Equatorial State Research Articles

Remote preparation of four-qubit states via two-qubit maximally entangled states

In this paper, an efficient scheme of remotely preparing four-qubit quantum states via two-qubit maximally entangled states is proposed. This scheme can be accomplished by using appropriate unitary transformations and some classical communication. The detailed processes for preparation of four-qubit states are presented in the general case and two special cases, respectively. The method of constructing special measurement basis in general case is provided, and the similar methods for real-parameter state case and equatorial state case are also discussed. Meanwhile, the probabilities of successful preparation under each case are calculated in our schemes. The results show that the successful probability is only 1 / 16 in the general case, and the probability can reach up to 100% when the relative phase factors are zero or the amplitude parameters are 1 / 4.

Asymmetric controlled bidirectional remote preparation of two- and three-qubit equatorial state

In this paper, a novel asymmetric controlled bidirectional remote preparation scheme is proposed. In our scheme, Alice and Bob are not only the senders but also the receivers with the control of Charlie. By using the eleven-qubit entangled state as the quantum channel, Alice prepares an arbitrary two-qubit equatorial state for Bob and Bob prepares an arbitrary three-qubit equatorial state for Alice simultaneously. Firstly, we give the construction process of the quantum channel. Secondly, the whole recovery operations are given. Alice and Bob can recover the prepared state determinately. Thirdly, we consider the effect of the noisy environment (amplitude-damping and phase-damping) in our scheme and calculate the fidelities of the output states. Finally, since our scheme does not need additional operations and auxiliary qubits, the efficiency of our scheme is higher than that of the previous schemes.

Deterministic Joint Remote State Preparation of an Arbitrary Equatorial Three-Qubit State

We propose a new scheme for joint remote preparation of an arbitrary equatorial three-qubit state by using three three-qubit GHZ states as the quantum channel. In our scheme, eight different projective measurement basis vectors are needed. It is shown that the successful probability of our scheme is 100% by performing the appropriate unitary operations.

Asymmetric Controlled Bidirectional Remote Preparation of Single- and Three-Qubit Equatorial State in Noisy Environment

We present an asymmetric controlled bidirectional remote preparation scheme under the control of Charlie, where Alice transmits an arbitrary single-qubit equatorial state to Bob and Bob transmits an arbitrary three-qubit equatorial state to Alice. First, the quantum channel is constructed by using <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Hadamard</i> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${H}$ </tex-math></inline-formula> ) and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CNOT</i> operations. Second, we consider our scheme in the noiseless environment and construct the appropriate measurement bases. In addition, the participants can recover the prepared states through implementing the corresponding recovery operations determinately. Third, we discuss our scheme in five types of noisy environments (amplitude-damping, phase-damping, bit-flip, phase-flip, and depolarizing noisy environment). The fidelities of the output states are calculated, which depend on the coefficients of the prepared states and the decoherence rates. Finally, some discussions and conclusions are given. Compared with previous schemes, our scheme does not need additional operations or auxiliary qubits. So it is slightly more efficient.

Neighbourhood\xa0level real-time forecasting of dengue cases in tropical urban Singapore

BackgroundDengue, a vector-borne infectious disease caused by the dengue virus, has spread through tropical and subtropical regions of the world. All four serotypes of dengue viruses are endemic in the equatorial city state of Singapore, and frequent localised outbreaks occur, sometimes leading to national epidemics. Vector control remains the primary and most effective measure for dengue control and prevention. The objective of this study is to develop a novel framework for producing a spatio-temporal dengue forecast at a neighbourhood level spatial resolution that can be routinely used by Singapore’s government agencies for planning of vector control for best efficiency.MethodsThe forecasting algorithm uses a mixture of purely spatial, purely temporal and spatio-temporal data to derive dynamic risk maps for dengue transmission. LASSO-based regression was used for the prediction models and separate sub-models were constructed for each forecast window. Data were divided into training and testing sets for out-of-sample validation. Neighbourhoods were categorised as high or low risk based on the forecast number of cases within the cell. The predictive accuracy of the categorisation was measured.ResultsClose concordance between the projections and the eventual incidence of dengue were observed. The average Matthew’s correlation coefficient for a classification of the upper risk decile (operational capacity) is similar to the predictive performance at the optimal 30% cut-off. The quality of the spatial predictive algorithm as a classifier shows areas under the curve at all forecast windows being above 0.75 and above 0.80 within the next month.ConclusionsSpatially resolved forecasts of geographically structured diseases like dengue can be obtained at a neighbourhood level in highly urban environments at a precision that is suitable for guiding control efforts. The same method can be adapted to other urban and even rural areas, with appropriate adjustment to the grid size and shape.

Deciphering the State of the Late Miocene to Early Pliocene Equatorial Pacific

AbstractThe late Miocene‐early Pliocene was a time of global cooling and the development of modern meridional thermal gradients. Equatorial Pacific sea surface conditions potentially played an important role in this global climate transition, but their evolution is poorly understood. Here we present the first continuous late Miocene‐early Pliocene (8.0–4.4 Ma) planktic foraminiferal stable isotope records from eastern equatorial Pacific Integrated Ocean Drilling Program Site U1338, with a new astrochronology spanning 8.0–3.5 Ma. Mg/Ca analyses on surface dwelling foraminifera Trilobatus sacculifer from carefully selected samples suggest that mean sea surface temperatures (SSTs) are ~27.8 ± 1.1°C (1σ) between 6.4 and 5.5 Ma. The planktic foraminiferal δ18O record implies a 2°C cooling between 7.2 and 6.1 Ma and an up to 3°C warming between 6.1 and 4.4 Ma, consistent with observed tropical alkenone paleo‐SSTs. Diverging fine‐fraction‐to‐foraminiferal δ13C gradients likely suggest increased upwelling between 7.1–6.0 and 5.8–4.6 Ma, concurrent with the globally recognized late Miocene Biogenic Bloom. This study shows that both warm and asymmetric mean states occurred in the equatorial Pacific during the late Miocene‐early Pliocene. Between 8.0–6.5 and 5.2–4.4 Ma, low east‐west δ18O and SST gradients and generally warm conditions prevailed. However, an asymmetric mean climate state developed between 6.5 and 5.7 Ma, with larger east‐west δ18O and SST gradients and eastern equatorial Pacific cooling. The asymmetric mean state suggests stronger trade winds developed, driven by increased meridional thermal gradients associated with global cooling and declining atmospheric pCO2 concentrations. These oscillations in equatorial Pacific mean state are reinforced by Antarctic cryosphere expansion and related changes in oceanic gateways (e.g., Central American Seaway/Indonesian Throughflow restriction).

Deterministic joint remote preparation of an equatorial hybrid state via high-dimensional Einstein–Podolsky–Rosen pairs: active versus passive receiver

Entanglement plays a vital and in many cases non-replaceable role in the quantum network communication. Here, we propose two new protocols to jointly and remotely prepare a special so-called bipartite equatorial state which is hybrid in the sense that it entangles two Hilbert spaces with arbitrary different dimensions D and N (i.e., a type of entanglement between a quDit and a quNit). The quantum channels required to do that are however not necessarily hybrid. In fact, we utilize four high-dimensional Einstein–Podolsky–Rosen pairs, two of which are quDit–quDit entanglements, while the other two are quNit–quNit ones. In the first protocol the receiver has to be involved actively in the process of remote state preparation, while in the second protocol the receiver is passive as he/she needs to participate only in the final step for reconstructing the target hybrid state. Each protocol meets a specific circumstance that may be encountered in practice and both can be performed with unit success probability. Moreover, the concerned equatorial hybrid entangled state can also be jointly prepared for two receivers at two separated locations by slightly modifying the initial particles’ distribution, thereby establishing between them an entangled channel ready for a later use.

Deterministic remote preparation of arbitrary multi-qubit equatorial states via two-qubit entangled states

We propose an efficient scheme for remotely preparing an arbitrary n-qubit equatorial state via n two-qubit maximally entangled states. Compared to the former scheme (Wei et al. in Quantum Inf Process 16:260, 2017) that has the 50% successful probability when the amplitude factors of prepared states are $$2^{-n{/}2}$$ , the probability would be increased to 100% by using of our modified proposal. The feasibility of our scheme for remote preparation arbitrary multi-qubit equatorial states is explicitly demonstrated by theoretical studies and concrete examples.

An economical state-dependent telecloning for a multiparticle GHZ state

The scheme for a 1–3 economical state-dependent telecloning of a multiparticle GHZ state is proposed. It shows that every one of spatially separated three receivers obtains one copy which is dependent on original state. Fidelity can hit to the optimal fidelity 5/6. Meantime, we also propose a 1–3 asymmetric economical telecloning of a particular multiparticle GHZ state by parameterizing coefficients of state in the channel. The three fidelities can reach the best match that is the same as the symmetric case. Furthermore, the above two schemes can be generalized into the case of $$1-M(M=2k+1,k>0)$$ telecloning of a multiparticle GHZ state. Satisfying some certain conditions, optimal fidelities with $$\frac{1}{2}+\frac{(M+1)}{4M}$$ can be obtained. As without ancilla in the channel, the number of entangled particles is less than one in current schemes and fidelities can be optimal if the original state is an equatorial state.

Quantum jointly assisted cloning of an unknown three-dimensional equatorial state

We present two schemes for perfectly cloning an unknown single-qutrit equatorial state with assistance from two and N state preparers, respectively. In the first scheme, the sender wishes to teleport an unknown single-qutrit equatorial state from two state preparers to a remote receiver, and then to create a perfect copy of the unknown state at her location. The scheme consists of two stages. The first stage of the scheme requires the usual teleportation. In the second stage, to help the sender realize the quantum cloning, two state preparers perform single-qutrit projective measurements on their own qutrits from the sender, then the sender can acquire a perfect copy of the unknown state. It is shown that, only if the two state preparers collaborate with each other, the sender can create a copy of the unknown state by means of some appropriate unitary operations. In the second scheme, we generalized the jointly assisted cloning in the first scheme to the case of N state prepares. In the present schemes, the total probability of success for assisted cloning of a perfect copy of the unknown state can reach 1.

Biophysical Effects Simulated by an Ocean General Circulation Model Coupled with a Biogeochemical Model in the Tropical Pacific

Controversy has surrounded the potential impacts of phytoplankton on the tropical climate, since climate models produce diverse behaviors in terms of the equatorial mean state and El Nino-Southern Oscillation (ENSO) amplitude. We explored biophysical impacts on the tropical ocean temperature using an ocean general circulation model coupled to a biogeochemistry model in which chlorophyll can modify solar attenuation and in turn feed back to ocean physics. Compared with a control model run excluding biophysical processes, our model with biogeochemistry showed that subsurface chlorophyll concentrations led to an increase in sea surface temperature (particularly in the western Pacific) via horizontal accumulation of heat contents. In the central Pacific, however, a mild cold anomaly appeared, accompanying the strengthened westward currents. The magnitude and skewness of ENSO were also modulated by biophysical feedbacks resulting from the chlorophyll affecting El Nino and La Nina in an asymmetric way. That is, El Nino conditions were intensified by the higher contribution of the second baroclinic mode to sea surface temperature anomalies, whereas La Nina conditions were slightly weakened by the absorption of shortwave radiation by phytoplankton. In our model experiments, the intensification of El Nino was more dominant than the dampening of La Nina, resulting in the amplification of ENSO and higher skewness.

Effect of AMOC collapse on ENSO in a high resolution general circulation model

We look at changes in the El Niño Southern Oscillation (ENSO) in a high-resolution eddy-permitting climate model experiment in which the Atlantic Meridional Circulation (AMOC) is switched off using freshwater hosing. The ENSO mode is shifted eastward and its period becomes longer and more regular when the AMOC is off. The eastward shift can be attributed to an anomalous eastern Ekman transport in the mean equatorial Pacific ocean state. Convergence of this transport deepens the thermocline in the eastern tropical Pacific and increases the temperature anomaly relaxation time, causing increased ENSO period. The anomalous Ekman transport is caused by a surface northerly wind anomaly in response to the meridional sea surface temperature dipole that results from switching the AMOC off. In contrast to a previous study with an earlier version of the model, which showed an increase in ENSO amplitude in an AMOC off experiment, here the amplitude remains the same as in the AMOC on control state. We attribute this difference to variations in the response of decreased stochastic forcing in the different models, which competes with the reduced damping of temperature anomalies. In the new high-resolution model, these effects approximately cancel resulting in no change in amplitude.

Joint remote state preparation (JRSP) of two-qubit equatorial state in quantum noisy channels

This letter reports the influence of noisy channels on JRSP of two-qubit equatorial state. We present a protocol for JRSP of two-qubit equatorial state. Afterward, we investigate the effects of five quantum noises on the protocol. We find that the system loses some of its properties as consequence of unwanted interactions with environment. For instance, within the domain 0<λ<0.65, the information lost via transmission of qubits in amplitude channel is most minimal, while for 0.65<λ≤1, the information lost in phase flip channel becomes the most minimal. Also, for any given λ, the information transmitted through depolarizing channel has the least chance of success.

Optimal Joint Remote State Preparation of Arbitrary Equatorial Multi-qudit States

As an important communication technology, quantum information transmission plays an important role in the future network communication. It involves two kinds of transmission ways: quantum teleportation and remote state preparation. In this paper, we put forward a new scheme for optimal joint remote state preparation (JRSP) of an arbitrary equatorial two-qudit state with hybrid dimensions. Moreover, the receiver can reconstruct the target state with 100 % success probability in a deterministic manner via two spatially separated senders. Based on it, we can extend it to joint remote preparation of arbitrary equatorial multi-qudit states with hybrid dimensions using the same strategy.

Effects of Noise on Joint Remote State Preparation of an Arbitrary Equatorial Two-Qubit State

By using a six-qubit cluster state as the quantum channel, we investigat the joint remote state preparation of an arbitrary equatorial two-qubit state. We analytically obtain the fidelities of the joint remote state preparation process in noisy environments, such as the amplitude-damping noise and phase-damping noise. In our scheme, the two different noise including amplitude-damping noise and the phase-damping noise only affect the travel qubits of the quantum channel, and then we show that the fidelities in these two noisy cases only depend on the decoherence noisy rate.

Boreal summer sub-seasonal variability of the South Asian monsoon in the Met Office GloSea5 initialized coupled model

Boreal summer sub-seasonal variability in the Asian monsoon, otherwise known as the monsoon intra-seasonal oscillation (MISO), is one of the dominant modes of intraseasonal variability in the tropics, with large impacts on total monsoon rainfall and India’s agricultural production. However, our understanding of the mechanisms involved in MISO is incomplete and its simulation in various numerical models is often flawed. In this study, we focus on the objective evaluation of the fidelity of MISO simulation in the Met Office Global Seasonal forecast system version 5 (GloSea5), an initialized coupled model. We analyze a series of nine-member hindcasts from GloSea5 over 1996–2009 during the peak monsoon period (July–August) over the South-Asian monsoon domain focusing on aspects of the time-mean background state and air–sea interaction processes pertinent to MISO. Dominant modes during this period are evident in power spectrum analysis, but propagation and evolution characteristics of the MISO are not realistic. We find that simulated air–sea interactions in the central Indian Ocean are not supportive of MISO initiation in that region, likely a result of the low surface wind variance there. As a consequence, the expected near-quadrature phase relationship between SST and convection is not represented properly over the central equatorial Indian Ocean, and northward propagation from the equator is poorly simulated. This may reinforce the equatorial rainfall mean state bias in GloSea5.

Efficient Schemes of Joint Remote State Preparation for Two-Qubit Equatorial States

Recently, Binayak S. Choudhury (Quantum Inf. Process 13, 239 2014), proposed a protocol of joint remote state preparation of an equatorial two-qubit pure quantum state using GHZ states. According to their scheme the probability of success is 0.25. In this letter, an improved scheme is proposed, which can enhance the probability of success to 100 %. Moreover, we propose a scheme to prepare the two-qubit pure quantum state whose coefficient is more general.

The intraseasonal atmospheric angular momentum associated with MJO convective initiations

The first part of this study examines the driving mechanisms of the equatorial intraseasonal relative atmospheric angular momentum (AAM) and its dynamical relationship to the upper‐tropospheric zonal wind over the Western Hemisphere (WH) during the convective initiation of the Madden–Julian Oscillation (MJO) over the Indian Ocean. The budget analysis shows that the main driver of the equatorial intraseasonal AAM anomaly is the meridional transport of momentum induced by the modulation of the background subtropical eddies by the intraseasonal eddies. While the subtropical eddies over the central Pacific basin partly drive the equatorial AAM by meridionally transporting the momentum, the equatorial zonal wind associated with the same subtropical eddies is zonally advected and locally amplified over the east Pacific and Atlantic basins. The common source phenomena that transport momentum result in simultaneous evolution of the WH upper‐tropospheric zonal wind and the AAM on intraseasonal time‐scales, but their main driving mechanisms are different.The second part of the study investigates the influence of the equatorial intraseasonal AAM state on the subsequent development of initiating MJO convection over the Indian Ocean. In the presence of the WH upper‐tropospheric easterly wind, MJO convection tends to develop a stronger enhanced convective envelope when the initiation occurs during the negative intraseasonal AAM state, which strengthens and extends the upper‐tropospheric easterly wind in the WH. When the AAM anomaly is positive, it tends to induce stronger mid‐tropospheric convergence above the region of convective initiation, thereby suppressing the lower‐tropospheric updraught and suppressing the further growth of convection. The results show that the combined effects of the WH circumnavigating circulation and the AAM can influence the subsequent development of MJO convection over the Indian Ocean.

Joint remote state preparation for two-qubit equatorial states

In this paper, we propose a protocol of joint remote state preparation of an equatorial two-qubit pure quantum state using GHZ states, performing projective measurements and appropriate unitary ope...

Single-outcome information gain of qubit measurements on different state ensembles

We calculate the single-outcome information gain of quantum measurements on a completely unknown qubit state randomly chosen from different state ensembles. It is shown that the information gain decreases when the ensemble size increases. We obtain analytic single-outcome information gain formulas for continuous equatorial and spherical state ensembles, which show that the states in the former ensemble are relatively easier to identify. The squared fidelity between post-measurement state and pre-measurement state is also calculated, and the qualitative tradeoff relations between information gain and fidelity are illustrated by our results.