We present a quantum secure direct communication protocol where the channels are not maximally entangled states. The communication parties utilize decoy photons to check eavesdropping. After ensuring the security of the quantum channel, the sender encodes the secret message and transmits it to the receiver by using Controlled-NOT operation and von Neumann measurement. The protocol is simple and realizable with present technology. We also show the protocol is secure for noisy quantum channel.
Random generation and confidential distribution of cryptographic keys are fundamental building blocks of secure communication. Using quantum states in which the transmitted quantum bit is entangled with a stationary memory quantum bit allows the secure generation and distribution of keys to be based on fundamental properties of quantum mechanics. At the same time, the reach of secure communication networks can be enhanced, in particular, since this architecture would be compatible with quantum repeaters which are an integral part for scaling quantum networks. Here, we realize a true single-pho…
A comparative study of protocols for secure quantum communication under noisy environment: single-qubit-based protocols versus entangled-state-based protocols
Quantum communication in general helps deter potential eavesdropping in the course of transmission of bits to enable secure communication between two or more parties. In this paper, we propose a novel quasi-deterministic secure quantum communication scheme using non-maximally entangled states. The proposed scheme follows a simple procedure, and cases where the entanglement required can be significantly reduced to carry out the protocol successfully are discussed. Long sequences or the whole sequence of data can be sent after error checking for a potential eavesdropper. The maximum qubit effici…
We discuss quantum position verification (QPV) protocols in which the verifiers create and send single-qubit states to the prover. QPV protocols using single-qubit states are known to be insecure against adversaries that share a small number of entangled qubits. We introduce QPV protocols that are practically secure: they only require single-qubit states from each of the verifiers, yet their security is broken if the adversaries share an impractically large number of shared entangled qubits. These protocols are a modification of known QPV protocols in which we include a classical random oracle…
Hereunder, we study the class of irreducible private states that are private states from which all the secret content is accessible via measuring their key part. We provide the first protocol which distills key not only from the key part, but also from the shield if only the state is reducible. We prove also a tighter upper bound on the performance of that protocol, given in terms of regularized relative entropy of entanglement instead of relative entropy of entanglement previously known. This implies in particular that the irreducible private states are all strictly irreducible if and only if…
Quantum secure direct communication (QSDC) based on entanglement can directly transmit confidential information. However, the inability to simultaneously distinguish the four sets of encoded entangled states limits its practical application. Here, we explore a deterministic QSDC network based on time-energy entanglement and sum-frequency generation. 15 users are in a fully connected QSDC network, and the fidelity of the entangled state shared by any two users is greater than 97%. The results show that when any two users are performing QSDC over 40 kilometers of optical fiber, the fidelity of t…
As one of the most prominent subfields of quantum communication research, remote state preparation (RSP) plays a crucial role in quantum networks. Here we present a deterministic remote state preparation scheme to prepare an arbitrary two-qubit state via a seven-qubit entangled channel created from Borras \emph{et al.} state. Quantum noises are inherent to each and every protocol for quantum communication that is currently in use, putting the integrity of quantum communication systems and their dependability at risk. The initial state of the system was a pure quantum state, but as soon as ther…
Violation of Bell inequalities and Quantum Tomography with Pure-states, Werner-states and Maximally Entangled Mixed States created by a Universal Quantum Entangler
We demonstrate one-sided device-independent self-testing of any pure entangled two-qubit state based on a fine-grained steering inequality. The maximum violation of a fine-grained steering inequality can be used to witness certain steerable correlations, which certify all pure two-qubit entangled states. Our experimental results identify which particular pure two-qubit entangled state has been self-tested and which measurement operators are used on the untrusted side. Furthermore, we analytically derive the robustness bound of our protocol, enabling our subsequent experimental verification of …
Entangled state generation with an intrinsically pure single-photon source and a weak coherent source
我们报道了一个光谱纯的单光子态和一个弱相干态的纠缠态的实验产生。通过选择非线性晶体中的群速度匹配，我们用于产生纠缠光子的系统比早期实验中的亮60倍[Phys. Rev. Lett. 90，240401（2003）]，不需要带通滤波器。这种纠缠系统对于需要来自独立源的不可区分光子的量子信息协议是有用的。
While it has recently been demonstrated how to certify the maximal amount of randomness from any pure two-qubit entangled state in a device-independent way [E. Woodhead et al., Phys. Rev. Research 2, 042028(R)(2020)], the problem of optimal randomness certification from entangled states of higher local dimension remains open. Here we introduce a method for device-independent certification of the maximal possible amount of $2\log_23$ random bits using pure bipartite entangled two-qutrit states and extremal nine-outcome general non-projective measurements. To this aim, we exploit the extended Be…
We consider the problem of $1$-sided device-independent self-testing of any pure entangled two-qubit state based on steering inequalities which certify the presence of quantum steering. In particular, we note that in the $2-2-2$ steering scenario (involving $2$ parties, $2$ measurement settings per party, $2$ outcomes per measurement setting), the maximal violation of a fine-grained steering inequality can be used to witness certain extremal steerable correlations, which certify all pure two-qubit entangled states. We demonstrate that the violation of analogous CHSH inequality of steering or n…
我们通过几个纠缠单调来研究是否所有的最大纠缠态都是纯的。在两体情况下，我们发现导致纠缠熵作为纠缠度量的唯一性的相同条件，排除了最大混合纠缠态的存在。在多体情况下，我们的结论使我们能够推广一夫一妻的纠缠的想法：我们建立了\textit{polygamy of entanglement}，表示如果一个一般的状态是最大的纠缠相对于某种多体纠缠，那么它必然是任何其他系统的因式分解。
