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Quantum coherence and entanglement are two basic aspects of nonclassicality. With the specific bipartite quantum systems which entanglement and coherence can be calculated, we provide a quantitative connection between the coherence and the dynamical entanglement that be created with the help of incoherent operations. We show that the coherence upper bounds the dynamical entanglement, and in particular conditions of the initial quantum states, the coherence of a single-party is equal to the dynamical entanglement. We extend these results to multipartite quantum systems. [ABSTRACT FROM AUTHOR]

We discuss the accuracy of phase estimation for single-qubit and multi-qubit systems under energy conservation constraints. For the case where both the target and the auxiliary system are qubits, we analytically maximize the FI over all possible energy-conserving joint measurements and auxiliary states, and derive the form of optimal measurement and state. Then, we generalize the results to the case where the auxiliary system is d-dimensional and discover that the achievable FI can approximate quantum Fisher information for large d. Finally, we discuss the difference between global and local measurements when considering multi-qubit target systems. Our results can contribute to the study of restrictions of conservation laws on quantum measurements. [ABSTRACT FROM AUTHOR]

Currently, many problems such as variable signal resources, complex execution environments, and low efficiency of scheduling algorithms are faced by heterogeneous signal processing platforms. The task scheduling algorithm is one of the key factors that directly affect the performance of the processing platform. In order to solve the problems of low efficiency of task scheduling algorithms and high computational cost of processors, a heterogeneous platform scheduling algorithm based on the quantum genetic algorithm is proposed in this paper. The algorithm constructs a task scheduling model by using a directed acyclic graph. This paper quantifies the mapping relationship between the quantum genetic algorithm and task scheduling. It corresponds qubits to binary, chromosomes to processor numbers, and individuals to processor scheduling strategies. In this paper, a new way of coding chromosomes using quantum coherence properties is designed to reduce the population size and increase population diversity. Crossover operations are performed on all individuals using full-interference crossover to avoid the results falling into local optimal solutions. The population of slow convergence is solved by implementing mutation operations on populations through quantum rotation gates. In addition, a task pre-ordering stage is designed based on the table scheduling algorithm. The task scheduling priority developed at this stage is used as the reference value for the initial encoding of the population, so that the search space for solutions is reduced. Finally, experiments are conducted using randomly generated task graphs. The algorithm is compared with improved genetic algorithms and existing intelligent scheduling algorithms. The results show that the algorithm can still obtain better results when the number of populations and iterations is small. It is more appropriate for heterogeneous platforms and computation-intensive tasks. [ABSTRACT FROM AUTHOR]

The novel weak-value-amplification (WVA) scheme of precision metrology is deeply rooted in the quantum nature of destructive interference between the pre- and post-selection states. And, an alternative version, termed as joint WVA (JWVA), which employs the difference-signal from the post-selection accepted and rejected results, has been found possible to achieve even better sensitivity (two orders of magnitude higher) under some technical limitations (e.g. misalignment errors). In this work, after erasing the quantum coherence, we analyze the difference-signal amplification (DSA) technique, which serves as a classical counterpart of the JWVA, and show that similar amplification effect can be achieved. We obtain a simple expression for the amplified signal, carry out characterization of precision, and point out the optimal working regime. We also discuss how to implement the post-selection of a classical mixed state. The proposed classical DSA technique holds similar technical advantages of the JWVA and may find interesting applications in practice. [ABSTRACT FROM AUTHOR]

This study examines the impact of random telegraph noise on non-separability, non-classicality, and steered coherence in a bipartite system initially prepared in a Gisin state and embedded in both Markovian and non-Markovian environments. To quantify non-separability, we employ the Bures distance entanglement measure (ℬ); for non-classicality detection, we utilize the quantum interferometric power (ℐ ); and to measure steered coherence, we employ the normalized steered coherence ( s ). We analyze the dynamics of these three metrics under the effects of the random telegraph noise through various theoretical and numerical techniques. Our findings demonstrate that the amount of quantum correlations in the system is closely tied to the parameters defining the random telegraph noise and the initial system state. Our results also reveal that all three measures exhibit oscillatory behavior in the non-Markovian regime and monotonic changes with time in the Markovian regime. These results provide a deeper understanding of the robustness and stability of non-separability and coherence under noisy conditions and may have implications for the design of noise-resistant quantum systems. [ABSTRACT FROM AUTHOR]

We address the effective generation of thermal non-classical correlations in two two-level atoms when exposed to a Fock-state cavity incorporated with classical decoherence effects. Using Bell non-locality, quantum coherence, and concurrence, we investigate the generation maps of non-locality, coherence, and entanglement. We show that the two atoms are initially separable, however, they become coherent and entangled within a short period of time when exploited with the Fock-state cavity. Interestingly, the Fock-state cavity shows dominant traits for the complete suppression of the classical decoherence effects. However, the decoherence effects appear initially and delay the generation of non-classical correlations. In addition, the generation delay of non-classical correlations is observed to be highly affected when the atom-cavity configuration is considered in a strong coupling regime. Compared to the entanglement and non-locality, the Fock-state cavity develops quantum coherence faster in the two-level systems. Finally, we also discuss the optimal feature settings of the Fock-state cavity, related significance, and experimental prospects of the study. [ABSTRACT FROM AUTHOR]

Quantum coherence and quantum entanglement are two different manifestations of the superposition principle. In this paper, we show that the right choice of basis to be used to estimate coherence is the separable basis. The quantum coherence estimated using the Bell basis does not represent the coherence in the system, since there is a coherence in the system due to the choice of the basis states. We first compute the entanglement and quantum coherence in the two-qubit mixed states prepared using the Bell states and one of the states from the computational basis. The quantum coherence is estimated using the ℓ 1 -norm of coherence, the entanglement is measured using the concurrence and the mixedness is measured using the linear entropy. Then we estimate these quantities in the Bell basis and establish that coherence should be measured only in separable basis, whereas entanglement and mixedness can be measured in any basis. We then calculate the teleportation fidelity of these mixed states and find the regions where the states have a fidelity greater than the classical teleportation fidelity. We also examine the violation of the Bell-CHSH inequality to verify the quantum nonlocal correlations in the system. The estimation of the above-mentioned quantum correlations, teleportation fidelity and the verification of Bell-CHSH inequality is also done for bipartite states obtained from the tripartite systems by the tracing out of one of their qubits. We find that for some of these states' teleportation is possible even when the Bell-CHSH inequality is not violated, signifying that nonlocality is not a necessary condition for quantum teleportation. [ABSTRACT FROM AUTHOR]

Some aspects of quantum damped harmonic oscillator (DHO) obeying a Markovian master equation are considered in the absence of thermal noise. The continuity equation is derived and Bohmian trajectories are constructed. As a solution of the master equation, we take a single coherent state and compute analytically the relative entropy of coherence, C r , in the energy, position and momentum bases. Although C r is constant in both the position and the momentum bases, it is a decreasing function of time in the energy basis becoming zero at long times, revealing its role as the preferred basis. Then, quantum coherence is computed for a superposition of two coherent states, a cat state, and also a superposition of two cat states in the energy basis as a function of separation, in the complex plane, between the two superposed states. It is seen that the quantum coherence increases with this separation. Furthermore, quantum coherence of superposition is compared to that of decomposed states in the superposition. Finally, by considering a system of two noninteracting DHOs, the effect of quantum statistics is studied on the coherence of reduced single-particle states, the joint detection probability and the mean square separation of particles. Our computations show that the single-particle coherence for antisymmetric states is always less than that of symmetric ones. Furthermore, boson anti-bunching and fermion bunching is seen in this open system. This behavior of bosons is the matter-wave analogue of photon anti-bunching seen in a modified Hanbury Brown–Twiss (HBT) interferometer. [ABSTRACT FROM AUTHOR]

Studying quantum properties in solid‐state systems is a significant avenue for research. In this scenario, double quantum dots appear as a versatile platform for technological breakthroughs in quantum computation and nanotechnology. This work inspects the thermal entanglement and quantum coherence in two‐coupled DODs, where the system is exposed to an external stimulus that induces an electronic transition within each subsystem. The results show that the introduction of external stimulus induces a quantum level crossing that relies upon the Coulomb potential changing the degree of quantum entanglement and coherence of the system. Thus, the quantum properties of the system can be tuned by changing the transition frequency, leading to the enhancement of its quantum properties. [ABSTRACT FROM AUTHOR]

We examine the temporal comportment of formation entanglement and quantum coherence in a quantum system made up of two superconducting charge qubits (SC-Qs), in the case of two different classes of nonlinear field. The results discussed the impact role of time-dependent coupling (T-DC) and dipole-dipole interaction (D-DI) on the temporal comportment of quantum coherence and entanglement in the ordinary and nonlinear field. In addition, we show that the main parameters of the quantum model affect the entanglement of formation and the coherence of the system in a similar way. [ABSTRACT FROM AUTHOR]

Quantum state generally belongs to complex Hilbert space. Based on quantum resource theory, imaginarity of a quantum state can be quantified by robustness of imaginarity. This paper explores the relationship between the robustness of imaginarity and quantum coherence. For a single qubit, its robustness of imaginarity is complementary to the quantum coherence. Moreover, the quantum coherence of a state in a d-dimensional Hilbert space (d being larger than two) is lower bounded by its robustness of imaginarity. [ABSTRACT FROM AUTHOR]

The quantum Hall effect (QHE) is a topologically protected phenomenon which has been observed in various systems. In experiments, the size of Hall bar device to realize the QHE is generally much larger than the phase coherence length, in which the quantum coherence of electrons is destroyed. Here, we theoretically study the influence of dephasing effect on the quantized Hall (QH) plateaus. We find that the QH plateaus disappear in perfectly quantum coherent systems if the coupling between leads and central region is imperfect. The Hall resistance is very large and strongly oscillates instead of presenting the QH plateaus in this case. However, by introducing the dephasing, Hall resistance decreases and the QH plateaus appear gradually. Similar results can also be observed for the quantum anomalous Hall effect. Our results propose that dephasing effect promotes the appearance of QH plateaus, which opens a new topic of the dephasing effect on topological systems. [ABSTRACT FROM AUTHOR]

We theoretically studied the quantum dynamics of a cavity–Bose–Einstein condensate (BEC) system in a gravitational field, which is composed of a Fabry–Pérot cavity and a BEC. We also show how to deterministically generate the transient macroscopic quantum superposition states (MQSSs) of the cavity by the use of optomechanical coupling between the cavity field and the BEC. The quantum dynamics of the cavity–BEC system specifically include phase space trajectory dynamics, system excitation number dynamics, quantum entanglement dynamics, and quantum coherence dynamics. We found that the system performs increasingly complex trajectories for larger values of the Newtonian gravity parameter. Moreover, the number of phonon excitations of the system can be increased by coupling the cavity–BEC system to Newtonian gravity, which is analogous to an external direct current drive. The scattering of atoms inside the BEC affects the periodicity of the quantum dynamics of the system. We demonstrate a curious complementarity relation between the quantum entanglement and quantum coherence of cavity–BEC systems and found that the complementarity property can be sustained to some extent, despite being in the presence of the cavity decay. This phenomenon also goes some way to show that quantum entanglement and quantum coherence can be referred to together as quantum resources.

Quantum coherence, the ability of a system to be in a quantum superposition of pure states, is a distinct feature of quantum mechanics that has no direct analog in classical mechanics. Quantum states that possess coherence efficiently outperform their classical counterparts in fundamental science and practical applications, including quantum metrology, computation, and simulation. Generation of coherence without the need to employ strong classical drives remains a challenging and not yet experimentally explored task. Beyond individual thermally-induced coherences already proposed for different experiments, correlated quantum coherences of multiple qubits represent a new target. We prove that correlated qubit coherence emerges thermally stimulated from incoherent states in hybrid superconducting and solid-state systems comprising non-interacting qubits coupled only via Dicke-type interaction to a shared thermal mechanical oscillator, exhibits coherences beyond the Tavis–Cummings coupling and, moreover, can be advantageous in quantum sensing.

Coherence is intrinsically related to projective measurement. When the fixed projective measurement involves higher-rank projectors, the coherence resource is referred to as block coherence, which comes from the superposition of orthogonal subspaces. Here, we establish a set of quantitative relations for the interconversion between block coherence and multipartite entanglement under the framework of the block-incoherent operations. It is found that the converted multipartite entanglement is upper bounded by the initial block coherence of single-party system. Moreover, the generated multipartite entanglement can be transferred to its subsystems and restored to block coherence of the initial single-party system by means of local block-incoherent operations and classical communication. In addition, when only the coarse-grained quantum operations are accessible for the ancillary subsystems, we further demonstrate that a lossless resource interconversion is still realizable, and give a concrete example in three four-level systems. Our results provide a versatile approach to utilize different quantum resources in a cyclic fashion.

In this paper, we use the concepts of quantum entanglement and coherence to analyze the Unruh and anti-Unruh effects based on the model of Unruh–DeWitt detector. For the first time, we find that (i) the Unruh effect reduces quantum entanglement but enhances quantum coherence; (ii) the anti-Unruh effect enhances quantum entanglement but reduces quantum coherence. This surprising result refutes the notion that the Unruh effect can only destroy quantum entanglement and coherence simultaneously, and that the anti-Unruh can only protect quantum resources. Consequently, it opens up a new source for discovering experimental evidence supporting the existence of the Unruh and anti-Unruh effects.

In this work, we investigate the impact of energetic coherence in nonthermal reservoirs on the performance of the Otto cycle. We first focus on the situation where the working substance is a qubit. Due to the existence of coherence of nonthermal reservoir, various anomalous operating regimes such as the engine and refrigerator with efficiencies exceeding Carnot limits, as well as the hybrid refrigerator that can simultaneously achieve cooling and supplying work to an external agent, can occur. We demonstrate that the energetic coherence of the system’s steady state plays a significant role in determining the cycle’s functions by adding an additional stroke implementing dephasing and phase modulation operations in the cycle. The energetic coherence of the system is necessary to trigger the reservoir’s coherence to exert influences on the cycle. We decompose the thermodynamic quantities to the components arising from the populations and coherence of the system, and find that the reservoir’s coherence impacts the cycle from two aspects: one is the modification of the system’s steady-state populations or temperatures, and the other is the direct contributions to the heat in the interaction between the system and reservoirs. We then explore the scenario where the working substance is two identical qubits, and the reservoirs are common to them. We show that the degenerate coherence of the system in the steady state can enhance the performances of the cycle as different machines. Additionally, the energetic coherence of the reservoir modifies the functions of the cycle still through the energetic coherence of the system rather than their degenerate coherence.

Quantum speed limits provide ultimate bounds on the time required to transform one quantum state into another. Here, we introduce a novel notion of quantum speed limits for collections of quantum states, investigating the time for converting a basis of states into an unbiased one as well as basis permutation. Establishing an unbiased basis, we provide tight bounds for the systems of dimension smaller than 5, and general bounds for multi-qubit systems and the Hilbert space dimension d . For two-qubit systems, we show that the fastest transformation implements two Hadamards and a swap of the qubits simultaneously. We further prove that for qutrit systems the evolution time depends on the particular type of the unbiased basis. Permuting a basis, we obtain the exact expression for the Hilbert space of dimension d . We also investigate speed limits for coherence generation, providing the minimal time to establish a certain amount of coherence with a unitary evolution.

Quantum collision models normally consist of a system interacting with a set of ancillary units representing the environment. While these ancillary systems are usually assumed to be either two level systems or harmonic oscillators, in this work we move further and represent each ancillary system as a structured system, i.e. a system made out of two or more subsystems. We show how this scenario modifies the kind of master equation that one can obtain for the evolution of the open systems. Moreover, we are able to consider a situation where the ancilla state is thermal yet has some coherence. This allows the generation of coherence in the steady state of the open system and, thanks to the simplicity of the collision model, this allows us to better understand the thermodynamic cost of creating coherence in a system. Specifically, we show that letting the system interact with the coherent degrees of freedom requires a work cost, leading to the natural fulfillment of the first and second law of thermodynamics without the necessity of ad hoc formulations.

The light-harvesting efficiency of a photoactive molecular complex is largely determined by the properties of its electronic quantum states. Those, in turn, are influenced by molecular vibrational states of the nuclear degrees of freedom. Here, we reexamine two recently formulated concepts that a coherent vibronic coupling between molecular states would either extend the electronic coherence lifetime or enhance the amplitude of the anticorrelated vibrational mode at longer times. For this, we study a vibronically coupled dimer and calculate the nonlinear two-dimensional (2D) electronic spectra that directly reveal electronic coherence. The time scale of electronic coherence is initially extracted by measuring the antidiagonal bandwidth of the central peak in the 2D spectrum at zero waiting time. Based on the residual analysis, we identify small-amplitude long-lived oscillations in the cross-peaks, which, however, are solely due to groundstate vibrational coherence, regardless of having resonant or off-resonant conditions. Our studies neither show an enhancement of the electronic quantum coherence nor an enhancement of the anticorrelated vibrational mode by the vibronic coupling under ambient conditions. [ABSTRACT FROM AUTHOR]

The theoretical study of open quantum systems strongly coupled to a vibrational environment remains computationally challenging due to the strongly non-Markovian characteristics of the dynamics. We study this problem in the case of a molecular dimer of the organic semiconductor tetracene, the exciton states of which are strongly coupled to a few hundreds of molecular vibrations. To do so, we employ a previously developed tensor network approach, based on the formalism of matrix product states. By analyzing the entanglement structure of the system wavefunction, we can expand it in a tree tensor network state, which allows us to perform a fully quantum mechanical time evolution of the exciton-vibrational system, including the effect of 156 molecular vibrations. We simulate the dynamics of hot states, i.e., states resulting from excess energy photoexcitation, by constructing various initial bath states, and show that the exciton system indeed has a memory of those initial configurations. In particular, the specific pathway of vibrational relaxation is shown to strongly affect the quantum coherence between exciton states in time scales relevant for the ultrafast dynamics of application-relevant processes such as charge transfer. The preferential excitation of low-frequency modes leads to a limited number of relaxation pathways, thus "protecting" quantum coherence and leading to a significant increase in the charge transfer yield in the dimer structure. [ABSTRACT FROM AUTHOR]

The delocalization of excitonic states and the interstate quantum coherence are of great importance in understanding fundamental mechanisms in exciton dynamics such as singlet fission. The accurate theoretical description on this key component requires dynamic simulations to be performed at the molecular level in a nonadiabatic framework. Here, we apply the recently developed nonadiabatic active state trajectory method to simulate fission dynamics in tetracene clusters of up to 10 monomers. It is shown that a global view of the topology of quantum coherence in terms of molecular details such as packing configurations, spatial delocalization of states, and the topology of coherent regime plays an important role in modulating fission dynamics, which suggests a new focus for nonadiabatic control of exciton dynamics and provides valuable dynamical information and physical insights for artificial design. [ABSTRACT FROM AUTHOR]

We investigate the effects of noise-induced coherence on average current and current fluctuations in a simple model of a quantum absorption refrigerator with degenerate energy levels. We describe and explain the differences and similarities between the system behavior when it operates in the classical regime, where the populations and coherences in the corresponding quantum optical master equation decouple in a suitably chosen basis, and in the quantum regime, where such a transformation does not exist. The differences between the quantum and the classical cases are observable only close to the maximum current regime, where the system steady-state becomes nonunique. This allows us to approximate the system dynamics by an analytical model based on a dichotomous process that explains the behavior of the average current both in the classical and in the quantum cases. Due to the nonuniqueness, the scaled cumulant generating function for the current at the vicinity of the critical point exhibits behavior reminiscent of the dynamical first-order phase transition. Unless the system parameters are fine-tuned to a single point in the parameter space, the corresponding current fluctuations are moderate in the quantum case and large in the classical case. [ABSTRACT FROM AUTHOR]

Many important open quantum systems, such as light harvesting systems irradiated with natural incoherent light, present challenging computational problems. Specifically, such systems are characterized by multiple time scales over many orders of magnitude. We describe and apply an efficient approach to determine rates and dynamics in such systems. As an example, we present a theoretical and computational analysis of retinal isomerization under incoherent solar excitation using a minimal retinal model. Solar- and bath-induced Fano coherences are shown to have a small but non-negligible effect on the reaction dynamics, and the effect of Fano coherences on the reaction rate is shown to depend strongly upon the form and strength of the system-bath coupling. Using the isomerization probability to obtain the time-dependent cellular hyperpolarization, we show that the effect of coherence on hyperpolarization dynamics is small compared to the effect of natural variations in the solar intensity. [ABSTRACT FROM AUTHOR]

The molecular dynamics following the electronic B Π u 3 0 + ⟵ X Σ g + 1 photoexcitation of the iodine molecule embedded in solid krypton are studied quantum mechanically using the Gaussian variant of the multiconfigurational time-dependent Hartree method (G-MCTDH). The accuracy of the Gaussian wave packet approximation is validated against numerically exact MCTDH simulations for a fully anharmonic seven-dimensional model of the I2Kr18 cluster in a crystal Kr cage. The linear absorption spectrum, time-evolving vibrational probability densities, and I2 energy expectation value are accurately reproduced by the numerically efficient G-MCTDH approach. The reduced density matrix of the chromophore is analyzed in the coordinate, Wigner and energy representations, so as to obtain a multifaceted dynamical view of the guest-host interactions. Vibrational coherences extending over the bond distance range 2.7 Å < RI–I < 4.0 Å are found to survive for several vibrational periods, despite extensive dissipation. The present results prepare the ground for the simulation of time-resolved coherent Raman spectroscopy of the I2-krypton system addressed in Paper II. [ABSTRACT FROM AUTHOR]

Quantum coherent control (QCC) has been successfully demonstrated experimentally and theoretically for two- and three-photon optical excitation of atoms and molecules. Here, we explore QCC using spectral phase functions with a single spectral phase step for controlling the yield of H3+ from methanol under strong laser field excitation. We observe a significant and systematic enhanced production of H3+ when a negative 3 4 π phase step is applied near the low energy region of the laser spectrum and when a positive 3 4 π phase step is applied near the high energy region of the laser spectrum. In some cases, most notably the HCO+ fragment, we found the enhancement exceeded the yield measured for transform limited pulses. The observation of enhanced yield is surprising and far from the QCC prediction of yield suppression. The observed QCC enhancement implies an underlying strong field process responsible for polyatomic fragmentation controllable by easy to reproduce shaped pulses. [ABSTRACT FROM AUTHOR]

We have applied the quantum coherence theory to the Jaynes–Cummings model for three types of quenched disorder distribution: uniform, Gaussian, and Cauchy-Lorentz. Under certain conditions, we have observed a beat-damping behavior on the dynamics of the l1-norm of coherence. This phenomenon is more evident for the uniform disorder distribution.

The tripartite quantum coherence for spin-12 and bipartite quantum coherence for spin-1 many-body systems are studied with the quantum renormalization group method to investigate the quantum criticality behaviour of both systems. We find both spin-12 and spin-1 systems exhibit quantum criticality behaviour after different number of iterations. However, the bipartite quantum coherence for spin-1 system reaches the quantum criticality behaviour in lesser number of iterations than the tripartite quantum coherence for spin-12 system. The quantum criticality behaviour of both systems is also investigated through non-analytic and the scaling behaviour of quantum coherence. Additionally, quantum correlations and quantum phase transition are observed to be more vigorous with higher spin comparatively to the number of parties (i.e., bipartite, tripartite, multipartite) involved in a quantum correlations.

Identification of the external electromagnetic fields and internal hyperfine parameters which optimize the quantum singlet-triplet yield of simplified radical pairs modeled by Schrödinger system with spin Hamiltonians given by the sum of Zeeman interaction and hyperfine coupling interaction terms are analyzed. A method that combines sensitivity analysis with Tikhonov regularization is implemented. Numerical results demonstrate that the quantum singlet-triplet yield of the radical pair system can be significantly reduced if optimization is pursued simultaneously for both external magnetic fields and internal hyperfine parameters. The results may contribute towards understanding the structure-function relationship of a putative magnetoreceptor to manipulate and enhance quantum coherences at room temperature and leveraging biofidelic function to inspire novel quantum devices. [ABSTRACT FROM AUTHOR]

Molecular entities with doublet or triplet ground states find increasing interest as potential molecular quantum bits (qubits). Complexes with higher multiplicity might even function as qudits and serve to encode further quantum bits. Vanadium(II) ions in octahedral ligand fields with quartet ground states and small zero‐field splittings qualify as qubits with optical read out thanks to potentially luminescent spin‐flip states. We identified two V2+ complexes [V(ddpd)2]2+ with the strong field ligand N,N'‐dimethyl‐N,N'‐dipyridine‐2‐yl‐pyridine‐2,6‐diamine (ddpd) in two isomeric forms (cis‐fac and mer) as suitable candidates. The energy gaps between the two lowest Kramers doublets amount to 0.2 and 0.5 cm−1 allowing pulsed EPR experiments at conventional Q‐band frequencies (35 GHz). Both isomers possess spin‐lattice relaxation times T1 of around 300 μs and a phase memory time TM of around 1 μs at 5 K. Furthermore, the mer isomer displays slow magnetic relaxation in an applied field of 400 mT. While the vanadium(III) complexes [V(ddpd)2]3+ are emissive in the near‐IR‐II region, the [V(ddpd)2]2+ complexes are non‐luminescent due to metal‐to‐ligand charge transfer admixture to the spin‐flip states. [ABSTRACT FROM AUTHOR]

We consider the effect of a thermal bath on quantum correlations induced by the gravitational interaction in the weak field limit between two massive cat states, called gravitational cat (gravcat) states. The main goal of this paper is to provide a good understanding of the effects of temperature and several parameters in the entanglement (measured by the concurrence) and quantum coherence (measured by the l 1 -norm that is defined from the minimal distance between the quantum state and the set of incoherent states) which are derived from the thermal quantum density operator. Our results show that the thermal concurrence and l 1 -norm can be significantly optimized by increasing the masses or decreasing the distance between them. We investigate and discuss the behavior of these quantities under temperature variations in different regimes, including some that are expected to be experimentally feasible in the future. In particular, we observe that thermal fluctuations raise non-entangled quantum correlations when entanglement suddenly drops. [ABSTRACT FROM AUTHOR]

In this work, the energies and eigenfunctions of ground state and first-excited states (GFES) of a strongly coupled polaron in a quantum pseudo-dot (QPD) were studied by using variational method of Pekar type (VMPT). A single qubit can be realized in this two-level quantum system. Then, we calculated the coherence time of a QPD qubit by employing the Fermi Golden Rule. The temperature effects on the coherence time are taken into account by using the quantum statistics theory (QST) and self-consistent calculation method. According to the obtained results, it is found that the coherence time increases with decreasing temperature. Also, this time is a decaying function of the chemical potential of the two-dimensional electron gas and the zero point of the PHP. [ABSTRACT FROM AUTHOR]

In this paper, we define the genuine multipartite coherence and genuine multipartite average coherence, discuss their properties and investigative the relationship between them and other quantum resources. Firstly, we prove that the genuine multipartite coherence can be represented by interaction information, and it can determine whether genuine multipartite discord exists. Secondly, comparing the global coherence and genuine multipartite coherence in noisy channels with different correlation strengths, the global coherence and genuine multipartite coherence are more stable with the increasing correlation strengths, and genuine multipartite coherence is more stable than global coherence. Finally, we find that the difference between genuine multipartite coherence and genuine multipartite average coherence can be expressed by quantum discord, and the genuine multipartite coherence is always greater than or equal to the genuine multipartite entanglement. For the tripartite pure states, we provide some trade-off relations between the total correlation, classical correlation, and quantum correlations. [ABSTRACT FROM AUTHOR]

Quantum coherence is a prime resource in quantum computing and quantum communication. Quantum coherence of an arbitrary qubit can be created at a remote location using maximally entangled state, local operation and classical communication. However, if there is a noisy channel acting on one side of the shared resource, then it is not possible to create perfect quantum coherence remotely. Here, we present a method for the creation of quantum coherence at a remote location via the use of entangled state and indefinite causal order. We show this specifically for the superposition of two completely depolarizing channels, two partially depolarizing channels and one completely depolarizing channel along with a unitary operator. We find that when the indefinite causal order of channels acts on one half of the entangled pair, then the shared state loses entanglement, but can retain nonzero quantum discord. This finding may have some interesting applications on its own where discord can be consumed as a resource. Our results suggest that the indefinite causal order along with a tiny amount of quantum discord can act as a resource in creating nonzero quantum coherence in the absence of entanglement. [ABSTRACT FROM AUTHOR]

A physical model in which a pair of two-level atoms interacting with a two-mode cavity field is investigated in the presence of Stark shift. The two atoms are initially prepared in a product state or a maximal mixture state, while the two modes of the field are in a pair coherent state. The physical properties of the atomic system are studied by using the Quantum-Memory-Assisted Entropic Uncertainty Relation (QMA-EUR), Relative Entropy of Quantum Coherence (REoC), Geometric Quantum Discord (GQD), and concurrence. The physical properties of photon statistics are investigated by using the bunching and anti-bunching tow-mode radiation field. We found that the atomic properties depend on the initial state and the strength of the Stark shift. The general behaviour of QMA-EUR is opposite the other three atomic measurements, such as the QMA-EUR increases then concurrence, GQD, and REoC decrease. The photon statistics are independent of the Stark shift, while it is stable at the maximum entangled state. [ABSTRACT FROM AUTHOR]

Nitrogen vacancy centers in diamond provide a spin-based qubit system with long coherence time even at room temperature, making them suitable ambient-condition quantum sensors for quantities including electromagnetic fields, temperature, and rotation. The optically addressable level structures of NV spins allow transduction of spin information onto light-field intensity. The sub-optimal readout fidelity of conventional fluorescence measurement remains a significant drawback for room-temperature ensemble sensing. Here, we discuss nanophotonic interfaces that provide opportunities to achieve near-unity readout fidelity based on IR absorption via resonantly enhanced spin-optic coupling. Spin-coupled resonant nanophotonic devices are projected to particularly benefit applications that utilize micro- to nanoscale sensing volume and to outperform present methods in their volume-normalized sensitivity. [ABSTRACT FROM AUTHOR]

Percolation, describing critical behaviors of phase transition in a geometrical context, prompts wide investigations in natural and social networks as a fundamental model. The introduction of quantum coherence and superposition brings percolation into quantum regime with more fascinating phenomena and unique features, which, however, has not been experimentally explored yet. Here we successfully map these large-scale porous structures into a photonic chip using femtosecond laser direct writing techniques and present an experimental demonstration of quantum transport in hexagonal percolation lattices, probed by coherent light. A quantum percolation threshold of 80% is observed in the prototyped laser-written lattices with up to 1,600 waveguides, which is significantly larger than the classical counterpart of 63%. We also investigate the spatial confinement by localization parameters and exhibit the transition from ballistic to diffusive propagation with the decrease of the occupation probability. Direct observation of quantum percolation may deepen the understanding of the relation among materials, quantum transport, geometric quenching, disorder and localization, and inspire applications for quantum technologies. [ABSTRACT FROM AUTHOR]

This article records for the first time the isolation of Ursolic acid from the leaves of Neolamarckia cadamba (Roxb.) Bosser (Family: Rubiaceae) using ultrasonic waves. This bioactive triterpenic acid was isolated without its isomer, oleanolic acid, in a very convenient way with good yield. The structure was identified by means of one dimensional Nuclear Magnetic Resonance (NMR) spectroscopic techniques like 1H NMR, 13C NMR, distortionless enhancement by polarization transfer (DEPT) and two dimensional NMR spectroscopic method for example, heteronuclear single quantum coherence (HSQC). It was also assayed for antidiabetic and antioxidant potencies. About 71.5 mg of pure ursolic acid was isolated from 2.6 grams of ethyl acetate soluble fraction using sono-maceration as an extraction technique. [ABSTRACT FROM AUTHOR]

Systems of spins engineered with tunable density and reduced dimensionality enable a number of advancements in quantum sensing and simulation. Defects in diamond, such as nitrogen-vacancy (NV) centers and substitutional nitrogen (P1 centers), are particularly promising solid-state platforms to explore. However, the ability to controllably create coherent, two-dimensional spin systems and characterize their properties, such as density, depth confinement, and coherence, is an outstanding materials challenge. We present a refined approach to engineer dense (≳1 ppm ⋅ nm), 2D nitrogen, and NV layers in diamond using delta-doping during plasma-enhanced chemical vapor deposition epitaxial growth. We employ both traditional materials techniques, e.g., secondary ion mass spectrometry, alongside NV spin decoherence-based measurements to characterize the density and dimensionality of the P1 and NV layers. We find P1 densities of 5–10 ppm ⋅ nm, NV densities between 1 and 3.5 ppm ⋅ nm tuned via electron irradiation dosage, and depth confinement of the spin layer down to 1.6 nm. We also observe high (up to 0.74) ratios of NV to P1 centers and reproducibly long NV coherence times, dominated by dipolar interactions with the engineered P1 and NV spin baths. [ABSTRACT FROM AUTHOR]

In the endeavor to make quantum computers a reality, integrated superconducting circuits have become a promising architecture. A major challenge of this approach is decoherence originating from spurious atomic tunneling defects at the interfaces of qubit electrodes, which may resonantly absorb energy from the qubit's oscillating electric field and reduce the qubit's energy relaxation time T1. Here, we show that qubit coherence can be improved by tuning dominating defects away from the qubit resonance using an applied DC-electric field. We demonstrate a method that optimizes the applied field bias and enhances the average qubit T1 time by 23%. We also discuss how local gate electrodes can be implemented in superconducting quantum processors to enable simultaneous in situ coherence optimization of individual qubits. [ABSTRACT FROM AUTHOR]

When an intense light field strongly interacts with the band structure of a solid, the formation of hybrid light-matter quantum states becomes possible. Examples of such Floquet-Bloch states have been reported, but engineering of the band structure using Floquet states can suffer from dissipation and decoherence. Sustaining the necessary quantum coherence of the light-matter interactions requires robust electronic states in combination with strong fields of suitable polarization and frequency. Here, we explore the quantum coherent coupling of nano-focused surface plasmon polaritons (SPP) to distinct electronic states in the band structure of a solid. We observe above-threshold electron emission from the Au(111) Shockley surface state by the absorption of up to seven SPP quanta. Using time-resolved photoelectron spectroscopy the coherence of the interaction of the SPPs with the surface state during electron emission is investigated and the process is shown to be similar to light-driven above threshold electron emission. Ultimately, our work could render SPP-based Floquet engineering in nano-optical systems feasible. Floquet theory describes transient states driven by a light-matter interaction and could potentially be used to engineer the band structure and the topology of solid-state systems. Here, the authors investigate coherent photoemission from a gold surface caused by a strong surface plasmon polariton excitation, which could be used to realize surface plasmon polariton driven Floquet effects in nanostructures. [ABSTRACT FROM AUTHOR]

A typical imaging scenario requires three basic ingredients: (1) a light source that emits light, which in turn interacts and scatters off the object of interest; (2) detection of the light being scattered from the object and (3) a detector with spatial resolution. These indispensable ingredients in typical imaging scenarios may limit their applicability in the imaging of biological or other sensitive specimens due to unavailable photon-starved detection capabilities and inevitable damage induced by interaction. Here, we propose and experimentally realize a quantum imaging protocol that alleviates all three requirements. By embedding a single-photon Michelson interferometer into a nonlinear interferometer based on induced coherence and harnessing single-pixel imaging technique, we demonstrate interaction-free, single-pixel quantum imaging of a structured object with undetected photons. Thereby, we push the capability of quantum imaging to the extreme point in which no interaction is required between object and photons and the detection requirement is greatly reduced. Our work paves the path for applications in characterizing delicate samples with single-pixel imaging at silicon-detectable wavelengths. [ABSTRACT FROM AUTHOR]

In this study, the "particle in a box" idea, which was broadly developed in semiconductor quantum dot research, was extended into mid-infrared (IR) cavity modes by applying lateral confinement in an optical cavity. The discrete cavity modes hybridized with molecular vibrational modes, resulting in a quartet of polariton states that can support multiple coherence states in the IR regime. We applied tailored pump pulse sequences to selectively prepare these coherences and verified the multi-coherence existence. The simulation based on Lindblad equation showed that because the quartet of polariton states resided in the same cavity, they were specifically robust toward decoherence caused by fluctuations in space. The multiple robust coherences paved the way for entangled states and coherent interactions between cavity polaritons, which would be critical for advancing polariton-based quantum information technology. [ABSTRACT FROM AUTHOR]

The question of with what we associate work and heat in a quantum thermodynamic process has been extensively discussed, mostly for systems with time-dependent Hamiltonians. In this paper, we aim to investigate the energy exchanged between two quantum systems through interaction where the Hamiltonian of the system is time-independent. An entropy-based re-definitions of heat and work are presented for these quantum thermodynamic systems therefore an entropy-based formalism of both the first and the second laws of thermodynamics are introduced. We will use the genuine reasoning based on which Clausius originally defined work and heat. The change in the energy which is accompanied by a change in the entropy is identified as heat, while any change in the energy which does not lead to a change in the entropy is known as work. It will be seen that quantum coherence does not allow all the energy exchanged between two quantum systems to be only of the heat form. Several examples will also be discussed. Finally, we will examine irreversibility from our entropy-based formalism of quantum thermodynamics. [ABSTRACT FROM AUTHOR]

The double-slit interferometer and the Mach–Zehnder interferometer (MZI) with balanced beam splitters are prototypical setups for investigating the quantum wave-particle duality. These setups induced a quantitative association of interferometric visibility (IVI) with the wave aspect of a single quantum system (WAQ). Recently, it was realized that quantum coherence (QC) can be better suited than IVI for quantifying the WAQ in complementarity relations. In this article, we investigate a MZI with biased beam splitters both in the input and in the output, and we show that in some cases the IVI is not adequate to quantify the WAQ since it does not reflect the behavior of the quantum coherence, even for a bi-dimensional closed quantum system. Using IBM quantum computers, we experimentally verify our theoretical findings by doing a full quantum simulation of the optical MZI with biased beam splitters. [ABSTRACT FROM AUTHOR]

We quantify the dynamical quantum resource in the resource non-increasing (RNI) framework, namely the free dynamical resource is defined by the channels that cannot increase the static "resourcefulness" of any input state. We present two kinds of approaches to quantifying the dynamical resource, the distance measures and the maximal increasing static resource. As a demonstration, we quantify the dynamical total coherence with our presented measures. It is shown that the distance-based measures have good operational interpretation through quantum processing tasks and can be numerically calculated by semidefinite programming (SDP) and the measures based on the maximal increasing static resource could lead to the analytical solution. As an application, we consider the dynamical total coherence of the qubit amplitude damping channel. Both the analytical measure based on the static l 2 norm and the numerical illustrations based on the SDP are given. [ABSTRACT FROM AUTHOR]

We study the current effectiveness of the dynamical decoupling technique on a publicly accessible IBM quantum computer (IBMQ). This technique, also known as bang-bang decoupling or dynamical symmetrization, consists of applying sequences of pulses for protecting a qubit from decoherence by symmetrizing the qubit–environment interactions. Works in the field have studied sequences with different symmetries and carried out tests on IBMQ devices typically considering single-qubit states. We show that the simplest universal sequences can be interesting for preserving two-qubit states on the IBMQ device. For this, we considered a collection of single-qubit and two-qubit states. The results indicate that a simple dynamical decoupling approach using available IBMQ pulses is not enough for protecting a general single-qubit state without further care. Nevertheless, the technique is beneficial for the Bell states. This encouraged us to study logical qubit encodings such as | 0 ⟩ L ≡ | 01 ⟩ , | 1 ⟩ L ≡ | 10 ⟩ , where a quantum state has the form | ψ a b ⟩ = a | 0 ⟩ L + b | 1 ⟩ L . Thus, we explored the effectiveness of dynamical decoupling with a large set of two-qubit | ψ a b ⟩ states, where a and b are real amplitudes. With this, we also determined that the | ψ a b ⟩ states most benefiting from this dynamical decoupling approach and slowed down the decay of their survival probability. [ABSTRACT FROM AUTHOR]

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