20 Mbps wireless communication demonstration using terahertz quantum devices

A wireless terahertz(THz) communication link is demonstrated, in which a THz quantum cascade laser and a THz quantum-well photo-detector(QWP) serve as the emitter and receiver, respectively. With the help of the well-matched THz QWP, the optical collection efficiency has greatly been improved. A data signal transmitted over 2.2 m with a low bit error rate(≤1 × 10-8) and data rate as high as 20 Mbps is achieved, which are almost 1order of magnitude higher than that previously reported.     

Controlled quantum secure direct communication using a non-symmetric quantum channel with quantum superdense coding

We present a controlled quantum secure direct communication protocol that uses a 2-dimensional Greenberger–Horne–Zeilinger (GHZ) entangled state and a 3-dimensional Bell-basis state and employs the high-dimensional quantum superdense coding, local collective unitary operations and entanglement swapping. The proposed protocol is secure and of high source capacity. It can effectively protect the communication against a destroying-travel-qubit-type attack. With this protocol, the information transmission is greatly increased. This protocol can also be modified, so that it can be used in a multi-party control system.     

Distributed wireless quantum communication networks

The distributed wireless quantum communication network （DWQCN） ha~ a distributed network topology and trans- mits information by quantum states. In this paper, we present the concept of the DWQCN and propose a system scheme to transfer quantum states in the DWQCN. The system scheme for transmitting information between any two nodes in the DWQCN includes a routing protocol and a scheme for transferring quantum states. The routing protocol is on-demand and the routing metric is selected based on the number of entangled particle pairs. After setting up a route, quantum tele- portation and entanglement swapping are used for transferring quantum states. Entanglement swapping is achieved along with the process of routing set up and the acknowledgment packet transmission. The measurement results of each entan- glement swapping are piggybacked with route reply packets or acknowledgment packets. After entanglement swapping, a direct quantum link between source and destination is set up and quantum states are transferred by quantum teleportation. Adopting this scheme, the measurement results of entanglement swapping do not need to be transmitted specially, which decreases the wireless transmission cost and transmission delay.     

Optical design for an LED-based handheld underwater wireless optical communication system

We propose an LED reshaping lens design for a handheld underwater wireless optical system to solve the problem of targeting the receiver. The simulation results shows that the designed lens can achieve 0.91 light intensity uniformity and 91.39% optical efficiency in hemisphere space, even with the actual LED model. After fabrication with computer numeric control, the work demonstrates the design to be effective.     

Dense coding using cluster states and its application on deterministic secure quantum communication

This work proposes a dense coding using four-particle cluster states. Based on the dense coding, an efficient deterministic secure quantum communication (DSQC) is devised. The quantum bit efficiency of the proposed DSQC is better than the other DSQCs also using four-particle cluster states.     

Cryptographic robustness of a quantum cryptography system using phase-time coding

A cryptographic analysis is presented of a new quantum key distribution protocol using phase-time coding. An upper bound is obtained for the error rate that guarantees secure key distribution. It is shown that the maximum tolerable error rate for this protocol depends on the counting rate in the control time slot. When no counts are detected in the control time slot, the protocol guarantees secure key distribution if the bit error rate in the sifted key does not exceed 50%. This protocol partially discriminates between errors due to system defects (e.g., imbalance of a fiber-optic interferometer) and eavesdropping. In the absence of eavesdropping, the counts detected in the control time slot are not caused by interferometer imbalance, which reduces the requirements for interferometer stability.     

Real-time coding in a parallel quantum communication channel

Coding theorems formulated as exchange protocols in the space of states of quantum systems do not answer one of the basic questions of real-time information transmission rate. Expressions obtained for the transmission capacity of a binary quantum communication channel describe the real-time information transmission rate.     

Two-step quantum secure direct communication scheme with frequency coding

Quantum secure direct communication(QSDC) is an important branch of quantum cryptography. It can transmit secret information directly without establishing a key first, unlike quantum key distribution which requires this precursory event. Here we propose a QSDC scheme by applying the frequency coding technique to the two-step QSDC protocol, which enables the two-step QSDC protocol to work in a noisy environment. We have numerically simulated the performance of the protocol in a noisy channel, and the results show that the scheme is indeed robust against channel noise and loss. We also give an estimate of the channel noise upper bound.     

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.     

基于量子远程传态的无线自组织量子通信网络路由协议

针对复杂结构的无线量子通信网络,提出了无线自组织量子通信网络概念并设计其路由协议．该路由协议为按需路由协议,路由度量基于相邻节点问的纠缠粒子对数目．需要发送携带信息的量子态的节点发起路由请求和建立过程,由目的节点根据路由度量选择路径．目的节点选择路径后,沿所选路径发送路由应答信息至源节点并通知路径中其他节点．信息传输过程中,若所选路径中相邻节点问无线信道或者量子信道中断,将重新发起一个路由发现过程．建立新路由．路径中节点收到路由应答信息后,利用纠缠交换和两端逼近方法,从路径两端向中间节点方向进行纠缠交换,建立量子信道后,通过量子远程传态传输携带信息的量子态,从而实现无线自组织量子通信网络中任意两节点问信息的传递．     

Optical bistability using quantum coherence in a microwave-driven four-level atomic system

The behavior of the optical bistability (OB) is investigated in an optical system which consists of a four-level atomic system with a microwave drive field and an optical cavity. It is found that the optical bistability can be accomplished by adjusting different physical parameters in both steady and transient process. Due to the existence of the microwave drive field, the optical bistability can be also obtained even under weak coherent coupling field condition. Since the intensity and phase of microwave drive field can be conveniently modulated, this optical system provides a new experimental method to test the optical bistability theory.     

Optical quantum computation using cluster States

We propose an approach to optical quantum computation in which a deterministic entangling quantum gate may be performed using, on average, a few hundred coherently interacting optical elements (beam splitters, phase shifters, single photon sources, and photodetectors with feedforward). This scheme combines ideas from the optical quantum computing proposal of Knill, Laflamme, and Milburn [Nature (London) 409, 46 (2001)]], and the abstract cluster-state model of quantum computation proposed by Raussendorf and Briegel [Phys. Rev. Lett. 86, 5188 (2001)]].     

Optical smart card using semipassive communication

An optical secure short-range communication system is presented. The mobile unit (optical smart card) of this system utilizes a retroreflector with an optical modulator, using light from the stationary unit; this mobile unit has very low power consumption and can be as small as a credit card. Such optical smart cards offer better security than RF-based solutions, yet do not require physical contact. Results from a feasibility study model are included.     

Efficient long-distance quantum communication using microtoroidal resonators

Based on the interaction between a three-level system and a microtoroidal resonator, we present a scheme for long-distance quantum communication in which entanglement generation with near 0.5 success probability and swaps can be implemented by accurate state detection via measuring about 100 photons. With this scheme the average time of successful entanglement distribution over 2500 km with high fidelity can be decreased to only about 30 ms.     

基于4F系统光学逻辑编码的实验

设计了用4F系统进行光学逻辑编码的方法.根据4F系统的工作原理,通过分析光栅衍射屏横向位移量与衍射光相位改变量之间的关系,约定两衍射级光强相加时为“1”,两衍射级光强相消时为“0”的光学逻辑编码规则.实验结果表明:输出信号线性好,符合编码要求.     

Optical wireless sensor networks using tunable optical filters

A novel decision gathering scheme for optical wireless sensor networks (OWSNs) is proposed and thoroughly analyzed in this article. The proposed technique relies on a tunable optical filter (TOF) that is mounted on each sensor node. Specifically, the received laser signal from a central unit at any particular node is modulated through the TOF, where it is either rejected or passed in accordance to the sensed result. The output of the TOF is passed to a corner cube reflector (CCR) that reflects the optical signal either back to the central unit or to another node in the OWSN. Three different setups are considered to implement the proposed scheme and the pros and cons of each setup are thoroughly discussed. It is revealed that the energy requirement of each sensor node is minimized as energy is only consumed in the process of sensing and adjusting the TOF. The performance of the proposed scheme is analyzed through a mathematical framework to derive the average decision error rate (DER) for all setups. Moreover, simulation results analyze the impact of key system parameters including atmospheric turbulence, transmit power, link distance, filter efficiency and detection threshold.     

基于光前置放大器的量子密钥分发融合经典通信方案

量子密钥分发融合经典通信方案将连续变量量子密钥分发和经典通信合并到了一起,为将来在现有的光网络上同时进行密钥分发和经典通信提供了一个有效的方法.然而,在量子信号上叠加一个经典信号将会给连续变量量子密钥分发系统引入过噪声从而大大降低系统的性能.本文提出基于光前置放大器的量子密钥分发融合经典通信方案,即在接收端插入光前置放...     

Deterministic quantum communication using the symmetric W state

This study proposes a new coding function for the symmetric W state.Based on the new coding function,a theoretical protocol of deterministic quantum communication(DQC) is proposed.The sender can use the proposed coding function to encode his/her message,and the receiver can perform the imperfect Bell measurement to obtain the sender’s message.In comparison to the existing DQC protocols that also use the W class state,the proposed protocol is more efcient and also more practical within today’s technology.Moreover,the security of this protocol is analyzed to show that any eavesdropper will be detected with a very high probability under both the ideal and the noisy quantum channel.     

Ultra-broadband indoor optical wireless communication system with multimode fiber

In this paper we experimentally demonstrate an ultra-broadband indoor full-duplex WDM optical wireless communication system with multimode fiber. The multimode fiber is used because it is employed in most of the already installed in-building fiber distribution networks. Simultaneous error-free (BER<10(-9)) transmission of 4×12.5 Gbps downlink and 800 Mbps uplink has been successfully demonstrated. The experimental results show that, although the use of multimode fiber will induce ~2.4 cm reduction in the maximum error-free beam footprint in the downlink, the bit rate of the uplink can be much higher compared to the system with single-mode fiber.