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 $M$ 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 $N$-dimensional systems, to be transformable to $k$-dimensional-subspace equivalent entangled states ($k\leq N$) by same local operations and classical communication. If $k=N$, 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 $c$=1; while the rest phase transitions in the phase diagram are found to be $c$=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