arXiv subjects

Anirban Pathak

Publications and source records attributed to Anirban Pathak.

At least 91 records · Page 5Linked to original sources

arXiv2018

How vulnerable are the Indian banks: A cryptographers' view

With the advent of e-commerce and online banking it has become extremely important that the websites of the financial institutes (especially, banks) implement up-to-date measures of cyber security (in accordance with the recommendations of the regulatory authority) and thus circumvent the possibilities of financial frauds that may occur due to vulnerabilities of the website. Here, we systematically investigate whether Indian banks are following the above requirement. To perform the investigation, recommendations of Reserve Bank of India (RBI), National Institute of Standards and Technology (NIST), European Union Agency for Network and Information Security (ENISA) and Internet Engineering Task Force (IETF) are considered as the benchmarks. Further, the validity and quality of the security certificates of various Indian banks have been tested with the help of a set of tools (e.g., SSL Certificate Checker provided by Digicert and SSL server test provided by SSL Labs). The analysis performed by using these tools and a comparison with the benchmarks, have revealed that the security measures taken by a set of Indian banks are not up-to-date and are vulnerable under some known attacks.

cs.CR↗

arXiv2018

Comment on "Quantum Teleportation of Eight-Qubit State via Six-Qubit Cluster State"

Recently, Zhao et al., (Int. J. Theor. Phys. 57, 516-522 (2018)) have proposed a scheme for quantum teleportation of an eight-qubit quantum state using a six qubit cluster state. In this comment, it's shown that the quantum resource (multi-partite entangled state used as the quantum channel) used by Zhao et al., is excessively high and the task can be performed using any two Bell states as the task can be reduced to the teleportation of an arbitrary two qubit state. Further, a trivial conceptual mistake made by Zhao et al., in the description of the quantum channel has been pointed out. It's also mentioned that recently a trend of proposing teleportation schemes with excessively high quantum resources has been observed and the essence of this comment is applicable to all such proposals.

quant-ph↗

arXiv2018

Higher-order nonclassical properties of a shifted symmetric cat state and a one-dimensional continuous superposition of coherent states

Role of quantum interference in the origin of higher-order nonclassical characteristics of radiation field has been probed vis-a-vis a discrete and a continuous superposition of coherent states. Specifically, the possibilities of observing higher-order nonclassical properties (e.g., higher-order antibunching (HOA), higher-order sub-Poissonian photon statistics (HOSPS), higher-order squeezing (HOS) of Hong-Mandel type and Hillery type) have been investigated using a shifted symmetric cat state that reduces to Yurke-Stoler, even and odd coherent states at various limits. This shifted symmetric cat state which can be viewed as a discrete superposition of coherent states is found to show HOA and HOSPS. Similarly, higher-order nonclassical properties of a one-dimensional continuous superposition of coherent states is also studied here. The investigation has revealed the existence of HOS and HOSPS in the one-dimensional continuous superposition of coherent states studied here. Effect of non-Gaussianity inducing operations (e.g., photon addition and addition followed by subtraction) on these superposition states have also been investigated. Finally, some comparisons have been made between the higher-order nonclassical properties of discrete and continuous superposition of coherent states.

quant-ph↗

arXiv2018

Kak's three-stage protocol of secure quantum communication revisited: Hitherto unknown strengths and weaknesses of the protocol

Kak's three-stage protocol for quantum key distribution is revisited with special focus on its hitherto unknown strengths and weaknesses. It is shown that this protocol can be used for secure direct quantum communication. Further, the implementability of this protocol in the realistic situation is analyzed by considering various Markovian noise models. It is found that the Kak's protocol and its variants in their original form can be implemented only in a restricted class of noisy channels, where the protocols can be transformed to corresponding protocols based on logical qubits in decoherence free subspace. Specifically, it is observed that Kak's protocol can be implemented in the presence of collective rotation and collective dephasing noise, but cannot be implemented in its original form in the presence of other types of noise, like amplitude damping and phase damping noise. Further, the performance of the protocol in the noisy environment is quantified by computing average fidelity under various noise models, and subsequently a set of preferred states for secure communication in noisy environment have also been identified.

quant-ph↗

arXiv2018

Quantum cryptography: key distribution and beyond

Uniquely among the sciences, quantum cryptography has driven both foundational research as well as practical real-life applications. We review the progress of quantum cryptography in the last decade, covering quantum key distribution and other applications.

quant-ph↗

arXiv2017

Higher order nonclassicalities of finite dimensional coherent states: A comparative study

Conventional coherent states (CSs) are defined in various ways. For example, CS is defined as an infinite Poissonian expansion in Fock states, as displaced vacuum state, or as an eigenket of annihilation operator. In the infinite dimensional Hilbert space, these definitions are equivalent. However, these definitions are not equivalent for the finite dimensional systems. In this work, we present a comparative description of the lower- and higher-order nonclassical properties of the finite dimensional CSs which are also referred to as qudit CSs (QCSs). For the comparison, nonclassical properties of two types of QCSs are used: (i) nonlinear QCS produced by applying a truncated displacement operator on the vacuum and (ii) linear QCS produced by the Poissonian expansion in Fock states of the CS truncated at (d-1)-photon Fock state. The comparison is performed using a set of nonclassicality witnesses (e.g., higher order antiubunching, higher order sub-Poissonian statistics, higher order squeezing, Agarwal-Tara parameter, Klyshko's criterion) and a set of quantitative measures of nonclassicality (e.g., negativity potential, concurrence potential and anticlassicality). The higher order nonclassicality witness have found to reveal the existence of higher order nonclassical properties of QCS for the first time.

quant-ph↗

arXiv2017

On the origin of nonclassicality in single systems

In the framework of certain general probability theories of single systems, we identify various nonclassical features such as incompatibility, multiple pure-state decomposability, measurement disturbance, no-cloning and the impossibility of certain universal operations, with the non-simpliciality of the state space. This is shown to naturally suggest an underlying simplex as an ontological model. Contextuality turns out to be an independent nonclassical feature, arising from the intransitivity of compatibility.

quant-ph↗

arXiv2017

Nonclassicality in non-degenerate hyper-Raman processes

A perturbative analytic operator solution of a completely quantum mechanical Hamiltonian of multi-photon pump non-degenerate hyper-Raman process is obtained. It is shown that the obtained solution is general in nature as the solutions of non-degenerate hyper-Raman and stimulated Raman processes can be obtained as special cases of the present solution. The analytic solutions obtained here are used to investigate the nonclassical properties of the different modes in the stimulated, spontaneous and partially spontaneous multi-photon pump non-degenerate hyper-Raman processes. The nonclassical nature of these processes is witnessed by means of single mode and intermodal quadrature squeezing, intermodal entanglement of different orders, lower order and higher order photon antibunching. Interestingly, manifesting the multiphoton nature of the pump modes, a bunch of nonclassicality involving them are observed due to self-interaction of various pump modes.

quant-ph↗

arXiv2017

Lower- and higher-order nonclassicality in a Bose-condensed optomechanical-like system and a Fabry-Perot cavity with one movable mirror: squeezing, antibunching and entanglement

Various lower- and higher-order nonclassical properties have been studied for two physical systems- (i) an optomechanical system composed of a Fabry-Perot cavity with one nonlinearly oscillating mirror and (ii) an optomechanical-like system formed using a Bose-Einstein condensate (BEC) trapped inside an optical cavity. The investigation is performed using a perturbation method that leads to closed form analytic expressions for the time evolution of the relevant bosonic operators. In the first system, it is observed that the radiation pressure coupling leads to the emergence of lower- and higher-order squeezing, antibunching, entanglement and intermodal squeezing. The effects of the coherent interaction of a nonlinear oscillating mirror with the cavity mode are studied, and it is observed that the optomechanical system studied here becomes more nonclassical (entangled) when the coupling strength is increased. It is also observed that the possibility of observing entanglement depends on the phase of the movable mirror. The Hamiltonian of the trapped BEC system is obtained as a special case of the Hamiltonian of the first system, and the existence of various nonclassicality in the trapped BEC system has been established, and variations of those with various physical parameters have been reported with an aim to understand the underlying physical process that leads to and controls the nonclassicality.

quant-ph↗

arXiv2017

Orthogonal-state-based and semi-quantum protocols for quantum private comparison in noisy environment

Private comparison is a primitive for many cryptographic tasks, and recently several schemes for the quantum private comparison (QPC) have been proposed, where two users can compare the equality of their secrets with the help of a semi-honest third party (TP) without knowing each other's secret and without disclosing the same to the TP. In the exisiting schemes, secrecy is obtained by using conjugate coding, and considering all participants as quantum users who can perform measurement(s) and/or create states in basis other than computational basis. In contrast, here we propose two new protocols for QPC, first of which does not use conjugate coding (uses orthogonal states only) and the second one allows the users other than TP to be classical whose activities are restricted to either reflecting a quantum state or measuring it in computational basis. Further, the performance of the protocols is evaluated under various noise models.

quant-ph↗

arXiv2017

Experimental realization of nondestructive discrimination of Bell states using a five-qubit quantum computer

A scheme for distributed quantum measurement that allows nondestructive or indirect Bell measurement was proposed by Gupta et al., (Int. J. Quant. Infor. \textbf{5} (2007) 627) and subsequently realized experimentally using an NMR-based three-qubit quantum computer by Samal et al., (J. Phys. B, \textbf{43} (2010) 095508). In the present work, a similar experiment is performed using the five-qubit super-conductivity-based quantum computer, which has been recently placed in cloud by IBM Corporation. The experiment confirmed that the Bell state can be constructed and measured in a nondestructive manner with a reasonably high fidelity. A comparison of the outcomes of this study and the results obtained earlier in the NMR-based experiment has also been performed. The study indicates that to make a scalable SQUID-based computer, errors by the gates (in the present technology) have to be reduced considerably.

quant-ph↗

arXiv2017

Comparison of lower order and higher order nonclassicality in photon added and photon subtracted squeezed coherent states

Nonclassical properties of photon added and photon subtracted squeezed coherent states have been compared with specific focus on the higher order nonclassicalities, such as higher order squeezing, higher order sub-Poissonian photon statistics, higher order antibunching. It is observed that both photon added and photon subtracted squeezed coherent states are highly nonclassical as they satisfy criteria for all of the above mentioned nonclassicalities and a set of other criteria including negativity of Wigner function, Klyshko's criterion and Agarwal's $(A_{3})$ parameter. Further, the amount of nonclassicality present in these two types of states has been compared quantitatively using a measure of nonclassicality known as nonclassical volume. Variation in the amount of nonclassicality with the number of photon(s) added/subtracted is also investigated, and it is found that the addition of photons makes the squeezed coherent state more nonclassical than what is done by the subtraction of photons.

quant-ph↗

arXiv2017

Classical light vs. nonclassical light: Characterizations and interesting applications

We briefly review the ideas that have shaped modern optics and have led to various applications of light ranging from spectroscopy to astrophysics, and street lights to quantum communication. The review is primarily focused on the modern applications of classical light and nonclassical light. Specific attention has been given to the applications of squeezed, antibunched, and entangled states of radiation field. Applications of Fock states (especially single photon states) in the field of quantum communication are also discussed.

quant-ph↗

arXiv2017

Design and experimental realization of an optimal scheme for teleportion of an $n$-qubit quantum state

An explicit scheme (quantum circuit) is designed for the teleportation of an $n$-qubit quantum state. It is established that the proposed scheme requires an optimal amount of quantum resources, whereas larger amount of quantum resources has been used in a large number of recently reported teleportation schemes for the quantum states which can be viewed as special cases of the general $n$-qubit state considered here. A trade off between our knowledge about the quantum state to be teleported and the amount of quantum resources required for the same is observed. A proof of principle experimental realization of the proposed scheme (for a 2-qubit state) is also performed using 5-qubit superconductivity-based IBM quantum computer. Experimental results show that the state has been teleported with high fidelity. Relevance of the proposed teleportation scheme has also been discussed in the context of controlled, bidirectional, and bidirectional-controlled state teleportation.

quant-ph↗

arXiv2017

Building a Completely Reversible Computer

A critical analysis of the feasibility of reversible computing is performed. The key question is: Is it possible to build a completely reversible computer? A closer look into the internal aspects of the reversible computing as well as the external constraints such as the second law of thermodynamics has demonstrated that several difficulties would have to be solved before reversible computer is being built. It is shown that a conventional reversible computer would require energy for setting up the reversible inputs from irreversible signals, for the reading out of the reversible outputs, for the transport of the information between logic elements and finally for the control signals that will require more energy dissipating into the environment. A loose bound on the minimum amount of energy required to be dissipated during the physical implementation of a reversible computer is obtained and a generalization of the principles for reversible computing is provided.

quant-ph↗

arXiv2017

Semi-quantum communication: Protocols for key agreement, controlled secure direct communication and dialogue

Semi-quantum protocols that allow some of the users to remain classical are proposed for a large class of problems associated with secure communication and secure multiparty computation. Specifically, first time semi-quantum protocols are proposed for key agreement, controlled deterministic secure communication and dialogue, and it is shown that the semi-quantum protocols for controlled deterministic secure communication and dialogue can be reduced to semi-quantum protocols for e-commerce and private comparison (socialist millionaire problem), respectively. Complementing with the earlier proposed semi-quantum schemes for key distribution, secret sharing and deterministic secure communication, set of schemes proposed here and subsequent discussions have established that almost every secure communication and computation tasks that can be performed using fully quantum protocols can also be performed in semi-quantum manner. Further, it addresses a fundamental question in context of a large number problems- how much quantumness is (how many quantum parties are) required to perform a specific secure communication task? Some of the proposed schemes are completely orthogonal-state-based, and thus, fundamentally different from the existing semi-quantum schemes that are conjugate-coding-based. Security, efficiency and applicability of the proposed schemes have been discussed with appropriate importance.

quant-ph↗

arXiv2017

General structures of reversible and quantum gates

The most general structure (in matrix form) of a single-qubit gate is presented. Subsequently, used that to obtain a set of conditions for testing (a) whether a given 2-qubit gate is genuinely a 2-qubit gate, i.e., not decomposable into two single qubit gates and (b) whether a given single qubit gate is self-inverse? Relevance of the results reported here is discussed in the context of optimization of reversible and quantum circuits, especially for the optimization of quantum cost. A systematic procedure is developed for the identification of the non-decomposable 2-qubit gates. Such a non-decomposable 2-qubit gate along with all possible single qubit gates form a universal quantum gate library. Further, some possible applications of the present work are also discussed.

quant-ph↗

arXiv2017

Statistical distribution of the reversible gates: what percentage of them are self-inverse?

It is well known that most of the frequently used reversible logic gates (e.g., NOT, CNOT, SWAP, Toffoli, Fredkin) are self-inverse and are represented by square matrices that are unitary and Hermitian. However, with a simple minded argument, it is established that the most of the allowed reversible gates are non-self-inverse (unitary but non-Hermitian) in nature. It is also shown that the % of non-Hermitian gates increases with the dimension. For example, 58.33% of the 2-bit gates, 98.10% of the 3-bit gates and 99.99% of the 4-bit gates are non-Hermitian. As classical reversible gates are essentially permutation gates, above statistics is strictly valid for classical reversible gates, but the argument can be easily extended to include quantum gates and to establish that the majority of the quantum gates are also non-self-inverse. Further, the % of genuinely 2-bit reversible gates (i.e., 2-bit gates that cannot be decomposed as a product of two single bit gates) among all possible gates has been computed as 83.3%, and the applicability of this analysis in the optimization of circuit cost is discussed.

quant-ph↗