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This paper investigates the regularity properties of quantum master equations with unbounded coefficients within the space of square-integrable complex-valued Bernoulli functionals. Initially, we demonstrate the existence of a unique regular solution to the linear stochastic Schrödinger equation driven by cylindrical Brownian motions. Subsequently, we establish the existence of regular solutions for the autonomous linear quantum master equation and provide a probabilistic representation of this solution in terms of the stochastic Schrödinger equation. Finally, by taking the expectation of some observables with respect to the solution of the quantum master equation, we derive a system of differential equations that describe the evolution of the mean values of certain quantum observables. [ABSTRACT FROM AUTHOR]

The Lindblad equation, which describes Markovian quantum dynamics under dissipation, is usually derived under the weak system-bath coupling assumption. Strong system-bath coupling often leads to non-Markov evolution. The singular-coupling limit is known as an exception: it yields a Lindblad equation with an arbitrary strength of dissipation. However, the singular-coupling limit requires high-temperature limit of the bath, and hence the system ends up in a trivial infinite-temperature state, which is not desirable in the context of quantum control. In this work, it is shown that we can derive a Markovian Lindblad equation for an arbitrary strength of the system-bath coupling by considering a new scaling limit that is called the singular-driving limit, which combines the singular-coupling limit and fast periodic driving. In contrast to the standard singular-coupling limit, an interplay between dissipation and periodic driving results in a nontrivial steady state. [ABSTRACT FROM AUTHOR]

Energy transfer is ubiquitous in natural and artificial lightharvesting systems, and coherent energy transfer, a highly efficient energy transfer process, has been accepted to play a vital role in such systems. However, the energy oscillation of coherent energy transfer is exceedingly difficult to capture because of its evanescence due to the interaction with a thermal environment. Here a microscopic quantum model is used to study the time evolution of electrons triggered energy transfer between coherently coupled donoracceptor molecules in scanning tunneling microscope (STM). A series of topics in the plasmonic nanocavity (PNC) coupled donor-acceptor molecules system are discussed, including resonant and nonresonant coherent energy transfer, dephasing assisted energy transfer, PNC coupling strength dependent energy transfer, Fano resonance of coherently coupled donor-acceptor molecules, and polariton-mediated energy transfer. [ABSTRACT FROM AUTHOR]

Three‐photon‐pumped (3PP) excitonic lasing in inorganic semiconductor quantum dots (QDs) is of particular importance for near‐infrared biophotonics and optical communications. However, the implementation of such lasers has been hindered severely by the required high pump thresholds. Here, 3PP excitonic lasing of all‐inorganic cesium lead bromide perovskite QDs (CsPbBr3 PQDs) embedded in a whispering‐gallery microcavity is demonstrated, and achieving a record low threshold of 3 mJ cm−2 by tuning the 3P pump energy in resonance with the S exciton state. Wavelength‐dispersive Z‐scan spectroscopy reveals that such reduced lasing threshold is attributed to the exciton resonance enhanced multiphoton absorption, which, as disclosed by the kinetics analysis of transient absorption spectroscopy (TAS), leads to the appearance of net gain at a pump fluence as low as 2.2 mJ cm−2, corresponding to an average S exciton population of 1.5. A microscopic model incorporating the quantum master equation reproduces the TAS results and provides the intrinsic parameters of biexciton relaxation for lasing. The 3PP resonant excitonic transition is the most favored multiphoton pumping process that minimizes quantum defect (6.8% of the pump photon energy) to realize optical gain at low threshold, marking a major step toward using all‐inorganic perovskite QDs for on‐chip integrated microlasers and multiphoton bioimaging. [ABSTRACT FROM AUTHOR]

We develop a consistent perturbative technique for obtaining a time-local linear master equation based on projection methods in the case where the projection operator depends on time. Then we introduce a generalization of the Kawasaki–Gunton projection operator, which allows us to use this technique to derive, generally speaking, nonlinear master equations in the case of arbitrary ansatzes consistent with some set of observables. Most of the results obtained are of a very general nature, but when discussing them, we put emphasis on the application of these results to the theory of open quantum systems. [ABSTRACT FROM AUTHOR]

We developed the projection method to derive an analog of the quantum master equation for propagators rather than density matrices themselves. As these propagators are superoperators, we call them superoperator master equations. Furthermore, as the projector maps superoperators to superoperators, we call it a hyperprojector. We gave general perturbative expansions for generators of the weak coupling superoperator master equation and the stroboscopic limit superoperator master equation. After that, we considered a particular example of a hyperprojector that is the infinite time average of unitary dynamics. We call it the averaging hyperprojector. We discussed the properties of this hyperprojector and its physical meaning. Then, we illustrated our general second order superoperator master equations arising in the weak coupling limit and the stroboscopic limit, taking the averaging hyperprojector as an example, which we call effective dynamics. We discussed some properties of these superoperator master equations, in particular, the entropy increase. [ABSTRACT FROM AUTHOR]

We discuss dynamics of periodically driven open quantum systems. The time evolution of the quantum state is described by the quantum master equation, and the form of the dissipator is chosen so that the instantaneous stationary state is given by the Gibbs distribution. We find that the correlation between the population part and the coherence part of the density operator is induced by an adiabatic gauge potential. Although the introduction of the counterdiabatic term eliminates the correlation, additional correlations prevent convergence to the Gibbs distribution. We study the performance of the control by the counterdiabatic term. The system has three different scales and the performance strongly depends on the relations between their magnitudes. This article is part of the theme issue 'Shortcuts to adiabaticity: theoretical, experimental and interdisciplinary perspectives'. [ABSTRACT FROM AUTHOR]

This paper systematically studied heat transfer through two transversely coupled qubits in contact with two types of heat reservoirs. One is the independent heat reservoir which essentially interacts with only a single qubit, the other is the common heat reservoir which is allowed to simultaneously interact with two qubits. Compared to independent heat reservoirs, common reservoirs always suppress heat current in most cases. However, the common environment could enhance heat current, if the dissipation rate corresponding to the higher eigenfrequency is significantly higher than that corresponding to the lower eigenfrequency. In particular, in the case of resonant coupling of two qubits and the proper dissipations, the steady state can be decomposed into a stationary dark state which does not evolve and contributes zero heat current, and a residual steady state which corresponds to the maximal heat current. This dark state enables us to control steady-state heat current with an external control field and design a thermal modulator. In addition, we find that inverse heat currents could be present in the dissipative subchannels between the system and reservoirs, which interprets the suppression roles of common heat reservoirs. We also calculate the concurrence of assistance (COA) of the system and find that heat current and COA have the same trend with temperature, which further indicates that entanglement can be regarded as a resource to regulate heat transport. [ABSTRACT FROM AUTHOR]

We study the time degradation of quantum information stored in a quantum memory device under a dissipative environment in a parameter range which is experimentally relevant. The quantum memory under consideration is comprised of an optomechanical system with additional Kerr nonlinearity in the optical mode and an anharmonic mechanical oscillator with quadratic nonlinearity. Time degradation is monitored, both in terms of loss of coherence, which is analyzed with the help of Wigner functions, as well as in terms of loss of amplitude of the original state, studied as a function of time. While our time trajectories explore the degree to which the stored information degrades depending upon the variation in values of various parameters involved, we suggest a set of parameters for which the original information can be retrieved without degradation. We identify a very interesting situation where the role played by the nonlinearity is insignificant, and the system behaves as if the information is stored in a linear medium. For this case, the information retrieval is independent of the coherence revival time and can be retrieved at any instant during the time evolution. [ABSTRACT FROM AUTHOR]

Nonequilibrium thermal transport in circuit quantum electrodynamics emerges as one interdisciplinary field, due to the tremendous advance of quantum technology. Here, we study steady-state heat flow in a two-mode qubit-resonator model under the influence of both the qubit-resonator and resonator-resonator interactions. The heat current is suppressed and enhanced by tuning up resonator-resonator interaction strength with given weak and strong qubit-resonator couplings respectively, which is cooperative contributed by the eigen-mode of coupled resonators and qubit-photon scattering. Negative differential thermal conductance and significant thermal rectification are exhibited at weak qubit-resonator coupling, which are dominated by cycle transition processes. Moreover, the heat flow through the resonator decoupled from the qubit can be dramatically enhanced via the resonator-resonator interaction, which is attributed by the generation of eigen-mode channels of resonators.

Motivated by recent proposals of a Majorana box qubit (MBQ) and the read-out of its quantum state, we reconsider the MBQ-quantum dot system and investigate the influence of noise on the transport properties and the measurement process. Specifically, in the frame of a quantum master equation approach, we show that the energy level fluctuations of higher energy state in the MBQ lead to dephasing and reduce the effective tunneling amplitude between the MBQ and the dots, thus influencing the transport properties and characteristic dynamics. Remarkably in a certain range of parameters, the visibility of the interference current is even enhanced by the fluctuations. The results of our analysis are expected to be useful for future work on Majorana qubits. [ABSTRACT FROM AUTHOR]

We study the time degradation of quantum information stored in a quantum memory device under a dissipative environment in a parameter range which is experimentally relevant. The quantum memory under consideration is comprised of an optomechanical system with additional Kerr nonlinearity in the optical mode and an anharmonic mechanical oscillator with quadratic nonlinearity. Time degradation is monitored, both in terms of loss of coherence, which is analyzed with the help of Wigner functions, as well as in terms of loss of amplitude of the original state, studied as a function of time. While our time trajectories explore the degree to which the stored information degrades depending upon the variation in values of various parameters involved, we suggest a set of parameters for which the original information can be retrieved without degradation. We identify a very interesting situation where the role played by the nonlinearity is insignificant, and the system behaves as if the information is stored in a linear medium. For this case, the information retrieval is independent of the coherence revival time and can be retrieved at any instant during the time evolution.

Using the quantum master equation method, we investigate size and monomer configuration dependences of singlet fission (SF) in pentacene J‐ and H‐type ring‐shaped aggregate (N‐mer) models. Interestingly, it is found that SF rates in the J‐aggregate models monotonically decrease with increasing N, while those in the H‐aggregate models show different variation behaviors depending on the parity of N, where the H‐type pentamer model exhibits the maximum SF rate. It is also found that correlated triplet‐pair yields in the J‐aggregate models rapidly increase from ∼0.45 toward 1, while those in the H‐aggregate gradually decrease from ∼0.96 toward 0. These features are explained by relative relaxation factor analysis between adiabatic states and by the point group symmetry of the ring‐shaped aggregate models. The present results contribute to a deeper understanding of the correlation between the aggregate size, monomer configuration and SF dynamics, and thus to constructing new design guidelines for highly efficient SF ring‐shaped aggregates. [ABSTRACT FROM AUTHOR]

Collisions of the metastable antiprotonic helium atoms with the atoms of the medium cause, among other processes, transitions between hyperfine structure (HFS) states, as well as shifts and broadening of microwave M1 spectral lines. To obtain the interaction potential matrix ( , the potential energy surface (PES) is calculated by the unrestricted Hartree–Fock method with consideration of the electron correlations within the second-order of perturbation theory (MP2). With this potential, the system of equations of close coupling of the HFS channels is numerically solved; the cross sections and transition rates, shifts, and broadenings of M1 spectral lines are calculated; they are then used to solve the kinetic equation that determines the time evolution of the HFS state density matrix. The results of these calculations are compared with the experimental data and with the results of model calculations. [ABSTRACT FROM AUTHOR]

We investigate the speed limit of the state transformation in open quantum systems described by the Lindblad type quantum master equation. We obtain universal bounds of the total entropy production described by the trace distance between the initial and final states in the interaction picture. Our bounds can be tighter than the bound of Vu and Hasegawa (2021 Phys. Rev. Lett. 126 010601) which measures the distance by the eigenvalues of the initial and final states: this distance is less than or equal to the trace distance. For this reason, our results can significantly improve Vu–Hasegawa’s bound. The trace distance in the Schrödinger picture is bounded by a sum of the trace distance in the interaction picture and the trace distance for unitary dynamics described by only the Hamiltonian in the quantum master equation.

We present the quantum-likemodel of information processing by the brain's neural networks. The model does not refer to genuine quantum processes in the brain. In this model, uncertainty generated by the action potential of a neuron is represented as quantum-like superposition of the basic mental states corresponding to a neural code. Neuron's state space is described as complex Hilbert space (quantum information representation). The brain's psychological functions perform self-measurements by extracting concrete answers to questions (solutions of problems) from quantum information states. This extraction is modeled in the framework of open quantum systems theory. In this way, it is possible to proceed without appealing to the state's collapse. Dynamics of the state of psychological function F is described by the quantum master equation. Its stationary states represent classical statistical mixtures of possible outputs of F (decisions). This model can be used for justification of quantum-like modeling cognition and decision-making. The latter is supported by plenty of statistical data collected in cognitive psychology. [ABSTRACT FROM AUTHOR]

We study the average fidelity of the standard quantum teleportation when the quantum channel is subjected to different local independent noise environments frequently encountered in real quantum communication protocol. We show that only Bell 1 = 1 2 00 + 11 is the best quantum channel in different independent noise environments, even in the depolaring noise environment. Our work can shed some light on the application of practical standard quantum teleportation protocol. [ABSTRACT FROM AUTHOR]

Quantum measurements disturb the quantum system being measured, and this is known as measurement-induced backaction. In this paper, we consider a double quantum dot monitored by a nearby quantum point contact, where the measurement-induced backaction plays an important role. Taking advantage of the quantum master equation approach, we calculate the tunneling current and propose a simple feedback-control law to realize and stabilize the tunneling current. Theoretical analysis and numerical simulations show that the feedback control law can make the current quickly convergent to the desired value. [ABSTRACT FROM AUTHOR]

Several experimental and theoretical studies report instances of concerted or correlated multiple proton tunnelling in solid phases of water. Here, we construct a pseudo-spin model for the quantum motion of protons in a hexameric H2O ring and extend it to open system dynamics that takes environmental effects into account in the form of O-H stretch vibrations. We approach the problem of correlations in tunnelling using quantum information theory in a departure from previous studies. Our formalism enables us to quantify the coherent proton mobility around the hexagonal ring by one of the principal measures of coherence, the l1 norm of coherence. The nature of the pairwise pseudo-spin correlations underlying the overall mobility is further investigated within this formalism. We show that the classical correlations of the individual quantum tunnelling events in long-time limit is sufficient to capture the behaviour of coherent proton mobility observed in low-temperature experiments.We conclude that longrange intra-ring interactions do not appear to be a necessary condition for correlated proton tunnelling in water ice. [ABSTRACT FROM AUTHOR]

This article is concerned with a system of particles interacting with the quantized electromagnetic field (photons) in the non relativistic Quantum Electrodynamics (QED) framework and governed by the Pauli–Fierz Hamiltonian. We are interested not only in deriving approximations of several quantities when the coupling constant is small but also in obtaining different controls of the error terms. First, we investigate the time dynamics approximation in two situations, the Markovian (Theorem 1.4 completed by Theorem 1.14) and non Markovian (Theorem 1.6) cases. These two contexts differ in particular regarding the approximation leading terms, the error control and the initial states. Second, we examine two applications. The first application is the study of marginal transition probabilities related to those analyzed by Bethe and Salpeter in (Bethe and Salpeter, 1957), such as proving the exponential decay in the Markovian case assuming the Fermi Golden Rule (FGR) hypothesis (Theorem 1.15 or Theorem 1.13) and obtaining a FGR type approximation in the non Markovian case (Theorem 1.5). The second application, in the non Markovian case, includes the derivation of Rabi cycles from QED (Theorem 1.7). All the results are established under the following assumptions at some steps of the proofs: an ultraviolet and an infrared regularization are imposed, the quadratic terms of the Pauli–Fierz Hamiltonian are dropped, and the dipole approximation is assumed but only to obtain optimal error controls. • Derivation of Bethe and Salpeter transition probabilities from QED. • Derivation of Rabi cycles from QED. • Markovian and non Markovian quantum master equations with error controls. [ABSTRACT FROM AUTHOR]

In the most general case of the Delta exact operator valued generators constructed of an arbitrary Fermion operator, we present a closed solution for the transformed master action in terms of the original master action in the closed form of the corresponding path integral. We show in detail how that path integral reduces to the known result in the case of being the Delta exact generators constructed of an arbitrary Fermion function.

Understanding the transport mechanism of electronic excitations in conjugated polymers is key to advancing organic optoelectronic applications, such as solar cells, organic light-emitting diodes and flexible electronics. While crystalline polymers can be studied using solid-state techniques based on lattice periodicity, the characterisation of amorphous polymers is hindered by an intermediate regime of disorder and the associated lack of symmetries. To overcome these hurdles we have developed a reduced state quantum master equation approach based on the Merrifield exciton formalism. This new approach allows us to study the dynamics of excitons’ centre of mass and charge separation (CS), going beyond the standard model of charge-neutral Frenkel excitons. Using this model we study exciton transport in conjugated polymers and its dependence on morphology and temperature. Exciton dynamics consists of a thermalisation process, whose features depend on the relative strength of thermal energy, electronic couplings and disorder, resulting in remarkably different transport regimes. By applying this method to representative systems based on poly(p-phenylene vinylene) (PPV) we obtain insight into the role of temperature and disorder on localisation, CS, non-equilibrium dynamics, and experimental accessibility of thermal equilibrium states of excitons in amorphous polymers.

We reveal the critical effect of ultrashort dephasing on the polarization of high harmonic generation in Dirac fermions. As the elliptically polarized laser pulse falls in or slightly beyond the multiphoton regime, the elliptically polarized high harmonic generation is produced and exhibits a characteristic polarimetry of the polarization ellipse, which is found to depend on the decoherence time T 2 . T 2 could then be determined to be a few femtoseconds directly from the experimentally observed polarimetry of high harmonics. This shows a sharp contrast with the semimetal regime of higher pump intensity, where the polarimetry is irrelevant to T 2 . An access to the dephasing dynamics would extend the prospect of high harmonic generation into the metrology of a femtosecond dynamic process in the coherent quantum control.

We investigate that the average fidelity of the standard quantum teleportation communication protocol when the quantum channel is affected by different local collective noise environments frequently encountered in real quantum communication protocol. We show that the quantum teleportation efficiency can be enhanced when the noise is unavoidable by choose the fit Bell state as the quantum channel, especially we can get perfect quantum teleportation efficiency under the local collective Pauli σy noise environment. Our work can shed some light on the application of practical standard quantum teleportation communication protocol. [ABSTRACT FROM AUTHOR]

The singlet fission (SF) dynamics of pentacene linear aggregate models are investigated using the quantum master equation method by focusing on the Frenkel excitonic (FE) coupling effects on the SF rate and double triplet (TT) yield as well as on their aggregate size dependences. It is found that for the dimer model, unrealistically large FE couplings are needed to provide significant effects on the SF dynamics, while for the larger aggregate models a realistic FE coupling causes significant variations in the SF dynamics: as increasing the aggregate size, the SF rate rapidly increases, attains the maximum at 8‐mer (~3 times enhancement as compared to the non‐FE‐coupling case) and then decreases, approaching a stationary value after 12‐mer, although the stationary TT yield at 20‐mer remains slightly smaller than that in the non‐FE‐coupling case. These features are explained based on the relative relaxation factors between the adiabatic exciton states. The present results contribute to constructing the design guidelines for highly efficient SF aggregates. © 2018 Wiley Periodicals, Inc. The singlet fission (SF) dynamics of pentacene linear aggregates are investigated using the quantum master equation method by focusing on the Frenkel excitonic (FE) coupling effects on the SF rate and double triplet yield as well as on their aggregate size dependences. It is found that a realistic FE coupling causes significant size‐dependent variations in the SF rate, which are explained by the relative relaxation factor analysis. [ABSTRACT FROM AUTHOR]

The conductivity of excitations in short chains of optical cavities containing two-level atoms capable of exchanging photons is considered. The Jaynes-Cummings-Hubbard (JCH) model is used taking into account the dephasing noise effect. Two counterintuitive quantum effects are reproduced for this model: the increase in conductivity by the dephasing noise (DAT effect) and the quantum bottleneck effect, which is a paradoxical slump in conductivity with the enhancement of the excitation transfer to the runoff. Using numerical simulation, we reveal an interesting relationship between those two effects. In particular, we found that the dephasing assisted transport (DAT) effect occurs only at the nonoptimal values of the runoff and inflow, i.e., in conditions where the conductivity is limited by the quantum bottleneck effect. [ABSTRACT FROM AUTHOR]

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Singlet fission is a photophysical process in molecules and molecular aggregates, in which a singlet exciton generated by irradiation splits into two triplet excitons. Recently, singlet fission has attracted a great deal of attention from the viewpoint of applications in organic photovoltaic cells, where singlet fission has a possibility of improving the photoelectric conversion efficiency. Although singlet fission was first observed about 50 years ago in anthracene crystals, and the mechanism has been investigated in detail for a small number of molecular systems such as tetracene and pentacene crystals, the relationships between molecular or crystal structures and singlet fission efficiency are yet to be precisely clarified. Thus, molecular structure – singlet fission relationships and molecular or crystal design guidelines for efficient singlet fission are intensely desired for realizing efficient photovoltaic energy conversion, and experimental and theoretical investigations advance rapidly. We introduce three investigation steps, which are based on bottom-up theoretical modeling from a molecule to a molecular aggregate or crystal. The modelling involves energy level matching at the molecular level, electronic coupling at the aggregate level, and singlet fission dynamics including exciton–phonon (vibronic) coupling, by emphasizing the importance of interplay between each step. From the modelling, we present several design guidelines for efficient singlet fission, which is together with practical molecular structures, chemical modifications and molecular configurations. [ABSTRACT FROM AUTHOR]