Quantum Inform Research Articles

Two-way unclonable encryption with a vulnerable sender

Unclonable Encryption, introduced by Gottesman in 2003 [Quantum Inform. Comput. 3 (2003) 581], is a quantum protocol that guarantees the secrecy of a successfully transferred classical message even when all keys leak at a later time. We propose an Unclonable Encryption protocol with the additional property that the sender’s key material is allowed to leak even in the case of an unsuccessful run. This extra feature makes it possible to achieve secure quantum encryption even when one of the parties is unable to protect its keys against after-protocol theft. Such an asymmetry occurs e.g. in case of server–client scenarios, where the client device is resource constrained and/or located in a hostile environment. Our protocol makes use of a bidirectional quantum channel in a manner similar to the two-way protocol LM05 [Phys. Rev. Lett. 94 (2005) 140501]. Bob sends random qubit states to Alice. Alice flips the states in a way that depends on the message and a shared key, and sends the resulting states back to Bob. Bob recovers Alice’s message by measuring the flips. We prove that our protocol satisfies the definition of unclonable encryption and additionally that the message remains secure even if all of Alice’s keys leak after the protocol. Furthermore, we show that some of the key materials can be safely re-used. Our security proof is formulated in terms of diamond norms, which makes it composable, and allows for noisy quantum channels. We work out the details only for the asymptotics in the limit of long messages. As a side result, we construct a two-way QKD scheme with a high key rate. We show that its key rate is higher than the rate of the two-way QKD scheme LM05 proven by Beaudry et al. [Phys. Rev. A 88 (2013) 062302] for the case of independent channel noise.

Quantum Algorithms for the Resiliency of Vectorial Boolean Functions

Recently, Cui and Guo (Quantum Inform. Process. 18, 182, 2019) gave some quantum testing algorithms of multi-output Boolean functions, one of them was for resiliency testing. However, through the algorithm, we cannot get the probability distribution of a Boolean function. Improving the algorithm there, we present quantum algorithms for this problem. Under the condition of non-resiliency, we obtain not only the conclusion that the function F(x) is statistically dependent of which t variables but also the distance of the probability distribution from the uniform distribution.

A brief note on the Scott measure as a multipartite entanglement criterion

In recent decades, various multipartite entanglement measures have been proposed by many researchers, with different characteristics. Meanwhile, Scott studied various interesting aspects of multipartite entanglement measures and he has defined a class of related multipartite entanglement measures in an obvious manner. Recently, Jafarpour et al (2015 Int. J. Quantum Inform. 13 1550 047) have calculated the entanglement quantity of a two-dimensional five-site spin system by means of the Scott measure. Their calculation presented . In this note, we would like to point out that in a five-qudit system, Q2 does not provide a stronger entanglement than Q3, while there is a simple relation between them.

Cryptanalysis of Zhang et al’s Quantum Private Comparison and the Improvement

Based on EPR pairs, Zhang et al. analyzed the security of Yang and Tseng et al’s two QPC protocols, and proposed some new improvement strategies (Zhang and Zhang, Quantum Inform. Process. 12(5):1981–1990 2013). This paper points that Zhang et al’s protocol is insecure under a special attack, i.e. Trojan-horse attacks. To avoid this attack, we present an improved QPC protocol based on single particle encryption. Through security analysis of presented protocol, the improved protocol can resist Trojan horse attack (THA). We give a suggestion that non-orthogonal quantum states can be used to transmit information for reducing the leakage in a QPC protocol.

QSWalk.jl: Julia package for quantum stochastic walks analysis

The paper describes QSWalk.jl package for Julia programming language, developed for the purpose of simulating the evolution of open quantum systems. The package enables the study of quantum procedures developed using stochastic quantum walks on arbitrary directed graphs. We provide a detailed description of the implemented functions, along with a number of usage examples. The package is compared with the existing software offering a similar functionality. Program summaryProgram Title:QSWalk.jlProgram Files doi:http://dx.doi.org/10.17632/6x37kcvvrp.1Licensing provisions: MITProgramming language: JuliaNature of problem: The package implements functions for simulating quantum stochastic walks, including local regime, global regime, and nonmoralizing global regime (Julia documentation, 2018). It can be used for arbitrary quantum continuous evolution based on GKSL master equation on arbitrary graphs.Solution method: We utilize Expokit routines for fast sparse matrix exponentials on vectors. For dense matrices, exponentiation is computed separately, which is faster for small matrices.Restrictions: Currently package requires Julia v0.6 or higher.[1] K. Domino, A. Glos, M. Ostaszewski, Superdiffusive quantum stochastic walk definable of arbitrary directed graph, Quantum Inform. Comput 17 (11-12) (2017) 973–986.

Notes on two multiparty quantum secret sharing schemes

In the paper [H. Abulkasim et al., Int. J. Quantum Inform. 15 (2017) 1750023], Abulkasim et al. proposed a quantum secret sharing scheme based on Bell states. We study the security of the multiparty case in the proposed scheme and detect that it is not secure. In the paper [Y. Du and W. Bao, Opt. Commun. 308 (2013) 159], Du and Bao listed Gao’s scheme and gave a attack strategy on the listed scheme. We point out that their listing scheme is not the genuine Gao’s scheme and their research method is not advisable.

Two-qubit separability probabilities as joint functions of the Bloch radii of the qubit subsystems

We detect a certain pattern of behavior of separability probabilities [Formula: see text] for two-qubit systems endowed with Hilbert–Schmidt (HS), and more generally, random induced measures, where [Formula: see text] and [Formula: see text] are the Bloch radii ([Formula: see text]) of the qubit reduced states ([Formula: see text]). We observe a relative repulsion of radii effect, that is [Formula: see text], except for rather narrow “crossover” intervals [Formula: see text]. Among the seven specific cases we study are, firstly, the “toy” seven-dimensional [Formula: see text]-states model and, then, the fifteen-dimensional two-qubit states obtained by tracing over the pure states in [Formula: see text]-dimensions, for [Formula: see text], with [Formula: see text] corresponding to HS (flat/Euclidean) measure. We also examine the real (two-rebit) [Formula: see text], the [Formula: see text]-states [Formula: see text], and Bures (minimal monotone)–for which no nontrivial crossover behavior is observed–instances. In the two [Formula: see text]-states cases, we derive analytical results; for [Formula: see text], we propose formulas that well-fit our numerical results; and for the other scenarios, rely presently upon large numerical analyses. The separability probability crossover regions found expand in length (lower [Formula: see text]) as [Formula: see text] increases. This report continues our efforts [P. B. Slater, arXiv:1506.08739] to extend the recent work of [S. Milz and W. T. Strunz, J. Phys. A 48 (2015) 035306.] from a univariate ([Formula: see text]) framework — in which they found separability probabilities to hold constant with [Formula: see text] — to a bivariate ([Formula: see text]) one. We also analyze the two-qutrit and qubit–qutrit counterparts reported in Quantum Inform. Process. 15 (2016) 3745 in this context, and study two-qubit separability probabilities of the form [Formula: see text]. A physics.stack.exchange link to a contribution by Mark Fischler addressing, in considerable detail, the construction of suitable bivariate distributions is indicated at the end of the paper.

Radmilla’s Voice: Music Genre, Blood Quantum, and Belonging on the Navajo Nation

In this article, I examine race, sound, and belonging through an analysis of the first Navajo/African American Miss Navajo Nation, Radmilla Cody. Cody, a professional singer and a Navajo citizen, has been a polarizing public figure in Navajo communities since her crowning in 1997. Utilizing a mixed methodology of participant observation, sound recordings, and press releases, I probe how sound and voice inform a politics of indigeneity in today’s Navajo Nation (Diné Bikéyah). Focusing on black/Native parentage and how sound serves as an additional form of marking, I foreground how voice, musical genre, and blood quantum inform public opinion about social authenticity and about who belongs as a Diné citizen. My larger contention becomes that both poetics and politics matter, albeit in differing ways and on divergent scales.

Robust variations of secret sharing through noisy quantum channel

In this paper, the perfect secret sharing in quantum cryptography is investigated. On one hand, the security of a recent protocol [Adhikari et al. Quantum Inform. \& Comput. 12 (2012) 0253-0261] is re-examined. We find that it violates the requirement of information theoretic security in the secret sharing and suffers from the information leakage. The cryptanalysis including several specific attack strategies are given, which shows that a dishonest participant can steal half or all of the secrets without being detected. On the other hand, we design a new quantum secret sharing protocol. The security of protocol is rigorously proved. It meets the fundamental requirement of information theoretic security. Furthermore, the security analysis including both the outside attacks and participant attacks is given in details. It is shown that our proposed protocol can achieve perfect secret sharing.

DISCUSSION ON QUANTUM PROXY GROUP SIGNATURE SCHEME WITH χ-TYPE ENTANGLED STATE

Recently, Yin et al. (Int. J. Quantum Inform. 10 (2012) 1250041) proposed a quantum proxy group signature scheme with χ-type entangled states. The scheme combines the properties of group signature and proxy signature. The study points out that the semi-honest Trent can give the forged signature under the assumption of this scheme. And, we find that even if the three parties honestly perform the scheme, the signature still cannot be realized with high efficiency.

Relation between quantum speed limits and metrics on U(n)

Recently, Chau (2011 Quantum Inform. Comp. 11 721) found a family of metrics and pseudo-metrics on n-dimensional unitary operators that can be interpreted as the minimum resources (given by certain tight quantum speed limit bounds) needed to transform one unitary operator to another. This result is closely related to the weighted ℓ1-norm on . Here we generalize this finding by showing that every weighted ℓp-norm on with 1 ⩽ p ⩽ π/2 induces a metric and a pseudo-metric on n-dimensional unitary operators with quantum information-theoretic meanings related to certain tight quantum speed limit bounds. Besides, we investigate how far the correspondence between the existence of metrics and pseudo-metrics of this type and the quantum speed limits can go.

Faster quantum chemistry simulation on fault-tolerant quantum computers

Quantum computers can in principle simulate quantum physics exponentially faster than their classical counterparts, but some technical hurdles remain. We propose methods which substantially improve the performance of a particular form of simulation, ab initio quantum chemistry, on fault-tolerant quantum computers; these methods generalize readily to other quantum simulation problems. Quantum teleportation plays a key role in these improvements and is used extensively as a computing resource. To improve execution time, we examine techniques for constructing arbitrary gates which perform substantially faster than circuits based on the conventional Solovay–Kitaev algorithm (Dawson and Nielsen 2006 Quantum Inform. Comput.6 81). For a given approximation error ϵ, arbitrary single-qubit gates can be produced fault-tolerantly and using a restricted set of gates in time which is O(log ϵ) or O(log log ϵ); with sufficient parallel preparation of ancillas, constant average depth is possible using a method we call programmable ancilla rotations. Moreover, we construct and analyze efficient implementations of first- and second-quantized simulation algorithms using the fault-tolerant arbitrary gates and other techniques, such as implementing various subroutines in constant time. A specific example we analyze is the ground-state energy calculation for lithium hydride.

On Universality of Quantum Fourier Transform

A methodology is presented to obtain the basis of qudits which are admissible to quantum Fourier transform (QFT) in the sense that the set of such kets are related by the QFT in the same way as the kets of the computational basis. We first study this method for qubits to characterize the ensemble that works for the Hadamard transformation (QFT for two dimension). In this regard we identify certain incompleteness in the result of Maitra and Parashar (Int. J. Quantum Inform. 4 (2006) 653). Next we characterize the ensemble of qutrits for which QFT is possible. Further, some theoretical results related to higher dimensions are also discussed. Considering the unitary matrix Un related to QFT, the issue boils down to the problem of characterizing matrices that commute with Un.

Induced metric and matrix inequalities on unitary matrices

Recently, Chau (2011 Quantum Inform. Comput. 11 721) showed that one can define certain metrics and pseudo-metrics on U(n), the group of all n × n unitary matrices, based on the arguments of the eigenvalues of the unitary matrices. More importantly, these metrics and pseudo-metrics have quantum information theoretical meanings. So it is instructive to study this kind of metrics and pseudo-metrics on U(n). Here we show that any symmetric norm on induces a metric on U(n). Furthermore, using the same technique, we prove an inequality concerning the eigenvalues of a product of two unitary matrices which generalizes a few inequalities obtained earlier by Chau (arXiv:1006.3614v1).

Classification of the phases of 1D spin chains with commuting Hamiltonians

We consider the class of spin Hamiltonians on a 1D chain with periodic boundary conditions that are (i) translational invariant, (ii) commuting and (iii) scale invariant, where by the latter we mean that the ground state degeneracy is independent of the system size. We correspond a directed graph to a Hamiltonian of this form and show that the structure of its ground space can be read from the cycles of the graph. We show that the ground state degeneracy is the only parameter that distinguishes the phases of these Hamiltonians. Our main tool in this paper is the idea of Bravyi and Vyalyi (2005 Quantum Inform. Comput. 5 187–215) in using the representation theory of finite-dimensional C*-algebras to study commuting Hamiltonians.

Towards minimal resources of measurement-based quantum computation

We improve the upper bound on the minimal resources required for measurement-only quantum computation (M A Nielsen 2003 Phys. Rev. A 308 96–100; D W Leung 2004 Int. J. Quantum Inform. 2 33; S Perdrix 2005 Int. J. Quantum Inform. 3 219–23). Minimizing the resources required for this model is a key issue for experimental realization of a quantum computer based on projective measurements. This new upper bound also allows one to reply in the negative to the open question presented by Perdrix (2004 Proc. Quantum Communication Measurement and Computing) about the existence of a trade-off between observable and ancillary qubits in measurement-only QC.

Entanglement capabilities of non-local Hamiltonians with maximally entangled ancillary particles

We quantify the entanglement capability where the parties share a particular kind of state in which the ancillas are maximally entangled with the qubits which acted on by the non-local Hamiltonian. We find a complete expression which consists with a conjecture proposed by Child et al. [Quantum Inform. Comput. 3 (2003) 97].