4,482 research outputs found
LAMOST J040643.69+542347.8: the fastest Rotator in the Galaxy
Rotation and binary interaction play important roles in understanding the
nature of massive stars (>8 Msun). Some interesting transients, such as the
long-duration gamma-ray bursts, are thought to be originated from fast-rotating
massive stars. Because the strong stellar wind can effectively spin down a
metal-rich massive star with fast rotation, it is very hard to find single
massive stars rotating critically in the Galaxy. In the present work reported
is the discovery of the fastest rotator in the Galaxy, LAMOST
J040643.69+542347.8, with a projected rotational velocity vsini ~540 km/s,
which is ~ 100 km/s faster than that of the previous record holder HD 191423.
The star has a spectral type of O6.5 Vnnn(f)p. Its He I 4471 absorption line is
blueshifted and asymmetric, while its He II 4686 and Ha have central absorption
reversals in their emissions. It is also a runaway star, which implies an
origin in a close binary interaction. Compared to VFTS 285 and VFTS 102 (their
vsini ~ 610 km/s) in the Large Magellanic Cloud, LAMOST J040643.69+542347.8 has
its own peculiar spectral characteristics and earlier spectral type. Moreover,
LAMOST J040643.69+542347.8 is bright (B ~ 13.9 mag) enough to allow future
high-resolution spectroscopic follow-ups.Comment: 7 pages, 3 figures, 1 table. Accepted by the ApJ Lette
Realization of Probabilistic Identification and Clone of Quantum-States II Multiparticles System
We realize the probabilistic cloning and identifying linear independent
quantum states of multi-particles system, given prior probability, with
universal quantum logic gates using the method of unitary representation. Our
result is universal for separate state and entanglement. We also provide the
realization in the condition given initial copies for each state.Comment: 18 Pages, 3 Figures, ReVTe
Conditions for manipulation of a set of entangled pure states
We derive a sufficient condition for a set of pure states, each entangled in
two remote -dimensional systems, to be transformable to
-dimensional-subspace equivalent entangled states () by same local
operations and classical communication. If , the condition is also
necessary. This condition reveals the function of the relative marginal density
operators of the entangled states in the entanglement manipulation without
sufficient information of the initial states.Comment: 5 Pages, no Figure, REVTeX. The generalization of quant-ph/990801
More randomness from a prepare-and-measure scenario with independent devices
How to generate genuine quantum randomness from untrusted devices is an
important problem in quantum information processing. Inspired by previous work
on a self-testing quantum random number generator [T. Lunghi et al., Phys. Rev.
Lett. 114, 150501 (2015)], we present a method to generate quantum randomness
from a prepare-and-measure scenario with independent devices. In existing
protocols, the quantum randomness depends only on a witness value (e.g.,
Clauser-Horne-Shimony-Holt value), which is calculated with the observed
probabilities. Differently, here all the observed probabilities are directly
used to calculate the min-entropy in our method. Through numerical simulation,
we find that the min-entropy of our proposed scheme is higher than that in the
previous work when a typical untrusted Bennett-Brassard 1984 (BB84) setup is
used. Consequently, thanks to the proposed method, more genuine quantum random
numbers may be obtained than before.Comment: 8 pages, 3 figure
Security of modified Ping-Pong protocol in noisy and lossy channel
The "Ping-Pong" (PP) protocol is a two-way quantum key protocol based on
entanglement. In this protocol, Bob prepares one maximally entangled pair of
qubits, and sends one qubit to Alice. Then, Alice performs some necessary
operations on this qubit and sends it back to Bob. Although this protocol was
proposed in 2002, its security in the noisy and lossy channel has not been
proven. In this report, we add a simple and experimentally feasible
modification to the original PP protocol, and prove the security of this
modified PP protocol against collective attacks when the noisy and lossy
channel is taken into account. Simulation results show that our protocol is
practical.Comment: 7 pages, 2 figures, published in scientific report
Quantum phase transitions and string orders in the spin-1/2 Heisenberg-Ising alternating chain with Dzyaloshinskii-Moriya interaction
Quantum phase transitions (QPTs) and the ground-state phase diagram of the
spin-1/2 Heisenberg-Ising alternating chain (HIAC) with uniform
Dzyaloshinskii-Moriya (DM) interaction are investigated by a
matrix-product-state (MPS) method. By calculating the odd- and even-string
order parameters, we recognize two kinds of Haldane phases, i.e., the odd- and
even-Haldane phases. Furthermore, doubly degenerate entanglement spectra on odd
and even bonds are observed in odd- and even-Haldane phases, respectively. A
rich phase diagram including four different phases, i.e., an antiferromagnetic
(AF), AF stripe, odd- and even-Haldane phases, is obtained. These phases are
found to be separated by continuous QPTs: the topological QPT between the odd-
and even-Haldane phases is verified to be continuous and corresponds to
conformal field theory with central charge =1; while the rest phase
transitions in the phase diagram are found to be =1/2. We also revisit, with
our MPS method, the exactly solvable case of HIAC model with DM interactions
only on odd bonds, and find that the even-Haldane phase disappears, but the
other three phases, i.e., the AF, AF stripe, and odd-Haldane phases, still
remain in the phase diagram. We exhibit the evolution of the even-Haldane phase
by tuning the DM interactions on the even bonds gradually.Comment: 21 pages, 13 figure
Security of "Counterfactual Quantum Cryptography"
Recently, a "counterfactual" quantum key distribution scheme was proposed by
Tae-Gon Noh [1]. In this scheme, two legitimate distant peers may share secret
keys even when the information carriers are not traveled in the quantum
channel. We find that this protocol is equivalent to an entanglement
distillation protocol (EDP). According to this equivalence, a strict security
proof and the asymptotic key bit rate are both obtained when perfect single
photon source is applied and Trojan-horse attack can be detected. We also find
that the security of this scheme is deeply related with not only the bit error
rate but also the yields of photons. And our security proof may shed light on
security of other two-way protocols.Comment: 5 pages, 1 figur
Quantum key distribution based on quantum dimension and independent devices
In this paper, we propose a quantum key distribution (QKD) protocol based on
only a two-dimensional Hilbert space encoding a quantum system and independent
devices between the equipment for state preparation and measurement. Our
protocol is inspired by the fully device-independent quantum key distribution
(FDI-QKD) protocol and the measurement-device-independent quantum key
distribution (MDI-QKD) protocol. Our protocol only requires the state to be
prepared in the two dimensional Hilbert space, which weakens the state
preparation assumption in the original MDI-QKD protocol. More interestingly,
our protocol can overcome the detection loophole problem in the FDI-QKD
protocol, which greatly limits the application of FDI-QKD. Hence our protocol
can be implemented with practical optical components
Universal Quantum Entanglement Concentration Gate
We construct a Universal Quantum Entanglement Concentration Gate (QEC-Gate).
Special times operations of QEC-Gate can transform a pure 2-level bipartite
entangled state to nearly maximum entanglement. The transformation can attain
any required fidelity with optimal probability by adjusting concentration step.
We also generate QEC-Gate to the Schmidt decomposable multi-partite system.Comment: 3 Pages, No Figure, REVTe
Enhanced Kerr electro-optic nonlinearity through cascaded Pockels effects
We demonstrated a large enhancement of Kerr electro-optic nonlinearity
through cascaded Pockels effects in a domain inversion ferroelectric crystal.
We designed a structure that can implement the cascaded Pockels effects and
second-harmonic generation simultaneously. The energy coupling between the
fundamental lights of different polarizations led to a large nonlinear phase
shift, and thus an effective electro-optic nonlinear refractive index. The
effective nonlinearity can be either positive or negative, causing the
second-harmonic spectra to move towards the coupling center, which in turn,
offered us a way to measure the effective electro-optic nonlinear refractive
index. The corresponding enhanced Kerr electro-optic nonlinearity is more than
three orders of magnitude higher than the intrinsic value. These results open a
door to manipulate the nonlinear phase by applying external electric field
instead of light intensity in noncentrosymmetric crystals.Comment: 15 pages, 6 figure
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