instead of a conventional two-slit interference, brings in surprising clarity. Some common mistakes in interpreting the experiment are pointed out. It is demonstrated that in the delayed mode there is no which-way information present after the particle is registered on the screen or the final detectors, contrary to popular belief. However, it is shown that another kind of path information is present even after the particle is registered in the final detectors. The registered particle can be used to predict the results of certain yet to be made measurements on the which-way detector. This novel correlation can be tested in a careful experiment. It is consequently argued that there is no big mystery in the experiment, and no retro-causal effect whatsoever.