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Multipartite quantum steering, a unique resource for asymmetric quantum network information tasks, is very fragile to the inevitable decoherence, which makes it useless for practical purposes. It is thus of importance to understand how it decays in the presence of noise channels. We study the dynamic behaviors of genuine tripartite steering, reduced bipartite steering, and collective steering of a generalized three-qubit W state when only one qubit interacts independently with the amplitude damping channel (ADC), phase damping channel (PDC) or depolarizing channel (DC). Our results provide the region of decoherence strength and state parameters that each type of steering can survive. The results show that these steering correlations decay the slowest in PDC and some non-maximally entangled states more robust than the maximally entangled ones. Unlike entanglement and Bell nonlocality, the thresholds of decoherence strength that reduced bipartite steering and collective steering can survive depend on the steering direction. In addition, we find that not only one party can be steered by a group system, but also two parties can be steered by a single system. There is a trade-off between the monogamy relation involving one steered party and two steered parties. Our work provides comprehensive information about the effect of decoherence on multipartite quantum steering, which will help to realize quantum information processing tasks in the presence of noise environments.

Classical simulation of quantum computation is vital for verifying quantum devices and assessing quantum algorithms. We present a new quantum circuit simulator developed on the Sunway TaihuLight supercomputer. Compared with other simulators, the present one is distinguished in two aspects. First, our simulator is more versatile. The simulator consists of three mutually independent parts to compute the full, partial and single amplitudes of a quantum state with different methods. It has the function of emulating the effect of noise and support more kinds of quantum operations. Second, our simulator is of high efficiency. The simulator is designed in a two-level parallel structure to be implemented efficiently on the distributed many-core Sunway TaihuLight supercomputer. Random quantum circuits can be simulated with 40, 75 and 200 qubits on the full, partial and single amplitude, respectively. As illustrative applications of the simulator, we present a quantum fast Poisson solver and an algorithm for quantum arithmetic of evaluating transcendental functions. Our simulator is expected to have broader applications in developing quantum algorithms in various fields., 21 pages, 9 figures

Noise-adding methods have been widely used to manipulate the direction of quantum steering, but all related experimental schemes only worked under the assumption that Gaussian measurements were performed and ideal target states were accurately prepared. Here, we prove, and then experimentally observe, that a class of two-qubit states can be flexibly changed among two-way steerable, one-way steerable and no-way steerable, by adding either phase damping noise or depolarization noise. The steering direction is determined by measuring steering radius and critical radius, each of which represents a necessary and sufficient steering criterion valid for general projective measurements and actually prepared states. Our work provides a more efficient and rigorous way to manipulate the direction of quantum steering, and can also be employed to manipulate other types of quantum correlations.

Quantum steering, a type of quantum correlation with unique asymmetry, has important applications in asymmetric quantum information tasks. We consider a new quantum steering scenario in which one half of a two-qubit Werner state is sequentially measured by multiple Alices and the other half by multiple Bobs. We find that the maximum number of Alices who can share steering with a single Bob increases from 2 to 5 when the number of measurement settings $N$ increases from 2 to 16. Furthermore, we find a counterintuitive phenomenon that for a fixed $N$, at most 2 Alices can share steering with 2 Bobs, while 4 or more Alices are allowed to share steering with a single Bob. We further analyze the robustness of the steering sharing by calculating the required purity of the initial Werner state, the lower bound of which varies from 0.503(1) to 0.979(5). Finally, we show that our both-sides sequential steering sharing scheme can be applied to control the steering ability, even the steering direction, if an initial asymmetric state or asymmetric measurement is adopted. Our work gives insights into the diversity of steering sharing and can be extended to study the problems such as genuine multipartite quantum steering when the sequential unsharp measurement is applied., 15 pages, 4 figures, 1 table

Underwater imaging is a challenging topic in the field of photography due to the absorption and scattering of light by water, which reduces the imaging distance and visibility. In this paper, the effects of seawater on the quality of ghost imaging (GI) are analyzed theoretically and experimentally. Our results indicate that GI technique, to a certain extent, can achieve better imaging quality than conventional imaging, especially under weak light condition in seawater environments. The compressed sensing ghost imaging (CSGI) can further enhance the visibility of ghost images with fewer measurements. Therefore, ghost imaging has the potential of realizing longer-distance underwater imaging, owing to its robustness against seawater environmental disturbance.

Underwater wireless optical communications are studied through single photon detection, photon states modulation and quantum key encryption. These studies will promote the development of optical communication applications in underwater vehicles and underwater sensor networks.

Demonstrating quantum communication complexity superiority non-trivially with currently available experimental systems is of utmost importance in quantum information science. Here, we propose a generalized entanglement-assisted communication complexity reduction protocol and analyze the robustness of its quantum superiority against the measurement imperfections, such as measurement basis deviation and choice probability bias, a common problem rarely studied before. We find that the quantum superiority can be obtained in a specific entangled state in a suitable range of measurement basis and basis choice parameters. And the quantum superiority strengthens with the increase of the entanglement degree of quantum states. By using the maximum entangled state and its corresponding optimal measurement, the result we obtained violated the optimal classical bound by 239 standard deviations. Besides, the robustness of effective measurement basis in dephasing and depolarizing quantum channels is also investigated. These results not only make a step forward in investigating sufficient experimental conditions to unambiguously demonstrate the superiority of quantum communication complexity but also help to develop relevant practical applications.

Black-box quantum state preparation is a fundamental primitive in quantum algorithms. Starting from Grover, a series of techniques have been devised to reduce the complexity. In this work, we propose to perform black-box state preparation using the technique of linear combination of unitaries (LCU). We provide two algorithms based on a different structure of LCU. Our algorithms improve upon the existed best results by reducing the required additional qubits and Toffoli gates to 2log(n) and n, respectively, in the bit precision n. We demonstrate the algorithms using the IBM Quantum Experience cloud services. The further reduced complexity of the present algorithms brings the black-box quantum state preparation closer to reality., Comment: 13 pages, 3 figures

The sequential quantum random access code (QRAC) allows two or more decoders to obtain a desired message with higher success probability than the best classical bounds by appropriately modulating the measurement sharpness. Here, we propose an entanglement-assisted sequential QRAC protocol which can enable device-independent tasks. By relaxing the equal sharpness and mutually unbiased measurement limits, we widen the sharpness modulation region from a one-dimensional interval to a two-dimensional triangle. Then, we demonstrate our scheme experimentally and get more than 27 standard deviations above the classical bound even when both decoders perform approximately projective measurements. We use the observed success probability to quantify the connection among sequential QRAC, measurement sharpness, measurement biasedness, and measurement incompatibility. Finally, we show that our protocol can be applied to sequential device-independent randomness expansion and our measurement strategy can enhance the success probability of decoding the entire input string. Our results may promote a deeper understanding of the relationship among quantum correlation, quantum measurement, and quantum information processing., Comment: 10 pages, 4 figures, 8 tables

The underwater environment is extremely complex and variable, which makes it difficult for underwater robots detecting or recognizing surroundings using images acquired with cameras. Ghost imaging as a new imaging technique has attracted much attention due to its special physical properties and potential for imaging of objects in optically harsh or noisy environments. In this work, we experimentally study three categories of image reconstruction methods of ghost imaging for objects of different transmittance. For high-transmittance objects, the differential ghost imaging is more efficient than traditional ghost imaging. However, for low-transmittance objects, the reconstructed images using traditional ghost imaging and differential ghost imaging algorithms are both exceedingly blurred and cannot be improved by increasing the number of measurements. A compressive sensing method named augmented Lagrangian and alternating direction algorithm (TVAL3) is proposed to reduce the background noise imposed by the low-transmittance. Experimental results show that compressive ghost imaging can dramatically subtract the background noise and enhance the contrast of the image. The relationship between the quality of the reconstructed image and the complexity of object itself is also discussed.

We present a protocol for accelerating adiabatic quantum state transfer through a spin chain by adding an effective control pulse. Using Feshbach P-Q partitioning technique, we obtain the one-component dynamical equation which guides us to set the amplitude and period of the control field. This field can be a sequence of alternatively negative and positive (zero-energy change) pulses which can be realized easily in experiment. As an example, we discuss a three particles spin chain and the numerical calculation shows that the accelerated quantum state transfer can be obtained.

Objective: Cancer patients with bone marrow metastases are rare and dismal. The study was to identify the clinical features and prognostic factors in cancer patients with bone marrow metastases. Patients and Methods: A total of 30 patients with bone marrow metastases were reviewed between September 2007 and September 2013. Bone marrow metastases were identified by bone marrow aspiration. Results: The median age was 56.5 years (range, 8–85 years). The two most common primary tumor sites were the stomach (7, 23.3%), breast (5, 16.7%). Bone metastases (27, 90.0%) were the most common concurrent metastases. The most common cause for bone marrow aspiration was anemia and thrombocytopenia (10, 33.3%). The median survival time was 3 months (range, 0.5–82 months). Patients with good performance status (n = 19) had a longer median survival time than patients with poor performance status (n = 11) (8 months vs. 1 months, P = 0.041). Patients with primary unknown origin (n = 5) had a significantly shorter overall survival time than patients with known origin (n = 25) (1 month vs. 6 months = 0.010). The median survival time was 9 months in the systemic therapy group (n = 21) and 1 month in the best supportive care group (n = 9) (P = 0.000). Conclusion: To make primary origin clear and start systemic antitumor therapy is beneficial for patients with bone marrow metastases.

Quantum arithmetic in the computational basis constitutes the fundamental component of many circuit-based quantum algorithms. There exist a lot of studies about reversible implementations of algebraic functions, while research on the higher-level transcendental functions is scant. We propose to evaluate the transcendental functions based on a novel methodology, which is called qFBE (quantum Function-value Binary Expansion) method. This method transforms the evaluation of transcendental functions to the computation of algebraic functions in a simple recursive way. We present the quantum circuits for solving the logarithmic, exponential, trigonometric and inverse trigonometric functions based on the qFBE method. The efficiency of the circuits is demonstrated on a quantum virtual computing system installed on the Sunway TaihuLight supercomputer. The qFBE method provides a unified and programmed solution for the evaluation of transcendental functions, and it will be an important building block for many quantum algorithms., Comment: 21 pages, 7 figures

We study pulse control assisted dynamical decoupling through a central spin model in a total Hilbert space. We find that the effective decoupling can be realized by applying a sequence of external pulses. Compared with the bang-bang control which needs infinite strength and infinitesimal short pulses, we show that there is a large parameter space that allows an effective nonperturbative dynamical control. Furthermore, our numerical calculation shows that the reliability can be held for random pulses, such as random pulse time interval or random strength.

“Shortcuts to adiabaticity” represents a strategy for accelerating a quantum adiabatic process, is useful for preparing or manipulating a quantum state. In this paper, we investigate the adiabaticity in the dynamics of an XY spin chain. During the process of cutting one long chain into two short chains, a “shortcut” can be obtained by applying a sequence of external pulses. The fidelity which measures the adiabaticity can be dramatically enhanced by increasing the pulse strength or pulse duration time. This reliability can be kept for different types of pulses, such as random pulse time interval or random strength. The free choice of the pulse can be explained by the adiabatic representation of the Hamiltonian, and it shows that the control effects are determined by the integral of the control function in the time domain.

We carry out a detailed study on underwater ghost imaging (GI) in oceanic turbulence. We set up a physical model of GI through oceanic turbulence, which includes light-field transmission, and interaction between light field and oceanic turbulence without considering the effects of water absorption and scattering of light. We obtain theoretical expressions for the impulse response function and the visibility of GI in oceanic turbulence based on the power spectrum of the turbulence and the extended Huygens-Fresnel integral. The results show that the quality of GI under the effects of oceanic turbulence is related to the intensity of turbulence and the propagation distance of light. The quality of GI could be maintained at a relatively small distance in strong oceanic turbulence, whereas the quality is degraded dramatically at a relatively long distance in strong oceanic turbulence. We further analyze the quality of GI under various turbulence conditions and over different propagation distances by numerical calculation. Our results provide guidance for the realization of adaptive underwater optical GI over different length scales under the effect of oceanic turbulence.

Quantum key distribution (QKD) has undergone significant development in recent decades, particularly with respect to free-space (air) and optical fiber channels. Here, we report the first proof-of-principle experiment for the BB84 protocol QKD over a water channel. Firstly, we demonstrate again the polarization preservation properties of the water channel in optical transmission according to the measured Mueller matrix, which is close to the unit matrix. The reason for the polarization preservation, revealed by Monte Carlo simulation, is that almost all the received photons are unscattered.Then, we performed the first polarization encoding BB84 protocol QKD over a 2.37m water channel. The results show that QKD can be performed with a low quantum bit error rate (QBER), less than 3.5%, with different attenuation coefficients., 14 pages, 5 figures

Underwater quantum key distribution (QKD) has potential applications in absolutely secure underwater communication. However, the performance of underwater QKD is limited by the optical elements, background light, and dark counts of the detector. In this paper, we propose a modified formula for the quantum bit error rate (QBER), which takes into account the effect of detector efficiency on the QBER caused by the background light. Then we calculate the QBER of the polarization encoding BB84 protocol in Jerlov type seawater by analyzing the effect of the background light and optical components in a more realistic situation. Finally, we further analyze the final key rate and the maximum secure communication distance in three propagation modes, i.e., upward, downward and horizontal modes. We find that secure QKD can be performed in the clearest Jerlov type seawater at a distance of hundreds of meters, even in the worst downward propagation mode. Specifically, by optimizing the system parameters, it is possible to securely transmit information with a rate of 67kbits/s at a distance of 100 m in the seawater channel with an attenuation coefficient of 0.03/m at night. For practical underwater QKD, the performance can also be improved by using decoy states. Our results are useful to long distance underwater quantum communication., Comment: 13pages, 8figures,accepted by Journal of the Optical Society of America A

We propose a protocol to implement the distributed hyper-entangled-Bell-state analysis (HBSA) for photonic qubits with weak cross-Kerr nonlinearities, QND photon-number-resolving detection, and some linear optical elements. The distinct feature of our scheme is that the BSA for two different degrees of freedom can be implemented deterministically and nondestructively. Based on the present HBSA, we achieve quantum super dense coding with double information capacity, which makes our scheme more significant for long-distance quantum communication.

Quantum illumination is one of the most basic ways to realize the quantum radar for detection of low-reflectivity targets embedded in a thermal-noise bath. It preserves a strong advantage over the classical counterparts even though its fragile quantum entanglement is completely destroyed by a large amount of noise and losses. In this paper, we describe and analyze a discrete-variable quantum illumination system with ancillary degrees of freedom of entangled photon pairs. Comparing the error probability bound, i.e., the quantum Chernoff bound, we identify that this system indeed offers higher accuracy than the single-photon illumination and quantum illumination with single degree of freedom of entangled photon pairs. Furthermore, the utilization of ancillary degrees of freedom exponentially enhances signal-to-noise ratio over quantum illumination without ancillary degrees of freedom. It means that this system reduces the necessary amount of signal photons to accurately determine whether the object is present or absent in the target region, which is absolutely crucial to the stealthiness of the radar system.

This study presents an efficient scheme to generate an arbitrary multi-photon polarization-entangled GHZ state with quantum non-demolition measurement based on weak cross-Kerr nonlinearity. The distinct feature of the present scheme is that it works in a near-deterministic way in principle. Compared with the previous protocols, our scheme consumes less weak cross-Kerr nonlinear resources and there is no need for minus conditional phase shifts, which make us more confident in the experimental feasibility of the proposed scheme.

We present schemes for deterministically generating multi-qubit electron-spin entangled cluster states by the giant circular birefringence, induced by the interface between the spin of a photon and the spin of an electron confined in a quantum dot embedded in a double-sided microcavity. Based on this interface, we construct the controlled phase flip (CPF) gate deterministically which is performed on electron-spin qubits and is the essential component of the cluster-state generation. As one of the universal gates, the CPF gate constructed can also be utilized in achieving scalable quantum computing. Besides, we propose the entanglement concentration protocol to reconstruct a partially entangled cluster state into a maximally entangled one, resorting to the projection measurement on an ancillary photon. By iterating the concentration scheme several times, the maximum success probability can be achieved. The fidelities and experimental feasibilities are analyzed with respect to currently available techniques, indicating that our schemes can work well in both the strong and weak (Purcell) coupling regimes.

We propose a simple scheme for generating three-photon polarization-entangled GHZ state via cross-Kerr medium, linear optical elements and P homodyne measurement. In our protocol, the two-photon interference is used rather than the single-photon interference, which decreases the difficulty in experimental realization. Besides, the generation scheme proposed doubles the phase shift θ , which will result in lower error probability and decoherence effect. These advantages make our scheme more feasible in the regime of weak cross-Kerr nonlinearity with current experimental technologies. In addition, we give two efficient schemes for the generation of arbitrary multi-photon GHZ state, which is significant to large-scale quantum information processing (QIP).

We investigate the effect of phase shift on the perfect state transfer through two parallel one-dimensional ring-shaped spin chains. We find that the total success probability can be significantly enhanced by phase shift control when the communication channel consists of two odd chains. The average time to gain unit success probability is discussed, showing that a proper phase shift can be used to enhance the efficiency of state transmission.

Techniques for accelerating the evolutionary processes associated with an adiabatic passage have recently been developed. Given that the context for which these speeding-up protocols, such as the shortcut to adiabaticity, have been formulated, their presentation rests on the assumption of the validity of the quantum adiabatic theorem. We investigate here the possibility of extending these methods to a regime in which the adiabatic theorem cannot be applied. Using a spin chain model and a typical nonadiabatic quantum communication protocol, we determine and compare certain indicative aspects of state transfer, such as the fidelity measure of quality and communication latency, associated with both normal and pulse-assisted transmission. The fidelity is found to be effectively enhanced by increasing the pulse strength or pulse duration, indicating a shortcut to nonadiabatic quantum state transmission. Numerical calculations also reveal the inherent reliability and fault tolerance of this method.

We investigate the state or entanglement transfer through a two-dimensional spin network. We show that for state transfer, better fidelity can be gained along the diagonal direction but for entanglement transfer, when the initial entanglement is created along the boundary, the concurrence is more inclined to propagate along the boundary. This behavior is produced by quantum mechanical interference and the communication quality depends on the precise size of the network. For some number of sites, the fidelity in a two-dimensional channel is higher than one-dimensional case. This is an important result for realizing quantum communication through high dimension spin chain networks.

We propose a scheme to generate a three-quhit three-level singlet state in cavity QED, by placing three A-type SQUIDs in a single mode cavity. In this scheme, we make use of the interaction between the SQUIDs and cavity filed, and the classical pulses. The cavity fields are in vacuum state during the whole operation processes of creating the entanglement, and there is no quantum information transformation between the SQUIDs and cavity fields. Because of the advantage of the SQUID-cavity system, the quality factor of the cavity is greatly relaxed.

Boson sampling can provide strong evidence that the computational power of a quantum computer outperforms a classical one via currently feasible linear optics experiments. However, how to identify an actual boson sampling device against any classical computing imposters is an ambiguous problem due to the computational complexity class in which boson sampling lies. The certification protocol based on bosonic bunching fails to rule out the so-called mean-field sampling. We propose a certification scheme to distinguish the boson sampling from the mean-field sampling for any random scattering matrices chosen via the Harr-measure. We numerically analyze our scheme and the influence of imperfect input states caused by non-simultaneous arrival photons., Comment: 10 pages, 4 figures

We present an explicit protocol for deterministic exact teleportation via two partially entangled pairs of particles. The protocol consists of a local generalized measurement described by a positive operator-valued measure, one-way classical communication, and a corresponding local unitary operation. We find the required generalized measurement, which can experimentally be realized by performing a unitary operation in the extended space and a conventional orthogonal measurement. A simple protocol for deterministic entanglement concentration is also obtained.

Noisy entangled resource and non-standard teleportation operations result in imperfect teleportation. In this paper, we derive an explicit expression for the output states of imperfect teleportation processes, thereby establishing a correspondence between teleportation and quantum channels. This result offers a different insight into teleportation. Also, it enables us to derive an expression for the fidelity of teleportation. Our results analytically reveal the dependence of the output states and the fidelity on the entangled resource and teleportation operations. The Nielsen–Caves teleportation formalism is used in the derivation.

Teleportation is viewed as a quantum channel. We present an explicit expression for the general teleportation channel in the Kraus decomposition form. We then analyse optimal teleportation procedures for a noisy entangled resource, Bell measurement by the sender and arbitrary operations by the receiver. Our general result allows us to derive the corresponding quantum channel and fidelity, thereby enabling us to formulate the fidelity-based optimization problem and to conclude that this is a problem of semidefinite programming. We offer an alternative viewpoint on optimal teleportation, namely one can perform corrective operations at the receiver's side instead of first manipulating entanglement, and we give an optimal teleportation strategy.

We propose an experimentally feasible scheme to implement quantum dense coding by the interaction of two three-level Rydberg atoms with nonresonant cavities. The success probability of the scheme is close to 1, and the distance of information transmission is much longer than that of NMR.

To study the effect of Acanthopanax senticosus saponin (ASS) on free radical injury induced neuron aging. On day 7 of fetal mice, cortical neuron primary passage cultures were divided into the normal control group, model group and ASS groups. The model group using free radical (FeSO4 plus H2O2) injury mode prepared in vivo cultured ICR mice cortical neuron aging model; ASS groups: 24 hrs before and after treated with H2O2 and FeSO4, different concentration of ASS was added, according to biochemical parameters such as lactate dehydrogenase (LDH), superoxide dismutase (SOD) and malondialdehyde (MDA) etc. and histomorphologic change to observe the protection of ASS on aging neurons. The LDH, SOD,MDA of the model group were compared with the normal group, < 0. 01; ASS groups added 1.25 mg/100 ml, 2.5 mg/100 ml, 5 mg/100 ml concentration of ASS, their LDH, SOD, MDA compared with the model group π.05-0.01, the difference was significant. In medicated groups the SOD activity of oxidization injured nerve cells obviously elevated, LDH activity and MDA content apparently lowered. Microscope and scanning electron microscopic observation showed that supplemented with ASS to protect the nerve cell injury abated, part of the cellular structure tended to normalize. ASS could act against free radical toxic effect, increase the anti-oxidase activity, strengthen the protection of neuron cells. It is assumed that the effect against nerve cell aging was possibly through scavenging oxygen free radical, strengthening the stability of cell membrane, thus delaying the development of aging.

Teleportation of a d-dimensional quantum state via a pure but partially entangled channel is studied. Two schemes are presented for conclusive teleportation aiming at both obtaining a faithful replica with optimal probability and achieving a maximum average fidelity of teleportation when conclusive teleportation fails. A single pair entanglement concentration scheme is also constructed.

We propose a scheme to construct the efficient universal quantum circuit for qubit systems with the assistance of possibly available auxiliary Hilbert spaces. An elementary two-ququart gate, termed the controlled-double-NOT gate, is proposed first in ququart (four-level) systems, and its physical implementation is illustrated in the four-dimensional Hilbert spaces built by the path and polarization states of photons. Then an efficient universal quantum circuit for ququart systems is constructed using the gate and the quantum Shannon decomposition method. By introducing auxiliary two-dimensional Hilbert spaces, the universal quantum circuit for qubit systems is finally achieved using the result obtained in ququart systems with the lowest complexity.