We propose the Modal-Disconnection Collapse (MDC) hypothesis: coherence between optical modes persists only while the physical coupling structure establishing their modal relation remains intact; removing that structure after photon(s) have passed triggers objective collapse without which-path measurement or decoherence. Standard quantum mechanics deems such post-departure manipulations irrelevant. To our knowledge, no experiment has directly tested this specific intervention. We propose two decisive tests. Experiment A: a single-photon polarization interferometer whose input beam splitter is removed after splitting but before detection. Experiment B: an entangled-photon Bell test where the source region is blocked after emission but before detection, spacelike-separated from detections. MDC predicts vanishing interference visibility (A) and reduction of the Bell-CHSH parameter to separable-state values (B); standard quantum mechanics predicts no change. These experiments close a basic empirical gap, exemplifying a core norm: seemingly obvious claims should remain provisional until directly verified.
We propose the Modal-Disconnection Collapse (MDC) hypothesis: coherence between optical modes persists only while the physical coupling structure establishing their modal relation remains intact; removing that structure after photon(s) have passed triggers objective collapse without which-path measurement or decoherence. Standard quantum mechanics deems such post-departure manipulations irrelevant. To our knowledge, no experiment has directly tested this specific intervention. We propose two decisive tests. Experiment A: a single-photon polarization interferometer whose input beam splitter is removed after splitting but before detection. Experiment B: an entangled-photon Bell test where the source region is blocked after emission but before detection, spacelike-separated from detections. MDC predicts vanishing interference visibility (A) and reduction of the Bell-CHSH parameter to separable-state values (B); standard quantum mechanics predicts no change. These experiments close a basic empirical gap, exemplifying a core norm: seemingly obvious claims should remain provisional until directly verified.
We propose the Modal-Disconnection Collapse (MDC) hypothesis: coherence between optical modes persists only while the physical coupling structure establishing their modal relation remains intact; functionally disconnecting that structure after photon(s) have passed triggers objective collapse without which-path measurement or decoherence. Standard quantum mechanics deems such post-departure manipulations irrelevant. To our knowledge, no experiment has directly tested this specific intervention. We propose two decisive tests. Experiment A: a single-photon polarization interferometer whose input beam splitter is functionally disconnected after splitting but before detection. Experiment B: an entangled-photon Bell test where the source region is blocked after emission but before detection, spacelike-separated from detections. MDC predicts vanishing interference visibility (A) and reduction of the Bell-CHSH parameter to separable-state values (B); standard quantum mechanics predicts no change. These experiments close a basic empirical gap, exemplifying a core norm: seemingly obvious claims should remain provisional until directly verified.
In 1935 Einstein, Podolsky and Rosen used the assumption of local realism to conclude in a Gedankenexperiment with two entangled particles that quantum mechanics is not complete. For this reason EPR motivated an extension of quantum mechanics by so-called local hidden variables. Based on this idea in 1964 Bell constructed a mathematical inequality whereby experimental tests could distinguish between quantum mechanics and local-realistic theories. Many experiments have since been done that are consistent with quantum mechanics, disproving the concept of local realism. But all these tests suffered from loopholes allowing a local-realistic explanation of the experimental observations by exploiting either the low detector efficiency or the fact that the detected particles were not observed space-like separated. In this context, of special interest is entanglement between different quantum objects like atoms and photons, because it allows one to entangle distant atoms by the interference of photons. The resulting space-like separation together with the almost perfect detection efficiency of the atoms allows a first loophole-free test of Bell's inequality. The primary goal of the present thesis is the experimental realization of entanglement between a single localized atom and a single spontaneously emitted photon at a wavelength suitable for the transport over long distances. In the experiment a single optically trapped Rb87 atom is excited to a state which has two selected decay channels. In the following spontaneous decay a photon is emitted coherently with equal probability into both decay channels. This accounts for perfect correlations between the polarization state of the emitted photon and the Zeeman state of the atom after spontaneous decay. Because these decay channels are spectrally and in all other degrees of freedom indistinguishable, the spin state of the atom is entangled with the polarization state of the photon. To verify entanglement, appropriate correlation measurements in complementary bases of the photon polarization and the internal quantum state of the atom are performed. It is shown, that the generated atom-photon state yields an entanglement fidelity of 0.82. The experimental results of this work mark an important step towards the generation of entanglement between space-like separated atoms for a first loophole-free test of Bell's inequality. Furthermore entanglement between a single atom and a single photon is an important tool for new quantum communication and information applications, e.g. the remote state preparation of a single atom over large distances.
This paper aims to clarify the true physical relation of photon pairs and to falsify the "entanglement collapse" hypothesis that standard quantum mechanics imposes upon them. Bell experiments violating Bell's inequality only rule out "local independent hidden variables," and are not a sufficient condition for proving "superposition plus wave-function collapse." The physical definition of entanglement in standard quantum mechanics is: subsystems are strongly correlated, the system is inseparable, and the individual subsystem has no definite independent physical state; its mathematical expressions are the non-factorizability of pure-state wave functions and the non-convex-combination of mixed-state density matrices. The physical definition and mathematical expressions are fully aligned: the individual subsystem cannot be written as a separate expression and has no definite independent physical state. Operationally, it is also absolutely impossible to realize an individual measurement of the subsystem. However, in Bell experiments, photon pairs are separately and individually measured on spatially separated detectors, which directly falsifies the premise that "the photon pair is in an entangled state." Stripping away mysticism, the true relation of two photons is a linear equation with two unknowns (independent particles under an initial-state constraint); the three-photon logic (a linear equation with three unknowns) proves that after measuring one photon, the other two still have not collapsed into definite values and must still be measured individually to obtain their states—"wave-function collapse into a definite value" is purely fictitious in algebraic logic.
In the past two decades, the union of quantum mechanics and information science has led to significant progress in our understanding of the quantum world and in our ability to coherently control individual quantum systems. New technologies have appeared, and some of them, such as quantum key distribution (QKD), are now commercially available. We are now envisioning quantum networks that could allow us to communicate over intercontinental scales, as the internet does, but with a provable security. An open question in this framework is how to certify that a given quantum network performs well, i.e. how to detect entanglement between 2, 5, 10 or 100 nodes located far away from each other. Bell tests are appealing for such a task as they allow one to certify the presence of entanglement deviceindependently, i.e. without assumptions on the Hilbert space dimension or on the proper alignment of the measurement devices. In the first chapter, I start by examining in depth the most standard approach to perform a Bell test in which a source based on spontaneous parametric down conversion (SPDC) is used to create photon pairs entangled in polarization. I show, in particular, that in this case the Bell inequality violation is fundamentally limited by vacuum and multi-photon emissions. In the second part of this thesis, I show how to overcome this limitation by using the SPDC source to create single photon entanglement, i.e. entanglement between two paths sharing a single photon, or two-mode squeezed states. Here, the non local content of the states is revealed using photon counting techniques preceded by small displacements in phase space. In the third part, I show how these measurements can be used for an optomechanical Bell test. This opens the way for device-independent quantum information processing with optomechanical systems and might be relevant to test collapse models in a theory independent manner. In the fourth chapter, the same measurements are used to build up a witness that can reveal genuine path entanglement. This witness has triggered an experiment which highlights its potential for network certification. I conclude the thesis by showing how path entanglement can be revealed with the human eye by exploiting these displacement operations.
This tutorial reviews recent theoretical and experimental findings on the open-system dynamics of entanglement, which can differ in remarkable ways from the dynamics of the individual components of the system. Decoherence leads to non-exponential decay of entanglement, which may vanish even when coherence is still present in the system. These results, which have been recently probed by quantum optics experiments, are relevant for assessing the robustness of applications like quantum communication and computation, as well as for addressing fundamental questions, already raised by Einstein and Schrödinger, concerning the classical limit of quantum mechanics.
We report on a Bell experiment with spacelike separation assuming that the measurement time is related to gravity-induced state reduction. Two energy-time entangled photons are sent through optical fibers and directed into unbalanced interferometers at two receiving stations separated by 18 km. At each station, the detection of a photon triggers the displacement of a macroscopic mass. The timing ensures spacelike separation from the moment a photon enters its interferometer until the mass has moved. Two-photon interference fringes with a visibility of up to 90.5% are obtained, leading to a violation of the Bell inequality.