Abstract
Mannel et al. demonstrate quantum stochastic resonance in single-electron tunnelling between a quantum dot and an electron reservoir and describe the noise source as the “fundamental randomness of individual quantum events.” We agree that the reported measurements establish stochastic tunnelling statistics and stochastic resonance. We question, however, whether the measured observables distinguish fundamental (ontological) randomness—an individual event remaining undetermined even given a complete physical state—from epistemic uncertainty arising from unobserved microscopic degrees of freedom. The distinction matters because a probability law characterizes observed event statistics but does not, by itself, identify why an individual event occurred. We therefore ask what experimental discriminator in the reported study establishes the stronger characterization of the noise as fundamental.
Main text
Mannel et al. report a highly controlled experiment in which a self-assembled quantum dot is tunnel-coupled to a highly doped electron reservoir at 4.2 K. The dot charge state is monitored in real time by resonance fluorescence, and the authors analyse the resulting tunnelling-event stream using tunnelling rates, full counting statistics, the Fano factor and higher-order factorial cumulants. Their central experimental result—the observation of quantum stochastic resonance—is therefore supported by a detailed statistical characterization of the measured switching process.
Our concern is narrower. The Article frames the quantum noise source as the “fundamental randomness of individual quantum events.” That adjective makes a stronger claim than the observation that the event stream is stochastic at the measured level. Two physically different hypotheses can be distinguished.
HF: complete physical state S → more than one individually possible tunnelling outcome
HE: (S, λi) → one definite outcome, while λi is experimentally unresolved
Under H_F, the probability is ontological: even a complete specification of the physical state would not determine an individual event or its timing. Under H_E, the probability is epistemic: different unresolved microscopic configurations λ_i give different definite event histories, while experimental lack of access to λ_i produces a distribution over observed tunnelling times.
The distinction is not merely semantic. Bohm showed that a deterministic hidden-variable description can reproduce the statistical predictions of ordinary quantum mechanics, and his measurement analysis explicitly allows the hidden variables to depend on both the measured system and the measuring apparatus. More recently, Sharoglazova et al. noted that the existence of Bohmian mechanics demonstrates that quantum phenomena need not rely on randomness at their core. These results do not establish that Bohmian mechanics is the correct description of the present semiconductor device. They do establish, however, that probabilistic quantum predictions alone cannot be identified with ontological randomness without an additional discriminating premise or test.
In the Mannel et al. experiment, the measured description does not specify a complete microscopic state of the dot–reservoir–detector system. The tunnelling rates γ_In(t) and γ_Out(t) are used in a master equation for state-resolved probabilities, and the measured event stream is summarized through event-count distributions and their cumulants. This is an effective stochastic description of the observed variables. Its successful agreement with the data establishes the statistical law followed by those variables; it does not, without a further criterion, decide whether the probabilities are ontological or arise from degrees of freedom that are not resolved in that description.
The same point applies to increasingly stringent statistical tests. Demonstrating a specific waiting-time distribution, a Fano-factor minimum, higher-order factorial cumulants, or agreement with a stochastic master equation can show that the observed process has the predicted statistical structure. Such tests do not automatically answer the different question of whether a complete underlying physical state could determine each individual event. A statistical distribution is therefore not itself an experimental discriminator between H_F and H_E.
We accordingly suggest that the attribution of the noise specifically to fundamental randomness requires an explicit operational criterion: a measured observable, theoretical bound, or hypothesis test that excludes H_E within a stated class of deterministic or latent-state descriptions. If no such discriminator is contained in the present experiment, the data support the more limited conclusion that quantum stochastic resonance is observed in statistically stochastic single-electron tunnelling. The stronger statement that the noise source is ontologically fundamental would then be an interpretive premise rather than an experimentally identified property of the tunnelling events.
Main-text word count: approximately 570 words.
Pre-submission status and required new analysis
Communications Physics requires a Matters Arising to challenge a main conclusion and contain new, unpublished data supporting the argument. This author-correspondence version therefore does not claim that the journal requirement has already been satisfied. Before journal submission, an independent quantitative analysis should be added using event-level data or another reproducible result that tests whether the observables reported in the Article can discriminate H_F from an explicitly defined H_E alternative.
References
1. Mannel, H., Zöllner, J., Kleinherbers, E. et al. Quantum stochastic resonance in a single-photon emitter. Commun. Phys. 8, 404 (2025). https://doi.org/10.1038/s42005-025-02334-4.
2. Bohm, D. A suggested interpretation of the quantum theory in terms of “hidden” variables. I. Phys. Rev. 85, 166–179 (1952). https://doi.org/10.1103/PhysRev.85.166.
3. Bohm, D. A suggested interpretation of the quantum theory in terms of “hidden” variables. II. Phys. Rev. 85, 180–193 (1952). https://doi.org/10.1103/PhysRev.85.180.
4. Sharoglazova, V., Puplauskis, M., Mattschas, C., Toebes, C. & Klaers, J. Energy–speed relationship of quantum particles challenges Bohmian mechanics. Nature 643, 67–72 (2025). https://doi.org/10.1038/s41586-025-09099-4.
5. Gallego, R., Masanes, L., De La Torre, G. et al. Full randomness from arbitrarily deterministic events. Nat. Commun. 4, 2654 (2013). https://doi.org/10.1038/ncomms3654.
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