Optimum quantum state of light for gravitational-wave interferometry

The laser interferometric gravitational-wave detectors are sensitive to the quantum state of light employed in the dark port of interferometric system. In this paper a general quantum state for the dark input port is assumed. The quantum state of light is expanded versus the Fock states. The quantum noise of interferometric system is computed as a function of the quantum state of light. The variational method and the genetic algorithm are employed to determine the coefficients of the dark input port and the laser input power for the minimization of the quantum noise. Calculation shows that the optimum quantum state for the dark input port is very close to the vacuum squeezed state. For this optimum quantum state the quantum noise and optimum laser power reduces one order of magnitude relative to the conventional interferometer.     

Quantum Entanglement in Two-Photon Tavis–Cummings Model with a Kerr Nonlinearity

The properties of quantum entanglement in the two-photon Tavis–Cummings model with a Kerr nonlinearity are studied in terms of quantum information entropy theory. The reduced quantum entropy is employed to investigate the quantum entanglement between two two-level atoms and a single-mode coherent field. The relative quantum entropy is employed to investigate the quantum entanglement between the two two-level atoms. The influences of the nonlinear interaction of the Kerr medium with the field and the atomic dipole-dipole interaction on the properties of quantum entanglement of the system are also examined. Some important results are obtained.     

Quantum teleportation of optical quantum gates

We show that a universal set of gates for quantum computation with optics can be quantum teleported through the use of EPR entangled states, homodyne detection, and linear optics and squeezing operations conditioned on measurement outcomes. This scheme may be used for fault-tolerant quantum computation in any optical scheme (qubit or continuous-variable). The teleportation of nondeterministic nonlinear gates employed in linear optics quantum computation is discussed.     

由非绝热相关获得的形式量子数及其在高激发振动态的经典解释

我们利用非绝热相关方法 ,通过关闭所有的振动模式间的耦合项并追溯到零级本征态 ,以得到体系的形式量子数 ,将形式量子数对高激发振动态的能级谱图进行归属 ,并重构本征能级图谱 ,使本征能级以有序的方式排列。这有助于对高激发振动态的能级进行分类和归属。形式量子数是体现高激发振动态的重要特征 ,是高激发振动态的近似运动守恒量。我们将多维陪集相空间的经典方法应用于高激发态的研究 ,发现形式量子数对应的李雅普诺夫指数为零或最小 ,并且它对应于较大的相空间密度     

Fuzzy amplitude densities and stochastic quantum mechanics

Fuzzy amplitude densities are employed to obtain probability distributions for measurements that are not perfectly accurate. The resulting quantum probability theory is motivated by the path integral formalism for quantum mechanics. Measurements that are covariant relative to a symmetry group are considered. It is shown that the theory includes traditional as well as stochastic quantum mechanics.     

Fidelity of isotropic-coupled oscillators interacting with a single atom

A model of a single atom interacting with isotropic two modes pumped simultaneously within a perfect cavity is examined. The quantum fidelity is employed to measure the quality of transmitted information as a function of the input state. The behavior of the quantum fidelity is studied at off-resonances between the atom and fields for different preparations of initial states.     

The Quantum Vacuum: A Scientific and Philosophical Concept,from Electrodynamics to String Theory and the Geometry of the Microscopic World,by Luciano Boi

The standards of measurement employed in physics are arbitrary; it is shown that in consequence, the equations of motion in classical and quantum mechanics ere linear first order differential equations and that macroscopic phenomena obey the transformations of special relativity. The relations of these statements to microscopic evidence for special relativity and to conservation laws are considered. The physical reasons for the choice of a number of independent physical standards are discussed. The use of quantum phenomena to establish standards of measurements is described and related to the occurrence of fundamental quantum constants of physics.     

Multiparty secret sharing of quantum information using and identifying Bell states

In this paper, only Bell states are employed and needed to be identified to realize the multiparty secret sharing of quantum information, where the secret is an arbitrary unknown quantum state in a qubit. In our multiparty quantum information secret sharing (QISS) scheme, no subset of all the quantum information receivers is sufficient to reconstruct the unknown state in a qubit but the entire is. The present multiparty QISS scheme is more feasible with present-day technique.     

Cylindrical dust acoustic waves in quantum dusty plasmas

The quantum hydrodynamic model is employed to study the nonlinear structure of non-planar dust acoustic waves in quantum dusty plasmas consisting of electrons, ions, and negatively/positively charged dust particles. A Kadomstev-Petviashvili equation is derived in cylindrical geometry. Based on the analytical solution, it is found that the Nebulon structure is significantly modified by the quantum effects including quantum diffraction effect and quantum statistical effect.     

Foundations of the quantum statistics of systems in equilibrium: A measuretheoretic approach

The fundamental equations of equilibrium quantum statistical mechanics are derived in the context of a measure-theoretic approach to the quantum mechanical ergodic problem. The method employed is an extension, to quantum mechanical systems, of the techniques developed by R. M. Lewis for establishing the foundations of classical statistical mechanics. The existence of a complete set of commuting observables is assumed, but no reference is made a priori to probability or statistical ensembles. Expressions for infinite-time averages in the microcanonical, canonical, and grand canonical ensembles are developed which reduce to conventional quantum statistical mechanics for systems in equilibrium when the total energy is the only conserved quantity. No attempt is made to extend the formalism at this time to deal with the difficult problem of the approach to equilibrium.     

Experimental and theoretical studies of the effects of collisions and magnetic fields on quantum beat

The effects of collisions and magnetic fields on quantum beat are treated by the density matrix method. Some experimental quantum beat results of biacetyl in the presence of collisions are presented and theoretically analysed. It is shown that in this case not only pure dephasing but also pressure dependent inherent decay rate constants can be observed; this implies that the Schrödinger method cannot be employed for this case. The magnetic field effect on quantum beat is examined also and it is shown that for the biacetyl molecule magnetic splitting can be observed even in fields of a few gauss.     

Improved Quantum Image Median Filtering in the Spatial Domain

In some image processing algorithms, such as those for image feature extraction and segmentation, filtering is a significant pre-processing step to remove noises and improve image quality. An improved quantum image median filtering approach is proposed, and its corresponding quantum circuit is designed in this work. The main idea of the approach is that first the classical image is converted into a quantum version based on the novel enhanced quantum representation (NEQR) of digital images, and then a unique quantum module is designed to realize the median calculation of neighborhood pixels for each pixel point in the image. Finally, in order to improve the filtering effect, extremum detection is employed to distinguish noises from true signals. The experimental results show that a competitive filtering performance is obtained compared with previous methods. In addition, a network complexity analysis of the quantum circuit suggests that the proposed filtering approach can perform enormous speed-up over its corresponding classical counterparts.

     

Nonlocal character of the Rastall model

The discussion of whether quantum theory is compatible with the locality idea that no causal influence can act outside the forward light cone has recently been tightly linked to the corresponding question for a much simpler model theory that enjoys all of the pertinent properties of quantum theory but is much easier to fully comprehend. It is shown here that, contrary to recent claims, the model theory is incompatible with the locality idea mentioned above. The logical structure of the argument, which is similar to the one employed for quantum theory, is discussed.     

Macroscopic simulation of violation of Bell’s inequality

A macroscopic quantum model of a two-level system (the analogue of a half-spin particle) is described. The model is employed for simulating not only the system under study, but the measurement process as well. Single- and two-particle state models of a quantum system are constructed. The Einstein-Podolsky-Rosen paradox and Bell’s inequality are discussed within the framework of the model.     

Local and global distinguishability in quantum interferometry

A statistical distinguishability based on relative entropy characterizes the fitness of quantum states for phase estimation. This criterion is employed in the context of a Mach-Zehnder interferometer and used to interpolate between two regimes of local and global phase distinguishability. The scaling of distinguishability in these regimes with photon number is explored for various quantum states. It emerges that local distinguishability is dependent on a discrepancy between quantum and classical rotational energy. Our analysis demonstrates that the Heisenberg limit is the true upper limit for local phase sensitivity. Only the "NOON" states share this bound, but other states exhibit a better trade-off when comparing local and global phase regimes.     

Tunneling current spectroscopy of a nanostructure junction involving multiple energy levels

A multilevel Anderson model is employed to simulate the system of a nanostructure tunnel junction with any number of one-particle energy levels. The tunneling current, including both shell-tunneling and shell-filling cases, is theoretically investigated via the nonequilibrium Green's function method. We obtain a closed form for the spectral function, which is used to analyze the complicated tunneling current spectra of a quantum dot or molecule embedded in a double-barrier junction. We also show that negative differential conductance can be observed in a quantum dot tunnel junction when the Coulomb interactions with neighboring quantum dots are taken into account.     

Absorption spectra of small semiconductor quantum dots

A density matrix approach has been employed to study analytically the absorption spectra of small semiconductor quantum dots under the strong confinement regime. The results are obtained for a single quantum dot (SQD) as well as for inhomogeneous distribution of quantum dots (IQDs) with Gaussian distribution of quantum dot sizes. A numerical analysis has been made for a SQD and IQDs in a CdS crystal with data taken from recent experimental work. A negative change in the absorption coefficient occurs in the shorter pump wavelength side of the spectrum due to the biexcitonic contribution. The wavelength at which crossover from positive to negative values of the change in absorption coefficient occurs is found to depend upon both the QD size as well as the excitation intensity. The results agree satisfactorily with the experimental observations in small CdS quantum dots.     

Tripartite Splitting Arbitrary 2-Qubit Quantum Information by Using Two Asymmetric W States

In this paper we propose a tripartite scheme for splitting an arbitrary 2-qubit quantum information by using two asymmetric W states as the quantum channel. In the schemem if the two recipients collaborate together, they can deterministically recover the quantum information by performing first a 4-qubit collective unitary operation and then two single-qubit unitary operations. In addition, since the asymmetric W states are employed as the quantum channel, the scheme is robust against decoherence.     

Implementation of ternary Shor's algorithm based on vibrational states of an ion in anharmonic potential

It is widely believed that Shor's factoring algorithm provides a driving force to boost the quantum computing research.However, a serious obstacle to its binary implementation is the large number of quantum gates. Non-binary quantum computing is an efficient way to reduce the required number of elemental gates. Here, we propose optimization schemes for Shor's algorithm implementation and take a ternary version for factorizing 21 as an example. The optimized factorization is achieved by a two-qutrit quantum circuit, which consists of only two single qutrit gates and one ternary controlled-NOT gate. This two-qutrit quantum circuit is then encoded into the nine lower vibrational states of an ion trapped in a weakly anharmonic potential. Optimal control theory(OCT) is employed to derive the manipulation electric field for transferring the encoded states. The ternary Shor's algorithm can be implemented in one single step. Numerical simulation results show that the accuracy of the state transformations is about 0.9919.