Unit Success Probability Research Articles

Controlled Quantum Secure Direct Communication by Using a Five-Atom Cluster State in Cavity QED

We propose an experimentally feasible scheme for implementing controlled quantum secure direct communication by using a five-atom cluster state in cavity QED. According to the results measured by the sender and the controller, the receiver can obtain different secret messages in a deterministic way with unit successful probability. In the communication processes, one only need separate measurements with the assistance of a strong classical driving field. In addition, the scheme is insensitive to the cavity decay and the thermal field.

Improved Deterministic N-To-One Joint Remote Preparation of an Arbitrary Qubit via EPR Pairs

Recently, Bich et al. (Int. J. Theor. Phys. 51: 2272, 2012) proposed two deterministic joint remote state preparation (JRSP) protocols of an arbitrary single-qubit state: one is for two preparers to remotely prepare for a receiver by using two Einstein-Podolsky-Rosen (ERP) pairs; the other is its generalized form in the case of arbitrary N (N > 2) preparers via N ERP pairs. While examining these two protocols, we find that the success probability for the receiver achieving the desired state is not deterministic, i.e., \(P^{N>2}_{suc}<1\), for N > 2 preparers in the second protocol. Through constructing two sets of adaptive projective measurement bases for both the real space and the complex space, an improved deterministic N-to-one JRSP protocol for an arbitrary single-qubit state is presented. Analysis shows our protocol can truly achieve the unit success probability, i.e., \(P^{N\geq 2}_{suc}=1\). What is more, the receiver can be randomly assigned even after the distribution of the qubits of EPR pairs, so it is more flexible and applicable in the network situation.

Efficient remote preparation of arbitrary two- and three-qubit states via the χ state

The application of χ state are investigated in remote state preparation (RSP). By constructing useful measurement bases with the aid of Hurwitz matrix equation, we propose several RSP schemes of arbitrary two- and three-qubit states via the χ state as the entangled resource. It is shown that the original state can be successfully prepared with the probability 100% and 50% for real coefficients and complex coefficients, respectively. For the latter case, the special ensembles with unit success probability are discussed by the permutation group. It is worth mentioning that the novel measurement bases have no restrictions on the coefficients of the prepared state, which means that the proposed schemes are more applicable.

Controlled Simultaneously State Preparation at Many Remote Locations with a New Cluster State Type

We succeed in the creation of a new cluster state type which has not been dealt with so far. After that we use it as quantum channel for quantum communication. Namely, in this paper one sender can simultaneously transmit two (three) different single-qubit states for two (three) different receivers under the control of a supervisor in only one protocol by using a five (seven)-qubit cluster state shared beforehand among the participants as quantum nonlocal resources. The merit of our work is that we can also generalize for sending N different single-qubit states to N receivers with also a controller by using a (2N + 1)-qubit cluster state. We follow the adaptive measurement strategy in order to achieve unit success probability.

Efficient and Economic Schemes for Remotely Preparing a Four-Qubit Cluster-Type Entangled State

We propose two novel schemes for remotely preparing a four-qubit cluster-type entangled state (FCES) with complex coefficients by using four EPR pairs and two three-qubit GHZ states as the quantum channel, respectively. To complete the remote state preparation (RSP) schemes, several novel sets of four-and two-qubit measuring basis were introduced. In these schemes, after the sender performs two different projective measurements, the receiver should introduce two auxiliary qubits and employ suitable C-NOT gates on his qubits, the original state can be reconstructed with unit successful probability. Compared with the previous schemes for the RSP of a FCES, the advantage of the present schemes is that the entanglement resource can be reduced.

Effect of Phase Shift in Dual-Rail Perfect State Transfer

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.

Proposal for Remotely Realizing Multi-qubit Controlled-Phase Gates

A feasible proposal is explored to remotely perform a family of multi-qubit controlled-phase gates (MQCPG), with the aid of entanglement transfer and quantum repeater. To remotely realize the gates, some local transformations, including single-qubit rotating operation, controlled-NOT gate and quantum phase gate, are employed during the realization. It turns out that MQCPG can be implemented among separate spatially agents with nearly unit fidelity and success probability. Besides, required classical information consumption of the proposed scenario is worked out. Furthermore, some attractive issues are discussed including the feature of present proposal and the experimental feasibility based on current technologies. Remarkably, it is revealed that our proposal essentially accesses to several nontrivial features lying in breaking through the limitation that error probability scales exponentially with the length of the channel in the course of the realization of the gates, and well compatibility with today’s experimental technologies.

Deterministic Three-Copy Entanglement Concentration of Photons through Direct Sum Extension and Auxiliary Degrees of Freedom

The schematic optical realization of deterministic multicopy (three-copy) entanglement concentration under local operations and classical communication (LOCC) is presented, which can resort to the linear optical elements, controlled-NOT gate that uses weak cross-Kerr nonlinearity effect and entangled qudits with different degrees of freedom. This concentration is based on Nielsen's theorem, which in principle quantifies the unit success probability. In addition, the required positive operator-valued measurement (POVM) is implemented through direct sum extension, because the least number of ancillary dimensions is demanded. The construction of POVM is systematically formulated, which results in the feasibility to generate the protocol to n-copy (n > 3) cases.

Deterministic Remote Preparation of a Four-Qubit Cluster-Type Entangled State

We propose a scheme for remotely preparing a four-qubit cluster-type state with complex coefficients by using six EPR pairs as the quantum channel. To complete the remote state preparation scheme, a novel set of four-qubit mutually orthogonal basis vectors has been introduced. It is shown that, after the sender performs two different four-qubit projective measurements, the receiver can reconstruct the original state (to be prepared remotely) with unit successful probability. Moreover, the scheme is also generalized to the case that non-maximally two-qubit entangled states are taken as the quantum channel.

Defending majority voting systems against a strategic attacker

Voting systems used in technical and tactical decision making in pattern recognition and target detection, data handling, signal processing, distributed and secure computing etc. are considered. A maxmin two period game is analyzed where the defender first protects and chooses units for participation in voting. The attacker thereafter attacks a subset of units. It is shown that when the defender protects all the voting units, the optimal number of units chosen for voting is either one or the maximal possible odd number. When the defender protects only the units chosen for voting, the optimal number of chosen units increases with the defender resource superiority (i.e., more resources than the attacker) and with probability of providing correct output by any unit. The system success probability always increases in the total number of voting units, the defender–attacker resource ratio, and the probability that each voting unit produces a correct output. The system success probability increases in the attacker–defender contest intensity if the defender achieves per-unit resource superiority, and otherwise decreases in the contest intensity. The presented model and enumerative algorithm allow obtaining optimal voting system defense strategy for any combination of parameters: total number of units, attack and defense resources, unit success probability and contest intensity.

New Deterministic Protocol for Joint Remote Preparation of Two-qubit States

Designing quantum protocols with unit success probability is highly desirable from a viewpoint of the overall resource cost. In this work, we propose a new deterministic protocol for joint remote preparation of the most general two-qubit state using the same quantum/classical resource as in [An et al., Phys. Lett. A {\bf 375} (2011) 3570] and, at the same time, retaining the passive role of the receiver as in [Xiao et al., J. Phys. B: At. Mol. Opt. Phys. {\bf 44} (2011) 075501], which employs a different kind of nonlocal resource. From a practical point of view, this protocol proves most suitable in situations when only Einstein- Podelsky-Rosen pairs are supplied and the receiver is not capable of performing any measurements nor controlled-NOT gates.

REMOTE IMPLEMENTATION OF AN UNKNOWN SINGLE-QUBIT OPERATION BY DIFFERENT DIMENSIONAL QUANTUM CHANNEL

We present two novel protocols for remote implementation of an unknown single-qubit operation with an EPR pair and a high-dimensional entangled state as the quantum channel, without and with quantum control. The main strategy of the protocols is teleportation of an unknown single-qubit operation, which consists of an usual teleportation of an arbitrary single-qubit state, nonsymmetric basis measurement, and corresponding local transformation. It is shown that the teleportation of the quantum operation can be implemented with unit successful probability.

Highly efficient remote preparation of an arbitrary three-qubit state via a four-qubit cluster state and an EPR state

An efficient protocol for remotely preparing an arbitrary three-qubit state is devised with a four-qubit cluster state and an Einstein---Podolsky---Rosen state as the shared quantum resource. Using an appropriate set of eight-qubit mutually orthogonal measurement basis, the remote three-qubit preparation is successfully completed with the probability of $${\frac{1}{8}}$$ in general case. Then to achieve our concerns of improving the probability of this protocol, some special ensembles of three-qubit states are minutely investigated. As a result, it is shown that the total probability of the RSP protocol, in these particular cases, can be improved to $${\frac{1}{4}}$$ and $${\frac{1}{2}}$$ , respectively, or even that the RSP protocol can be realized with unit success probability.

Remotely Preparing a Four-Dimensional Quantum State via Positive Operator-Valued Measure

Several protocols for remote preparation of a single-quadbit state and a two-quadbit entangle state with real and complex coefficients are presented via positive operator-valued measure, respectively. In these protocols, two- and three-quadbit non-maximally entangled state(s) have been employed as the quantum channel respectively. To complete the protocols, several novel sets of single- and two-quadbit mutually orthogonal basis vectors are introduced. The advantage of the present protocols is that, if the quantum channel consists of maximally entangled state(s), all the considered RSP can be completed with unit successful probability.

Efficient heralding of photonic qubits with applications to device-independent quantum key distribution

We present an efficient way of heralding photonic qubit signals using linear optics devices. First we show that one can obtain asymptotically perfect heralding and unit success probability with growing resources. Second, we show that even using finite resources, we can improve qualitatively and quantitatively over earlier heralding results. In the latte r scenario, we can obtain perfect heralded photonic qubits while maintaining a finite success probability. We demonstrate the advantage of our heralding scheme by predicting key rates for device independent quantum key distribution, taking imperfections of sources and detectors into account.

Remote state preparation with unit success probability

Remote state preparation is a secure and faithful method for transmitting known quantum states by means of local operation and classical communication. Existing protocols in the general case succeed just with probabilities of less than 100%. In this paper, we design a protocol to remotely prepare the most general single-qubit state that always succeeds. To achieve unit success probability, the preparer is allowed to use additional local resources and implement adaptive measurements. Our protocol is meaningful because the most expensive resource, i.e. the quantum channel previously shared between the preparer and the receiver, remains the same as in the original protocol (Pati 2000 Phys. Rev. A 63 014302), which, however, succeeds only half the time.

Quantum Teleportation of an Unknown Two-Atom Entangled State Using Four-Atom Cluster State

A simply protocol for quantum teleportation of an unknown two-atom entangled state using four-atom cluster state is investigated in cavity quantum electrodynamics (QED). In this protocol, by using a one-dimensional maximally four-atom cluster state as quantum channel, an unknown two-atom entangled state can be transmitted from the sender (Alice) to the receiver without apparent joint Bell-state measurement. According to the results measured by the sender, the receiver can obtain the original state with unit successful probability. The important features of our scheme can also be demonstrated in ion trap system.

Deterministic remote preparation of an arbitrary W-class state with multiparty

Our concern is to design some deterministic schemes for remotely preparing an arbitrary W-class state from one sender to one of a number of receivers. Compared with previous remote preparation schemes, the real receiver in our schemes is unknown to the sender. Firstly, by introducing a novel entanglement transformation the sender can deterministically prepare an arbitrary W-class state with complex spectra to one of two remote receivers via two four-particle GHZ states as the quantum channel. As for preparing a W-class state with real spectra, by constructing a general and useful measurement basis for the sender, another economical protocol can be designed with unit success probability. These schemes are extended to multiparties via two multi-particle GHZ states as the quantum channel. The classical communication costs of all the schemes are calculated to determine the classical resources required.

Controlled Quantum Secure Direct Communication with Local Separate Measurements in Cavity QED

In this paper, we proposed an experimentally feasible new scheme for controlled quantum secure direct communication in cavity quantum electrodynamics without apparent joint Bell-state measurement. According to the results measured by the sender and the controller, the receiver can obtain different secret messages in a deterministic way using GHZ state as the quantum channel with unit successful probability if controller cooperates with it. In the communication processes, with the assistance of a strong classical driving field, the interactions between atoms and a single-mode nonresonant cavity substitute the generalized joint Bell-basis measurements. So this scheme only need separate measurements. In addition, the scheme is insensitive to the cavity decay and the thermal field. The discussion of the scheme indicates that it is simple and realizable with present technology.

Exact quantum algorithm to distinguish Boolean functions of different weights

In this work, we exploit the Grover operator for the weight analysis of a Boolean function, specifically to solve the weight-decision problem. The weight w is the fraction of all possible inputs for which the output is 1. The goal of the weight-decision problem is to find the exact weight w from the given two weights w1 and w2 satisfying a general weight condition as w1 + w2 = 1 and 0 < w1 < w2 < 1. First, we propose a limited weight-decision algorithm where the function has another constraint: a weight is in for integer k. Second, by changing the phases in the last two Grover iterations, we propose a general weight-decision algorithm which is free from the above constraint. Finally, we show that when our algorithm requires O(k) queries to find w with a unit success probability, any classical algorithm requires at least Ω(k2) queries for a unit success probability. In addition, we show that our algorithm requires fewer queries to solve this problem compared with the quantum counting algorithm.