High efficient scheme for remote state preparation with cavity QED

In this paper, a scheme is proposed for remote state preparation （RSP） with cavity quantum electrodynamics （QED）. In our scheme, two observers share two-atom nonmaximally entangled state as quantum channels and can realize remote preparation of state of an atom. We also propose a generalization for remote preparation of N-atom entangled state by （N＋1）-atom GHZ-like state （N ≥ 2）. By this scheme, one single-atom projective measurement is enough for the RSP of a qubit or N-atom entangled state, and the probability of success for RSP is unity. Furthermore, we have considered the case where observers use W-like state as quantum channels to realize RSP of a qubit. We compare our scheme with existing ones.     

Probabilistic Multiparty Joint Remote Preparation of an Arbitrary m-Qubit State with a Pure Entangled Channel Against Collective Noise

We present a scheme for multiparty joint remote preparation of an arbitrary m-qubit state with a multiparticle entangled quantum channel against collective noise. All the senders share the information of the prepared state and perform corresponding measurement according to their knowledge of the prepared state, the receiver can reconstruct the original state by performing corresponding unitary operation on his particles if he cooperates with all the senders. Moreover, the agents use decoherence-free subspace to tolerate the collective noise. This scheme has the advantage of having high success probability for multiparty joint remote preparation of an arbitrary m-qubit state via pure entangled states.     

噪声环境下基于两体纠缠态的远程态制备

本文研究了量子噪声对分别以Einstein-Podolsky-Rosen （EPR）态和两体部分纠缠态作为量子信道来远程制备单比特态的量子过程的影响. 通过求解Lindblad形式的主方程,得到量子信道随时间的演化,采用迹距离来度量不同噪声情况下输出态与初态的接近程度. 研究表明,作用在z方向的噪声对远程态制备的影响最弱,而同时作用在x,y,z方向的噪声对远程态制备的影响最强. 关键词： 远程态制备 迹距离 纠缠态 噪声信道     

Deterministic remote state preparation of arbitrary three-qubit state through noisy cluster-GHZ channel

We propose a novel scheme for remote state preparation of an arbitrary three-qubit state with unit success probability, utilizing a nine-qubit cluster-GHZ state without introducing auxiliary qubits. Furthermore, we proceed to investigate the effects of different quantum noises (e.g., amplitude-damping, phase-damping, bit-flip and phase-flip noises) on the systems. The fidelity results of three-qubit target state are presented, which are usually used to illustrate how close the output state is to the target state. To compare the different effects between the four common types of quantum noises, the fidelities under one specific identical target state are also calculated and discussed. It is found that the fidelity of the phase-flip noisy channel drops the fastest through the four types of noisy channels, while the fidelity is found to always maintain at 1 in bit-flip noisy channel.     

Scheme for Probabilistic Remotely Preparing a d-Dimensional Equatorial Quantum State

We present a scheme for probabilistic remote preparation of a d-dimensional equatorial quantum state. In the scheme, a bipartite d-dimensional partial entangled state is used as the quantum channel, and the single-qudit projective measurement and appropriate unitary transformation are needed. As a special, the remote preparation in three dimension is studied. The project supported Natural Science Foundation of Education Bureau of Jiangsu Province of China (Grant No 05 KJD 140035 and 06 KJD 520027).     

Some Quantum States Prepared with Polynomial Quantum Circuit

The quantum state preparation involved in quantum information processing greatly depends on the quantum computer models. In this paper we give a novel scheme for some quantum states preparation without any decomposition of global quantum gates. Our circuit reduces the exponential CNOT gates to polynomial of qubit numbers, i.e., n(n?1)/2 without requirements of quantum register. And the depth is changed from the currently known exponential circuits to n blocks, or polynomial for its detailed implementation. This method is also useful for multi-level quantum systems and expected to help in designing and building large-scale quantum applications using present physical technologies.     

Remote preparation of a two-particle state using a four-qubit cluster state

We present a scheme of remote preparation of two-particle states using a particular four-qubit cluster state as the quantum channel. The probability of success regarding this preparation scheme is calculated in both general and some particular cases. Our results show that in general such remote state preparation can be realized with a probability of 1/4. But in several special cases, the probability of success can be improved to 1/2 or even 1.     

Analysis of Control Power in Controlled Remote State Preparation Schemes

We quantify and analyze the controller’s power in controlled remote state preparation schemes. Our analysis provides a lower bound on the control power required for controlled remote preparation of arbitrary D-dimensional states. We evaluate several existing controlled remote state preparation protocols and show that some proposed non-maximally entangled channels are not suitable for perfect controlled remote preparation of arbitrary quantum states from the controller’s point of view. We find that for remotely preparing D-dimensional states, the entropy of each controller should be no less than log2D bits. Our new criteria are not only useful for evaluating controlled remote state preparation schemes but can also be used for other controlled quantum communication schemes.     

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.     

Deterministic Joint Remote Preparation of a Four-Qubit Cluster-Type State via GHZ States

A scheme for the deterministic joint remote preparation of a four-qubit cluster-type state using only two Greenberger-Horne-Zeilinger (GHZ) states as quantum channels is presented. In this scheme, the first sender performs a two-qubit projective measurement according to the real coefficient of the desired state. Then, the other sender utilizes the measurement result and the complex coefficient to perform another projective measurement. To obtain the desired state, the receiver applies appropriate unitary operations to his/her own two qubits and two CNOT operations to the two ancillary ones. Most interestingly, our scheme can achieve unit success probability, i.e., P _{s u c} =1. Furthermore, comparison reveals that the efficiency is higher than that of most other analogous schemes.     

Joint Remote Preparation of a Multipartite GHZ-class State

For two parties sharing the original state, a scheme for remote preparation of the two-particle entangled state by three partial two-particle entangled states as the quantum channel is presented, and then directly generalize the scheme for remotely preparing a multipartite GHZ-class state for M senders. It is shown that the receiver can obtain the unknown state with certain probability under the condition that only and only if all the senders collaborate with each other. The N-particle projective measurement and the von Neumann measurement are needed in our scheme. The probability of the successful remote state preparation and classical communication cost are calculated.     

Controlled Joint Remote State Preparation of an Arbitrary Equatorial Two-Qubit State

We propose a scheme for controlled joint remote state preparation of an arbitrary equatorial two-qubit state by using a seven-qubit entangled state as the quantum channel. In this scheme, two senders wish to help a receiver to remotely prepare an arbitrary equatorial two-qubit state, and the receiver can obtain the original quantum state with 100% success probability by performing the appropriate unitary operations.

     

Quantum limit for the atom-light interferometer

The standard quantum limit is calculated for the atom-light interferometer. It is shown that the smallest detectable phase is $$\delta \phi _{\min } = \frac{1}{2}[N_{atoms} + 4N_{photons} )/N_{atoms} N_{photons} ]^{1/2} .$$ Therefore, in practical experiments, the accuracy is limited by the square root of the number of atoms. We propose a novel correlated atom-photon state interferometer which makes a transition to the Heisenberg limit, δφ_min ∝ 1/N _atoms, as the atoms approach a Bose condensate. Such an interferometer may serve as a sensitive probe of the onset of Bose condensation. Finally, we point out that the correlated atom-photon state preparation scheme we propose may be used in a different way to approach the Heisenberg limit for non-Bose-condensed atoms.     

Unitary state preparation,local position measurements,and spin in quantum mechanics

The orthodox presentation of quantum theory often includes statements on state preparation and measurements without mentioning how these processes can be achieved. The often quoted projection postulate is regarded by many as problematical. This paper presents a systematic framework for state preparation and measurement. Within the existing Hilbert space formulation of quantum mechanics for spinless particles we show that it is possible (1)to prepare an arbitrary state and (2)to reduce all quantum measurements to local position measurements in an asymptotic way by unitary evolution processes without recourse to the projection postulate. A generalization to spin-1/2particles is also given. The theory presented provides a general mathematical and theoretical foundation for many practical schemes for state preparation and measurement.     

Bidirectional Controlled Remote State Preparation of an Arbitrary Two-Qubit State

We propose a scheme of bidirectional controlled remote state preparation of an arbitrary two-qubit state, where a nine-qubit entangled state is used as the quantum channel. In our scheme, Alice and Bob can prepare simultaneously an arbitrary two-qubit state for each other’s place with the help of the controller Charlie. The total success probability for our scheme reaches 100%. PACS numbers 03.67.Hk, 03.65.Ud, 42.50.Dv.

     

Remotely and Conclusively Mapping One Finite Set of Qudit States onto Another Assisted by Qubit Entanglements

Alice and Bob are two remote parties. We propose a probabilistic method which allows Alice to map remotely and conclusively Bob’s set of nonorthogonal symmetric d-level quantum states onto another. The procedure we use is a remote positive operator valued measurement (POVM) in Bob’s (2d-1)-level direct sum space. We construct a quantum network for implementing this (2d-1)-level remote nonunitary POVM with (d-1) two-level remote unitary rotations. The fact that the two-level remote rotation, which is hired to rotate remotely a basis vector, can been implementing rapidly using only one ebit (a two-level Einstein-Podolsky-Rosen (EPR) pair) and one cbit (classical communication) is notable. This scheme is simpler but with less resource, which will make it more feasible and suitable for large-scale quantum network.     

Remote preparation of a class of three-qubit states

We propose a remote state preparation (RSP) scheme of a three-particle Greenberger-Horne-Zeilinger (GHZ) class state by using three 2-qubit maximally entangled states as the quantum channel. The success probability of preparation and classical communication cost are calculated. Generally speaking, conditioned on Alice’s classical message, with probability 1/4 Bob can successfully prepare the original state by performing one appropriate unitary operation. However, for four kinds of special states, the success probability of preparation can be increased to 1/2 or even 1 after consuming some extra bits.     

Deterministic joint remote preparation of an arbitrary two-qubit state in the presence of noise

Using two tripartite Greenberger-Horne-Zeilinger （GHZ） states as the shared channels, we investigate the noise effects on the deterministic joint remote preparation of an arbitrary two-qubit state. By unitary matrix decomposition procedure, we first construct the quantum logic circuit of the deterministic joint remote state preparation protocol. Then, we analytically derive the fidelity and the average fidelity for the deterministic joint remote preparation of an arbitrary two- qubit state and of four types of special two-qubit states under the influence of the Pauli noises. It is found that the fidelity depends on the noise types, the qubit-environment coupling strength, and the state to be remotely prepared. Moreover, even if the two GHZ channels are subject to the same environmental noises, the average fidelities for remotely preparing different two-qubit states display different time evolution behaviors. The remote preparation of the identical two-qubit states also shows that the average fidelities affected by different noisy environments exhibit different evolution actions.     

Controlled Remote State Preparation of an Arbitrary Two-Qubit State by Using Two Sets of Four-Qubit GHZ States

Recently, Huang and Zhao (Int. J. Theor. Phys. 56, 678, 2017) proposed a new scheme for controlled remote state preparation of an arbitrary two-qubit state by using two sets of three-qubit GHZ states as the quantum channel. In the scheme, Alice and Bob choose four different kinds of two-qubit projective measurement bases to measure their local qubits, respectively. We demonstrate that two sets of four-qubit GHZ states can be used to realize the deterministic controlled remote state preparation of an arbitrary two-qubit state by performing only two-qubit projective measurements.     

Remote state preparation of a photonic quantum state via quantum teleportation

We demonstrate an experimental realization of remote state preparation via the quantum teleportation algorithm, using an entangled photon pair in the polarization degree of freedom as the quantum resource. The input state is encoded on the path of one of the photons from the pair. The improved experimental scheme allows us to control the preparation and teleportation of a state over the entire Bloch sphere with a resolution of the degree of mixture given by the coherence length of the photon pair. Both the preparation of the input state and the implementation of the quantum gates are performed in a pair of chained displaced Sagnac interferometers, which contribute to the overall robustness of the setup. An average fidelity above 0.9 is obtained for the remote state preparation process. This scheme allows for a prepared state to be transmitted on every repetition of the experiment, thus giving an intrinsic success probability of 1.