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Planarian is an intriguing model system wherein the effect of electric and magnetic fields can be studied on various biochemical pathways during cell morphogenesis. Recent experimental observations have demonstrated the non-trivial modulation of reactive oxygen species (ROS) levels by a weak magnetic field during planaria regeneration. However, the underlying biophysical mechanism behind this remains elusive. In this paper, we study the radical pair mechanism to explain the effect of weak magnetic fields on ROS modulation during planaria regeneration to explain the experimental results. We also investigate the effect of chirality-induced spin selectivity (CISS) on ROS levels by including it in the framework of the radical pair mechanism. We conclude that the inclusion of CISS explains the experimental results better and allows the radical pair model to have more parametric space to satisfy the experimental constraints. This study explains the crucial process of ROS modulation by the weak magnetic field with and without CISS, thereby paving the way to unraveling the vast domain of ROS modulation for desired outcomes.

In this article, a spaser (surface plasmon amplification by stimulated emission of radiation) system consisting of a metal nanoparticle surrounded by a large number of quantum dots (QDs) is studied. Usually, the effect of electron-phonon interaction is neglected in the spaser related literature. But some gain media, attributed by the large Raman scattering cross-section, exhibit stronger electron-phonon interaction. No such study has been performed for a QD-based spaser. Hence, it warrants investigation of the same in spaser system. In the present work, we investigate the effects of electron-phonon interaction on a three-level QD-based spaser. We consider two types of interaction potentials, linear and quadratic, and analyze their effects individually. First, we focus on the linear electron-phonon interaction that perturbs the electrons present in the excited state. This yields a periodic steady-state number of localized surface plasmon (LSP). The accompanying analytic solution reveals that the population inversion of the gain medium depends on the linear potential strength (Frohlich constant) but does not affect the threshold of spaser considerably for the given numerical parameters. In addition to the LSP, phonons may be generated during this process, the temporal dynamics of which are also detailed. Initially, the number of phonons exhibit decaying periodic oscillations, whose amplitude depends on the strength of the electron-phonon interaction. Under continuous pumping, at later times, the number of phonons reaches a steady-state value, which may find application in realization of continuous phonon nanolasers. Further, the effect of the quadratic potential is studied phenomenologically by increasing the excited-state decay rate. This results in a large number of LSP and an intense spaser spectrum., Comment: 11 pages, 6 figures

This work investigates the effect of chiral-induced spin selectivity (CISS) on quantum spin coherence in the radical pair mechanism of avian magnetoreception. Additionally, we examine the utilitarian role of coherence for the avian compass by analyzing its correlation with the yield of the signaling state. We find that both the relative entropy of global coherence and local coherence in the radical pair increases with CISS. However, only global coherence exhibit the utilitarian role for the avian compass. We also analyze the interplay of dipolar interaction with the CISS and their effect on the coherence of the radical pair. Further, we analyze the effect of environmental decoherence along with CISS. We conclude that a high CISS results in a high correlation of global coherence with signaling state yield. It confirms that CISS plays an important role both for compass sensitivity and coherence in the avian compass.

We propose a quantum algorithm (in the form of a quantum oracle) that estimates the closeness of a given Boolean function to one that satisfies the ``strict avalanche criterion'' (SAC). This algorithm requires $n$ queries of the Boolean function oracle, where $n$ is the number of input variables, this is fewer than the queries required by the classical algorithm to perform the same task. We compare our approach with other quantum algorithms that may be used for estimating the closeness to SAC and it is shown our algorithm verifies SAC with the fewest possible calls to quantum oracle and requires the fewest samples for a given confidence bound.

In this paper, we investigate the effect of chiral-induced spin selectivity (CISS) on the radical pair model of avian magnetoreception. We examine the impact of spin selectivity on the avian compass sensitivity. In this analysis, we also consider the dipolar and exchange interactions and observe their interplay with CISS. We find that CISS results in multifold increase in avian compass sensitivity. Interestingly, we also observe that CISS can counter the deleterious effect of dipolar interaction and increase system sensitivity.The analysis has been performed for both the toy model (only 1 nucleus) and a more general case where we consider 4-nuclei from the cryptochrome radical pair system. We observe that the CISS allows the radical pair model to have a more realistic rate with good sensitivity. We also do analysis of functional window of avian compass reported in behavioral experiments in functional window. We could not find a parameter set where functional window can be observed along with CISS.

Quantum dot-based spin qubits are resilient towards charge noise and are affected by magnetic noise only. However, environmental interaction leads to decoherence in these qubit systems. The external control parameters are directly related to the magnitude of decoherence. This in turn limits the range of values of those parameters for which operations can be done with high fidelity. In this work, using a model of quantum dot spin qubit system, we investigate the impact of varying ac magnetic fields on suppression of decoherence. We report an increment in the usable range of static magnetic field value using our technique.

Quantum dot-based spin qubit realization is one of the most promising quantum computing systems owing to its integrability with classical computation hardware and its versatility in realizing qubits and quantum gates. In this work, we investigate a quantum dot-based universal set of quantum gates (single qubit gates and the Toffoli gate) in the presence of hyperfine fluctuation noise and phononic charge noise. We model the spin dynamics and noise processes in the NOT gate, Hadamard gate and the Toffoli gate using the Lindblad master equation formalism to estimate the operating ranges of the external static and ac magnetic fields to achieve high fidelity operation of these gates in a noisy environment. In addition, the generality of the framework proposed in this paper enables modeling of larger quantum processors based on spin qubits in realistic conditions.

In this work, we propose an efficient photocell based on GaN quantum dots. We exploit the strong built-in electric field in GaN QDs and excitonic dipole-dipole coupling between adjacent QDs to break detailed balance. This is a much stronger effect than Fano interference, and we show that such a photocell exhibits enhanced photo-voltage and photocurrent over its conventional counterpart. The proposed quantum photocell could be the first step towards harnessing quantum effects in practical energy harvesting devices., Comment: 8 pages, 9 figures

We explicitly derive a connection between quantum circuits utilising IBM's quantum gate set and multivariate quadratic polynomials over integers modulo 8. We demonstrate that the action of a quantum circuit over input qubits can be written as generalized Walsh-Hadamard transform. Here, we derive the polynomials corresponding to implementations of the Swap gate and Toffoli gate using IBM-Q gate set., Comment: 7 pages, 8 figures, Accepted to Publish in: 10th International Conference on Computing, Communication and Networking Technologies and IEEE Xplore

The photosynthetic reaction center of plants and bacteria is an extremely efficient energy to charge conversion device. Solar photons create excitons in the pigment molecules. These excitons are then transferred to the reaction center where charge separation takes place. These processes - excitonic generation and subsequent charge separation are extremely efficient with almost unity efficiency. Taking pointers from this biophysical process, we propose a GaN quantum dot based solid state energy to charge conversion device idea that emulates the photosynthetic reaction center. This further suggests that highly efficient quantum biological processes can give important pointers for developing energy harvesting quantum technologies., Comment: 7 pages, 8 figures

Theoretical studies indicating the presence of long-lived coherence in the radical pair system have engendered questions about the utilitarian role of sustained coherence in the avian compass. In this manuscript, we investigate this for a realistic multi-nuclear radical pair system, along with the related question of its sensitivity to the geomagnetic field. Firstly, we find that sustenance of long-lived coherence is unlikely in a realistic hyperfine environment. Secondly, probing the role of the hyperfine interactions on the compass sensitivity, we establish the hyperfine anisotropy as an essential parameter for the sensitivity. Thereby, we are able to identify a parameter regime where the compass would exhibit sensitivity even without sustained coherence., Comment: Submitted version

The spin dynamics of the diamond NV$^{-}$ center turns out to be similar to that of the chemical compass responsible for avian magnetoreception. We present a simulation framework based on quantum master equation for the former that is based upon the Radical Pair model of the latter. We show that this framework captures all the experimentally studied behavior of the NV$^{-}$ center spin system and can therefore be a predictive modeling tool., Comment: 8 pages, 6 figures

The functional window is an experimentally observed property of the avian compass that refers to its selectivity around the geomagnetic field strength. We show that the radical-pair model, using biologically feasible hyperfine parameters, can qualitatively explain the salient features of the avian compass as observed from behavioral experiments: its functional window, as well as disruption of the compass action by an RF field of specific frequencies. Further, we show that adjustment of the hyperfine parameters can tune the functional window, suggesting a possible mechanism for its observed adaptability to field variation. While these lend strong support to the radical-pair model, we find it impossible to explain quantitatively the observed width of the functional window within this model, or even with simple augmentations thereto. This suggests that a deeper generalization of this model may be called for; we conjecture that environmental coupling may be playing a subtle role here that has not been captured accurately. Lastly, we examine a possible biological purpose to the functional window; assuming evolutionary benefit from radical-pair magnetoreception, we conjecture that the functional window is simply a corollary thereof and brings no additional advantage., Comment: 7 pages, 4 figures

The radical pair model has been successful in explaining behavioral characteristics of the geomagnetic compass believed to underlie the navigation capability of certain avian species. In this study, the spin dynamics of the radical pair model and decoherence therein are interpreted from a microscopic state transition point of view. This helps to elucidate the interplay between the hyperfine and Zeeman interactions that enables the avian compass, and the distinctive effects of nuclear and environmental decoherence on it. Using a quantum information theoretic quantifier of coherence, we find that nuclear decoherence induces new structure in the spin dynamics without materially affecting the compass action; environmental decoherence, on the other hand, completely disrupts it., Comment: 6 pages, 6 figures