24,754 research outputs found
The Angular Momentum Distribution within Halos in Different Dark Matter Models
We study the angular momentum profile of dark matter halos for a statistical
sample drawn from a set of high-resolution cosmological simulations of
particles. Two typical Cold Dark Matter (CDM) models have been analyzed, and
the halos are selected to have at least particles in order to
reliably measure the angular momentum profile. In contrast with the recent
claims of Bullock et al., we find that the degree of misalignment of angular
momentum within a halo is very high. About 50 percent of halos have more than
10 percent of halo mass in the mass of negative angular momentum . After the
mass of negative is excluded, the cumulative mass function follows
approximately the universal function proposed by Bullock et al., though we
still find a significant fraction of halos () which exhibit
systematic deviations from the universal function. Our results, however, are
broadly in good agreement with a recent work of van den Bosch et al.. We also
study the angular momentum profile of halos in a Warm Dark Matter (WDM) model
and a Self-Interacting Dark Matter (SIDM) model. We find that the angular
momentum profile of halos in the WDM is statistically indistinguishable from
that in the CDM model, but the angular momentum of halos in the SIDM is reduced
by the self-interaction of dark matter.Comment: 23 pages, 10 figures, 2 tables. Revised version, added a new table,
accepted for publication in MNRA
Measuring the degree of unitarity for any quantum process
Quantum processes can be divided into two categories: unitary and non-unitary
ones. For a given quantum process, we can define a \textit{degree of the
unitarity (DU)} of this process to be the fidelity between it and its closest
unitary one. The DU, as an intrinsic property of a given quantum process, is
able to quantify the distance between the process and the group of unitary
ones, and is closely related to the noise of this quantum process. We derive
analytical results of DU for qubit unital channels, and obtain the lower and
upper bounds in general. The lower bound is tight for most of quantum
processes, and is particularly tight when the corresponding DU is sufficiently
large. The upper bound is found to be an indicator for the tightness of the
lower bound. Moreover, we study the distribution of DU in random quantum
processes with different environments. In particular, The relationship between
the DU of any quantum process and the non-markovian behavior of it is also
addressed.Comment: 7 pages, 2 figure
Graphical description of local Gaussian operations for continuous-variable weighted graph states
The form of a local Clifford (LC, also called local Gaussian (LG)) operation
for the continuous-variable (CV) weighted graph states is presented in this
paper, which is the counterpart of the LC operation of local complementation
for qubit graph states. The novel property of the CV weighted graph states is
shown, which can be expressed by the stabilizer formalism. It is distinctively
different from the qubit weighted graph states, which can not be expressed by
the stabilizer formalism. The corresponding graph rule, stated in purely graph
theoretical terms, is described, which completely characterizes the evolution
of CV weighted graph states under this LC operation. This LC operation may be
applied repeatedly on a CV weighted graph state, which can generate the
infinite LC equivalent graph states of this graph state. This work is an
important step to characterize the LC equivalence class of CV weighted graph
states.Comment: 5 pages, 6 figure
Multicast With Prioritized Delivery: How Fresh is Your Data?
We consider a multicast network in which real-time status updates generated
by a source are replicated and sent to multiple interested receiving nodes
through independent links. The receiving nodes are divided into two groups: one
priority group consists of nodes that require the reception of every update
packet, the other non-priority group consists of all other nodes without the
delivery requirement. Using age of information as a freshness metric, we
analyze the time-averaged age at both priority and non-priority nodes. For
shifted-exponential link delay distributions, the average age at a priority
node is lower than that at a non-priority node due to the delivery guarantee.
However, this advantage for priority nodes disappears if the link delay is
exponential distributed. Both groups of nodes have the same time-averaged age,
which implies that the guaranteed delivery of updates has no effect the
time-averaged freshness.Comment: IEEE SPAWC 201
Experimental demonstration of tripartite entanglement and controlled dense coding for continuous variables
A tripartite entangled state of bright optical field is experimentally
produced using an Einstein-Podolsky-Rosen entangled state for continuous
variables and linear optics. The controlled dense coding among a sender, a
receiver and a controller is demonstrated by exploiting the tripartite
entanglement. The obtained three-mode position correlation and relative
momentum correlation between the sender and the receiver and thus the
improvements of the measured signal to noise ratios of amplitude and phase
signals with respect to the shot noise limit are 3.28dB and 3.18dB
respectively. If the mean photon number equals 11 the channel
capacity can be controllably inverted between 2.91 and 3.14. When is
larger than 1.0 and 10.52 the channel capacities of the controlled dense coding
exceed the ideal single channel capacities of coherent and squeezed state light
communication.Comment: 8 pages, 4 figure
- …