Two-way Quantum Research Articles

Two-way quantum communication: Generalization of secure quantum information exchange to quantum network

The idea of secure quantum information exchange (SQIE) [J. Phys. B: At. Mol. Opt. Phys.44, 115504 (2011)] is introduced for the secure exchange of single qubit information states between two legitimate users, Alice and Bob. In the present paper, we extend this original SQIE protocol by presenting a scheme, which enables the secure exchange of n-single qubit information states among the n nodes of a quantum network, with the aid of a special kind of 4n-qubit entangled state and the classical assistance of an extra participant Charlie. For experimental realization of our extended SQIE protocol, we suggest an efficient scheme for the generation of a special kind of 4n-qubit entangled state using the interaction between highly detuned Λ-type three-level atoms and optical coherent field. Further, by discussing the various experimental parameters, we show that the special kind 4n-qubit entangled state can be generated with the presently available technology.

Two-way deterministic quantum key distribution against passive detector side channel attacks in the forward line

In the four-state two-way deterministic quantum key distribution (DQKD) protocol, Bob prepares a qubit randomly in one of four states and sends it to Alice. Alice encodes her key bit on the arrival qubit and returns it to Bob who measures the redux qubit to decode Alice's key bit in a deterministic manner, without basis reconciliation. The unconditional security of the final key of this protocol has been proven in the ideal-device settings. Recently, it has been proven that two-way DQKD protocol is immune to all detector side channel attacks in the backward line A-to-B. In this paper, we study the security of two-way DQKD against passive detector side channel attacks in the forward line B-to-A. In a passive detector side channel attack, the eavesdropper Eve does not disturb quantum state of travel photon but utilizes the efficiency mismatch of two single-photon detectors to estimate the value of key bits, such as the time-shift attack. We prove that two-way DQKD is immune against all passive detector side channel attacks in the forward line B-to-A, although such attacks are efficient on BB84 protocol.

Finite Key Size Analysis of Two-Way Quantum Cryptography

Quantum cryptographic protocols solve the longstanding problem of distributing a shared secret string to two distant users by typically making use of one-way quantum channel. However, alternative protocols exploiting two-way quantum channel have been proposed for the same goal and with potential advantages. Here, we overview a security proof for two-way quantum key distribution protocols, against the most general eavesdropping attack, that utilize an entropic uncertainty relation. Then, by resorting to the “smooth” version of involved entropies, we extend such a proof to the case of finite key size. The results will be compared to those available for one-way protocols showing some advantages.

Quantum Secure Communication Protocol Based on Single-photon

Two-way quantum secure communication protocol and one-way quantum secure communication protocol based on single photon sequence and the XOR operation have been proposed, one-way communication can confuse the eavesdroppers and two-way communication only a single authentication and there is not visible to eavesdropping and delayed photon attack Trojan horse attack. The new agreement the use of single photon sequence and no regularity not only to achieve unconditional security, and semantics confuse eavesdroppers and has a high transmission efficiency, easy implementation, especially suitable for use in noisy channels.

Power of the interactive proof systems with verifiers modeled by semi-quantum two-way finite automata

Interactive proof systems (IP) are very powerful – languages they can accept form exactly PSPACE. They represent also one of the very fundamental concepts of theoretical computing and a model of computation by interactions. One of the key players in IP is verifier. In the original model of IP whose power is that of PSPACE, the only restriction on verifiers is that they work in randomized polynomial time. Because of such key importance of IP, it is of large interest to find out how powerful will IP be when verifiers are more restricted. So far this was explored for the case that verifiers are two-way probabilistic finite automata (Dwork and Stockmeyer, 1990) and one-way quantum finite automata as well as two-way quantum finite automata (Nishimura and Yamakami, 2009). IP in which verifiers use public randomization is called Arthur–Merlin proof systems (AM). AM with verifiers modeled by Turing Machines augmented with a fixed-size quantum register (qAM) were studied also by Yakaryilmaz (2012). He proved, for example, that an NP-complete language Lknapsack, representing the 0–1 knapsack problem, can be recognized by a qAM whose verifier is a two-way finite automaton working on quantum mixed states using superoperators.In this paper we explore the power of AM for the case that verifiers are two-way finite automata with quantum and classical states (2QCFA) – introduced by Ambainis and Watrous in 2002 – and the communications are classical. It is of interest to consider AM with such “semi-quantum” verifiers because they use only limited quantum resources. Our main result is that such Quantum Arthur–Merlin proof systems (QAM(2QCFA)) with polynomial expected running time are more powerful than the models in which the verifiers are two-way probabilistic finite automata (AM(2PFA)) with polynomial expected running time. Moreover, we prove that there is a language which can be recognized by an exponential expected running time QAM(2QCFA), but cannot be recognized by any AM(2PFA), and that the NP-complete language Lknapsack can also be recognized by a QAM(2QCFA) working only on quantum pure states using unitary operators.

Effects of initial states on the quantum correlation in Bose-Hubbard model

Quantum correlation is an important resource in quantum information, quantum computation, and quantum metrology. Quantum entanglement, Einstein-Podolsky-Rosen (EPR) quantum steering and Bell nonlocality are the major quantum correlations. For quantum entanglement and Bell nonlocality, two subsystems play the same significant roles. EPR quantum steering is stronger than entanglement and weaker than Bell nonlocality. It represents the ability of one subsystem to nonlocally affect another subsystem's states through local measurements. In this paper, the dynamic quantum correlation between the modes in the two-site Bose-Hubbard model is investigated. According to Hillery-Zubairy entanglement criterion and based on maximum mean quantum Fisher information, the influences of initial states on the quantum entanglement evolutions are explored. If the coupling between the modes is much greater than that of the particles at the same site, and the initial states are symmetric or anti-symmetric SU(2) coherent states, the quantum correlations show simple periodic evolutions. The oscillation amplitudes of the evolutions increase with the interaction between the particles at the same site. The oscillation period decreases with the coupling strength between the modes. The dependence of the period on the interaction of the particles at the same site is related to the initial states. In other words, the time evolutions of quantum correlation are closely related to the symmetry of the initial states. In the case of symmetric (anti-symmetric) SU(2) coherent state and repulsive (attractive) interaction of the particles at the same site, the system presents two-way quantum steering. When the subsystem exchange symmetry of the initial states is broken, the collapse and revival of quantum correlation appear, moreover one-way quantum steering emerges in the infancy. One-way quantum steering is asymmetric for two subsystems. So exchange asymmetry of the initial state is necessary condition of one-way quantum steering when the Hamiltonian of the system is symmetric for two subsystems.

Security of two-way continuous-variable quantum key distribution with source noise

We investigate the security of reverse reconciliation two-way continuous-variable quantum key distribution with source noise at both legitimate sides. Because the source noise originates from imperfect devices, we ascribe it to the legitimate sides rather than the eavesdropper. The trusted model consists of a thermal noise injected into a beam splitter. The expressions of secret key rate are derived against collective entangling cloner attacks for homodyne and heterodyne detections. Simulation results show that by applying the trusted model, the security bound of the reverse reconciliation two-way protocols can be tightened, while the advantage over one-way protocols still maintains.

Quantum key distribution using a two-way quantum channel

We review a quantum key distribution protocol, recently proposed by us, that makes use of a two-way quantum channel. We provide a characterization of such a protocol from a practical perspective, and consider the most relevant individual-particle eavesdropping strategies against it. This allows us to compare its potentialities with those of the standard BB84 protocol which uses a one-way quantum channel.

Quantum identity authentication based on ping-pong technique without entanglements

A quantum identity authentication scheme based on ping-pong technique without entanglements is proposed. It can verify the legitimate user's identity and update the initial authentication key for reuse. The security of the proposed scheme is extensively analyzed and accordingly confirmed in the case of general individual attacks. The present scheme owns high efficiency due to the use of single-particle states in a two-way quantum channel. Moreover, the scheme is economical and feasible with present-day technique.

Restricted attacks on semi-quantum key distribution protocols

In this paper, we investigate single-state, semi-quantum key distribution protocols. These are protocols whereby one party is limited to measuring only in the computational basis, while the other, though capable of measuring in both computational and Hadamard bases, is limited to preparing and sending only a single, publicly known qubit state. Such protocols rely necessarily on a two-way quantum communication channel making their security analysis difficult. However, we will show that, for single-state protocols, we need only consider a restricted attack operation by Eve. We will also describe a new single-state protocol that permits "reflections" to carry information and use our results concerning restricted attacks to show its robustness.

Constant-space quantum interactive proofs against multiple provers

We present upper and lower bounds of the computational complexity of the two-way communication model of multiple-prover quantum interactive proof systems whose verifiers are limited to measure-many two-way quantum finite automata. We prove that (i) the languages recognized by those multiple-prover systems running in expected polynomial time are exactly the ones in NEXP, the nondeterministic exponential-time complexity class, (ii) if we further require verifiers to be one-way quantum finite automata, then their associated proof systems recognize context-free languages but not beyond languages in NE, the nondeterministic linear exponential-time complexity class, and moreover, (iii) when no time bound is imposed, the proof systems become as powerful as Turing machines. The first two results answer affirmatively an open question, posed by Nishimura and Yamakami [J. Comput. System Sci. 75 (2009) 255–269], of whether multiple-prover quantum interactive proof systems are more powerful than single-prover ones. Our proofs are simple and intuitive, although they heavily rely on an earlier result on multiple-prover classical interactive proof systems of Feige and Shamir [J. Comput. System Sci. 44 (1992) 259–271].

Security of modified Ping-Pong protocol in noisy and lossy channel.

The “Ping-Pong” (PP) protocol is a two-way quantum key protocol based on entanglement. In this protocol, Bob prepares one maximally entangled pair of qubits, and sends one qubit to Alice. Then, Alice performs some necessary operations on this qubit and sends it back to Bob. Although this protocol was proposed in 2002, its security in the noisy and lossy channel has not been proven. In this report, we add a simple and experimentally feasible modification to the original PP protocol, and prove the security of this modified PP protocol against collective attacks when the noisy and lossy channel is taken into account. Simulation results show that our protocol is practical.

Nonorthogonal unitaries in two-way quantum key distribution

Two-way Quantum Key Distribution (QKD) schemes commonly make use of a set of unitaries corresponding to binary encodings which can in principle be distinguished perfectly. In this paper, inline with the proposal in Chiribella et al. (2008) [13], we introduce a non-entangled two-way QKD scheme with two sets of unitaries of which the elements in one set can be viewed as ‘nonorthogonal’ to elements in the other with the aim of naturally suppressing an eavesdropper's information to provide for a higher security threshold. Security analysis is done in the context of individual attack strategies for a quick comparison with the conventional two-way QKD scheme. Given the richer structure of the improvement, future direction is also discussed.

Improvement of two-way continuous-variable quantum key distribution using optical amplifiers

The imperfections of a receiver's detector affect the performance of two-way continuous-variable (CV) quantum key distribution (QKD) protocols and are difficult to adjust in practical situations. We propose a method to improve the performance of two-way CV-QKD by adding a parameter-adjustable optical amplifier at the receiver. A security analysis is derived against a two-mode collective entangling cloner attack. Our simulations show that the proposed method can improve the performance of protocols as long as the inherent noise of the amplifier is lower than a critical value, defined as the tolerable amplifier noise. Furthermore, the optimal performance can approach the scenario where a perfect detector is used.

Two-way quantum cryptography at different wavelengths

We study the security of two-way quantum cryptography at different wavelengths of the electromagnetic spectrum, from the optical range down to the microwave range. In particular, we consider a two-way quantum communication protocol where Gaussian-modulated thermal states are subject to random Gaussian displacements and finally homodyned. We show how its security threshold (in reverse reconciliation) is extremely robust with respect to the preparation noise and able to outperform the security thresholds of one-way protocols at any wavelength. As a result, improved security distances are now accessible for implementing quantum key distribution at the very challenging regime of infrared frequencies.

基于四粒子GHz态的可控量子双向隐形传态及安全性

A scheme for controlled two-way quantum teleportation of unknown one-qubit state via GHZ quadripartite entangled state was proposed.Two sides of communication(Alice and Bob)and the controller,secretly share two pairs of GHZ quadripartite entangled state in advance to construct quantum channel.According to the different ways of distribution along with different measuring vectors choosed to use,two-way quantum teleportation controlled by a third party and a fouth party were realized.After communication,Alice and Bob perform quantum projection measurement on parts of their qubits respectively.If the controller agrees to intercommunication,he should measure his qubits and announce the results via classical channel.Then the both sides of communication can make appropriate unitary transformations on their own certain qubit on the basis of the controller′s results,thus they are able to reconstruct each other′s unknown state on their own qubit.The security of the whole two-way communication is greatly impoved owing to the join of the third party Charlie and the fourth party Dennis.

Checking noise correlations for safer two-way quantum key distribution

We check for noise correlations between forward and backward paths in two-way quantum key distribution, which leads to reduced potentialities for an eavesdropper since she can only hide herself behind uncorrelated (natural) noise. The security enhancement is evaluated through the ratio of eavesdropper’s information and legitimate users’ information achievable against the most relevant individual attacks.

Security of two-way quantum key distribution

Quantum key distribution protocols typically make use of a one-way quantum channel to distribute a shared secret string to two distant users. However, protocols exploiting a two-way quantum channel have been proposed as an alternative route to the same goal, with the potential advantage of outperforming one-way protocols. Here we provide a strategy to prove security for two-way quantum key distribution protocols against the most general quantum attack possible by an eavesdropper. We utilize an entropic uncertainty relation, and only a few assumptions need to be made about the devices used in the protocol. We also show that a two-way protocol can outperform comparable one-way protocols.

Two-way deterministic quantum key distribution against detector-side-channel attacks

In a two-way deterministic quantum key distribution (DQKD) protocol, Bob randomly prepares qubits in one of four states and sends them to Alice. To encode a bit, Alice performs an operation on each received qubit and returns it to Bob. Bob then measures the backward qubits to learn about Alice's operations and hence the key bits. Recently, we proved the unconditional security of the final key of this protocol in the ideal device setting. In this paper, we prove that two-way DQKD protocols are immune to all detector side channel attacks at Bob's side, while we assume ideal detectors at Alice's side for error testing. Our result represents a step forward in making DQKD protocols secure against general detector side channel attacks.

Cooperative Quantum Two-Way Communications via Quantum Teleportation Based on Brown State with the Partial Entanglement Analysis

We demonstrate two explicit cooperative two-way quantum communications based on the Brown state in a forward-and-backward fashion. One realizes the duplex exchange of an arbitrary unknown state and a certain state between Alice and Bob with the aid of the trusty Charlie via the partial entanglement analysis. The other realizes the half-duplex exchange of arbitrary unknown states. Their securities are both guaranteed due to the fact that each participant either faithfully recovers the transmitted unknown states after performing some suitable unitary operations in a deterministic way or, in a case of any irregularity, generates no results. In addition, the present half-duplex cooperative quantum communication can be similarly extended for transmitting arbitrary unknown states via the two-way quantum teleportation based on the generalized Brown-like state in a probabilistic way.