Phase-encoded measurement device independent quantum key distribution without a shared reference frame

In this paper, a phase-encoded measurement device independent quantum key distribution (MDI-QKD) protocol without a shared reference frame is presented, which can generate secure keys between two parties while the quantum channel or interferometer introduces an unknown and slowly time-varying phase. The corresponding secret key rate and single photons bit error rate is analysed, respectively, with single photons source (SPS) and weak coherent source (WCS), taking finite-key analysis into account. The numerical simulations show that the modified phase-encoded MDI-QKD protocol has apparent superiority both in maximal secure transmission distance and key generation rate while possessing the improved robustness and practical security in the high-speed case. Moreover, the rejection of the frame-calibrating part will intrinsically reduce the consumption of resources as well as the potential security flaws of practical MDI-QKD systems.     

Proposal for a new scheme for producing a two-photon,high dimensional hyperentangled state

We propose an experimentally feasible scheme for generating a two 2?×?4?×?4 dimensional photon hyperentangled state, entangled in polarization, frequency and spatial mode. This scheme is mainly based on a parametric down-conversion source and cross-Kerr nonlinearities, which avoids the complicated uncertain post-selection. Our method can be easily expanded to the production of hyperentangled states with more photons in multidimensions. Hence the expectation for vast quantities of information in quantum information processing will possibly come true. Finally, we put forward a realizable quantum key distribution (QKD) protocol based on the high dimensional hyperentangled state.     

Quantum Secure Direct Communication Protocol with Mutual Authentication Based on Single Photons and Bell States

Quantum secure direct communication (QSDC) can transmit secret messages directly from one user to another without first establishing a shared secret key, which is different from quantum key distribution. In this paper, we propose a novel quantum secure direct communication protocol based on signal photons and Bell states. Before the execution of the proposed protocol, two participants Alice and Bob exchange their corresponding identity IDA and IDB through quantum key distribution and keep them secret, respectively. Then the message sender, Alice, encodes each secret message bit into two single photons (| 01〉or|10〉) or a Bell state , and composes an ordered secret message sequence. To insure the security of communication, Alice also prepares the decoy photons and inserts them into secret message sequence on the basis of the values of IDA and IDB. By the secret identity IDA and IDB, both sides of the communication can check eavesdropping and identify each other. The proposed protocol not only completes secure direct communication, but also realizes the mutual authentication. The security analysis of the proposed protocol is presented in the paper. The analysis results show that this protocol is secure against some common attacks, and no secret message leaks even if the messages are broken. Compared with the two-way QSDC protocols, the presented protocol is a one-way quantum communication protocol which has the immunity to Trojan horse attack. Furthermore, our proposed protocol can be realized without quantum memory.     

Privacy-Preserving Decision Protocols Based on Quantum Oblivious Key Distribution

Oblivious key transfer (OKT) is a fundamental problem in the field of secure multi-party computation. It makes the provider send a secret key sequence to the user obliviously, i.e., the user may only get almost one bit key in the sequence which is unknown to the provider. Recently, a number of works have sought to establish the corresponding quantum oblivious key transfer model and rename it as quantum oblivious key distribution (QOKD) from the well-known expression of quantum key distribution (QKD). In this paper, a new QOKD model is firstly proposed for the provider and user with limited quantum capabilities, where both of them just perform computational basis measurement for single photons. Then we show that the privacy for both of them can be protected, since the probability of getting other’s raw-key bits without being detected is exponentially small. Furthermore, we give the solutions to some special decision problems such as set-member decision and point-inclusion by announcing the improved shifting strategies followed QOKD. Finally, the further discussions and applications of our ideas have been presented.     

Measurement device independent quantum key distribution assisted by hybrid qubit

Abstract

Measurement device independent Quantum Key Distribution (MDI-QKD), is immune to all attacks on detection and achieve immense improvement with respect to quantum key distribution system security. However, Bell state measurement (BSM), the kernel processing in MDI-QKD, can only identify two of the four Bell states, which limits the efficiency of the protocol. In this paper, a modified MDI-QKD with hybrid qubit is proposed to provide a major step towards answering this question. The hybrid qubits, which are composed of single photon qubit qubits and coherent qubit, are sent to the quantum relay to perform parallel BSMs synchronously and bit flip can be easily operated to complete the whole key distribution process. The secure key rate can be improved with our modified protocol owing to the higher success probability of BSM, which is increased by adding the parity check of coherent qubit. Furthermore, though our protocol requires photon number resolving detectors, the BSM of coherent state could be instead implemented using squeezed state which makes our scheme practical with state-of-the-art devices.     

Measurement-device-independent quantum key distribution: from idea towards application

We assess the overall performance of our quantum key distribution (QKD) system implementing the measurement-device-independent (MDI) protocol using components with varying capabilities such as different single-photon detectors and qubit preparation hardware. We experimentally show that superconducting nanowire single-photon detectors allow QKD over a channel featuring 60 dB loss, and QKD with more than 600 bits of secret key per second (not considering finite key effects) over a 16 dB loss channel. This corresponds to 300 and 80 km of standard telecommunication fiber, respectively. We also demonstrate that the integration of our QKD system into FPGA-based hardware (instead of state-of-the-art arbitrary waveform generators) does not impact on its performance. Our investigation allows us to acquire an improved understanding of the trade-offs between complexity, cost and system performance, which is required for future customization of MDI-QKD. Given that our system can be operated outside the laboratory over deployed fiber, we conclude that MDI-QKD is a promising approach to information-theoretic secure key distribution.     

Frequency shift attack on ‘plug-and-play’ quantum key distribution systems

Many imperfections in a practical quantum key distribution (QKD) system have been exploited by an eavesdropper (Eve) to attack the system. However, most of these attacks will introduce perturbations to the system while collecting information about the key. For example, the phase-remapping attack [Phys. Rev. A2007,75, 032314], in which Eve performs time shift on the signal pulse from the constant acting range of the phase modulation voltage to its rising edge to introduce an imperfection, results in an quantum bit error rate (QBER) of 14.6%, which is too high and will be discovered by careful users. In this paper, a frequency shift (FS) attack on ‘plug-and-play’ QKD systems with phase-coding BB84 protocol is proposed, in which Eve introduces an imperfection by the same method as she used in the phase-remapping attack. The most novel advantage of our FS attack is that Eve can get full information without introducing detectable QBER, which is more deceptive than the phase-remapping attack.     

Continuous-Variable Quantum Network Coding Based on Quantum Discord

Establishing entanglement is an essential task of quantum communication technology. Beyond entanglement, quantum discord, as a measure of quantum correlation, is a necessary prerequisite to the success of entanglement distribution. To realize efficient quantum communication based on quantum discord, in this paper, we consider the practical advantages of continuous variables and propose a feasible continuous-variable quantum network coding scheme based on quantum discord. By means of entanglement distribution by separable states, it can achieve quantum entanglement distribution from sources to targets in a butterfly network. Compared with the representative discrete-variable quantum network coding schemes, the proposed continuous-variable quantum network coding scheme has a higher probability of entanglement distribution and defends against eavesdropping and forgery attacks. Particularly, the deduced relationship indicates that the increase in entanglement is less than or equal to quantum discord.     

Quadrature operators with arbitrary phase and applications to phase-space distribution and quantum communication

Quadrature operators with arbitrary phase are studied from a point of view of the phase-space representation of quantum states, and the results are applied to simultaneous measurement and quantum communication. The Wigner function of arbitrary phase quadrature variables is introduced, which is a generalization of the usual Wigner function of position and momentum. The Kirkwood distribution is also extended for arbitrary phase quadrature variables. The simultaneous measurement of two quadrature operators is investigated using a beam splitter model and a generalized version of the Arthurs-Kelley model. The quantum teleportation of continuous variables is considered in terms of arbitrary phase quadrature variables. A general formula is derived that provides the quantum teleportation channel. The fidelity of the quantum teleportation with an uncontrollable phase is calculated for a coherent state. Furthermore, the mutual information of the quantum dense coding of continuous variables is obtained when classical information is encoded on arbitrary phase quadrature variables. The result is compared with that of the communication system, where information is transmitted using coherent and squeezed states.     

High Speed Quantum Key Distribution Over Optical Fiber Network System

The National Institute of Standards and Technology (NIST) has developed a number of complete fiber-based high-speed quantum key distribution (QKD) systems that includes an 850 nm QKD system for a local area network (LAN), a 1310 nm QKD system for a metropolitan area network (MAN), and a 3-node quantum network controlled by a network manager. This paper discusses the key techniques used to implement these systems, which include polarization recovery, noise reduction, frequency up-conversion detection based on a periodically polled lithium nitrate (PPLN) waveguide, custom high-speed data handling boards and quantum network management. Using our quantum network, a QKD secured video surveillance application has been demonstrated. Our intention is to show the feasibility and sophistication of QKD systems based on current technology.     

Alternative design for quantum cryptographic entangling probe

An alternative design is given for an optimized quantum cryptographic entangling probe for attacking the BB84 protocol of quantum key distribution. The initial state of the probe has a simpler analytical dependence on the set error rate to be induced by the probe than in the earlier design. The new device yields the same maximum information to the probe for a full range of induced error rates. As in the earlier design, the probe contains a single CNOT gate which produces the optimum entanglement between the BB84 signal states and the correlated probe states.     

Tailored bright illumination attack on distributed-phase-reference protocols

Detector control attacks on quantum key distribution systems exploit the linear mode of avalanche photodiode in single photon detectors. So far, the protocols under consideration have been the BB84 protocol and its derivatives. Here we present how bright tailored illumination exploiting the linear mode of detectors can be used to eavesdrop on distributed-phase-reference protocols, such as differential-phase-shift and coherent-one-way.     

Hyper-entangled states

Abstract

Entangled states are key ingredients to the new field of quantum information, including quantum dense coding, teleportation, and computation. However, only a relatively small class of entangled states has been investigated experimentally, or even discussed extensively. In particular, efforts to date have focused on two particles entangled in a single degree of freedom, for example polarization, or energy, or momentum direction. Novel phase-matching arrangements in spontaneous parametric down-conversion allow the preparation of pairs of photons that are simultaneously entangled in all of these. We shall call such a multiply-entangled state ?hyper-entangled‘. In addition, an even more general state–-a non-maximally entangled state–-should be realizable, in which the amplitudes of the contributing terms are not equal.     

背景光对星地量子密钥分配量子误码率的影响

量子误码率是量子密钥分配系统的重要参数之一.对于星地量子密钥分配,采用具有泊松分布的高度衰减激光脉冲作为单光子源,建立了由背景光引起的量子误码率理论模型,给出了量子误码率的表达式.针对轨道高度为300km的低轨卫星-地面站间链路,进行了数值仿真分析.研究表明,背景光是限制自由空间量子密钥分配链路距离的主要因素之一,在低轨卫星-地面站间进行量子密钥分配是可行的.在白天,量子误码率的量级为10-3～10-2;在夜晚,满月时为10-4,新月时为10-6～10-5.     

Quantum encoder and decoder for practical quantum key distribution using a planar lightwave circuit

To launch quantum key distribution (QKD) into the commercial market, it is important to develop a system that is simpler and more reliable using current technology. This report proposes quantum encoders and decoders using a passive planar lightwave circuit (PLC) that is useful for implementing optical-fiber-based QKD systems. Our encoders and decoders are based on an asymmetric Mach–Zehnder interferometer and allow us to prepare and analyze various photonic time-bin qubits reliably. The system can be stable and polarization-insensitive merely by stabilizing and controlling the device temperature. Our PLC-based devices enables us to simplify the QKD system and increase its reliability.     

An optimal photon counting polarimeter

We present the experimental results for a method used to perform polarimetry on ensembles of single photons. Our setup is based on a measurement method known to be optimal for estimating the state of two-level systems. The setup has no moving parts and is sensitive to weak sources (emitting single photons) of light as it relies on photon counting, and has potential applications in both classical polarization measurements and quantum communication scenarios. In our implementation, we are able to reconstruct the Stokes parameters of pure polarization states with an average fidelity of 99.9%.     

Asynchronous quantum key distribution on a relay network

We show how quantum key distribution on a multi-user, multi-path, network can be used to establish a key between any two end-users in an asynchronous fashion using the technique of bit-transport. By a suitable adaptation of our previous secret-sharing scheme we show that an attacker has to compromise all of the intermediate relays on the network in order to obtain the key. Thus, two end-users can establish a secret key provided they trust at least one of the network relays.     

Memory-assisted measurement device-independent quantum key distribution with parametric down-conversion sources

The memory-assisted measurement device-independent quantum key distribution (MDI-QKD), which requires less stringent conditions on the memory modules than that of quantum repeaters scheme, offers a practical mid-term solution to long-distance quantum key distribution. In this paper, considering the high cost and the high multi-photon probability, respectively, of single-photon source (SPS) and weak coherent source (WCS), we present schemes on implementing the parametric down-conversion sources, including the heralded single-photon source (HSPS) and single-photon-added coherent source (SPACS), in the memory-assisted MDI-QKD. By numerical simulations, we show that HSPS and SPACS scheme have apparent superiorities both in the key generation rate and the required minimal coherence time of quantum memory compared to WCS scheme. Moreover, we find that the robustness of SPACS against intensity fluctuations is better than WCS, but still worse than HSPS.     

Measurement-device-independent quantum key distribution with odd coherent state

Measurement-device-independent quantum key distribution (MDI-QKD) is immune to all the detection attacks, thus when it is combined with the decoy-state method, the final key rate can be obtained by estimating the gain and quantum bit error rate for various input photon numbers. In this paper, we propose to perform MDI-QKD with odd coherent state (OCS) and compare the results with weak coherent source scenario. Our simulation indicates that both the secure key rate and transmission distance can be improved evidently with OCS owing to the lower probability of multi-photon events of the OCS. Furthermore, we apply the finite key analysis to the decoy-state MDI-QKD with OCS and obtain a practical key rate.