arXiv subjects

Marcin Pawłowski

Publications and source records attributed to Marcin Pawłowski.

At least 19 recordsLinked to original sources

arXiv2026

Coherent Control of Channel Dilations Activate Temporal Bell Nonclassicality

The temporal Clauser-Horne-Shimony-Holt (CHSH) inequality witnesses the nonclassicality of temporal correlations, but its violation is generally degraded by environmental noise. Here, we show that violation of the temporal CHSH inequality can be revived through coherent control of noisy quantum evolutions. We compare two physically distinct implementations: coherent control of noisy evolutions induced by interaction of the system with independent environments, and coherent control of two physically distinct, unitarily equivalent Stinespring dilations of the same noisy channel. Although these constructions generate identical deterministic system dynamics, they induce distinctly different post-selected evolutions. With a focus on the amplitude damping channel (ADC), we show that coherent control of equivalent dilations extend the range of temporal CHSH inequality violation well beyond both the incoherently controlled, or deterministic, scenario and what is achievable with independent environments. Under setting-independent post-selection of the coherent control implementation, the resulting violation further certifies that the channel is not strongly CHSH nonlocality-breaking. Our results identify the choice of Stinespring dilation as an operationally relevant resource in coherently controlled tests of temporal quantum correlations.

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arXiv2026

Neural Information Causality

Query-separated computation forces a representation to play an operational role: data are encoded before a query is known, and a later decoder can answer only through the intermediate interface. In this regime the representation functions as a message rather than merely as a feature map. We formalize this observation by embedding information causality (IC) into representation learning, obtaining a framework called neural information causality (Neural-IC). The revised formulation separates two logically distinct statements. First, every query-separated architecture induces a random-access communication experiment and obeys the embedding inequality $I_{\mathrm{N\text{-}RAC}}\le I(\vec a:H,B)$. Second, any independently certified physical capacity bound on the interface, such as a hard $m$-bit alphabet, a finite-precision register, or a power-constrained noisy channel, implies $I_{\mathrm{N\text{-}RAC}}\le C_H$. This separation avoids treating capacity as a post hoc definition and makes Neural-IC an operational diagnostic for query leakage, precision leakage, and episode-specific memory. We also provide an exact one-bit classical RAC benchmark, showing explicitly that the relevant quantum enhancement is not total information beyond the bottleneck, but fair query-conditioned access. For CHSH-type correlation layers, nested Neural-RAC protocols multiply correlation biases across depth; requiring stability of a one-bit bottleneck for arbitrary depth selects the Tsirelson threshold. We extend the analysis to asymmetric seed biases, to multi-capacity finite-depth phase diagrams, and to correlated data via a conditional information score. Controlled simulations, including straight-through binary bottlenecks and deliberately leaky ablations, verify that apparent violations are accounted for by broken query separation or undercounted capacity.

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arXiv2026

Exponentially decreasing critical detection efficiency for any Bell inequality

We address the problem of closing the detection efficiency loophole in Bell experiments, which is crucial for real-world applications. Every Bell inequality has a critical detection efficiency $η$ that must be surpassed to avoid the detection loophole. Here, we propose a general method for reducing the critical detection efficiency of any Bell inequality to arbitrary low values. This is accomplished by entangling two particles in $N$ orthogonal subspaces (e.g., $N$ degrees of freedom) and conducting $N$ Bell tests in parallel. Furthermore, the proposed method is based on the introduction of penalized $N$-product (PNP) Bell inequalities, for which the so-called simultaneous measurement loophole is closed, and the maximum value for local hidden-variable theories is simply the $N$th power of the one of the Bell inequality initially considered. We show that, for the PNP Bell inequalities, the critical detection efficiency decays exponentially with $N$. The strength of our method is illustrated with a detailed study of the PNP Bell inequalities resulting from the Clauser-Horne-Shimony-Holt inequality.

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arXiv2026

Quantum description of reality is epistemically incomplete

We ask whether the operational quantum description is complete at the level of preparations: can the empirically accessible properties of a finite preparation set be reproduced exactly by a hidden-variable description, or must every such completion contain additional structure that is not operationally accessible? We formalize this through epistemic completeness, a preparation-side notion of classicality requiring exact preservation of empirical preparation-properties by the corresponding ontic quantities obtained by conditioning on the ontic state and allowing all response schemes compatible with positivity and normalization. For the canonical family of set-distinguishability tasks, we prove that every epistemically complete theory satisfies an equality: for every finite preparation set, the average pairwise distinguishability equals the average set-distinguishability. Any nonzero deviation certifies epistemic incompleteness and lower-bounds the excess ontic communication power that every ontic completion must conceal. Because unrestricted classical communication models, and more generally commuting quantum theories, are epistemically complete, every nonzero deviation also yields a quantum communication advantage and witnesses of coherence and measurement incompatibility. We formulate semidefinite-programming relaxations and see-saw lower bounds, and show that quantum theory violates the equality in both directions. The trine and tetrahedral qubit ensembles are numerically certified maximizers for the n=3 and n=4 equalities; their violations persist for arbitrarily low positive visibility and arbitrarily large leakage short of complete disclosure; and the Kochen--Specker ψ-epistemic model exactly saturates the hidden ontic excess for these maximal positive violations. Numerics suggest that the maximal positive deviation increases with the number of preparations.

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arXiv2026

Communication-constrained nonlocal correlations

Identifying the physical grounds distinguishing quantum theory from broader probabilistic frameworks remains an open challenge. Communication-based proposals -- most notably the principles of impossibility of superluminal signaling and information causality (IC) -- highlight the role of communication in ruling out unphysical theories and offer an operational rationale on why quantum predictions prevail over these alternative models. Nevertheless, most such developments rely on communicating parts optimizing over specific tasks, such as communication complexity problems and random access codes (RAC). In this work, we systematically extend this communication-based approach. We characterize the class of communication tasks relevant for this context, and employ the general information-theoretic framework to derive new operational constraints preventing such unphysical behaviors. Remarkably, our results reveal a broad family of previously undetected implausible behaviors, independent of any particular encoding or decoding strategy, reinforcing the role of communication as a fundamental lens through which physically meaningful theories can be identified.

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arXiv2026

Autonomous Optical Alignment of Satellite-Based Entanglement Sources using Reinforcement Learning

Quantum entanglement distributed via satellites enable global-scale quantum communication. However, onboard sources are susceptible to misalignment due to dynamical orbital conditions. Here, we present two recalibration techniques for efficient generation of high quality entanglement using a periodically poled lithium niobate (PPLN)-based spontaneous parametric down-conversion (SPDC) source with minimum intervention. The first is a heuristic algorithm (HA) which mimics the manual alignment process in a laboratory. The second is based on reinforcement learning (RL). Our simulation demonstrates superior performance of RL with AUC=0.9119 compared to HA's 0.7042 in the modified ROC analysis (60 min threshold). RL achieves perfect alignment in 10 min as opposed to HA's 30 min. Both the methods operate within feasible satellite constraints, offering scalable automation for complex quantum communication scenarios.

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arXiv2025

The future of secure communications: device independence in quantum key distribution

In the ever-evolving landscape of quantum cryptography, Device-independent Quantum Key Distribution (DI-QKD) stands out for its unique approach to ensuring security based not on the trustworthiness of the devices but on nonlocal correlations. Beginning with a contextual understanding of modern cryptographic security and the limitations of standard quantum key distribution methods, this review explores the pivotal role of nonclassicality and the challenges posed by various experimental loopholes for DI-QKD. Various protocols, security against individual, collective and coherent attacks, and the concept of self-testing are also examined, as well as the entropy accumulation theorem, and additional mathematical methods in formulating advanced security proofs. In addition, the burgeoning field of semi-device-independent models (measurement DI--QKD, Receiver DI--QKD, and One--sided DI--QKD) is also analyzed. The practical aspects are discussed through a detailed overview of experimental progress and the open challenges toward the commercial deployment in the future of secure communications.

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arXiv2025

High-dimensional detection-loophole-free measurement-device-independent quantum random number generator

Certifying random number generators is challenging, especially in security-critical fields like cryptography. Here, we demonstrate a measurement-device-independent quantum random number generator (MDI-QRNG) using high-dimensional photonic path states. Our setup extends the standard qubit beam-splitter QRNG to a three-output version with tunable fiber-optic interferometers acting as tunable beam splitters and superconducting detectors. This setup generates over 1.2 bits per round and 1.77 Mbits per second of certifiably secure private randomness without requiring \emph{any} trust in the measurement apparatus, a critical requirement for the security of real-world cryptographic applications. Our results demonstrate certifiably secure high-dimensional quantum random-number generation, paving the way for practical, scalable QRNGs without the need for complex devices.

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arXiv2025

Security of device-independent quantum key distribution via monogamy relations from multipartite information causality

Beyond the foundational significance, the problem of bounding nonlocal correlations by reasonable physical principles has meaningful practical consequences, particularly for device-independent (DI) cryptographic security. In this work, we advance in this direction, demonstrating that the IC is enough to ensure DI security on quantum key distribution (QKD) protocols. Security is proven for a range of theoretically quantum-attainable parameters against individual attacks by a potentially post-quantum eavesdropper. This result follows as a consequence of a strong form of monogamy of Bell's inequality violations, which we have proven to be implied by the recently proposed multipartite formulation for IC. Additionally, we demonstrated that the original bipartite formulation of IC fails to imply monogamy relations and hence, ensure security of DIQKD, thus stressing the necessity of the multipartite framework.

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arXiv2025

Certifying semi-device-independent security via wave-particle duality experiments

Wave-particle duality is known to be equivalent to an entropic uncertainty relation based on the min- and max-entropies, which have a clear operational meaning in quantum cryptography. Here, we derive a connection between wave-particle relations and the semi-device-independent (SDI) security framework. In particular, we express an SDI witness entirely in terms of two complementary interferometric quantities: visibility and input distinguishability. Applying a symmetry condition to the interferometric quantities, we identify a scenario in which the classical bound is violated and the security condition is met in wave-particle experiments with a tunable beam splitter. This enables the certification of non-classicality and the positivity of the key rate directly from complementary interferometric quantities. Moreover, we perform a proof-of-principle experiment using orbital-angular-momentum encoded quantum states of light in a tunable interferometer, validating our theoretical predictions. Finally, we analyze an improved bound on the SDI security condition, effectively enlarging the parameter region where secure communication can be certified.

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arXiv2025

Extending quantum correlations to arbitrary distances via parallel repetition of routed Bell tests

Applications such as Device-Independent Quantum Key Distribution (DIQKD) require loophole-free certification of long-distance quantum correlations. However, these distances remain severely constrained by detector inefficiencies and unavoidable transmission losses. To overcome this challenge, we consider parallel repetitions of the recently proposed routed Bell experiments, where transmissions from the source are actively directed either to a nearby or a distant measurement device. We analytically show that the threshold detection efficiency of the distant device--needed to certify non-jointly-measurable measurements, a prerequisite of secure DIQKD--decreases exponentially, optimally, and robustly, following $η^*=1/2^N$, with the number $N$ of parallel repetitions.

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arXiv2025

Hacking quantum computers with row hammer attack

We demonstrate a hardware vulnerability in quantum computing systems by exploiting cross-talk effects on an available commercial quantum computer (IBM). Specifically, based on the cross-talk produced by certain quantum gates, we implement a row hammer attack that ultimately allows us to flip a qubit. Both single-qubit and two-qubit operations are performed and analyzed. Our findings reveal that two-qubit operations applied near the target qubit significantly influence it through cross-talk, effectively compromising its state.

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arXiv2024

Experimental demonstration of the equivalence of entropic uncertainty with wave-particle duality

Wave-particle duality is one of the most striking and counter-intuitive features of quantum mechanics, illustrating that two incompatible observables cannot be measured simultaneously with arbitrary precision. In this work, we experimentally demonstrate the equivalence of wave-particle duality and entropic uncertainty relations using orbital angular momentum (OAM) states of light. Our experiment utilizes an innovative and reconfigurable platform composed of few-mode optical fibers and photonic lanterns, showcasing the versatility of this technology for quantum information processing. Our results provide fundamental insights into the complementarity principle from an informational perspective, with implications for the broader field of quantum technologies.

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arXiv2024

Advantages of quantum communication revealed by the reexamination of hyperbit theory limitations

Pawłowski and Winter's hyperbit theory, proposed in 2012, presented itself as an alternative to quantum theory, suggesting novel ways of redefining entanglement and classical communication paradigms. This research undertakes a meticulous reevaluation of hyperbit theory, uncovering significant operational constraints that question its equivalence with quantum mechanics. Crucially, the supposition that hyperbit theory and quantum theory are equivalent relies on the receiver having unattainable additional knowledge about the sender's laboratory, indicating that the work by Pawlowski and Winter is incorrect. This study accentuates the constraints of hyperbits in information processing and sheds light on the superiority of quantum communication, thereby advancing the investigation at the intersection of classical and quantum communication.

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arXiv2023

Extending loophole-free nonlocal correlations to arbitrarily large distances

One of the most striking features of quantum theory is that it allows distant observers to share correlations that resist local hidden variable (classical) explanations, a phenomenon referred to as Bell nonlocality. Besides their foundational relevance, the nonlocal correlations enable distant observers to accomplish classically inconceivable information processing and cryptographic feats such as unconditionally secure device-independent key distribution schemes. However, the distances over which nonlocal correlations can be realized in state-of-the-art Bell experiments remain severely limited owing to the high threshold efficiencies of the detectors and the fragility of the nonlocal correlations to experimental noise. Instead of looking for quantum strategies with marginally lower threshold requirements, we exploit the properties of loophole-free nonlocal correlations, which are experimentally attainable today, albeit at short distances, to extend them over arbitrarily large distances. Specifically, we consider Bell experiments wherein the spatially separated parties randomly choose the location of their measurement devices in addition to their measurement settings. We demonstrate that when devices close to the source are perfect and witness extremal loophole-free nonlocal correlations, such correlations can be extended to devices placed arbitrarily far from the source, with almost-zero detection efficiency and visibility. To accommodate imperfections close to the source, we demonstrate a specific analytical tradeoff: the higher the loophole-free nonlocality close to the source, the lower the threshold requirements away from the source. We utilize this analytical tradeoff paired with optimal quantum strategies to estimate the critical requirements of a measurement device placed away from the source and formulate a versatile numerical method applicable to generic network scenarios.

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arXiv2023

Entanglement witnessing with untrusted detectors

We consider the problem of entanglement detection in the presence of faulty, potentially malicious detectors. A common - and, as of yet, the only - approach to this problem is to perform a Bell test in order to identify nonlocality of the measured entangled state. However, there are two significant drawbacks in this approach: the requirement to exceed a critical, and often high, detection efficiency, and much lower noise tolerance. In this paper, we propose an alternative approach to this problem, which is resilient to the detection loophole and is based on the standard tool of entanglement witness. We discuss how the two main techniques to detection losses, namely the discard and assignment strategies, apply to entanglement witnessing. We demonstrate using the example of a two-qubit Bell state that the critical detection efficiency can be significantly reduced compared to the Bell test approach.

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arXiv2022

Quantum Bell inequalities from Information Causality -- tight for Macroscopic Locality

In a Bell test, the set of observed probability distributions complying with the principle of local realism is fully characterized by Bell inequalities. Quantum theory allows for a violation of these inequalities, which is famously regarded as Bell nonlocality. However, finding the maximal degree of this violation is, in general, an undecidable problem. Consequently, no algorithm can be used to derive quantum analogs of Bell inequalities, which would characterize the set of probability distributions allowed by quantum theory. Here we present a family of inequalities, which approximate the set of quantum correlations in Bell scenarios where the number of settings or outcomes can be arbitrary. We derive these inequalities from the principle of Information Causality, and thus, we do not assume the formalism of quantum mechanics. Moreover, we identify a subspace in the correlation space for which the derived inequalities give the necessary and sufficient conditions for the principle of Macroscopic Locality. As a result, we show that in this subspace, the principle of Information Causality is strictly stronger than the principle of Macroscopic Locality.

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arXiv2021

Tangible reduction in learning sample complexity with large classical samples and small quantum system

Quantum computation requires large classical datasets to be embedded into quantum states in order to exploit quantum parallelism. However, this embedding requires considerable resources. It would therefore be desirable to avoid it, if possible, for noisy intermediate-scale quantum (NISQ) implementation. Accordingly, we consider a classical-quantum hybrid architecture, which allows large classical input data, with a relatively small-scale quantum system. This hybrid architecture is used to implement an oracle. It is shown that in the presence of noise in the hybrid oracle, the effects of internal noise can cancel each other out and thereby improve the query success rate. It is also shown that such an immunity of the hybrid oracle to noise directly and tangibly reduces the sample complexity in the probably-approximately-correct learning framework. This NISQ-compatible learning advantage is attributed to the oracle's ability to handle large input features.

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