Quantum particles can exist in temporal superpositions
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A peer-reviewed physics experiment reports the successful creation of a single quantum state in a temporal superposition, existing across widely separated moments.
Quantum theory is compatible with scenarios in which the order of operations is indefinite. Experimental investigations of such scenarios, all of which have been based on a process known as the quantum switch, have provided demonstrations of indefinite causal order conditioned on assumptions on the devices used in the laboratory. But is a device-independent certification possible, similar to the certification of Bell nonlocality through the violation of Bell inequalities? Previous results have shown that the answer is negative if the switch is considered in isolation. Here, however, we present an inequality that can be used to device-independently certify indefinite causal order in the quantum switch in the presence of an additional spacelike-separated observer under an assumption asserting the impossibility of superluminal and retrocausal influences.
Quantum superposition and entanglement of mesoscopic plasmons
Quantum superpositions and entanglement are at the heart of the quantum information science. There have been only a few investigations of these phenomena at the mesoscopic level, despite the fact that these systems are promising for quantum state storage and processing. Here we present two novel experiments with surface plasmons propagating on cm-long metallic stripe waveguides. We demonstrate that two plasmons can be entangled at remote places. In addition, we create a single plasmon in a temporal superposition state: it exists in a superposition of two widely separated moments. These quantum states, created using photons at telecom wavelength, are collectively held by a mesoscopic number of electrons coding a single quantum bit of information; They are shown to be very robust against decoherence.
Published as: New J. Phys. 8, 13 (2006)
DOI: 10.1088/1367-2630/8/1/013
arXiv categories: quant-ph
Quantum mechanics provides a successful mathematical description of physical phenomena, yet the ontological status of the quantum particle remains unresolved. Building upon the geometric framework developed in the preceding papers of this research program, this paper proposes the Temporal Intersection Principle, according to which a quantum particle is interpreted not as a fundamentally localized physical object, but as the localized temporal intersection of a continuous physical object embedded within globally non-orientable time. This interpretation preserves the established mathematical formalism of quantum mechanics while providing a unified ontology for the geometric framework previously developed for quantum evolution, entanglement, delayed-choice behavior, quantum erasure, and measurement. Rather than introducing new quantum dynamics, the paper develops the ontological consequences of the existing geometric framework and argues that localized quantum particles are best understood as observable temporal intersections of continuous physical objects embedded within globally non-orientable time.
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