We define "coherent communication" in terms of a simple primitive, show it is equivalent to the ability to send a classical message with a unitary or isometric operation, and use it to relate other resources in quantum information theory. Using coherent communication, we are able to generalize super-dense coding to prepare arbitrary quantum states instead of only classical messages. We also derive single-letter formulae for the classical and quantum capacities of a bipartite unitary gate assisted by an arbitrary fixed amount of entanglement per use.
We present a subtle idea to economically improve message-unilaterally-transmitted quantum secure direct communication (QSDC) protocols to realize two-way secure direct communication.
The possibility of attaining current position of the message sender without person's consent seriously compromises the secrecy of correspondence. Classical communication systems cannot guarantee the security of communication against unwanted location tracking, because the sender must broadcast a signal at the moment of sending the message. The source of the signal could be always located, at least in principle. We show that quantum communication enables sending the message with pre-distributed entangled quantum systems, local weak measurements, time synchronization between the sender and the r…
We propose a class of quantum no-key protocols for private communication of classical message based on quantum computing of random Boolean permutations, and demonstrate that they are information-theoretic secure. These protocols are designed to resist middleman attack for two parties preshared authentication key, and achieve perfect mutual data origin authentication which ensures the permanent reusing of authentication key. Finally, we simplify the protocol to a 4-round one, and show that any protocol with 3 or less rounds cannot achieve perfect security without consuming preshared key.
Recently an orthogonal state based protocol of direct quantum communication without actual transmission of particles is proposed by Salih \emph{et al.}{[}Phys. Rev. Lett. \textbf{110} (2013) 170502{]} using chained quantum Zeno effect. As the no-transmission of particle claim is criticized by Vaidman {[}arXiv:1304.6689 (2013){]}, the condition (claim) of Salih \emph{et al.} is weaken here to the extent that transmission of particles is allowed, but transmission of the message qubits (the qubits on which the secret information is encoded) is not allowed. Remaining within this weaker condition i…
A protocol for quantum secure direct communication using blocks of EPR pairs is proposed. A set of ordered $N$ EPR pairs is used as a data block for sending secret message directly. The ordered $N$ EPR set is divided into two particle sequences, a checking sequence and a message-coding sequence. After transmitting the checking sequence, the two parties of communication check eavesdropping by measuring a fraction of particles randomly chosen, with random choice of two sets of measuring bases. After insuring the security of the quantum channel, the sender, Alice encodes the secret message direct…
A novel scheme for secure direct communication between Alice and Bob is proposed, where there is no need for establishing a shared secret key. The communication is based on Einstein-Podolsky-Rosen pairs and teleportation between Alice and Bob. After insuring the security of the quantum channel (EPR pairs), Bob encodes the secret message directly on a sequence of particle states and transmits them to Alice by teleportation. In this scheme teleportation transmits Bob's message without revealing any information to a potential eavesdropper. Alice can read out the encoded messages directly by the m…
The communication cost of a classical protocol is typically measured in terms of the number of bits communicated for this determines the time required for communication during the protocol. Similarly, for quantum communication protocols, which use finite-dimensional quantum states, the communication cost is measured in terms of the number of qubits communicated. However, in quantum physics, one can also use infinite-dimensional states, like optical quantum states, for communication protocols. Communication cost measures based on counting the (equivalent) number of qubits transmitted during com…
A theoretical scheme for controlled and secure direct communication is proposed. The communication is based on GHZ state and controlled quantum teleportation. After insuring the security of the quantum channel (a set of qubits in the GHZ state), Alice encodes the secret message directly on a sequence of particle states and transmits them to Bob supervised by Charlie using controlled quantum teleportation. Bob can read out the encoded messages directly by the measurement on his qubits. In this scheme, the controlled quantum teleportation transmits Alice's message without revealing any informati…
We give the first exponential separation between quantum and classical multi-party communication complexity in the (non-interactive) one-way and simultaneous message passing settings. For every k, we demonstrate a relational communication problem between k parties that can be solved exactly by a quantum simultaneous message passing protocol of cost O(log n) and requires protocols of cost n^{c/k^2}, where c>0 is a constant, in the classical non-interactive one-way message passing model with shared randomness and bounded error. Thus our separation of corresponding communication classes is superp…
We study the simultaneous message passing (SMP) model of communication complexity, for the case where one party is quantum and the other is classical. We show that in an SMP protocol that computes some function with the first party sending q qubits and the second sending c classical bits, the quantum message can be replaced by a randomized message of O(qc) classical bits, as well as by a deterministic message of O(q c log q) classical bits. Our proofs rely heavily on earlier results due to Scott Aaronson. In particular, our results imply that quantum-classical protocols need to send Omega(sqrt…
Most of the quantum secure direct communication protocol needs a pre-established secure quantum channel. Only after insuring the security of quantum channel, could the sender encode the secret message and send them to the receiver through the secure channel. In this paper, we present a quantum secure direct communication protocol using Einstein-Podolsky-Rosen pairs. It is not necessary for the present protocol to insure the security of quantum channel before transmitting the secret message. In the present protocol, all Einstein-Podolsky-Rosen pairs are used to transmit the secret message excep…
We present a protocol for sending a message over a quantum channel with different layers of security that will prevent an eavesdropper from deciphering the message without being detected. The protocol has two versions where the bits are encoded in either pairs of entangled photons or separate photons. Unlike many other protocols, it requires a one-way, rather than a two-way, quantum channel and does not require a quantum memor. A quantum key is used to encrypt the message and both the key and the message are sent over the quantum channle with the same quantum encoding technique. The key is sen…
Base on the idea of dense coding of three-photon entangled state and qubit transmission in blocks, we present a multiparty controlled quantum secret direct communication scheme using Greenberger-Horne-Zeilinger state. In the present scheme, the sender transmits her three bits of secret message to the receiver directly and the secret message can only be recovered by the receiver under the permission of all the controllers. All three-photon entangled states are used to transmit the secret messages except those chosen for eavesdropping check and the present scheme has a high source capacity becau…
We propose a simultaneous quantum secure direct communication scheme between one party and other three parties via four-particle GHZ states and swapping quantum entanglement. In the scheme, three spatially separated senders, Alice, Bob and Charlie, transmit their secret messages to a remote receiver Diana by performing a series local operations on their respective particles according to the quadripartite stipulation. From Alice, Bob, Charlie and Diana's Bell measurement results, Diana can infer the secret messages. If a perfect quantum channel is used, the secret messages are faithfully transm…
We present a deterministic secure direct communication scheme via entanglement swapping, where a set of ordered maximally entangled three-particle states (GHZ states), initially shared by three spatially separated parties, Alice, Bob and Charlie, functions as a quantum information channel. After ensuring the safety of the quantum channel, Alice and Bob apply a series local operations on their respective particles according to the tripartite stipulation and the secret message they both want to send to Charlie. By three Alice, Bob and Charlie's Bell measurement results, Charlie is able to infer …
A multipartner secure direct communication protocol is presented, using quantum nonlocality. Security of this protocol is based on `High fidelity implies low entropy'. When the entanglement was successfully distributed, anyone of the multipartner can send message secretly by using local operation and reliable public channel. Since message transfered only by using local operation and public channel after entanglement successfully distributed, so this protocol can protect the communication against destroying-travel-qubit-type attack.
We present a quantum secure direct communication scheme achieved by swapping quantum entanglement. In this scheme a set of ordered Einstein-Podolsky-Rosen (EPR) pairs is used as a quantum information channel for sending secret messages directly. After insuring the safety of the quantum channel, the sender Alice encodes the secret messages directly by applying a series local operations on her particles sequence according to their stipulation. Using three EPR pairs, three bits of secret classical information can be faithfully transmitted from Alice to remote Bob without revealing any information…
Quantum secure direct communication (QSDC) can directly transmit secrete messages through quantum channel. Device-independent (DI) QSDC can guarantee the communication security relying only on the observation of the Bell inequality violation, but not on any detailed description or trust of the inner workings of users' devices. In the paper, we propose a DI-QSDC protocol with practical high-efficient single photon sources. The communication parties construct the entanglement channel from single photons by adopting the heralded architecture, which makes the message leakage rate independent of th…
Quantum secure direct communication (QSDC) and deterministic secure quantum communication (DSQC) are two important branches of quantum cryptography, where one can transmit a secret message securely without encrypting it by a prior key. In the practical scenario, an adversary can apply detector-side-channel attacks to get some non-negligible amount of information about the secret message. Measurement-device-independent (MDI) quantum protocols can remove this kind of detector-side-channel attack, by introducing an untrusted third party (UTP), who performs all the measurements during the protocol…
We demonstrate a two-player communication problem that can be solved in the one-way quantum model by a 0-error protocol of cost O (log n) but requires exponentially more communication in the classical interactive (bounded error) model.
We consider several models of 1-round classical and quantum communication, some of these models have not been defined before. We "almost separate" the models of simultaneous quantum message passing with shared entanglement and the model of simultaneous quantum message passing with shared randomness. We define a relation which can be efficiently exactly solved in the first model but cannot be solved efficiently, either exactly or in 0-error setup in the second model. In fact, our relation is exactly solvable even in a more restricted model of simultaneous classical message passing with shared e…
We consider attacks on two-way quantum key distribution protocols in which an undetectable eavesdropper copies all messages in the message mode. We show that under the attacks there is no disturbance in the message mode and that the mutual information between the sender and the receiver is always constant and equal to one. It follows that recent proofs of security for two-way protocols cannot be considered complete since they do not cover the considered attacks.
We show how continuous variable systems can allow the direct communication of messages with an acceptable degree of privacy. This is possible by combining a suitable phase-space encoding of the plain message with real-time checks of the quantum communication channel. The resulting protocol works properly when a small amount of noise affects the quantum channel. If this noise is non-tolerable, the protocol stops leaving a limited amount of information to a potential eavesdropper.
The schemes proposed by S. Bose et al [Phys. Rev. Lett. 83, 5158 (1999)] and others for long distance atomic teleportation using cavity decay, gives message state dependent fidelity on successful attempt and in case of failure message state destroys. We propose a different scheme for teleportation of an atomic state from one cavity to a distant cavity by reflecting optical-pulse modes of an entangled coherent state (ECS) from single atom-cavity systems and detecting whether light is on or off. Unit success with unit fidelity is obtained for large mean photon number (|α|^2). For small |α|^2, ho…
In some scenarios there are ways of conveying information with many fewer, even exponentially fewer, qubits than possible classically. Moreover, some of these methods have a very simple structure--they involve only few message exchanges between the communicating parties. It is therefore natural to ask whether every classical protocol may be transformed to a ``simpler'' quantum protocol--one that has similar efficiency, but uses fewer message exchanges. We show that for any constant k, there is a problem such that its k+1 message classical communication complexity is exponentially smaller than …
Communication Complexity of Private Simultaneous Quantum Messages Protocols
Graduate School of Engineering, Mie University（三重大学大学院工学研究科）；Graduate School of Informatics/Institute for Advanced Study, Nagoya University（名古屋大学情报学研究科／高等研究院）
