6,595 research outputs found
Criterion on remote clocks synchronization within a Heisenberg scaling accuracy
We propose a quantum method to judge whether two spatially separated clocks
have been synchronized within a specific accuracy . If the measurement
result of the experiment is obviously a nonzero value, the time difference
between two clocks is smaller than ; otherwise the difference is beyond
. On sharing the 2-qubit bipartite maximally entangled state in this
scheme, the accuracy of judgement can be enhanced to
. This criterion is consistent with Heisenberg
scaling that can be considered as beating standard quantum limit, moreover, the
unbiased estimation condition is not necessary.Comment: 5 pages, 1 figur
Transmit Optimization with Improper Gaussian Signaling for Interference Channels
This paper studies the achievable rates of Gaussian interference channels
with additive white Gaussian noise (AWGN), when improper or circularly
asymmetric complex Gaussian signaling is applied. For the Gaussian
multiple-input multiple-output interference channel (MIMO-IC) with the
interference treated as Gaussian noise, we show that the user's achievable rate
can be expressed as a summation of the rate achievable by the conventional
proper or circularly symmetric complex Gaussian signaling in terms of the
users' transmit covariance matrices, and an additional term, which is a
function of both the users' transmit covariance and pseudo-covariance matrices.
The additional degrees of freedom in the pseudo-covariance matrix, which is
conventionally set to be zero for the case of proper Gaussian signaling,
provide an opportunity to further improve the achievable rates of Gaussian
MIMO-ICs by employing improper Gaussian signaling. To this end, this paper
proposes widely linear precoding, which efficiently maps proper
information-bearing signals to improper transmitted signals at each transmitter
for any given pair of transmit covariance and pseudo-covariance matrices. In
particular, for the case of two-user Gaussian single-input single-output
interference channel (SISO-IC), we propose a joint covariance and
pseudo-covariance optimization algorithm with improper Gaussian signaling to
achieve the Pareto-optimal rates. By utilizing the separable structure of the
achievable rate expression, an alternative algorithm with separate covariance
and pseudo-covariance optimization is also proposed, which guarantees the rate
improvement over conventional proper Gaussian signaling.Comment: Accepted by IEEE Transactions on Signal Processin
Fitting magnetic field gradient with Heisenberg-scaling accuracy
We propose a quantum fitting scheme to estimate the magnetic field gradient
with -atom spins preparing in W state, which attains the Heisenberg-scaling
accuracy. Our scheme combines the quantum multi-parameter estimation and the
least square linear fitting method to achieve the quantum Cram\'{e}r-Rao bound
(QCRB). We show that the estimated quantity achieves the Heisenberg-scaling
accuracy. In single parameter estimation with assumption that the magnetic
field is strictly linear, two optimal measurements can achieve the identical
Heisenberg-scaling accuracy. Proper interpretation of the
super-Heisenberg-scaling accuracy is presented. The scheme of quantum metrology
combined with data fitting provides a new method in fast high precision
measurements.Comment: 7 pages, 2 figure
The global geometrical property of jet events in high-energy nuclear collisions
We present the first theoretical study of medium modifications of the global
geometrical pattern, i.e., transverse sphericity () distribution of
jet events with parton energy loss in relativistic heavy-ion collisions. In our
investigation, POWHEG+PYTHIA is employed to make an accurate description of
transverse sphericity in the p+p baseline, which combines the next-to-leading
order (NLO) pQCD calculations with the matched parton shower (PS). The Linear
Boltzmann Transport (LBT) model of the parton energy loss is implemented to
simulate the in-medium evolution of jets. We calculate the event normalized
transverse sphericity distribution in central Pb+Pb collisions at the LHC, and
give its medium modifications. An enhancement of transverse sphericity
distribution at small region but a suppression at large
region are observed in A+A collisions as compared to their p+p references,
which indicates that in overall the geometry of jet events in Pb+Pb becomes
more pencil-like. We demonstrate that for events with 2 jets in the final-state
of heavy-ion collisions, the jet quenching makes the geometry more sphere-like
with medium-induced gluon radiation. However, for events with ~jets,
parton energy loss in the QCD medium leads to the events more pencil-like due
to jet number reduction, where less energetic jets may lose their energies and
then fall off the jet selection kinematic cut. These two effects offset each
other and in the end result in more jetty events in heavy-ion collisions
relative to that in p+p.Comment: 9 pages, 9 figure
Extrusion Processing of Ultra-High Molecular Weight Polyethylene
Ultra-high molecular weight polyethylene (UHMWPE) is a unique thermoplastic polymer with excellent performances. It has ultra-high molecular weight and extreme rheological behaviour, which make it a worldwide challenge to process UHMWPE continuously with little or without processing aids. Although the polymer processing technology has been increasingly maturated, it still cannot carry out the industrialized production efficiency by conventional processing methods and apparatus at present. In this chapter, we review the progress of extrusion processing technology for UHMWPE, including ram extrusion, single screw extrusion, twin screw extrusion and novel extrusion technology based on extensional rheology. By summarizing of these processing technologies, a basic framework of the processing principles and methods for UHMWPE is clearly presented. It is helpful for us to understand the processing characteristics and methods for such thermoplastic polymer with ultra-high molecular weight
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