**Interaction-Free Polarimetry** (2022, arXiv:2207.13539)

The combination of interaction-free measurement and the quantum Zeno effect has been shown to both increase the signal-to-noise ratio of imaging, and decrease the light intensity flux through the imaged object. So far though, this has only been considered for discrimination between translucent and opaque areas of an object. In this paper, we extend this to the polarimetry of a given sample. This will allow the identification and characterisation of these samples with far less absorbed energy than current approaches — a key concern for delicate samples being probed with high-frequency radiation.

**Comment on “Experimentally adjudicating between different causal accounts of Bell-inequality violations via statistical model selection”** (2022, arXiv:2206.10619)

In a recent paper (Phys. Rev. A 105, 042220 (2022)), Daley et al claim that superdeterministic models are disfavoured against standard quantum mechanics, because such models overfit the statistics of a Bell-type experiment which the authors conducted. We argue here that their claim is based on a misunderstanding of what superdeterministic models are.

**Is the dynamical quantum Cheshire cat detectable?** (2022, arXiv:2204.03374)

We explore how one might detect the dynamical quantum Cheshire cat proposed by Aharonov et al. We show that, in practice, we need to bias the initial state by adding/subtracting a small probability amplitude (`field’) of the orthogonal state, which travels with the disembodied property, to make the effect detectable (i.e. if our initial state is |↑z⟩, we need to bias this with some small amount δ of state |↓z⟩). This biasing, which can be done either directly or via weakly entangling the state with a pointer, effectively provides a phase reference with which we can measure the evolution of the state. The outcome can then be measured as a small probability difference in detections in a mutually unbiased basis, proportional to this biasing δ. We show this is different from counterfactual communication, which provably does not require any probe field to travel between sender Bob and receiver Alice for communication. We further suggest an optical polarisation experiment where these phenomena might be demonstrated in a laboratory.

**Comment on “Why interference phenomena do not capture the essence of quantum theory” by Catani et al **(2022, arXiv: 2204.01768)

It was recently argued by Catani et al that it is possible to reproduce the phenomenology of the double-slit experiment with a deterministic, local, and classical model (arXiv:2111.13727). The stated aim of their argument is to falsify the claim made by Feynman (in his third book of Lectures on Physics) that the double-slit experiment is “impossible, absolutely impossible, to explain in any classical way” and that it “contains the only mystery” of quantum mechanics. We here want to point out some problems with their argument, and defend Feynman’s position.

**Reply to arXiv:2111.13357 (“The Quantum Eraser Non-Paradox”)** (2021, arXiv:2112.00436)

In a recent criticism (arXiv:2111.13357) of our paper arXiv:2111.09347, Drezet argues that we have forgotten to consider superpositions of detector eigenstates. However, such superpositions do not occur in the models our paper is concerned with. We also note that no one has ever observed such detector superpositions.

**The Quantum Eraser Paradox** (2021, arXiv:2111.09347)

The Delayed-Choice Quantum Eraser experiment is commonly interpreted as implying that in quantum mechanics a choice made at one time can influence an earlier event. We here suggest an extension of the experiment that results in a paradox when interpreted using a local realist interpretation combined with backward causation (“retrocausality”). We argue that resolving the paradox requires giving up the idea that, in quantum mechanics, a choice can influence the past, and that it instead requires a violation of Statistical Independence without retrocausality. We speculate what the outcome of the experiment would be.

**Do weak values show the past of a quantum particle?** (2021, arXiv:2109.14060)

We investigate the use of weak values to determine the presence of an individual quantum particle. Specifically, we show issues with both Vaidman’s weak trace approach, and other approaches where a nonzero weak value of the spatial projection operator is implicitly assumed to indicate the presence of an individual quantum particle.

**Properties of Invariant Set Theory** (2021, arXiv:2108.08144)

In a recent paper (arXiv:2107.04761), Sen critiques a superdeterministic model of quantum physics, Invariant Set Theory, proposed by one of the authors. He concludes that superdeterminism is `unlikely to solve the puzzle posed by the Bell correlations’. He also claims that the model is neither local nor ψ-epistemic. We here detail multiple problems with Sen’s argument.

**Experimental Tests of Invariant Set Theory** (2021, arXiv:2102.07795)

We identify points of difference between Invariant Set Theory and standard quantum theory, and evaluate if these would lead to noticeable differences in predictions between the two theories. From this evaluation, we design a number of experiments, which, if undertaken, would allow us to investigate whether standard quantum theory or invariant set theory best describes reality.

**Deterministic Teleportation and Universal Computation Without Particle Exchange ** (2020, arXiv:2009.05564)

Teleportation is a cornerstone of quantum technologies, and has played a key role in the development of quantum information theory. Pushing the limits of teleportation is therefore of particular importance. Here, we apply a different aspect of quantum weirdness to teleportation—namely exchange-free computation at a distance. The controlled-phase universal gate we propose, where no particles are exchanged between control and target, allows complete Bell detection among two remote parties, and is experimentally feasible. Our teleportation-with-a-twist, which we extend to telecloning, then requires no pre-shared entanglement between sender and receiver, nor classical communication, with the teleported state gradually appearing at its destination.

**Counterfactuality, Definiteness and Bell’s Theorem** (2019, arXiv:1909.06608)

We show counterfactual definiteness separates classical from quantum physics, by analysing Bell’s Theorem. By comparing what it prohibited by various interpretations, we show most interpretations just require counterfactual semi-definiteness (the definiteness of possible options available after a measurement event), rather than full counterfactual indefiniteness. While less definite than classical counterfactual definiteness, it allows us a far more sophisticated tool to consider the physical interpretation of multi-valued variables in a way not yet done. Working from this, we further consider its relation to how counterfactual possibilities interact.