arXiv subjects

Kishore Thapliyal

Publications and source records attributed to Kishore Thapliyal.

At least 37 records · Page 2Linked to original sources

arXiv2021

Ideal pairing of the Stokes and anti-Stokes photons in the Raman process

A quantum model of the Raman process with the independent Stokes and anti-Stokes nonlinear interactions is developed to study nonclassical correlations between the photons in the Stokes and anti-Stokes fields. The role of the laser pump amplitude, the ratio of the Stokes and anti-Stokes coupling constants and the population and losses of the vibrational mode in forming the correlations is elucidated. The $ g^{(2)} $ intensity cross-correlation function, noise-reduction-factor, two-mode principal squeezing variance, logarithmic negativity, non-classicality depth, steering parameter and the Bell parameter are analyzed side-by-side to shed light to the correlations between the Stokes and anti-Stokes fields. Conditions for having the Stokes and anti-Stokes fields composed of only photon pairs, similarly as it occurs in twin beams in parametric down-conversion, are revealed. They allow for nonzero mean thermal phonon numbers.

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arXiv2020

Quantifying quantum correlation of quasi-Werner state and probing its suitability for quantum teleportation

The significance of photon addition in engineering the single- and two-mode (bipartite correlations) nonclassical properties of a quantum state is investigated. Specifically, we analyzed the behavior of the Wigner function of two quasi-Werner states theoretically constructed by superposing two normalized bipartite $m$-photon added coherent states. This allowed us to quantify the amount of nonclassicality present in the quantum states using Wigner logarithmic negativity (WLN), while quantum correlations are measured in terms of concurrence, entanglement of formation, and quantum discord. The WLN for a two-mode state corresponds to the sum of the single-mode nonclassicality as well as quantum correlations, and both of these are observed to enhance with photon addition manifesting the efficacy of photon addition in the entanglement distillation. Usefulness of photon addition is further established by showing that the performance of the quasi-Werner states as quantum channel for the teleportation of a single-mode coherent and squeezed states, as quantified via teleportation fidelity, improves with the photon addition. Further, in contrast to a set of existing results, it is established that the negative values of two-mode Wigner function cannot be used in general as a witness of quantum correlation.

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arXiv2020

Continuous variable direct secure quantum communication using Gaussian states

Continuous variable one-way and controlled-two-way secure direct quantum communication schemes have been designed using Gaussian states. Specifically, a scheme for continuous variable quantum secure direct communication and another scheme for continuous variable controlled quantum dialogue are proposed using single-mode squeezed coherent states. The security of the proposed schemes against a set of attacks (e.g., Gaussian quantum cloning machine and intercept resend attacks) has been proved. Further, it is established that the proposed schemes do not require two-mode squeezed states which are essential for a set of existing proposals. The controlled two-way communication scheme is shown to be very general in nature as it can be reduced to schemes for various relatively simpler cryptographic tasks like controlled deterministic secure communication, quantum dialogue, quantum key distribution. In addition, it is briefly discussed that the proposed schemes can provide us tools to design quantum cryptographic solutions for several socioeconomic problems.

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arXiv2020

Interplay between quantum Zeno and anti-Zeno effects in a non-degenerate hyper-Raman nonlinear optical coupler

Quantum Zeno and anti-Zeno effects are studied in an asymmetric nonlinear optical coupler composed of a probe waveguide and a system waveguide. The system is a nonlinear waveguide operating under non-degenerate hyper-Raman process, while both the pump modes in the system are constantly interacting with the probe waveguide. The effect of the presence of probe on the temporal evolution of the system in terms of the number of photons in Stokes and anti-Stokes modes as well as phonon number is quantified as Zeno parameter. The negative (positive) values of the Zeno parameter in the specific mode are considered as the signatures of the quantum Zeno (anti-Zeno)effect in that mode of the system. It is observed that the phase mismatch in Stokes and anti-Stokes generation processes can be controlled to induce a transition between quantum Zeno and anti-Zeno effects for both off-resonant and resonant hyper-Raman process. However, in case of off-resonant hyper-Raman process in the system waveguide, the frequency detuning parameters can also be used analogously to cause the desired crossover. Further, the general nature of the physical system and the perturbative technique used here allowed us to analytically study the possibilities of observing quantum Zeno and anti-Zeno effects in a large number of special cases, including situations where the process is spontaneous, partially spontaneous and/or the system is operated under degenerate hyper-Raman process, or a simple Raman process.

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arXiv2020

Noisy three-player dilemma game: Robustness of the quantum advantage

Games involving quantum strategies often yield higher payoff. Here, we study a practical realization of the three-player dilemma game using the superconductivity-based quantum processors provided by IBM Q Experience. We analyze the persistence of the quantum advantage under corruption of the input states and how this depends on parameters of the payoff table. Specifically, experimental fidelity and error are observed not to be properly anti correlated, i.e., there are instances where a class of experiments with higher fidelity yields a greater error in the payoff. Further, we find that the classical strategy will always outperform the quantum strategy if corruption is higher than half.

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arXiv2020

Optical designs for realization of a set of schemes for quantum cryptography

Several quantum cryptographic schemes have been proposed and realized experimentally in the past. However, even with an advancement in quantum technology and escalated interest in the designing of direct secure quantum communication schemes there are not many experimental implementations of these cryptographic schemes. In this paper, we have provided a set of optical circuits for such quantum cryptographic schemes, which have not yet been realized experimentally by modifying some of our theoretically proposed secure communication schemes. Specifically, we have proposed optical designs for the implementation of two single photon and one entangled state based controlled quantum dialogue schemes and subsequently reduced our optical designs to yield simpler designs for realizing other secure quantum communication tasks, i.e., controlled deterministic secure quantum communication, quantum dialogue, quantum secure direct communication, quantum key agreement, and quantum key distribution. We have further proposed an optical design for an entanglement swapping based deterministic secure quantum communication and its controlled counterpart.

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arXiv2019

Are optical quantum information processing experiments possible without beamsplitter?

The significance of beamsplitter in experimental optical quantum information processing and quantum technology is discussed with a focus on the role of a beamsplitter-type Hamiltonian in the recent development in this field of research. Here, we follow a new approach to briefly describe quantum measurement, Bell measurement, quantum state engineering, quantum teleportation, cryptography, and computation using both discrete and continuous variables to establish the wide applications of beamsplitter-type operation. Finally, we also discuss the limitations of this linear optical element.

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arXiv2019

Impact of photon addition and subtraction on nonclassical and phase properties of a displaced Fock state

Various nonclassical and quantum phase properties of photon added then subtracted displaced Fock state have been examined systematically and rigorously. Higher-order moments of the relevant bosonic operators are computed to test the nonclassicality of the state of interest, which reduces to various quantum states (having applications in quantum optics, metrology and information processing) in different limits ranging from the coherent (classical) state to the Fock (most nonclassical) states. The nonclassical features are discussed using Klyshko's, Vogel's, and Agarwal-Tara's criteria as well as the criteria of lower- and higher-order antibunching, sub-Poissonian photon statistics and squeezing. In addition, phase distribution function and quantum phase fluctuation have been studied. These properties are examined for various combinations of number of photon addition and/or subtraction and Fock parameter. The examination has revealed that photon addition generally improves nonclassicality, and this advantage enhances for the large (small) values of displacement parameter using photon subtraction (Fock parameter). The higher-order sub-Poissonian photon statistics is only observed for the odd orders. In general, higher-order nonclassicality criteria are found to detect nonclassicality even in the cases when corresponding lower-order criteria failed to do so. Photon subtraction is observed to induce squeezing, but only large number of photon addition can be used to probe squeezing for large values of displacement parameter. Further, photon subtraction is found to alter the phase properties more than photon addition, while Fock parameter has an opposite effect of the photon addition/subtraction. Finally, nonclassicality and non-Gaussianity is also established using $Q$ function.

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arXiv2019

Quasidistribution of phases in Raman process with weak and strong pumps

Nonclassicality is studied through a quasidistribution of phases for the Raman process under both weak and strong pump conditions. In the former case, the solution is applicable to both resonant and off-resonant Raman processes, while strong classical pump is assumed at resonance. Under weak pump conditions (i.e., in a complete quantum treatment), the phase difference of phases described by single nonclassical modes is required to be filtered to describe a regular distribution function, which is not the case with strong pump. Compound Stokes-phonon mode shows nonclassical features of phases in both weak and strong pumping, which effect is similar to that for compound pump-phonon (Stokes-anti-Stokes) mode with weak (strong) pump. While anti-Stokes-phonon mode is observed to be classical and coherence conserving in strong pump case, pump-Stokes mode shows similar behavior in a special case in quantum treatment.

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arXiv2019

Manipulating nonclassicality via quantum state engineering processes: Vacuum filtration and single photon addition

The effect of two quantum state engineering processes that can be used to burn hole at vacuum in the photon number distribution of quantum states of radiation field are compared using various witnesses of lower- and higher-order nonclassicality as well as a measure of nonclassicality. Specifically, the witnesses of nonclassical properties due to the effect of vacuum state filtration and a single photon addition on an even coherent state, binomial state and Kerr state are investigated using the criteria of lower- and higher-order antibunching, squeezing and sub-Poissonian photon statistics. Further, the amount of nonclassicality present in these engineered quantum states is quantified and analyzed by using an entanglement potential based on linear entropy. It is observed that all the quantum states studied here are highly nonclassical, and on many occasions the hole burning processes are found to introduce/enhance nonclassical features. However, it is not true in general. The investigation has further revealed that despite the fact that a hole at vacuum implies a maximally nonclassical state (as far as Lee's nonclassical depth is used as the quantitative measure of nonclassicality). However, any particular process of hole burning at vacuum does not ensure the existence of a particular nonclassical feature. Specifically,lower- and higher-order squeezing are not observed for photon added even coherent state and vacuum filtered even coherent state.

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arXiv2019

Continuous variable B92 quantum key distribution protocol using single photon added and subtracted coherent states

In this paper, a continuous variable B92 quantum key distribution (QKD) protocol is proposed using single photon added and subtracted coherent states, which are prepared by adding and subsequently subtracting a single photon on a coherent state. It is established that in contrast to the traditional discrete variable B92 protocol, this protocol for QKD is intrinsically robust against the unambiguous state discrimination attack, which circumvents the requirement for any uninformative states or entanglement used in corresponding discrete variable case as a remedy for this attack. Further, it is shown that the proposed protocol is intrinsically robust against the eavesdropping strategies exploiting classical communication during basis reconciliation, such as beam splitter attack. Security against some individual attacks, key rate, and bit-error rate estimation for the proposed scheme are also provided. Specifically, the proposed scheme ensures very small bit-error rate due to properties of the states used. Thus, the proposed scheme is shown to be preferable over the corresponding discrete variable B92 protocol as well as some similar continuous variable quantum key distribution schemes.

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arXiv2019

Quantum phase properties of photon added and subtracted displaced Fock states

Quantum phase properties of photon added and subtracted displaced Fock states (and a set of quantum states which can be obtained as the limiting cases of these states) are investigated from a number of perspectives, and it is shown that the quantum phase properties are dependent on the quantum state engineering operations performed. Specifically, the analytic expressions for quantum phase distributions and angular $Q$ distribution as well as measures of quantum phase fluctuation and phase dispersion are obtained. The uniform phase distribution of the initial Fock states is observed to be transformed by the unitary operation (i.e., displacement operator) into non-Gaussian shape, except for the initial vacuum state. It is observed that the phase distribution is symmetric with respect to the phase of the displacement parameter and becomes progressively narrower as its amplitude increases. The non-unitary (photon addition/subtraction) operations make it even narrower in contrast to the Fock parameter, which leads to broadness. The photon subtraction is observed to be a more powerful quantum state engineering tool in comparison to the photon addition. Further, one of the quantum phase fluctuation parameters is found to reveal the existence of antibunching in both the engineered quantum states under consideration. Finally, the relevance of the engineered quantum states in the quantum phase estimation is also discussed, and photon added displaced Fock state is shown to be preferable for the task.

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arXiv2019

Continuous variable controlled quantum dialogue and secure multiparty quantum computation

A continuous variable controlled quantum dialogue scheme is proposed. The scheme is further modified to obtain two other protocols of continuous variable secure multiparty computation. The first one of these protocols provides a solution of two party socialist millionaire problem, while the second protocol provides a solution for a special type of multi-party socialist millionaire problem which can be viewed as a protocol for multiparty quantum private comparison. It is shown that the proposed scheme of continuous variable controlled quantum dialogue can be performed using bipartite entanglement and can be reduced to obtain several other two and three party cryptographic schemes in the limiting cases. The security of the proposed scheme and its advantage over corresponding discrete variable counterpart are also discussed. Specifically, the ignorance of an eavesdropper in the proposed scheme is shown to be very high compared with corresponding discrete variable scheme and thus the present scheme is less prone to information leakage inherent with the discrete variable quantum dialogue based schemes.It is further established that the proposed scheme can be viewed as a continuous variable counterpart of quantum cryptographic switch which allows a supervisor to control the information transferred between the two legitimate parties to a continuously varying degree.

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arXiv2018

Nonclassicality in off-resonant Raman process

Raman process is used for generation of nonclassical states and subsequent applications due to its simplicity. In view of the experimental feasibility of the off-resonant Raman process at single photon level useful in long distance quantum communication and quantum memory, we perform here a detailed study of possibility of generation of nonclassical states under off-resonance conditions. Specifically, we have studied nonclassicality in the off-resonant Raman process with the help of a characteristic function written using more general solution than the conventional short-time solution under complete quantum treatment and established the significance of frequency detuning parameter in generation of nonclassical states. The obtained characteristic function remains Gaussian and reveals that larger values of frequency detuning parameters are favorable to induce nonclassicality in some cases. The single- and two-mode squeezing and antibunching as well as intermodal entanglement are reported in terms of experimentally accessible quantum noise fluctuations considering either phonon mode coherent or chaotic. Subsequently, the joint photon number and integrated intensity distributions are studied to analyze the performance of pair generation in Stokes-phonon and pump-phonon modes. The present study discusses the role of resonance conditions in generation of nonclassical states and establishes that experimentally controllable detuning parameter can be used to probe and enhance the generated nonclassicality.

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arXiv2018

Interaction of light and semiconductor can generate quantum states required for solid state quantum computing: Entangled, steered and other nonclassical states

Proposals for solid state quantum computing are extremely promising as they can be used to built room temperature quantum computers. If such a quantum computer is ever built it would require in-built sources of nonclassical states required for various quantum information processing tasks. Possibilities of generation of such nonclassical states are investigated here for a physical system composed of a monochromatic light coupled to a two-band semiconductor with direct band gap. The model Hamiltonian includes both photon-exciton and exciton-exciton interactions. Time evolution of the relevant bosonic operators are obtained analytically by using a perturbative technique that provides operator solution for the coupled Heisenberg's equations of motion corresponding to the system Hamiltonian. The bosonic operators are subsequently used to study the possibilities of observing single and two mode squeezing and antibunching after interaction in the relevant modes of light and semiconductor. Further, entanglement between the exciton and photon modes is reported. Finally, the nonclassical effects have been studied numerically for the open quantum system scenario. In this situation, the nonlocal correlations between two modes are shown to violate EPR steering inequality. The observed nonclassical features, induced due to exciton-exciton pair interaction, can be controlled by the phase of input field and the correlations between two modes are shown to enhance due to nonclassicality in the input field.

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arXiv2018

Comparing coherence measures for X states: Can quantum states be ordered based on quantum coherence?

Quantum coherence is an essential resource for quantum information processing and various quantitative measures of it have been introduced. However, the interconnections between these measures are not yet understood properly. Here, using a large set of randomly prepared $X$ states and analytically obtained expressions of various measures of coherence (e.g., relative entropy of coherence, $l1$ norm of coherence, coherence via skew information, and first-order coherence), it is established that these measures of quantum coherence cannot be used to perform ordering of a set of quantum states based on the amount of coherence present in a state. Further, it is shown that for a given value of quantum coherence measured by the relative entropy of coherence, maximally nonlocal mixed states of $X$ type (which are characterized by maximal violation of the CHSH inequality) have maximum quantum coherence as measured by $l1$ norm of coherence. In addition, the amount of coherence measured by $l1$ norm of coherence for a Werner state is found to be always less than that for a maximally nonlocal mixed state even when they possess an equal amount of coherence measured by the relative entropy of coherence. These resource theory based measures of coherence are not observed to show any relation with the first-order coherence, while its maximum (hidden coherence) is found to be more connected to concurrence both being basis independent quantities. These observations could be of use in obtaining a deeper understanding of the interconnections between various measures of quantum coherence.

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arXiv2018

Quantum Zeno effect and nonclassicality in a PT symmetric system of coupled cavities

The interplay between the nonclassical features and the parity-time (PT) symmetry (or its breaking) is studied here by considering a PT symmetric system consisting of two cavities with gain and loss. The conditions for PT invariance is obtained for this system. The behavior of the average photon number corresponding to the gain and loss modes for different initial states (e.g., vacuum, NOON, coherent, and thermal states) has also been obtained. With the help of the number operators, quantum Zeno and anti-Zeno effects are studied, and the observed behavior is compared in PT symmetric (PTS) and PT symmetry broken (PTSB) regimes. It has been observed that the relative phase of the input coherent fields plays a key role in the occurrence of these effects. Further, some nonclassicality features are witnessed using criteria based on the number operator(s). Specifically, intermodal antibunching, sum and difference squeezing, are investigated for specific input states. It is found that the various nonclassical features, including the observed quantum Zeno and anti-Zeno effects, are suppressed when one goes from PTS to PTSB regime. In other words, the dominance of the loss/gain rate in the field modes over the coupling strength between them diminishes the nonclassical features of the system.

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arXiv2018

Lower- and higher-order nonclassical properties of photon added and subtracted displaced Fock states

Nonclassical properties of photon added and subtracted displaced Fock states have been studied using various witnesses of lower- and higher-order nonclassicality. Compact analytic expressions are obtained for the nonclassicality witnesses. Using those expressions, it is established that these states and the states that can be obtained as their limiting cases (except coherent states) are highly nonclassical as they show the existence of lower- and higher-order antibunching and sub-Poissonian photon statistics, in addition to the nonclassical features revealed through the Mandel $Q_M$ parameter, zeros of Q function, Klyshko's criterion, and Agarwal-Tara criterion. Further, some comparison between the nonclassicality of photon added and subtracted displaced Fock states have been performed using witnesses of nonclassicality. This has established that between the two types of non-Gaussianity inducing operations (i.e., photon addition and subtraction) used here, photon addition influences the nonclassical properties more strongly. Further, optical designs for the generation of photon added and subtracted displaced Fock states from squeezed vacuum state have also been proposed.

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