Relativistic Communication Protocols: Assumptions and Status

Relativistic communication protocols range from algebraic theorems to detector-model calculations and proposed laboratory analogues. Their status should be reported on separate axes: causal assumptions, physical channel realization, energy and localization control, coding theorem, numerical validation, and experiment. A theoretical possibility in a specified QFT model is not a demonstrated platform rate.

Required background. Signaling and causal composition supplies the invariant causal criterion used in every comparison.

Helpful background. Review quantum communication, entanglement harvesting, energy-constrained capacities, and Bell nonlocality before comparing their evidence.

A claim–evidence rubric

Classify a protocol by the strongest level it actually reaches:

1. Structural theorem: a result follows under precisely stated algebraic, causal, and domain hypotheses.
2. Controlled analytic model: a finite or perturbatively bounded detector or mode model gives a reproducible channel or witness.
3. Numerically validated model: independent convergence, null, causal, and fault-injection tests support a parameter region.
4. Component demonstration: the relevant coupling, state preparation, or readout is measured, but not yet the complete protocol.
5. End-to-end demonstration: localized encoding, propagation, decoding, resource account, and declared performance metric are measured together.

These levels are not automatic maturity labels. A theorem may be definitive for its hypotheses while saying little about apparatus feasibility; an experiment may be compelling for one platform while not establishing a continuum theorem.

The same physical chain supports several task claims, but each arrow needs evidence: localized encoding, causal propagation, receiver matching, and task-specific performance. The diagram is schematic.

Representative protocol status

Localized causal channels. Supported system–probe constructions and algebraic locality provide theorem-level causal composition under their net and coupling hypotheses. The main implementation gap is not the consistency of the framework but realizing and calibrating the assumed local instrument.

Detector-mediated classical communication. Explicit scalar-field detector models yield nonzero timelike classical channels and analyzable one-shot or capacity expressions. Cliche and Kempf 2010, §§ III–V and Tjoa and Gallock-Yoshimura 2022, §§ III–VI are controlled theoretical models. Their numerical values remain conditional on switching, detector idealization, and receiver access.

Quantum and entanglement-assisted transmission. Nonperturbative localized-coupling models provide channel and energy analyses, including Barcellos and Landulfo 2021, §§ III–VI. Claims about quantum rate must retain the code, energy constraint, reference resources, and error criterion. The cited model results do not by themselves constitute an end-to-end quantum-field transducer demonstration.

Entanglement harvesting. Perturbative and numerical detector studies establish parameter regions in which initially separable probes become entangled for controlled spacelike models; Pozas-Kerstjens and Martín-Martínez 2015, §§ II–IV is a central benchmark. Support tails, higher-order exchange, detector realization, and experimental readout remain protocol-specific limitations.

Bell correlations. Algebraic QFT gives structural existence results for strong violations in local algebras, notably Summers and Werner 1987, Theorems 3.1 and 4.1, pp. 252–257. An apparatus-level field Bell test additionally needs bounded accessible observables, random settings, spacelike implementation, detection efficiency, and loophole-aware statistics.

Broadcast channels. Barcellos and Landulfo 2024, §§ III–VI construct a nonperturbative scalar-field broadcast model and analyze causal rate constraints. It is a controlled generalization of point-to-point theory, not evidence that arbitrary receivers can simultaneously achieve their individual point-to-point optima.

Automatic downgrade tests

Remove one assumption at a time and downgrade only the affected claim.

• If compact support is replaced by an unbounded Gaussian tail without a quantitative bound, downgrade exact spacelike separation to approximate localization.
• If the mean-energy or bandwidth constraint is removed, withdraw the physical capacity comparison while retaining any finite-input channel calculation.
• If a rare herald is reported without its probability and classical record, withdraw the rate claim while retaining the conditional-state statement.
• If only second moments are measured for a non-Gaussian state, withdraw full tomography while retaining a valid covariance witness.
• If perturbative remainders overlap the entanglement or signaling threshold, downgrade a sharp positive claim to unresolved within error.
• If setting independence or detection accounting fails, withdraw Bell certification while retaining the observed correlator.

The map supports targeted downgrades: losing an energy constraint does not erase a causal theorem, and losing strict spacelike support does not erase a measured correlation. It changes the strongest licensed interpretation. The map is schematic.

Evidence boundary and update rule

This comparison was assessed through 2026-08-10. For a future update, record the exact protocol, field theory and state, spacetime supports, physical transducer, energy and bandwidth constraints, error metric, evidence type, independent validation, and unresolved alternative explanations. A new calculation should update only the row of reasoning it actually strengthens; a proposed implementation is not a demonstration, and a component demonstration is not an end-to-end channel rate.

References

• Barcellos, I. B., and Landulfo, A. G. S. (2021). “Relativistic Quantum Communication: Energy Cost and Channel Capacities.” Physical Review D 104, 105018. DOI. Open PDF.
• Barcellos, I. B., and Landulfo, A. G. S. (2024). “Relativistic Quantum Broadcast Channel.” Physical Review D 109, 065020. DOI. Open PDF.
• Cliche, M., and Kempf, A. (2010). “The Relativistic Quantum Channel of Communication through Field Quanta.” Physical Review A 81, 012330. DOI. Open PDF.
• Pozas-Kerstjens, A., and Martín-Martínez, E. (2015). “Harvesting Correlations from the Quantum Vacuum.” Physical Review D 92, 064042. DOI. Open PDF.
• Summers, S. J., and Werner, R. (1987). “Maximal Violation of Bell’s Inequalities Is Generic in Quantum Field Theory.” Communications in Mathematical Physics 110, 247–259. DOI.
• Tjoa, E., and Gallock-Yoshimura, K. (2022). “Channel Capacity of Relativistic Quantum Communication with Rapid Interaction.” Physical Review D 105, 085011. DOI. Open PDF.