arXiv subjects

Anirban Pathak

Publications and source records attributed to Anirban Pathak.

At least 37 records · Page 2Linked to original sources

arXiv2024

Protocols for counterfactual and twin-field quantum digital signature

Quantum digital signature (QDS) is the quantum version of its classical counterpart, and can offer security against attacks of repudiation, signature forging and external eavesdropping, on the basis of quantum mechanical no-go principles. Here we propose a QDS scheme based on quantum counterfactuality, which leverages the concept of interaction-free measurement. Employing the idea behind twin-field cryptography, we show how this two-way protocol can be turned into an equivalent non-counterfactual, one-way protocol, that is both more practical and also theoretically helpful in assessing the experimental feasibility of the first protocol. The proposed QDS protocol can be experimentally implemented with current quantum technology.

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arXiv2024

Revisiting Majumdar-Ghosh spin chain model and Max-cut problem using variational quantum algorithms

In this work, energy levels of the Majumdar-Ghosh model (MGM) are analyzed up to 15 spins chain in the noisy intermediate-scale quantum framework using noisy simulations. This is a useful model whose exact solution is known for a particular choice of interaction coefficients. We have solved this model for interaction coefficients other than that required for the exactly solvable conditions as this solution can be of help in understanding the quantum phase transitions in complex spin chain models. The solutions are obtained using quantum approximate optimization algorithms (QAOA), and variational quantum eigensolver (VQE). To obtain the solutions, the one-dimensional lattice network is mapped to a Hamiltonian that corresponds to the required interaction coefficients among spins. Then, the ground states energy eigenvalue of this Hamiltonian is found using QAOA and VQE. Further, the validity of the Lieb-Schultz-Mattis theorem in the context of MGM is established by employing variational quantum deflation to find the first excited energy of MGM. Solution for an unweighted Max-cut graph for 17 nodes is also obtained using QAOA and VQE to know which one of these two techniques performs better in a combinatorial optimization problem. Since the variational quantum algorithms used here to revisit the Max-cut problem and MGM are hybrid algorithms, they require classical optimization. Consequently, the results obtained using different types of classical optimizers are compared to reveal that the QNSPSA optimizer improves the convergence of QAOA in comparison to the SPSA optimizer. However, VQE with EfficientSU2 ansatz using the SPSA optimizer yields the best results.

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arXiv2024

Controlled-Joint Remote Implementation of Operators and its Possible Generalization

The existing notion of the shared entangled state-assisted remote preparation of unitary operator (equivalently the existing notion of quantum remote control) using local operation and classical communication is generalized to a scenario where under the control of a supervisor two users can jointly implement arbitrary unitaries (one unknown unitary operation by each or equivalently a single unitary decomposed into two unitaries of the same dimension and given to two users) on an unknown quantum state available with a geographically separated user. It is explicitly shown that the task can be performed using a four-qubit hyperentangled state, which is entangled simultaneously in both spatial and polarization degrees of freedom of photons. The proposed protocol which can be viewed as primitive for distributed photonic quantum computing is further generalized to the case that drops the restrictions on the number of controllers and the number of parties performing unitaries and allows both the numbers to be arbitrary. It is also shown that all the existing variants of quantum remote control schemes can be obtained as special cases of the present scheme.

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arXiv2024

Quantum networks using counterfactual quantum communication

Counterfactual quantum communication is one of the most interesting facets of quantum communication, allowing two parties to communicate without any transmission of quantum or classical particles between the parties involved in the communication process. This aspect of quantum communication originates from the interaction-free measurements where the chained quantum Zeno effect plays an important role. Here, we propose a new counterfactual quantum communication protocol for transmitting an entangled state from a pair of electrons to two independent photons. Interestingly, the protocol proposed here shows that the counterfactual method can be employed to transfer information from house qubits to flying qubits. Following this, we show that the protocol finds uses in building quantum repeaters leading to a counterfactual quantum network, enabling counterfactual communication over a linear quantum network.

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arXiv2024

Coherently Driven Quantum Harmonic Oscillator Battery

Quantum harmonic oscillator (QHO) battery models have been studied with significant importance in the recent past because these batteries are experimentally realizable and have high ergotropy and capacity to store more than one quanta of energy. QHO battery models are reinvestigated here to answer a set of fundamental questions: Do such models have any benefit? Is unbounded charging possible? Does the use of a catalyst system enhance the energy transfer to quantum batteries? These questions are answered both numerically and analytically by considering a model that allows a laser to shine on a QHO charger that interacts with a QHO battery. In contrast to some of the existing works, the obtained answers are mostly negative. Specifically, in the present work, the laser frequency is tuned with the frequency of the global charger-battery system, which is affected by the interaction between QHOs. It is reported that for a fixed laser field amplitude $\textit{F}$, the battery can store more energy when tuned with the frequency of the global charger-battery system compared to energy stored by tuning the laser frequency with local frequencies of the charger and battery. The charging process of the open QHO, which is a simplified model, and the self-discharging (dissipation) process after switching off the laser field are also investigated to reveal that the charging process of QHO in the simplified model is faster than the charging process of the catalytic (non-catalytic) battery. Further, it's observed that the self-discharging process is almost two times faster than the charging process which makes such models unstable against interaction with the environment.

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arXiv2023

Experimental implementation of distributed phase reference quantum key distribution protocols

Quantum cryptography is now considered as a promising technology due to its promise of unconditional security. In recent years, rigorous work is being done for the experimental realization of quantum key distribution (QKD) protocols to realize secure networks. Among various QKD protocols, coherent one way and differential phase shift QKD protocols have undergone rapid experimental developments due to the ease of experimental implementations with the present available technology. In this work, we have experimentally realized optical fiber based coherent one way and differential phase shift QKD protocols at telecom wavelength. Both protocols belong to a class of protocols named as distributed phase reference protocol in which weak coherent pulses are used to encode the information. Further, we have analyzed the key rates with respect to different parameters such distance, disclose rate, compression ratio and detector dead time.

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arXiv2023

A Comprehensive Review of Quantum Random Number Generators: Concepts, Classification and the Origin of Randomness

Random numbers are central to cryptography and various other tasks. The intrinsic probabilistic nature of quantum mechanics has allowed us to construct a large number of quantum random number generators (QRNGs) that are distinct from the traditional true number generators. This article provides a review of the existing QRNGs with a focus on their various possible features (e.g., device independence, semi-device independence) that are not achievable in the classical world. It also discusses the origin, applicability, and other facets of randomness. Specifically, the origin of randomness is explored from the perspective of a set of hierarchical axioms for quantum mechanics, implying that succeeding axioms can be regarded as a superstructure constructed on top of a structure built by the preceding axioms. The axioms considered are: (Q1) incompatibility and uncertainty; (Q2) contextuality; (Q3) entanglement; (Q4) nonlocality and (Q5) indistinguishability of identical particles. Relevant toy generalized probability theories (GPTs) are introduced, and it is shown that the origin of random numbers in different types of QRNGs known today are associated with different layers of nonclassical theories and all of them do not require all the features of quantum mechanics. Further, classification of the available QRNGs has been done and the technological challenges associated with each class are critically analyzed. Commercially available QRNGs are also compared.

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arXiv2023

Partial Loopholes Free Device Independent Quantum Random Number Generator Using IBM's Quantum Computers

Random numbers form an intrinsic part of modern day computing with applications in a wide variety of fields. But due to their limitations, the use of pseudo random number generators (PRNGs) is certainly not desirable for sensitive applications. Quantum systems due to their intrinsic randomness form a suitable candidate for generation of true random numbers that can also be certified. In this work, the violation of CHSH inequality has been used to propose a scheme by which one can generate device independent quantum random numbers by use of IBM quantum computers that are available on the cloud. The generated random numbers have been tested for their source of origin through experiments based on the testing of CHSH inequality through available IBM quantum computers. The performance of each quantum computer against the CHSH test has been plotted and characterized. Further, efforts have been made to close as many loopholes as possible to produce device independent quantum random number generators. This study will provide new directions for the development of self-testing and semi-self-testing random number generators using quantum computers.

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arXiv2023

A Review on Practical Challenges of Aerial Quantum Communication

The increasing demand for the realization of global-scale quantum communication services necessitates critical investigation for a practical quantum secure communication network that relies on full-time all-location coverage. In this direction, the non-terrestrial quantum key distribution is expected to play an important role in providing agility, maneuverability, relay link, on-demand network, and last-mile coverage. In this work, we have summarized the research and development that has happened until now in the domain of quantum communication using non-terrestrial platforms with a specific focus on the associated challenges and the relevant models. Further, to extend the analysis beyond the existing know-how, a hybrid model involving the features of Vasylyev et al. model and Liorni et al. model is introduced here. The hybrid model entails us adapting a spherical beam to an elliptic beam approximation and effectively capturing the characteristics of transmittance in densely humid weather conditions and at low altitudes. Further, to understand the potential impact of the weather conditions of a region on atmospheric attenuation, as an example the average monthly visibility of Pune city was analyzed for the years 2021 and 2022. In addition, a simulation of a generic model is performed using a software-defined network paradigm where quantum teleportation is simulated between distant parties using a swarm of drones in NetSquid.

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arXiv2023

Implementation of coherent one way protocol for quantum key distribution up to an effective distance of 145 km

In the present work, we report experimental realization of an optical fiber based COW protocol for QKD in the telecom wavelength (1550 nm) where the attenuation in the optical fiber is minimum. A laser of 1550 nm wavelength, attenuator and intensity modulator is used for the generation of pulses having average photon number 0.5 and repetition rate of 500 MHz. The experiment is performed over 40 km, 80 km and 120 km of optical fiber and several experimental parameters like disclose rate, compression ratio, dead time and excess bias voltage of the detector are varied for all the cases (i.e., for 40 km, 80 km and 120 km distances) to observe their impact on the final key rate. Specifically, It is observed that there is a linear increase in the key rate as we decrease compression ratio or disclose rate. The key rate obtains its maximum value for least permitted values of disclose rate, compression ratio and dead time. It seems to remain stable for various values of excess bias voltage. While changing various parameters, we have maintained the quantum bit error rate (QBER) below 6%. The key rate obtained is also found to remain stable over time. Experimental results obtained here are also compared with the earlier realizations of the COW QKD protocol. Further, to emulate key rate at intermediate distances and at a distance larger than 120 km, an attenuator of 5 dB loss is used which can be treated as equivalent to 25 km of the optical fiber used in the present implementation. This has made the present implementation equivalent to the realization of COW QKD upto 145 km.

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arXiv2023

Many facets of multiparty broadcasting of known quantum information using optimal quantum resource

The no-quantum broadcasting theorem which is a weaker version of the nocloning theorem restricts us from broadcasting completely unknown quantum information to multiple users. However, if the sender is aware of the quantum information (state) to be broadcasted then the above restriction disappears and the task reduces to a multiparty remote state preparation. Without recognizing this fact, several schemes for broadcasting of known quantum states have been proposed in the recent past (e.g., Quantum Inf Process (2017) 16:41) and erroneously/misleadingly referred to as protocols for quantum broadcasting. Here we elaborate on the relation between the protocols of remote state preparation and those of broadcasting of known quantum information and show that it's possible to broadcast known quantum information to multiple receivers in deterministic as well as probabilistic manner with optimal resources. Further, the effect of noise on such schemes, and some new facets (like joint broadcasting) of such schemes have been discussed. A proof of principle realization of the proposed optimal scheme using IBM quantum computer is also reported. Possibilities of generalizations of the so-called broadcasting schemes and potential applications are also discussed with appropriate importance.

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arXiv2023

Quantum Zeno and anti-Zeno effects in the dynamics of non-degenerate hyper-Raman processes coupled to two linear waveguides

The effect of the presence of two probe waveguides on the dynamics of hyper-Raman processes is studied in terms of quantum Zeno and anti-Zeno effects. Specifically, the enhancement (diminution) of the evolution of the hyper-Raman processes due to interaction with the probe waveguides via evanescent waves is viewed as quantum Zeno (anti-Zeno) effect. We considered the two probe waveguides interacting with only one of the optical modes at a time. For instance, as a specific scenario, it is considered that the two non-degenerate pump modes interact with each probe waveguide linearly while Stokes and anti-Stokes modes do not interact with the probes. Similarly, in another scenario, we assumed both the probe waveguides interact with Stokes (anti-Stokes) mode simultaneously. The present results show that quantum Zeno (anti-Zeno) effect is associated with phase-matching (mismatching). However, we did not find any relation between the presence of the quantum Zeno effect and antibunching in the bosonic modes present in the hyper-Raman processes.

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arXiv2023

Entanglement Routing and Bottlenecks in Grid Networks

Distributing entangled pairs among multiple users is a fundamental problem in quantum networks. Existing protocols like $X$ protocol introduced in (npj Quantum Information 5, 76 (2019)) use graph theoretic tools like local complementation to optimize the number of measurements required to extract any Bell pair among the network users. However, such a protocol relies on finding the shortest path between the users. Here, the existing results are extended to establish a counter-intuitive notion that, in general, the most optimal path to perform the $X$ protocol is not along the shortest path. Specific examples of this advantage are provided on networks of size as small as 12 qubits. Bottlenecks in establishing simultaneous Bell pairs in nearest-neighbor architectures are also explored. Recent results suggesting the unsuitability of the line and ring networks for the implementation of quantum networks due to the existence of bottlenecks are revisited, and using local equivalency relations from graph theory, it is hinted at the possibility that even grid graphs are not exempt from bottleneck issues. Further, it's noted that the results obtained here would be of use in analyzing the advantages of measurement-based quantum network coding.

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arXiv2022

An efficient quantum-classical hybrid algorithm for distorted alphanumeric character identification

An algorithm for image processing is proposed. The proposed algorithm, which can be viewed as a quantum-classical hybrid algorithm, can transform a low-resolution bitonal image of a character from the set of alphanumeric characters (A-Z, 0-9) into a high-resolution image. The quantum part of the proposed algorithm fruitfully utilizes a variant of Grover's search algorithm, known as the fixed point search algorithm. Further, the quantum part of the algorithm is simulated using CQASM and the advantage of the algorithm is established through the complexity analysis. Additional analysis has also revealed that this scheme for optical character recognition (OCR) leads to high confidence value and generally works in a more efficient manner compared to the existing classical, quantum, and hybrid algorithms for a similar task.

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arXiv2022

Multiparty Entanglement Routing in Quantum Networks

Distributing entanglement among multiple users is a fundamental problem in quantum networks, requiring an efficient solution. In this work, a protocol is proposed for extracting maximally entangled (GHZn) states for any number of parties in quantum networks of arbitrary topology. It is based on the graph state formalism and requires minimal assumptions on the network state. The protocol only requires local measurements at the network nodes and just a single qubit memory per user. Existing protocols on bipartite entanglement routing are also improved for specific nearest-neighbor network architectures. To this end, the concept of majorization is utilized to establish a hierarchy among different paths in a network based on their efficacy. This approach utilizes the symmetry of the underlying graph state to obtain better-performing algorithms.

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arXiv2022

Open quantum system dynamics of $X$-states: Entanglement sudden death and sudden birth

The origin of disentanglement for two specific sub-classes of $X$-states namely maximally nonlocal mixed states (MNMSs) and maximally entangled mixed states (MEMSs) is investigated analytically for a physical system consisting of two spatially separated qubits interacting with a common vacuum bath. The phenomena of entanglement sudden death (ESD) and the entanglement sudden birth (ESB) are observed, but the characteristics of ESD and ESB are found to be different for the case of two photon coherence and single photon coherence states. The role played by initial coherence for the underlying entanglement dynamics is investigated. Further, the entanglement dynamics of MNMSs and MEMSs under different environmental noises namely phase damping, amplitude damping and RTN noise with respect to the decay and revival of entanglement is analyzed. It's observed that the single photon coherence states are more robust against the sudden death of entanglement indicating the usability of such states in the development of technologies for the practical implementation of quantum information processing tasks.

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arXiv2022

Anonymous voting scheme using quantum assisted blockchain

Voting forms the most important tool for arriving at a decision in any institution. The changing needs of the civilization currently demands a practical yet secure electronic voting system, but any flaw related to the applied voting technology can lead to tampering of the results with the malicious outcomes. Currently, blockchain technology due to its transparent structure forms an emerging area of investigation for the development of voting systems with a far greater security. However, various apprehensions are yet to be conclusively resolved before using blockchain in high stakes elections. Other than this, the blockchain based voting systems are vulnerable to possible attacks by upcoming noisy intermediate scale quantum (NISQ) computer. To circumvent, most of these limitations, in this work, we propose an anonymous voting scheme based on quantum assisted blockchain by enhancing the advantages offered by blockchain with the quantum resources such as quantum random number generators and quantum key distribution. The purposed scheme is shown to satisfy the requirements of a good voting scheme. Further, the voting scheme is auditable and can be implemented using the currently available technology.

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arXiv2022

Quantum and Semi-Quantum Lottery: Strategies and Advantages

Lottery is a game in which multiple players take chances in the hope of getting some rewards in cash or kind. In addition, from the time of the early civilizations, lottery has also been considered as an apposite method to allocate scarce resources. Technically, any scheme for lottery needs to be fair and secure, but none of the classical schemes for lottery are unconditionally secure and fair. As fairness demands complete unpredictability of the outcome of the lottery, it essentially requires perfect randomness. Quantum mechanics not only guarantees the generation of perfect randomness, it can also provide unconditional security. Motivated by these facts, a set of strategies for performing lottery using different type of quantum resources (e.g., single photon states, and entangled states) are proposed here, and it's established that the proposed strategies leads to unconditionally secure and fair lottery schemes. A scheme for semi-quantum lottery that allows some classical users to participate in the lottery involving quantum resources is also proposed and the merits and demerits of all the proposed schemes are critically analysed. Its also established that the level of security is intrinsically related to the type of quantum resources being utilized. Further, its shown that the proposed schemes can be experimentally realized using currently available technology, and that may herald a new era of commercial lottery.

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