609 research outputs found
Warped dust lanes in elliptical galaxies - Transient or stationary phenomena?
No full textSpectroscopic observations of NGC 5128 show that the stellar component possesses a velocity gradient along its major axis with a total velocity difference of 160 km/s. This velocity, together with a velocity dispersion of 140 km/s, places NGC 5128 among the fast rotating elliptical galaxies. It is found that the motion of the warped dust lane with respect to that of the stars is direct. Prograde motions are also found in the warp of the E4 Anon 0151-498, while observations of a warped dust lane with retrograde motion in the E3.5 NGC 5363 are reported. The conditions under which the warped configurations in these galaxies are transient or stationary are analyzed. The intrinsic shape of these systems is also discussed
Macroscopic Greenberger-Horne-Zeilinger and W states in flux qubits
No full textWe investigate two types of genuine three-qubit entanglement, known as the Greenberger-Horne-Zeilinger (GHZ) and W states, in a macroscopic quantum system. Superconducting flux qubits are theoretically considered in order to generate such states. A phase coupling is proposed to offer enough strength of interactions between qubits. While an excited state can be the W state, the GHZ state is formed at the ground state of the three flux qubits. The GHZ and W states are shown to be robust against external flux fluctuations for feasible experimental realizations
High-fidelity interconversion between Greenberger-Horne-Zeilinger and states through Floquet-Lindblad engineering in Rydberg atom arrays
No full textGreenberger-Horne-Zeilinger and W states feature genuine tripartite
entanglement that cannot be converted into each other by local operations and
classical communication. Here, we present a dissipative protocol for
deterministic interconversion between Greenberger-Horne-Zeilinger and W states
of three neutral Rb atoms arranged in an equilateral triangle of a
two-dimensional array. With three atomic levels and diagonal van der Waals
interactions of Rydberg atoms, the interconversion between tripartite entangled
states can be efficiently accomplished in the Floquet-Lindblad framework
through the periodic optical pump and dissipation engineering. We evaluate the
feasibility of the existing methodology using the experimental parameters
accessible to current neutral-atom platforms. We find that our scheme is robust
against typical noises, such as laser phase noise and geometric imperfections
of the atom array. In addition, our scheme can integrate the Gaussian soft
quantum control technique, which further reduces the overall conversion time
and increases the resilience to timing errors and interatomic distance
fluctuations. The high-fidelity and robust tripartite entanglement
interconversion protocol provides a route to save physical resources and
enhance the computational efficiency of quantum networks formed by neutral-atom
arrays.Comment: 18 pages, 14 figures, accepted by Physical Review Applie
Macroscopic Greenberg-Horne-Zeilinger state and W state in charge qubits based on Coulomb blockade
No full textBased on Coulomb blockade, we propose a scheme to generate two types of three-qubit entanglement, known as Greenberg-Horne-Zeilinger (GHZ) state and W state, in a macroscopic quantum system. The qubit is encoded in the charge qubit in the superconducting system, and the scheme can
be generalized to generate the GHZ state and W state in multi-partite charge qubits. The GHZ state and W state are the eigenstates of the respective idle Hamiltonian, so they have the long lifetime
The (log re,μe) Plane of Hot Stellar Systems
No full textTwo families of hot stellar systems, named `ordinary' and {\it 'bright'\/}, are identified in the (log R_e, mu_e) plane built with a luminosity--limited sample of ellipticals and bulges of S0s and spirals of the Virgo and Fornax clusters. This finding, based on ad hoc new observations, is confirmed by a much larger set of literature data for ~1500 galaxies. The `ordinary' family is biparametric: L_T~ I_e R_e^2; its members are fainter that M_B~-19.3 and smaller than re~3 kpc (whatever M_B is). The 'bright' family is uniparametric (mu_e depends on R_e alone) and hosts brightest cluster members and QSO parent galaxies. We show that the segregation in the (log R_e, mu_e) plane has an important counterpart in the behavior of various physical parameters, which is markedly different for galaxies smaller ({`ordinary' family) and larger ('bright' family) than R_e=3 kpc
Pressure-supported ionized gas in S0 galaxies
No full textRotation curves and velocity dispersion profiles are presented for both the stellar and gaseous components of a sample of S0 galaxies. In all galaxies the central velocity dispersion of the ionized gas exceeds 150 km/s. In some galaxies the gas dispersion remains as high as the stellar one over an extended radial range, showing that random motions are crucial for the dynamical support of the gas. Such a pressure support may explain why the observed gas rotation curves in galaxy bulges often fall short of the circular velocity predicted from the stellar kinematic models. It is suggested that, in addition to the acquisition of external material, some of the observed gas in S0 galaxies may have been shed from bulge stars
Dynamical generation of chiral and Greenberger-Horne-Zeilinger states in laser-controlled Rydberg-atom trimers
No full textMotivated by the significantly improved scalability of optically-trapped
neutral-atom systems, extensive efforts have been devoted in recent years to
quantum-state engineering in Rydberg-atom ensembles. Here we investigate the
problem of engineering generalized (``twisted'') states, as well as
Greenberger-Horne-Zeilinger (GHZ) states, in the strongly-interacting regime of
a neutral-atom system. We assume that each atom in the envisioned system
initially resides in its ground state and is subject to several external laser
pulses that are close to being resonant with the same internal atomic
transition. In particular, in the special case of a three-atom system
(Rydberg-atom trimer) we determine configurations of field alignments and
atomic positions that enable the realization of chiral states -- a special
type of twisted three-qubit states of interest for implementing
noiseless-subsystem qubit encoding. Using chiral W states as an example we also
address the problem of deterministically converting twisted states into
their GHZ counterparts in the same three-atom system, thus significantly
generalizing recent works that involve only ordinary states. We show that
starting from twisted -- rather than ordinary -- states is equivalent to
renormalizing downwards the relevant Rabi frequencies. While this leads to
somewhat longer state-conversion times, we also demonstrate that those times
are at least two orders of magnitude shorter than typical lifetimes of relevant
Rydberg states.Comment: final, published versio
Robustness of Entanglement for Dicke-W and Greenberger-Horne-Zeilinger Mixed States
No full textQuantum entanglement is a fundamental characteristic of quantum mechanics, and understanding the robustness of entanglement across different mixed states is crucial for comprehending the entanglement properties of general quantum states. In this paper, the robustness of entanglement of Dicke–W and Greenberger–Horne–Zeilinger (GHZ) mixed states under different mixing ratios is calculated using the entanglement witness method. The robustnesses of entanglement of Dicke–W and GHZ mixed states are different when the probability ratio of Dicke to W is greater than 32 and less than 32. For the probability of Dicke and W states greater than or equal to 32, we study the robustness of entanglement of Dicke and GHZ mixed states and analyze and calculate their upper and lower bounds. For the probability of Dicke and W states less than 32, we take the equal probability ratio of Dicke and W states as an example and calculate and analyze the upper and lower bounds of their robustness of entanglement in detail
Nearby early-type galaxies with ionized gas. IV. Origin and powering mechanism of the ionized gas
No full textAims. A significant fraction of early-type galaxies (ETGs) exhibit emission lines in their optical spectra. We attempt to identify the producing the emission mechanism and the ionized gas in ETGs, and its connection with the host galaxy evolution. Methods. We analyzed intermediate-resolution optical spectra of 65 ETGs, mostly located in low density environments and exhibiting spectros-copic diagnostic lines of ISM from which we had previously derived stellar population properties. To extract the emission lines from the galaxy spectra, we developed a new fitting procedure that accurately subtracts the underlying stellar continuum, and accounts for the uncertainties caused by the age-metallicity degeneracy. Results. Optical emission lines are detected in 89% of the sample. The incidence and strength of emission correlate with neither the E/S0 classification, nor the fast/slow rotator classification. By means of the classical [OIII]/Hβ versus [NII]/Hα diagnostic diagram, the nuclear galaxy activity is classified such that 72% of the galaxies with emission are LINERs, 9% are Seyferts, 12% are composite/transition objects, and 7% are non-classified. Seyferts have young luminostiy-weighted ages (≲5 Gyr), and appear, on average, significantly younger than LINERs and composites. Excluding the Seyferts from our sample, we find that the spread in the ([OIII], Hα, or [NII]) emission strength increases with the galaxy central velocity dispersion . Furthermore, the [NII]/Hα ratio tends to increase with . The [NII]/Hα ratio decreases with increasing galactocentric distance, indicative of either a decrease in the nebular metallicity, or a progressive “softening” of the ionizing spectrum. The average nebular oxygen abundance is slightly less than solar, and a comparison with the results obtained in Paper III from Lick indices shows that it is ≈0.2 dex lower than that of stars. Conclusions. The nuclear (r < re/16) emission can be attributed to photoionization by PAGB stars alone only for ≈22% of the LINER/composite sample. On the other hand, we cannot exclude an important role of PAGB star photoionization at larger radii. For the major fraction of the sample, the nuclear emission is consistent with excitation caused by either a low-accretion rate AGN or fast shocks (200–500 km s-1) in a relatively gas poor environment ( cm-3), or both. The derived [SII]6717/6731 ratios are consistent with the low gas densities required by the shock models. The derived nebular metallicities are indicative of either an external origin of the gas, or an overestimate of the oxygen yields by SN models
Conditions for Monogamy of Quantum Discord: Greenberger-Horne-Zeilinger versus W states
No full textQuantum correlations are expected to respect all the conditions required for them to be good measures of quantumness in the bipartite scenario. In a multipartite setting, sharing entanglement between several parties is restricted by the monogamy of entanglement. We take over the concept of monogamy to an information-theoretic quantum correlation measure, and find that it violates monogamy in general. Using the notion of interaction information, we identify necessary and sufficient conditions for the measure to obey monogamy, for arbitrary pure and mixed quantum states. We show that while three-qubit generalized Greenberger-Horne-Zeilinger states follow monogamy, generalized W states do not
- …
