327,839 research outputs found
Experimental realization of secure multi-party computation in an entanglement access to network
To construct a quantum network with many end users, it is critical to have a
cost-efficient way to distribute entanglement over different network ends. We
demonstrate an entanglement access network, where the expensive resource, the
entangled photon source at the telecom wavelength and the core communication
channel, is shared by many end users. Using this cost-efficient entanglement
access network, we report experimental demonstration of a secure multiparty
computation protocol, the privacy-preserving secure sum problem, based on the
network quantum cryptography
Quantum teleportation from light beams to vibrational states of a macroscopic diamond
With the recent development of optomechanics, the vibration in solids,
involving collective motion of trillions of atoms, gradually enters into the
realm of quantum control. Built on the recent remarkable progress in optical
control of motional states of diamonds, here we report an experimental
demonstration of quantum teleportation from light beams to vibrational states
of a macroscopic diamond under ambient conditions. Through quantum process
tomography, we demonstrate average teleportation fidelity (90.6+/- 1.0)%,
clearly exceeding the classical limit of 2/3. The experiment pushes the target
of quantum teleportation to the biggest object so far, with interesting
implications for optomechanical quantum control and quantum information
science.Comment: 7 pages, 4 figure
Observation of entanglement sudden death and rebirth by controlling solid-state spin bath
Quantum entanglement, the essential resource for quantum information
processing, has rich dynamics under different environments. Probing different
entanglement dynamics typically requires exquisite control of complicated
system-environment coupling in real experimental systems. Here, by a simple
control of the effective solid-state spin bath in a diamond sample, we observe
rich entanglement dynamics, including the conventional asymptotic decay as well
as the entanglement sudden death, a term coined for the phenomenon of complete
disappearance of entanglement after a short finite time interval. Furthermore,
we observe counter-intuitive entanglement rebirth after its sudden death in the
same diamond sample by tuning an experimental parameter, demonstrating that we
can conveniently control the non-Markovianity of the system-environment
coupling through a natural experimental knob. Further tuning of this
experimental knob can make the entanglement dynamics completely coherent under
the same environmental coupling. Probing of entanglement dynamics, apart from
its fundamental interest, may find applications in quantum information
processing through control of the environmental coupling
Multilevel quantum Otto heat engines with identical particles
A quantum Otto heat engine is studied with multilevel identical particles
trapped in one-dimensional box potential as working substance. The symmetrical
wave function for Bosons and the anti-symmetrical wave function for Fermions
are considered. In two-particle case, we focus on the ratios of ()
to , where and are the work done by two Bosons and Fermions
respectively, and is the work output of a single particle under the same
conditions. Due to the symmetric of the wave functions, the ratios are not
equal to . Three different regimes, low temperature regime, high temperature
regime, and intermediate temperature regime, are analyzed, and the effects of
energy level number and the differences between the two baths are calculated.
In the multiparticle case, we calculate the ratios of to , where
can be seen as the average work done by a single particle in
multiparticle heat engine.
For other working substances whose energy spectrum have the form of , the results are similar. For the case , two different
conclusions are obtained
Non-Markovian Quantum Jump with Generalized Lindblad Master Equation
The Monte Carlo wave function method or the quantum trajectory/jump approach
is a powerful tool to study dissipative dynamics governed by the Markovian
master equation, in particular for high-dimensional systems and when it is
difficult to simulate directly. In this paper, we extend this method to the
non-Markovian case described by the generalized Lindblad master equation. Two
examples to illustrate the method are presented and discussed. The results show
that the method can correctly reproduce the dissipative dynamics for the
system. The difference between this method and the traditional Markovian jump
approach and the computational efficiency of this method are also discussed
The Dynamical Invariant of Open Quantum System
The dynamical invariant, whose expectation value is constant, is generalized
to open quantum system. The evolution equation of dynamical invariant (the
dynamical invariant condition) is presented for Markovian dynamics. Different
with the dynamical invariant for the closed quantum system, the evolution of
the dynamical invariant for the open quantum system is no longer unitary, and
the eigenvalues of it are time-dependent. Since any hermitian operator
fulfilling dynamical invariant condition is a dynamical invariant, we propose a
sort of special dynamical invariant (decoherence free dynamical invariant) in
which a part of eigenvalues are still constant. The dynamical invariant in the
subspace spanned by the corresponding eigenstates evolves unitarily. Via the
dynamical invariant condition, the results demonstrate that this dynamical
invariant exists under the circumstances of emergence of decoherence free
subspaces
Exploring Quantum Contextuality to Generate True Random Numbers
Random numbers represent an indispensable resource for many applications. A
recent remarkable result is the realization that non-locality in quantum
mechanics can be used to certify genuine randomness through Bell's theorem,
producing reliable random numbers in a device independent way. Here, we explore
the contextuality aspect of quantum mechanics and show that true random numbers
can be generated using only single qutrit (three-state systems) without
entanglement and non-locality. In particular, we show that any observed
violation of the Klyachko-Can-Binicioglu-Shumovsky (KCBS) inequality [Phys.
Rev. Lett. 101, 20403 (2008)] provides a positive lower bound on genuine
randomness. As a proof-of-concept experiment, we demonstrate with photonic
qutrits that at least 5246 net true random numbers are generated with a
confidence level of 99.9%.Comment: Paper : 4.5 pages, 4 figures; Supplementary material : 5 pages, 2
figure
Core-dominance parameter, black hole mass and jet-disc connection in Fermi blazars
We study the relationship between jet power and accretion for Fermi and
non-Fermi blazars, respectively. We also compare the relevant parameter between
them. Our main results are as follows. (i) Fermi and non-Fermi blazars have
significant difference in redshift, black hole mass, and broad line luminosity.
(ii) Fermi blazars have higher average core-dominance parameter than non-Fermi
blazars, which suggests that Fermi blazars have strong beaming effect. (iii) We
find significant correlation between broad line emission and jet power for
Fermi and non-Fermi blazars, respectively, which suggests a direct tight
connection between jet and accretion. (iv) The accretion and black hole mass
may have a different contribution to jet power for Fermi and non-Fermi blazars,
respectively.Comment: 16pages,12figures,accepted for publication in MNRA
The Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Quasar Survey: Quasar Properties from Data Release Two and Three
This is the second installment for the Large Sky Area Multi-Object Fibre
Spectroscopic Telescope (LAMOST) Quasar Survey, which includes quasars observed
from September 2013 to June 2015. There are 9024 confirmed quasars in DR2 and
10911 in DR3. After cross-match with the SDSS quasar catalogs and NED, 12126
quasars are discovered independently. Among them 2225 quasars were released by
SDSS DR12 QSO catalogue in 2014 after we finalised the survey candidates. 1801
sources were identified by SDSS DR14 as QSOs. The remaining 8100 quasars are
considered as newly founded, and among them 6887 quasars can be given reliable
emission line measurements and the estimated black hole masses. Quasars found
in LAMOST are mostly located at low-to-moderate redshifts, with a mean value of
1.5. The highest redshift observed in DR2 and DR3 is 5. We applied emission
line measurements to H, H, Mg{\sc ii} and C{\sc iv}. We deduced
the monochromatic continuum luminosities using photometry data, and estimated
the virial black hole masses for the newly discovered quasars. Results are
compiled into a quasar catalog, which will be available online.Comment: 41 pages, 13 figures, 2 electronic tables available upon inquiry,
accepted by A
Converse flexoelectricity around ferroelastic domain walls
Domain walls (DWs) are ubiquitous in ferroelectric materials. Ferroelastic
DWs refer to those who separate two domains with unparalleled polarizations (or
two different ferroelastic variants). It is long believed that the structures
of ferroelastic DWs can be simply explained from the perspective of mechanical
and electric compatibilities in the framework of the Landau-Ginzburg-Devonshire
(LGD) theory. Here we show that the converse flexoelectricity must be taken
into account for fully describing the nature of ferroelastic DWs. In our work,
an unexpected asymmetric structure is identified, which is beyond the
prediction of the conventional LGD theory. By incorporating the converse
flexoelectricity into the LGD theory and using it to analyze high-resolution
images acquired by the aberration-corrected transmission electron microscope
(TEM), we demonstrate that it is the converse flexoelectricity that result in
the asymmetric structure. Moreover, the flexoelectric coefficient is derived by
quantifying the converse flexoelectricity around the DWs. This quantification
is deterministic in both the magnitude and sign of flexoelectric coefficients,
by the mutual verification of atomic mapping and first-principles calculations.
Our results suggest that the converse flexoelectricity cannot be neglected for
understanding the ferroelastic DWs and other boundaries in ferroelectric
materials
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