Quantum communication and entanglement between two distant atoms via vacuum fields

This paper proposes an efficient scheme for quantum communication between two atoms trapped in distant cavities which are connected by an optical fibre. During the operation, all the atomic system, the cavity modes and the fibre are not excited. The quantum state is mediated by the vacuum fields. The idea can be used to realize quantum entanglement between two distant atoms via vacuum.

Hierarchical simultaneous entanglement swapping for multi-hop quantum communication based on multi-particle entangled states

Entanglement swapping is a key technology for multi-hop communication based on entanglement in quantum networks. However, the end-to-end delay of the traditional sequential entanglement swapping (SEQES) grows rapidly withthe increase of network scale. To solve this problem, we first propose a low-delay multi-particle simultaneous entanglementswapping (SES) scheme to establish the remote four-particle Greenberger–Horne–Zeilinger (GHZ) channel states for thebidirectional teleportation of three-particle GHZ states, in which the intermediate nodes perform Bell state measurements,send the measurement results and the Bell state type to the user node Bob (or Alice) through classical channel simultaneously. Bob (or Alice) only needs to carry out a proper unitary operation according to the information he (or she) hasreceived. Further, we put forward a hierarchical simultaneous entanglement swapping (HSES) scheme to reduce the classical information transmission cost, which is composed of level-1 SES and level-2 SES (schemes). The former is an innersegment SES, and the latter is an inter segments SES. Theoretical analysis and simulation results show the HSES can obtainthe optimal performance tradeoff between end-to-end delay and classical cost.

Two-Way Cooperative Quantum Communication with Partial Entanglement Analysis

In this paper, we describe an improved cooperative two-way quantum communication scheme that works in a forward-and-backward fashion. In this scheme, partial entanglement analysis based on five-qubit entangled Brown state allows for the simultaneous exchange of arbitrary unknown states between Alice and Bob （with the help of trusted Charlie）. Security is guaranteed because opposing unknown states are transmitted by performing the suitable recovery operations in a deterministic way or, in the case of irregularities, no results are generated. The current two-way quantum communication scheme can also be extended to transmit arbitrary unknown states. This is done in a probabilistic way by using two-way quantum teleportation based on the generalized Brown-like state.

Design and Implementation of Quantum Repeaters:Insights on Quantum Entanglement Purification

Quantum communication is a groundbreaking technology that is driving the future of information transmission and communication technologies to a new paradigm.It relies on quantum entanglement to facilitate the transmission of quantum states between parties.Quantum repeaters are crucial for facilitating long-distance quantum communication.These quantum devices act as intermediaries between adjacent communication channel segments within a fragmented quantum network,allowing for entanglement swapping between the channel segments.This entanglement swapping process establishes entanglement links between the endpoints of adjacent segments,gradually creating a continuous entanglement connection over the entire length of the transmission channel.The established quantum link can be utilized for secure and efficient quantum communication between distant sender and receiver nodes.This study focuses on quantum entanglement purification,a protocol aimed at maintaining high fidelity entangled states above the operational threshold of the communication channel.This study investigates the optimal stage for executing the purification protocol and applies optimization schemes to evaluate various purification protocols.We use IBM Qiskit for circuit implementation and simulation.The results offer valuable insights into future approaches to implementing practical quantum repeaters and shed light on existing and anticipated challenges.

An efficient deterministic secure quantum communication scheme based on cluster states and identity authentication

A novel efficient deterministic secure quantum communication scheme based on four-qubit cluster states and single-photon identity authentication is proposed. In this scheme, the two authenticated users can transmit two bits of classical information per cluster state, and its efficiency of the quantum communication is 1/3, which is approximately 1.67 times that of the previous protocol presented by Wang et al [Chin. Phys. Lett. 23 （2006） 2658]. Security analysis shows the present scheme is secure against intercept-resend attack and the impersonator＇s attack. Furthermore, it is more economic with present-day techniques and easily processed by a one-way quantum computer.

Controlled mutual quantum entity authentication using entanglement swapping

In this paper, we suggest a controlled mutual quantum entity authentication protocol by which two users mutually certify each other on a quantum network using a sequence of Greenberger–Horne–Zeilinger（GHZ）-like states. Unlike existing unidirectional quantum entity authentication, our protocol enables mutual quantum entity authentication utilizing entanglement swapping; moreover, it allows the managing trusted center（TC） or trusted third party（TTP） to effectively control the certification of two users using the nature of the GHZ-like state. We will also analyze the security of the protocol and quantum channel.

Quantum Entanglement and Cryptography for Automation and Control of Dynamic Systems

This paper addresses the application of quantum entanglement and cryptography for automation and control of dynamic systems.A dynamic system is a system where the rates of changes of its state variables are not negligible.Quantum entanglement is realized by the Spontaneous Parametric Down-conversion process.Two entangled autonomous systems exhibit correlated behavior without any classical communication in between them due to the quantum entanglement phenomenon.Specifically,the behavior of a system,Bob,at a distance,is correlated with a corresponding system,Alice.In an automation scenario,the"Bob Robot"is entangled with the"Alice Robot"in performing autonomous tasks without any classical connection between them.Quantum cryptography is a capability that allows guaranteed security.Such capabilities can be implemented in control of autonomous mechanical systems where,for instance,an"Alice Autonomous System"can control a"Bob Autonomous System"for applications of automation and robotics.The applications of quantum technologies to mechanical systems,at a scale larger than the atomistic scale,for control and automation,is a novel contribution of this paper.Notably,the feedback control transfer function of an integrated classical dynamic system and a quantum state is proposed.

Quantum Secure Direct Intercommunication with Superdense Coding and Entanglement Swapping

A quantum secure direct intercommunication scheme is proposed to exchange directly the communicators'secret messages by making use of swapping entanglement of Bell states.It has great capacity to distribute the secretmessages since these messages have been imposed on high-dimensional Bell states via the local unitary operations withsuperdense coding.The security is ensured by the secure transmission of the travel sequences and the application ofentanglement swapping.

Quantum frequency doubling based on tripartite entanglement with cavities

We analyze the entanglement characteristics of three harmonic modes, which are the output fields from three cav- ities with an input tripartite entangled state at fundamental frequency. The entanglement properties of the input beams can be maintained after their frequencies have been up-converted by the process of second harmonic generation. We have calculated the parametric dependences of the correlation spectrum on the initial squeezing factor, the pump power, the trans- naission coefficient, and the normalized analysis frequency of cavity. The numerical results provide references to choose proper experimental parameters for designing the experiment. The frequency conversion of the multipartite entangled state can also be applied to a quantum communication network.

Probabilistic direct counterfactual quantum communication

It is striking that the quantum Zeno effect can be used to launch a direct counterfactual communication between two spatially separated parties, Alice and Bob. So far, existing protocols of this type only provide a deterministic counterfactual communication service. However, this counterfactuality should be payed at a price. Firstly, the transmission time is much longer than a classical transmission costs. Secondly, the chained-cycle structure makes them more sensitive to channel noises. Here, we extend the idea of counterfactual communication, and present a probabilistic-counterfactual quantum communication protocol, which is proved to have advantages over the deterministic ones. Moreover, the presented protocol could evolve to a deterministic one solely by adjusting the parameters of the beam splitters.

A Review of Quantum Cryptography Communication for Wireless Networks

We analyze the development of quantum cryptography communication,including analyze the problems lie in the existent literatures and give the resolve methods according to these problems.Then discuss the quantum cryptography communication for wireless networks and also point out the shortcoming of current research and the future of quantum wireless networks.

Distributed wireless quantum communication networks with partially entangled pairs

Wireless quantum communication networks transfer quantum state by teleportation. Existing research focuses on maximal entangled pairs. In this paper, we analyse the distributed wireless quantum communication networks with partially entangled pairs. A quantum routing scheme with multi-hop teleportation is proposed. With the proposed scheme, is not necessary for the quantum path to be consistent with the classical path. The quantum path and its associated classical path are established in a distributed way. Direct multi-hop teleportation is conducted on the selected path to transfer a quantum state from the source to the destination. Based on the feature of multi-hop teleportation using partially entangled pairs, if the node number of the quantum path is even, the destination node will add another teleportation at itself. We simulated the performance of distributed wireless quantum communication networks with a partially entangled state. The probability of transferring the quantum state successfully is statistically analyzed. Our work shows that multi-hop teleportation on distributed wireless quantum networks with partially entangled pairs is feasible,

Faithful quantum entanglement sharing based on linear optics with additional qubits

This paper presents a scheme for faithfully distributing a pure entanglement between two parties over an arbitrary collective-noise channel with linear optics. The transmission is assisted by an additional qubit against collective noise. The receiver can take advantage of the time discrimination and the measurement results of the assistant qubit to reconstruct a pure entanglement with the sender. Although the scheme succeeds probabilistically, the resource used to get a pure entanglement state is finite, and so is easier to establish entanglement in practice than quantum entanglement purification.

Efficient entanglement purification in quantum repeaters

We present an efficient entanglement purification protocol （EPP） with controlled-not （CNOT） gates and linear optics. With the CNOT gates, our EPP can reach a higher fidelity than the conventional one. Moreover, it does not require the fidelity of the initial mixed state to satisfy 1 2. If the initial state is not entangled, it still can be purified. With the linear optics, this protocol can get pure maximally entangled pairs with some probabilities. Meanwhile, it can be used to purify the entanglement between the atomic ensembles in distant locations. This protocol may be useful in long-distance quantum communication.

Purification in entanglement distribution with deep quantum neural network

Entanglement distribution is important in quantum communication. Since there is no information with value in this process, purification is a good choice to solve channel noise. In this paper, we simulate the purification circuit under true environment on Cirq, which is a noisy intermediate-scale quantum(NISQ) platform. Besides, we apply quantum neural network(QNN) to the state after purification. We find that combining purification and quantum neural network has good robustness towards quantum noise. After general purification, quantum neural network can improve fidelity significantly without consuming extra states. It also helps to obtain the advantage of entangled states with higher dimension under amplitude damping noise. Thus, the combination can bring further benefits to purification in entanglement distribution.

Quantum communication for satellite-to-ground networks with partially entangled states

To realize practical wide-area quantum communication,a satellite-to-ground network with partially entangled states is developed in this paper.For efficiency and security reasons,the existing method of quantum communication in distributed wireless quantum networks with partially entangled states cannot be applied directly to the proposed quantum network.Based on this point,an efficient and secure quantum communication scheme with partially entangled states is presented.In our scheme,the source node performs teleportation only after an end-to-end entangled state has been established by entanglement swapping with partially entangled states.Thus,the security of quantum communication is guaranteed.The destination node recovers the transmitted quantum bit with the help of an auxiliary quantum bit and specially defined unitary matrices.Detailed calculations and simulation analyses show that the probability of successfully transferring a quantum bit in the presented scheme is high.In addition,the auxiliary quantum bit provides a heralded mechanism for successful communication.Based on the critical components that are presented in this article an efficient,secure,and practical wide-area quantum communication can be achieved.

Quantum dual signature scheme based on coherent states with entanglement swapping

A novel quantum dual signature scheme, which combines two signed messages expected to be sent to two diverse receivers Bob and Charlie, is designed by applying entanglement swapping with coherent states. The signatory Alice signs two different messages with unitary operations（corresponding to the secret keys） and applies entanglement swapping to generate a quantum dual signature. The dual signature is firstly sent to the verifier Bob who extracts and verifies the signature of one message and transmits the rest of the dual signature to the verifier Charlie who verifies the signature of the other message. The transmission of the dual signature is realized with quantum teleportation of coherent states. The analysis shows that the security of secret keys and the security criteria of the signature protocol can be greatly guaranteed.An extensional multi-party quantum dual signature scheme which considers the case with more than three participants is also proposed in this paper and this scheme can remain secure. The proposed schemes are completely suited for the quantum communication network including multiple participants and can be applied to the e-commerce system which requires a secure payment among the customer, business and bank.

Self-error-rejecting multipartite entanglement purification for electron systems assisted by quantum-dot spins in optical microcavities

We present a self-error-rejecting multipartite entanglement purification protocol(MEPP)for N-electron-spin entangled states,resorting to the single-side cavity-spin-coupling system.Our MEPP has a high efficiency containing two steps.One is to obtain high-fidelity N-electron-spin entangled systems with error-heralded parity-check devices(PCDs)in the same parity-mode outcome of three electron-spin pairs,as well as M-electron-spin entangled subsystems(2≤M<N)in the different parity-mode outcomes of those.The other is to regain the N-electron-spin entangled systems from Melectron-spin entangled states utilizing entanglement link.Moreover,the quantum circuits of PCDs make our MEPP works faithfully,due to the practical photon-scattering deviations from the finite side leakage of the microcavity,and the limited coupling between a quantum dot and a cavity mode,converted into a failed detection in a heralded way.

An arbitrated quantum signature scheme based on entanglement swapping with signer anonymity

In this paper an arbitrated quantum signature scheme based on entanglement swapping is proposed. In this scheme a message to be signed is coded with unitary operators. Combining quantum measurement with quantum encryption, the signer can generate the signature for a given message. Combining the entangled states generated by the TTP＇s Bell measurement with the signature information, the verifier can verify the authentication of a signature through a single quantum state measurement. Compared with previous schemes, our scheme is more efficient and less complex, furthermore, our scheme can ensure the anonymity of the signer.

A Simple Security Proof for Entanglement-Based Quantum Key Distribution

Quantum cryptography exploits the quantum mechanical properties of communication lines to enhance the security of the so-called key distribution. In this work, we explain the role played by quantum mechanics in cryptographic tasks and also investigate how secure is quantum cryptography. More importantly, we show by a simple security proof that for any state sent by the sender, the eavesdropper can only guess the output state with a probability that will allow her not to learn more than half of the classical Shannon information shared between the legitimate parties. This implies that with high probability, the shared key is secure.