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This Defense Intelligence Reference Document, dated 30 March 2010, was prepared by the Defense Intelligence Agency's Defense Warning Office under its Advanced Aerospace Weapon System Applications Program. It reviews quantum entanglement, nonlocality and EPR experiments, and asks whether nonlocal quantum effects could carry observer-to-observer signals faster than light. The paper describes proposed experiments and an example of real-time Earth control of a Mars rover. It concludes that there is no compelling answer yet and that experimental tests are needed.
From the source: Release of 2026-09-18 Incident: 3/30/10, Las Vegas, Nevada. Released with redactions. This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD reviews quantum entanglement and nonlocality with a focus on whether those phenomena might be usable as a means of faster-than-light communication between observers, especially for real-time space operations over interplanetary distances. The report surveys the relevant quantum experiments and no-signal theorems, then examines proposed communication schemes based mainly on momentum-entangled photons, including scenarios involving superluminal and retro-causal signaling. However, it repeatedly acknowledges that the central question remains unresolved experimentally, and it gives substantial attention to the coherence-versus-entanglement tradeoff and other features of standard quantum mechanics that may prevent usable signaling even if non-local correlations are experimentally validated. Overall, the document is an exploratory analysis of whether quantum nonlocality could conceivably support a practical communications application rather than a demonstration of prospective utility.
UNCLASSIFIED/ /FOR 8FFI@IsT.tk WSE 8Hk¥ viewed from the slits will have reduced coherence. The path length difference at the slits is, to a good approximation, inversely proportional to Lxs, Therefore, making Lxs large-that is, placing the slits some distance from the source volume-can reduce the path length differences to a value that increases coherence and allows observation of a sharp two-slit interference pattern signal at detector D1. Alternatively, placing a thin, double-concave diverging lens at point P of Figure 6 can have the same effect by causing the shorter path lengths to pass through a greater thickness of lens glass. Such a lens would also demagnify the source, producing the equivalent of a longer path length and smaller source solid angle. However, increasing source coherence has another consequence. The momentum entanglement of photons from the source arises from momentum conservation. Restricting the solid angle of the source, as viewed from the slits, means fewer photon pairs can be entangled and still satisfy the geometrical constraints of the experimental configuration. The Saleh group at Boston University has shown that there is a complementary relation between source coherence and two-photon entanglement (Reference 18). As the source-slit distance Lxs is increased, there are smooth transitions from one-slit to two-slit interference patterns and from a highly entangled source to a highly coherent source. We note, as mentioned above, that the parametric down conversion technology used in the Ghost Interference and Dopfer experiments was fairly inefficient and noisy, with fairly improbable production of entangled pairs competing with much more probable production of unentangled "noise" photons of the same wavelength from pumped fluorescence in the crystal. This would tend to limit the entanglement of the source. Nonlocal communication using momentum entanglement requires source coherence. Source coherence is needed in order to observe the "signal" of a two-slit interference pattern and two-photon entanglement so that a measurement of one of the photons "connects" with the interference pattern produced by the other photon. Where there is coherence without entanglement or entanglement without coherence, nonlocal communication with momentum-entangled photons is not possible. An unresolved issue that requires further theoretical consideration and experimental testing is whether there is a "sweet spot" in the experimental design that embraces both partial coherence and partial entanglement and that permits the transmission of nonlocal signals. VI. Nonlocal Communication Versus Signaling The possibility of nonlocal communication is an unresolved issue. It is perhaps likely that the coherence-versus-entanglement tradeoff is nature's way of preventing nonlocal signaling, but that has not been demonstrated. In this section, we assume that nonlocal signaling is possible and will examine its implications. As will be seen, they are so far reaching that they could be taken as a strong indication that nature would not allow such things and therefore nonlocal signaling must be impossible. Figure 7 shows a variation of the Ghost Interference experiment (Reference 16) in which the slit-imaging technique of the Dopfer experiment (Reference 17) is used to ensure that entangled photon pairs passing through slits reach both detectors, and that those intercepted by the opaque regions of the slits reach neither detector. In particular, a lens of focal length f is placed in the path alter the BBO crystal and before the polarization splitter so that both entangled photons pass through this lens. A pair of slits S1 is placed at a path distance f beyond the lens in the path of the "o" photons, UNCLASSIFIED/ /f81l Offl@IAL WSIE 8HLY 11
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Official release, from the pursue collection. The PDF is mirrored here; the original link is above. 32 pages are in the text index: search them above, or from the library's search.