Spatial quantum coherent modulation with perfect hybrid vector vortex beam based on atomic medium

The perfect hybrid vector vortex beam(PHVVB)with helical phase wavefront structure has aroused significant concern in recent years,as its beam waist does not expand with the topological charge(TC).In this work,we investigate the spatial quantum coherent modulation effect with PHVVB based on the atomic medium,and we observe the absorption characteristic of the PHVVB with different TCs under variant magnetic fields.We find that the transmission spectrum linewidth of PHVVB can be effectively maintained regardless of the TC.Still,the width of transmission peaks increases slightly as the beam size expands in hot atomic vapor.This distinctive quantum coherence phenomenon,demonstrated by the interaction of an atomic medium with a hybrid vector-structured beam,might be anticipated to open up new opportunities for quantum coherence modulation and accurate magnetic field measurement.

Quantum block coherence with respect to projective measurements

Quantum coherence serves as a defining characteristic of quantum mechanics,finding extensive applications in quantum computing and quantum communication processing.This study explores quantum block coherence in the context of projective measurements,focusing on the quantification of such coherence.Firstly,we define the correlation function between the two general projective measurements P and Q,and analyze the connection between sets of block incoherent states related to two compatible projective measurements P and Q.Secondly,we discuss the measure of quantum block coherence with respect to projective measurements.Based on a given measure of quantum block coherence,we characterize the existence of maximal block coherent states through projective measurements.This research integrates the compatibility of projective measurements with the framework of quantum block coherence,contributing to the advancement of block coherence measurement theory.

Quantum synchronization with correlated baths

We study quantum synchronization under the nonequilibrium reservoirs.We consider a two-qubit XXZ chain coupled independently to their own reservoirs modeled by the collisional model.Two reservoir particles,initially prepared in a thermal state or a state with coherence,are correlated through a unitary transformation and afterward interact locally with the two quantum subsystems.We study the quantum effect of reservoir on synchronous dynamics of system.By preparing different reservoir initial states or manipulating the reservoir particles coupling and the temperature gradient,we find that quantum entanglement of reservoir is the key to control quantum synchronization of system qubits.

The application of quantum coherence as a resource

Quantum coherence is a basic concept in quantum mechanics, representing one of the most fundamental characteristics that distinguishes quantum mechanics from classical physics. Quantum coherence is the basis for multi-particle interference and quantum entanglement. It is also the essential ingredient for various physical phenomena in quantum optics, quantum information, etc. In recent years, with the proposal of a quantum coherence measurement scheme based on a resource theory framework, quantum coherence as a quantum resource has been extensively investigated. This article reviews the resource theories of quantum coherence and introduces the important applications of quantum coherence in quantum computing,quantum information, and interdisciplinary fields, particularly in quantum thermodynamics and quantum biology. Quantum coherence and its applications are still being explored and developed. We hope this review can provide inspiration for relevant research.

External Cavity Tuning of Coherent Quantum Cascade Laser Array Emitting at^7.6μm

An external cavity quantum cascade laser （QCL） array with a wide tuning range and high output power is pre- sented. The coherent QCL array combined with a diffraction grating and gold mirror is tuned in the Littrow configuration. Taking advantage of the single-lobed fundamental supermode far-field pattern, the tuning capa- bility of 30.6cm-1 is achieved with a fixed injected current of 3.5 A at room temperature. Single-mode emission can be observed in the entire process. The maximum single-mode output power of the external cavity setup is as high as 25mW and is essential in real applications.

Enhancement of charging performance of quantum battery via quantum coherence of bath

An open quantum battery(QB)model of a single qubit system charging in a coherent auxiliary bath(CAB)consisting of a series of independent coherent ancillae is considered.According to the collision charging protocol we derive a quantum master equation and obtain the analytical solution of QB in a steady state.We find that the full charging capacity(or the maximal extractable work(MEW))of QB,in the weak QB-ancilla coupling limit,is positively correlated with the coherence magnitude of ancilla.Combining with the numerical simulations we compare with the charging properties of QB at finite coupling strength,such as the MEW,average charging power and the charging efficiency,when considering the bath to be a thermal auxiliary bath(TAB)and a CAB,respectively.We find that when the QB with CAB,in the weak coupling regime,is in fully charging,both its capacity and charging efficiency can go beyond its classical counterpart,and they increase with the increase of coherence magnitude of ancilla.In addition,the MEW of QB in the regime of relative strong coupling and strong coherent magnitude shows the oscillatory behavior with the charging time increasing,and the first peak value can even be larger than the full charging MEW of QB.This also leads to a much larger average charging power than that of QB with TAB in a short-time charging process.These features suggest that with the help of quantum coherence of CAB it becomes feasible to switch the charging schemes between the long-time slow charging protocol with large capacity and high efficiency and the short-time rapid charging protocol with highly charging power only by adjusting the coupling strength of QB-ancilla.This work clearly demonstrates that the quantum coherence of bath can not only serve as the role of“fuel”of QB to be utilized to improve the QB's charging performance but also provide an alternative way to integrate the different charging protocols into a single QB.

Quantum dynamical resource theory under resource non-increasing framework

We define the resource non-increasing(RNI)framework to study the dynamical resource theory.With this definition,we propose several potential quantification candidates under various free operation sets.For explicit demonstrations,we quantify the quantum dynamical coherence in the scenarios with and without post-selective measurements.Correspondingly,we show that the maximally incoherent operations(MIO)and the incoherent operations(IO)in the static coherence resource theory are free in the sense of dynamical coherence.We also provide operational meanings for the measures by the quantum discrimination tasks.Moreover,for the dynamical total coherence,we also present convenient measures and give the analytic calculation for the amplitude damping channel.

Application of a Discrete Phase-Randomized Coherent State Source in Round-Robin Differential Phase-Shift Quantum Key Distribution

Recently, a novel kind of quantum key distribution called the round-robin differential phase-shift （RRDPS） protocol was proposed, which bounds the amount of leakage without monitoring signal disturbance. The protocol can be implemented by a weak coherent source. The security of this protocol with a simply characterized source has been proved. The application of a common phase shift can improve the secret key rate of the protocol. In practice, the randomized phase is discrete and the secret key rate is deviated from the continuous case. In this study, we analyze security of the RRDPS protocol with discrete-phase-randomized coherent state source and bound the secret key rate. We fix the length of each packet at 32 and 64, then simulate the secret key rates of the RRDPS protocol with discrete-phase randomization and continuous-phase randomization. Our simulation results show that the performance of the discrete-phase randomization case is close to the continuous counterpart with only a small number of discrete phases. The research is practically valuable for experimental implementation.

Quantum interference effects in a multidriven transition Fg=3←→Fe=2

We have theoretically and experimentally studied the quantum coherence effects of a degenerate transition Fg =3←→Fe=2 system interacting with a weak linearly polarized （with σ＋ components） probe light and a strong linearly polarized （with σ＋ components） coupling field. Due to the competition between the drive Rabi frequency and the Zeeman splitting, electromagnetically induced transparency （EIT） and electromagnetically induced absorption （EIA） are present at the different values of applied magnetic field in the case where the Zeeman splitting of excited state Δe is larger than the Zeeman splitting of ground state Δg （i.e.Δe 〉 Δg）.

Nonlocal advantage of quantum coherence in a dephasing channel with memory

We investigate nonlocal advantage of quantum coherence(NAQC)in a correlated dephasing channel modeled by themultimode bosonic reservoir.We obtain analytically the dephasing and memory factors of this channel for the reservoirhaving a Lorentzian spectral density,and analyze how they affect the NAQC defined by the l1 norm and relative entropy.It is shown that the memory effects of this channel on NAQC are state-dependent,and they suppress noticeably the rapiddecay of NAQC for the family of input Bell-like states with one excitation.For the given transmission time of each qubit,we also obtain the regions of the dephasing and memory factors during which there is NAQC in the output states.

Comparative investigation of freezing phenomena for quantum coherence and correlations

We show that the freezing phenomenon,exhibited by a specific class of two-qubit state under local nondissipative decoherent evolutions,is a common feature of the relative entropy measure of quantum coherence and correlation.All those measurement outcomes,preserve a constant value in the considered noisy channels,but the condition,property and mechanism of the freezing phenomenon for quantum coherence are different from those of the quantum correlation.

A Pursuit of Quantum Neuroscience’s Principles: Coherence Field Theory and the Physics of Mind

Some basic physics of burgeoning quantum neuroscience is described. Anatomy of the neuron suggests that nonsynaptic mechanisms of signal transmittance occur via electric current acceleration and companion electromagnetic field fluctuation. I have named this mechanism of solution chemistry the ebb effect. Phase-locking between neural structure and electric fields that are emergent from cellular EM field fluctuations, in addition to feedback loops within neural networks, are the probable driver of macroscopic oscillation and flow shapes in the brain. CEMI (conscious electromagnetic information) theory is a promising framework for explaining intentionality and the spectrum of arousal as EM field effects. Relatively low frequency electromagnetic radiation is emitted by the accelerating electric currents of neurons. It is hypothesized that this EM radiation superpositions with molecular structure as it spreads to comprise percepts, the hybrid wavelengths of which form subjective images while wavelength vibrations result in subjective feel. These superposition arrays are termed a coherence field, and in combination with the synchronizing influence of quantum entanglement and electromagnetic fluctuations may constitute much of awareness’ substance. If conclusively verified, coherence field theory should have significance ranging from the treatment of perceptual disorders such as anosognosia to advancing foundational constructs like atomic theory.

Multiformity of Optical Quantum Coherence Systems with Y and Inverted Y-type Schemes

Y and inverted Y-type four-level schemes for optical quantum coherence systems,which may be intuitivelyconsidered to be very simple,have not been studied intensively till now.In this paper,we present the multiformity ofthese two types of schemes by considering that they can be classified into nine possible level styles as the second-ordersub-schemes using laser fields.Further we point out the complexity of their more than one hundred realistic configurationsas the third-order four-level sub-schemes that may appear in the optical quantum coherence experiments.Throughoutthis paper we review which configurations have been studied in some research aspects and which ones not,accordingto our knowledge,in order to be propitious to next steps of theoretical and experimental investigations,especially forapplications in the fields of quantum optics,quantum information science,laser spectroscopy,and so on.

Quantum coherence in A-three-level system driven by bichromatic coupling field

We present a theoretical study of quantum coherent effects in a A-three-level system with a strong bichromatic coupling field and a weak probe field. When one component of the strong bichromatic coupling field is resonant with a corresponding transition and the other is detuning with an integer fraction of the Rabi frequency of the resonant field, the absorption spectrum exhibits a series of symmetrical doublets. While two frequencies of the strong bichromatic coupling field are symmetrically detuned from the transition, the position and the relative intensity of the absorption peak are both affected by the coupling field intensity and detuning. An explanation of the spectrum is given in term of the dressed-state formalism.

Optical bistability induced by quantum coherence in a negative index atomic medium

Bistability behaviors in an optical ring cavity filled with a dense V-type four-level atomic medium are theoretically investigated. It is found that the optical bistability can appear in the negative refraction frequency band, while both the bistability and multi-stability can occur in the positive refraction frequency bands. Therefore, optical bistability can be realized from conventional material to negative index material due to quantum coherence in our scheme.

Quantum coherence and non-Markovianity of an atom in a dissipative cavity under weak measurement

Quantum coherence and non-Markovianity of an atom in a dissipative cavity under weak measurement are investigated in this work. We find that： the quantum coherence obviously depends on the initial atomic state, the strength of the weak measurement and its reversal, the atom-cavity coupling constant and the non-Markovian effect. It is obvious that the weak measurement effect protects the coherence better. The quantum coherence is preserved more efficiently for larger atom- cavity coupling. The stronger the non-Markovian effect is, the more slowly the coherence reduces. The quantum coherence can be effectively protected by means of controlling these physical parameters.

Macroscopic Quantum Coherence in Antiferromagnetic Molecular Magnets

The macroscopic quantum coherence in a biaxial antiferromagnetic molecular magnet in the presence of magnetic field acting parallel to its hard anisotropy axis is studied within the two-sublattice model. On the basis of instanton technique in the spin-coherent-state path-integral representation, both the rigorous Wentzel-Kramers-Brillouin exponent and pre-exponential factor for the ground-state tunnel splitting are obtained. We find that the quantum fluctuations around the classical paths can not only induce a new quantum phase previously reported by Chiolero and Loss (Phys. Rev. Lett. 80 (1998) 169), but also have great influence on the intensity of the ground-state tunnel splitting. Those features clearly have no analogue in the ferromagnetic molecular magnets. We suggest that they may be the universal behaviors in all antiferromagnetic molecular magnets. The analytical results are complemented by exact diagonalization calculation.

Theoretical study on the exciton dynamics of coherent excitation energy transfer in the phycoerythrin 545 light-harvesting complex

The experimental observation of long-lived quantum coherence in the excitation energy transfer(EET)process of the several photosynthetic light-harvesting complexes at low and room temperatures has aroused hot debate.It challenges the common perception in the field of complicated pigment molecular systems and evokes considerable theoretical efforts to seek reasonable explanations.In this work,we investigate the coherent exciton dynamics of the phycoerythrin 545(PE545)complex.We use the dissipation equation of motion to theoretically investigate the effect of the local pigment vibrations on the population transfer process.The result indicates that the realistic local pigment vibrations do assist the energy transmission.We demonstrate the coherence between different pigment molecules in the PE545 system is an essential ingredient in the EET process among various sites.The coherence makes the excitation energy delocalized,which leads to the redistribution of the excitation among all the chromophores in the steady state.Furthermore,we investigate the effects of the complex high-frequency spectral density function on the exciton dynamics and find that the high-frequency Brownian oscillator model contributes most to the exciton dynamic process.The discussions on the local pigment vibrations of the Brownian oscillator model suggest that the local heterogeneous protein environments and the effects of active vibration modes play a significant role in coherent energy transport.

Nonlocal advantage of quantum coherence and entanglement of two spins under intrinsic decoherence

We investigate the nonlocal advantage of quantum coherence(NAQC)and entanglement for two spins coupled via the Heisenberg interaction and under the intrinsic decoherence.Solutions of this decoherence model for the initial spin-1/2 and spin-1 maximally entangled states are obtained,based on which we calculate the NAQC and entanglement.In the weak region of magnetic field,the NAQC behaves as a damped oscillation with the time evolves,while the entanglement decays exponentially(behaves as a damped oscillation)for the spin-1/2(spin-1)case.Moreover,the decay of both the NAQC and entanglement can be suppressed significantly by tuning the magnetic field and anisotropy of the spin interaction to some decoherence-rate-determined optimal values.

The heat and work of quantum thermodynamic processes with quantum coherence

Energy is often partitioned into heat and work by two independent paths corresponding to the change in the eigenenergies or the probability distributions of a quantum system. The discrepancies of the heat and work for various quantum thermodynamic processes have not been well characterized in literature. Here we show how the work in quantum machines is differentially related to the isochoric, isothermal, and adiabatic processes. We prove that the energy exchanges during the quantum isochoric and isothermal processes are simply depending on the change in the eigenenergies or the probability distributions. However, for a time-dependent system in a non-adiabatic quantum evolution, the transitions between the different quantum states representing the quantum coherence can affect the essential thermodynamic properties, and thus the general definitions of the heat and work should be clarified with respect to the microscopic generic time-dependent system. By integrating the coherence effects in the exactly-solvable dynamics of quantum-spin precession, the internal energy is rigorously transferred as the work in the thermodynamic adiabatic process. The present study demonstrates that the quantum adiabatic process is sufficient but not necessary for the thermodynamic adiabatic process.