A single quantum particle can be described by a wavefunction that spreads over arbitrarily large distances; however, it is never detected in two (or more) places. This strange phenomenon is explained in the quantum theory by what Einstein repudiated as ‘spooky action at a distance’: the instantaneous nonlocal collapse of the wavefunction to wherever the particle is detected. Here we demonstrate this single-particle spooky action, with no efficiency loophole, by splitting a single photon between two laboratories and experimentally testing whether the choice of measurement in one laboratory really causes a change in the local quantum state in the other laboratory. To this end, we use homodyne measurements with six different measurement settings and quantitatively verify Einstein’s spooky action by violating an Einstein–Podolsky–Rosen-steering inequality by 0.042±0.006. Our experiment also verifies the entanglement of the split single photon even when one side is untrusted. Quantum mechanics exhibit many unusual features, including Einstein’s so-called ‘spooky action at a distance’, wherein a wavefunction collapses at all points except where it is detected. Using homodyne measurements, Fuwa et al. verify this effect for a single photon split between two labs.
A single quantum particle can be described by a wavefunction that spreads over arbitrarily large distances; however, it is never detected in two (or more) places. This strange phenomenon is explained in the quantum theory by what Einstein repudiated as ‘spooky action at a distance’: the instantaneous nonlocal collapse of the wavefunction to wherever the particle is detected. Here we demonstrate this single-particle spooky action, with no efficiency loophole, by splitting a single photon between two laboratories and experimentally testing whether the choice of measurement in one laboratory really causes a change in the local quantum state in the other laboratory. To this end, we use homodyne measurements with six different measurement settings and quantitatively verify Einstein’s spooky action by violating an Einstein–Podolsky–Rosen-steering inequality by 0.042±0.006. Our experiment also verifies the entanglement of the split single photon even when one side is untrusted. Quantum mechanics exhibit many unusual features, including Einstein’s so-called ‘spooky action at a distance’, wherein a wavefunction collapses at all points except where it is detected. Using homodyne measurements, Fuwa et al. verify this effect for a single photon split between two labs.
In 1927, at the Solvay conference, Einstein posed a thought experiment with the primary intention of showing the incompleteness of quantum mechanics; to prove it, he employed the instantaneous nonlocal effects caused by the collapse of the wavefunction of a single particle-the spooky action at a distance-, when a measurement is done. This historical event preceded the well-know Einstein-Podolsk-Rosen criticism over the incompleteness of quantum mechanics. Here, by using the Stern-Gerlach experiment, we demonstrate how the instantaneous nonlocal feature of the collapse of the wavefunction together with the single-particle entanglement can be used to produce the nonlocal effect of steering, i.e. the single-particle steering. In the steering process Bob gets a quantum state depending on which observable Alice decides to measure. To accomplish this, we fully exploit the spreading (over large distances) of the entangled wavefunction of the single-particle. In particular, we demonstrate that the nonlocality of the single-particle entangled state allows the particle to "know" about the kind of detector Alice is using to steer Bob's state. Therefore, notwithstanding strong counterarguments, we prove that the single-particle entanglement gives rise to truly nonlocal effects at two faraway places. This opens the possibility of using the single-particle entanglement for implementing truly nonlocal task.
The term `spooky action at a distance' was coined by A. Einstein to show inconsistency of quantum mechanics with the principle of locality and reality. However, quantum mechanics is nonlocal and violates Bell's inequality. A quantum state measurement of a particle of an entangled pair collapses the total quantum state and the quantum state of the distant particle is immediately determined without making any interaction with it. The isolated collapsed quantum state of both particles remains unentangled in the future. An inertial frame of reference moving with a relativistic speed perceives these events differently is space and time and their simultaneity is relative. In this paper, it is shown that the quantum state collapse happens not only in the present but it also happens in the past of the collapse event.
Spooky Action at a Distance In the context of correlation experiments involving pairs of experiments performed at very nearly the same time in very far-apart experimental regions, Einstein famously said [1], But on one supposition we should in my opinion hold absolutely fast: “The real factual situation of the system S2 is independent of what is done with system S1 which is spatially separated from the former.” This demand is incompatible with the basic ideas of standard (Copenhagen/orthodox) quantum mechanics, which makes two relevant claims: (1) Experimenters in the two labs make “local free choices” that determine which experiments will be performed in their respective labs. These choices are free in the sense of not being predetermined by the prior history of the physically described aspects of the universe, and they are localized in the sense that the physical effects of these free choices are inserted into the physically described aspects of the universe only within the laboratory in which the associated experiment is being performed. (2) These choices of what is done with the system being measured in one lab can (because of a measurement-induced global collapse of the quantum state) influence the outcome of the experiment performed at very close to the same time in the very faraway lab. This influence of what is done with the system being measured in one region upon the outcome appearing at very nearly the same time in a very faraway lab was called “spooky action at a distance” by Einstein, and was rejected by him as a possible feature of “reality.” John Bell's Quasi-classical Statistical Theory Responding to the seeming existence in the quantum world of “spooky actions,” John Bell [2] proposed a possible alternative to the standard approach that might conceivably be able to reconcile quantum spookiness with “reality.” This alternative approach rests on the fact that quantum mechanics is a statistical theory.We already have in physics a statistical theory called “classical statistical mechanics.”
This article develops an expanded critical-propositional analysis of Maria Fuwa, Shuntaro Takeda, Marcin Zwierz, Howard M. Wiseman, and Akira Furusawa’s 2015 experiment, “Experimental Proof of Nonlocal Wavefunction Collapse for a Single Particle Using Homodyne Measurements,” published in Nature Communications, in systematic dialogue with the Theory of Objectivity (TO) developed by Vidamor Cabannas and Denivaldo Silva. Fuwa et al. experimentally investigated Einstein-Podolsky-Rosen steering in a single-photon spatial-mode entangled state. A heralded photon was incident on a beam splitter and thereby represented by a coherent quantum state distributed between spatial modes assigned to Alice and Bob. Through phase-sensitive homodyne measurements with six settings on Alice’s side and full homodyne tomography on Bob’s side, the experiment violated a nonlinear EPR-steering inequality by 0.042 ± 0.006, approximately seven standard deviations, with Alice’s homodyne efficiency reaching 0.96 ± 0.01. The experiment thereby demonstrated single-photon EPR steering without the efficiency loophole used as an explanatory alternative, although the authors did not claim closure of the separation loophole (Fuwa et al. 2015). The present analysis adopts the modal discipline developed in the recent literature of the Theory of Objectivity and distinguishes three epistemological levels: (1) empirical confirmation of a physical phenomenon; (2) structural compatibility between that phenomenon and categories derived from the TO; and (3) theory-specific, discriminating empirical confirmation. This distinction is indispensable because the Seven Absolute Truths of the TO—VA1 through VA7—are presented within the theory as modal or logically necessary foundations rather than as empirical generalizations. Experiments therefore do not create their modal necessity. Rather, experiments may corroborate, constrain, challenge, or refine operational bridges connecting the modal structure of the TO with contingent physical phenomena. The article argues that the strongest structural convergences between Fuwa et al. and the TO concern VA2, the unique field or aura; VA4, boundary or interface; VA5, simultaneous or triangular observation; VA6, composition from preceding elements; and VA7, the transcendent informational element. Particular attention is given to the TO thesis that the transcendent element consists of knowledge or information produced in atomic relations and is equivalent to atomic radiation. The Fuwa experiment provides significant indirect support for the physical relevance of the relation among radiation, correlation, and information, but it does not establish an ontological identity between information and radiation in the specific sense proposed by the TO. The experiment is further interpreted in relation to the Phenomenic Table of the TO, especially light and electromagnetism; to the Inducing Effects EIE and EIR, cautiously associated with differentiation/distribution and convergence/integration; to the TO cosmogenic theorem; and, with substantially weaker evidential force, to its cosmological Eras. The analysis emphasizes that EPR steering must not be conflated with controllable faster-than-light signalling. Bob’s unconditioned local state does not provide him with a means of determining Alice’s measurement choice without an additional comparison of information. Consequently, any TO interpretation of nonlocality must remain compatible with the operational no-signalling structure of quantum mechanics unless it produces a new discriminating experiment. The central conclusion is therefore neither that Fuwa et al. prove the Theory of Objectivity nor that their result is irrelevant to it. Instead, their experiment provides strong empirical evidence for a class of physical phenomena—nonclassical relationality, single-particle mode entanglement, EPR steering, boundary-mediated differentiation, conditioned quantum determination, and the operational centrality of information—that can be articulated with several core categories of the TO. The article proposes a research program for transforming such structural compatibility into discriminating scientific tests through quantitative TO-specific predictions concerning information-radiation equivalence, boundary conditions, and EIE-EIR dynamics. Keywords: Theory of Objectivity; EPR steering; quantum nonlocality; single-photon entanglement; wavefunction collapse; homodyne detection; information; radiation; modal ontology; boundary; EIE; EIR; quantum foundations.
A single-photon incident on a beam splitter produces an entangled field state, and in principle could be used to violate a Bell inequality, but such an experiment (without postselection) is beyond the reach of current experiments. Here we consider the somewhat simpler task of demonstrating Einstein-Podolsky-Rosen (EPR) steering with a single photon (also without postselection). We demonstrate that Alice's choice of measurement on her portion of the entangled state can affect Bob's portion of the entangled state in his laboratory, in a sense rigorously defined by us and Doherty [Phys. Rev. Lett. 98, 140402 (2007)]. Previous work by Lvovsky and coworkers [Phys. Rev. Lett. 92, 047903 (2004)] has addressed this phenomenon (which they called remote preparation) experimentally using homodyne measurements on a single photon. Here we show that, unfortunately, their experimental parameters do not meet the bounds necessary for a rigorous demonstration of EPR steering with a single photon. However, we also show that modest improvements in the experimental parameters, and the addition of photon counting to the arsenal of Alice's measurements, would be sufficient to allow such a demonstration.