arXiv subjects

Marcin Pawlowski

Publications and source records attributed to Marcin Pawlowski.

At least 19 recordsLinked to original sources

arXiv2025

Areon: Latency-Friendly and Resilient Multi-Proposer Consensus

We present Areon, a family of latency-friendly, stake-weighted, multi-proposer proof-of-stake consensus protocols. By allowing multiple proposers per slot and organizing blocks into a directed acyclic graph (DAG), Areon achieves robustness under partial synchrony. Blocks reference each other within a sliding window, forming maximal antichains that represent parallel ``votes'' on history. Conflicting subDAGs are resolved by a closest common ancestor (CCA)-local, window-filtered fork choice that compares the weight of each subDAG -- the number of recent short references -- and prefers the heavier one. Combined with a structural invariant we call Tip-Boundedness (TB), this yields a bounded-width frontier and allows honest work to aggregate quickly. We formalize an idealized protocol (Areon-Ideal) that abstracts away network delay and reference bounds, and a practical protocol (Areon-Base) that adds VRF-based eligibility, bounded short and long references, and application-level validity and conflict checks at the block level. On top of DAG analogues of the classical common-prefix, chain-growth, and chain-quality properties, we prove a backbone-style $(k,\varepsilon)$-finality theorem that calibrates confirmation depth as a function of the window length and target tail probability. We focus on consensus at the level of blocks; extending the framework to richer transaction selection, sampling, and redundancy policies is left to future work. Finally, we build a discrete-event simulator and compare Areon-Base against a chain-based baseline (Ouroboros Praos) under matched block-arrival rates. Across a wide range of adversarial stakes and network delays, Areon-Base achieves bounded-latency finality with consistently lower reorganization frequency and depth.

cs.DC↗

arXiv2022

Compression Optimality of Asymmetric Numeral Systems

Compression also known as entropy coding has a rich and long history. However, a recent explosion of multimedia Internet applications (such as teleconferencing and video streaming for instance) renews an interest in fast compression that also squeezes out as much redundancy as possible. In 2009 Jarek Duda invented his asymmetric numeral system (ANS). Apart from a beautiful mathematical structure, it is very efficient and offers compression with a very low residual redundancy. ANS works well for any symbol source statistics. Besides, ANS has become a preferred compression algorithm in the IT industry. However, designing ANS instance requires a random selection of its symbol spread function. Consequently, each ANS instance offers compression with a slightly different compression rate. The paper investigates compression optimality of ANS. It shows that ANS is optimal (i.e. the entropies of encoding and source are equal) for any symbol sources whose probability distribution is described by natural powers of 1/2. We use Markov chains to calculate ANS state probabilities. This allows us to determine ANS compression rate precisely. We present two algorithms for finding ANS instances with high compression rates. The first explores state probability approximations in order to choose ANS instances with better compression rates. The second algorithm is a probabilistic one. It finds ANS instances, whose compression rate can be made as close to the best rate as required. This is done at the expense of the number $θ$ of internal random ``coin'' tosses. The algorithm complexity is ${\cal O}(θL^3)$, where $L$ is the number of ANS states. The complexity can be reduced to ${\cal O}(θL\log{L})$ if we use a fast matrix inversion. If the algorithm is implemented on quantum computer, its complexity becomes ${\cal O}(θ(\log{L})^3)$.

cs.IT↗

arXiv2019

How Quantum Information can improve Social Welfare

It has been shown elsewhere that quantum resources can allow us to achieve a family of equilibria that can have sometimes a better social welfare, while guaranteeing privacy. We use graph games to propose a way to build non-cooperative games from graph states, and we show how to achieve an unlimited improvement with quantum advice compared to classical advice.

cs.GT↗

arXiv2018

Amplifying the randomness of weak sources correlated with devices

The problem of device-independent randomness amplification against no-signaling adversaries has so far been studied under the assumption that the weak source of randomness is uncorrelated with the (quantum) devices used in the amplification procedure. In this work, we relax this assumption, and reconsider the original protocol of Colbeck and Renner using a Santha-Vazirani (SV) source. To do so, we introduce an SV-like condition for devices, namely that any string of SV source bits remains weakly random conditioned upon any other bit string from the same SV source and the outputs obtained when this further string is input into the devices. Assuming this condition, we show that a quantum device using a~singlet state to violate the chained Bell inequalities leads to full randomness in the asymptotic scenario of a large number of settings, for a restricted set of SV sources (with $0 \leq \varepsilon < (2^{(1/12)} - 1)/(2(2^{(1/12)} + 1)) \approx 0.0144$). We also study a device-independent protocol that allows for correlations between the sequence of boxes used in the protocol and the SV source bits used to choose the particular box from whose output the randomness is obtained. Assuming the SV-like condition for devices, we show that the honest parties can achieve amplification of the weak source, for the parameter range $0 \leq \varepsilon<0.0132$, against a class of attacks given as a mixture of product box sequences, made of extremal no-signaling boxes, with additional symmetry conditions. Composable security proof against this class of attacks is provided.

quant-ph↗

arXiv2018

On the Security of Semi Device Independent QKD protocols

While fully device-independent security in (BB84-like) prepare and measure Quantum Key Distribution (QKD) is impossible, it can be guaranteed against individual attacks in a semi device-independent (SDI) scenario, wherein no assumptions are made on the characteristics of the hardware used are made except for an upper bound on the the dimension of the communicated system. Studying security under such minimal assumptions is especially relevant in the context of the recent {\it quantum hacking} attacks wherein the eavesdroppers can not only construct the devices used by the communicating parties but are also able to remotely alter their behavior. In this work we study the security of a SDIQKD protocol based on the prepare and measure quantum implementation of a well-known cryptographic primitive, the Random Access Code (RAC). We consider imperfect detectors and establish the critical values of the security parameters (the observed success probability of the RAC and the detection efficiency) required for guaranteeing security against eavesdroppers with and without quantum memory. Furthermore we suggest a minimal characterization of the preparation device in order to lower the requirements for establishing a secure key.

quant-ph↗

arXiv2017

Complementarity between entanglement-assisted and quantum distributed random access code

Collaborative communication tasks such as random access codes (RACs) employing quantum resources have manifested great potential in enhancing information processing capabilities beyond the classical limitations. The two quantum variants of RACs, namely, quantum random access code (QRAC) and the entanglement-assisted random access code (EARAC), have demonstrated equal prowess for a number of tasks. However, there do exist specific cases where one outperforms the other. In this article, we study a family of $3 \rightarrow 1$ distributed RACs \cite{network} and present its general construction of both the QRAC and the EARAC. We demonstrate that, depending on the function of inputs that is sought, if QRAC achieves the maximal success probability then EARAC fails to do so and vice versa.Moreover, a tripartite Bell-type inequality associated with the EARAC variants reveals the genuine multipartite nonlocality exhibited by our protocol. We conclude with an experimental realization of the $3 \rightarrow 1$ distributed QRAC that achieves higher success probabilities than the maximum possible with EARACs for a number of tasks.

quant-ph↗

arXiv2016

Reformulating noncontextuality inequalities in an operational approach

A new theory-independent noncontextuality inequality is presented [Phys. Rev. Lett. 115, 110403 (2015)] based on Kochen-Specker (KS) set without imposing the assumption of determinism. By proposing novel noncontextuality inequalities, we show that such result can be generalized from KS set to the noncontextuality inequalities not only for state-independent but also for state-dependent scenario. The YO-13 ray and $n$ cycle ray are considered as examples.

quant-ph↗

arXiv2016

1-out-of-2 Oblivious transfer using flawed Bit-string quantum protocol

Oblivious transfer (OT) is an important tool in cryptography. It serves as a subroutine to other complex procedures of both theoretical and practical significance. Common attribute of OT protocols is that one party (Alice) has to send a message to another party (Bob) and has to stay oblivious on whether Bob did receive the message. Specific (OT) protocols vary by exact definition of the task - in the all-or-nothing protocol Alice sends a single bit-string message, which Bob is able to read only with 50% probability, whereas in 1-out-of-2 OT protocol Bob reads one out of two messages sent by Alice. These two flavours of protocol are known to be equivalent. Recently a computationally secure all-or-nothing OT protocol based on quantum states was developed in [A. Souto et. al., PRA 91, 042306], which however cannot be reduced to 1-out-of-2 OT protocol by standard means. Here we present an elaborated reduction of this protocol which retains the security of the original.

quant-ph↗

arXiv2016

The Magical Number Seven: An Unexpected Dimensional Threshold in Quantum Communication Complexity

Entanglement-assisted classical communication and transmission of a quantum system are the two quantum resources for information processing. Many information tasks can be performed using either quantum resource. However, this equivalence is not always present since entanglement assisted classical communication is known to sometimes be the better performing resource. Here, we show not only the opposite phenomenon; that there exists tasks for which transmission of a quantum system is a more powerful resource than entanglement assisted classical communication, but also that such phenomena can have a surprisingly strong dependence on the dimension of Hilbert space. We introduce a family of communication complexity problems parametrized by dimension of Hilbert space and study the performance of each quantum resource. We find that for low dimensions, the two resources perform equally well, whereas for dimension seven and above, the equivalence is suddenly broken and transmission of a quantum system becomes more powerful than entanglement assisted classical communication. Moreover, we find that transmission of a quantum system may even outperform classical communication assisted by the stronger-than-quantum correlations obtained from the principle of Macroscopic Locality.

quant-ph↗

arXiv2016

Random access codes and non-local resources

It is known that a PR-BOX (PR), a non-local resource and $(2\rightarrow 1)$ random access code (RAC), a functionality (wherein Alice encodes 2 bits into 1 bit message and Bob learns one of randomly chosen Alice's inputs) are equivalent under the no-signaling condition. In this work we introduce generalizations to PR and $(2\rightarrow 1)$ RAC and study their inter-convertibility. We introduce generalizations based on the number of inputs provided to Alice, $B_n$-BOX and $(n\rightarrow 1)$ RAC. We show that a $B_n$-BOX is equivalent to a no-signaling $(n\rightarrow 1)$ RACBOX (RB). Further we introduce a signaling $(n\rightarrow 1)$ RB which cannot simulate a $B_n$-BOX. Finally to quantify the same we provide a resource inequality between $(n\rightarrow 1)$ RB and $B_n$-BOX, and show that it is saturated. As an application we prove that one requires atleast $(n-1)$ PRs supplemented with a bit of communication to win a $(n\rightarrow 1)$ RAC. We further introduce generalizations based on the dimension of inputs provided to Alice and the message she sends, $B_n^d(+)$-BOX, $B_n^d(-)$-BOX and $(n\rightarrow 1,d)$ RAC ($d>2$). We show that no-signaling condition is not enough to enforce strict equivalence in the case of $d>2$. We introduce classes of no-signaling $(n\rightarrow 1,d)$ RB, one which can simulate $B_n^d(+)$-BOX, second which can simulate $B_n^d(-)$-BOX and third which cannot simulate either. Finally to quantify the same we provide a resource inequality between $(n\rightarrow 1,d)$ RB and $B_n^d(+)$-BOX, and show that it is saturated.

quant-ph↗

arXiv2016

Tight bound on the classical value of generalized Clauser-Horne-Shimony-Holt games

Non-local games are an important part of quantum information processing. Recently there has been an increased interest in generalizing non-local games beyond the basic setup by considering games with multiple parties and/or with large alphabet inputs and outputs. In this paper we consider another interesting generalization -- games with non-uniform inputs. Here we derive a tight upper bound for the classical winning probability for a specific family of non-local games with non-uniform input distribution, known as $\mathrm{CHSH}_q(p)$ which was introduced recently in the context of relativistic bit-commitment protocols by [Chakraborty et. al., PRL 115, 250501, 2015].

quant-ph↗

arXiv2016

Increased Certification of Semi-device Independent Random Numbers using Many Inputs and More Postprocessing

Quantum communication with systems of dimension larger than two provides advantages in information processing tasks. Examples include higher rates of key distribution and random number generation. The main disadvantage of using such multi-dimensional quantum systems is the increased complexity of the experimental setup. Here, we analyze a not-so-obvious problem: the relation between randomness certification and computational requirements of the postprocessing of experimental data. In particular, we consider semi-device independent randomness certification from an experiment using a four dimensional quantum system to violate the classical bound of a random access code. Using state-of-the-art techniques, a smaller quantum violation requires more computational power to demonstrate randomness, which at some point becomes impossible with today's computers although the randomness is (probably) still there. We show that by dedicating more input settings of the experiment to randomness certification, then by more computational postprocessing of the experimental data which corresponds to a quantum violation, one may increase the amount of certified randomness. Furthermore, we introduce a method that significantly lowers the computational complexity of randomness certification. Our results show how more randomness can be generated without altering the hardware and indicate a path for future semi-device independent protocols to follow.

quant-ph↗

arXiv2016

Spatial versus Sequential Correlations for Random Access Coding

Random access codes are important for a wide range of applications in quantum information. However, their implementation with quantum theory can be made in two very different ways: (i) by distributing data with strong spatial correlations violating a Bell inequality, or (ii) using quantum communication channels to create stronger-than-classical sequential correlations between state preparation and measurement outcome. Here, we study this duality of the quantum realization. We present a family of Bell inequalities tailored to the task at hand and study their quantum violations. Remarkably, we show that the use of spatial and sequential quantum correlations imposes different limitations on the performance of quantum random access codes. We also show that there exist random access codes for which spatial quantum correlations offer no gain over classical strategies, whereas sequential quantum correlations can yield an advantage. We discuss the physics behind the observed discrepancy between spatial and sequential quantum correlations.

quant-ph↗

arXiv2015

Maximal Non-Classicality in Multi-Setting Bell Inequalities

The discrepancy between maximally entangled states and maximally non-classical quantum correlations is well-known but still not well understood. We aim to investigate the relation between quantum correlations and entanglement in a family Bell inequalities with $N$-settings and $d$ outcomes. Using analytical as well as numerical techniques, we derive both maximal quantum violations and violations obtained from maximally entangled states. Furthermore, we study the most non-classical quantum states in terms of their entanglement entropy for large values of $d$ and many measurement settings. Interestingly, we find that the entanglement entropy behaves very differently depending on whether $N=2$ or $N> 2$: when $N=2$ the entanglement entropy is a monotone function of $d$ and the most non-classical state is far from maximally entangled, whereas when $N> 2$ the entanglement entropy is a non-monotone function of $d$ and converges to that of the maximally entangled state in the limit of large $d$.

quant-ph↗

arXiv2015

Robust amplification of Santha-Vazirani sources with three devices

We demonstrate that amplification of arbitrarily weak randomness is possible using quantum resources. We present a randomness amplification protocol that involves Bell experiments. We find a Bell inequality which can amplify arbitrarily weak randomness and give a detailed analysis of the protocol involving it. Our analysis includes finding a sufficient violation of Bell inequality as a function of the initial quality of randomness. It has a very important property that for any quality the required violation is strictly lower than possible to obtain using quantum resources. Among other things, it means that the protocol takes a finite amount of time to amplify arbitrarily weak randomness.

quant-ph↗

arXiv2015

Detection efficiency loophole in Pusey-Barrett-Rudolph theorem

Detection efficiency loophole poses a significant problem for experimental tests of Bell inequalities. Recently discovered Pusey-Barrett-Rudolph (PBR) theorem suffers from the same vulnerability. In this paper we calculate the critical detection efficiency, below which the PBR argument for the ontic nature of quantum state is inconclusive. This is done for the maximally $ψ$-epistemic models. We use two different definitions of this property. The optimal number of parties, for which the critical detection efficiency is the lowest is given. We also approach the problem from the opposite direction. We provide a function which enables us to specify which epistemic models are ruled out by the results of an experiment with a given detection efficiency.

quant-ph↗

arXiv2015

Detection efficiency and noise in semi-device independent randomness extraction protocol

In this paper, we analyze several critical issues in semi-device independent quantum information processing protocol. In practical experimental realization randomness generation in that scenario is possible only if the efficiency of the detectors used is above a certain threshold. Our analysis shows that the critical detection efficiency is 0.7071 in the symmetric setup, while in the asymmetric setup if one of the bases has perfect critical detection efficiency then the other one can be arbitrarily close to 0. We also analyze the semi-device independent random number generation efficiency based on different averages of guessing probability. To generate more randomness, the proper averaging method should be applied. Its choice depends on the value of a certain dimension witness. More importantly, the general analytical relationship between the maximal average guessing probability and dimension witness is given.

quant-ph↗

arXiv2015

Detection loophole attacks on semi-device-independent quantum and classical protocols

Semi-device-independent quantum protocols realize information tasks - e.g. secure key distribution, random access coding, and randomness generation - in a scenario where no assumption on the internal working of the devices used in the protocol is made, except their dimension. These protocols offer two main advantages: first, their implementation is often less demanding than fully-device-independent protocols. Second, they are more secure than their device-dependent counterparts. Their classical analogous is represented by random access codes, which provide a general framework for describing one-sided classical communication tasks. We discuss conditions under which detection inefficiencies can be exploited by a malicious provider to fake the performance of semi-device-independent quantum and classical protocols - and how to prevent it.

quant-ph↗