Two-way Quantum Research Articles

Generation of quantum entanglement and Einstein–Podolsky–Rosen steering in a hybrid qubit-cavity optomagnonic system

We propose a scheme to generate quantum entanglement and Einstein–Podolsky–Rosen (EPR) steering in a hybrid qubit-cavity optomagnonic system. This hybrid system consists of a microwave cavity, a yttrium-iron-garnet (YIG) sphere, and a superconducting qubit. Due to the existence of the effective parametric (beamsplitter) coupling between the optical mode and the magnon mode (superconducting qubit), the quantum entanglement and EPR steering between the magnon and qubit modes can be achieved. It is found that bipartite entanglement and one-way quantum steering are limited to a narrow range of parameters, while two-way quantum steering appears in a wide range of parameters. Furthermore, we demonstrate that the entanglement between the magnon and the collective dressed modes, as well as the conversion of one-way quantum steering, can also be achieved. Our scheme may provide a feasible approach to exploring quantum information processing.

Comparative analysis of quantum two-way time transfer and quantum round-trip time transfer in consistent spatiotemporal settings

In this study, we conducted experiments using a single energy-time entangled biphoton source to compare the performance of quantum two-way time transfer (Q-TWTT) and quantum round-trip time transfer (Q-RTTT) under consistent spatiotemporal conditions. By conducting experiments with different fiber links of 11.3 km, 22.4 km, and 55.6 km, while ensuring uniform photon counts received by the single-photon detectors, we measured standard deviations (SDs) and stabilities of the time offsets. The measured SDs for Q-TWTT and Q-RTTT were 0.46 ps and 0.65 ps over the 11.3 km fiber, 1.14 ps and 1.3 ps over the 22.4 km fiber, 3.98 ps and 4.39 ps over the 55.6 km fiber, respectively. These results show good agreement with theoretical predictions, and the smaller SDs for Q-TWTT can be directly attributed to protocol-specific factors related to system symmetry. The long-term time stabilities of Q-TWTT and Q-RTTT were evaluated in terms of time deviation (TDEV). At an average time of 12680 s, the measured TDEVs were 0.49 ps and 0.63 ps for the 11.3 km fiber, 0.59 ps and 0.7 ps for the 22.4 km fiber, 1.01 ps and 1.36 ps for the 55.6 km fiber, respectively. The results validate that Q-TWTT exhibits superior time transfer performance compared to Q-RTTT, highlighting the advantages of Q-TWTT in practical applications.

Two-way quantum time transfer: a method for daytime space-Earth links

Two-way quantum time transfer: a method for daytime space-Earth links

Fully measurement-device-independent two-way quantum key distribution with finite single-photon sources

Fully measurement-device-independent two-way quantum key distribution with finite single-photon sources

Generation of entanglement and quantum steering via Josephson parametric amplifier in a dual cavity-magnon system

In the two microwave (MW) cross-shaped cavity magnon system, we describe a method to produce multipartite entanglement and quantum steering. To achieve squeezed states of the magnons, a Josephson parametric amplifier (JPA) creates a squeezed vacuum field that drives the two cavities. We theoretically demonstrate that the cavity-cavity entanglement can be generated at the resonance point, however, increasing the cavity and magnon decay rates generate the cavity-magnon entanglement. By changing the squeezing parameter and increasing the decay rates, we can transfer the cavity-cavity entanglement to cavity-magnon entanglement. Furthermore, the cavity-cavity entanglement (survive up to 2.8 K) was not only found to be much stronger but also more robust as compared to cavity-magnon entanglement (survive up to 0.4 K). More importantly, the genuine photon-magnon-photon tripartite entanglement could be achieved, which is robust against thermal fluctuations and depends strongly on the squeezing parameter. Furthermore, for the current dual cavity-magnon system, two-way quantum steering is found when the optomagnonical couplings are equal. The current study offers a straightforward and practical method for achieving multipartite quantum correlations.

Lifting query complexity to time-space complexity for two-way finite automata

Time-space tradeoff has been studied in a variety of models, such as Turing machines, branching programs, and finite automata, etc. While communication complexity as a technique has been applied to study finite automata, it seems it has not been used to study time-space tradeoffs of finite automata. We design a new technique showing that separations of query complexity can be lifted, via communication complexity, to separations of time-space complexity of two-way finite automata. As an application, one of our main results exhibits the first example of a language L such that the time-space complexity of two-way probabilistic finite automata with a bounded error (2PFA) is Ω˜(n2), while of exact two-way quantum finite automata with classical states (2QCFA) is O˜(n5/3), that is, we demonstrate for the first time that exact quantum computing has an advantage in time-space complexity comparing to classical computing.

Quantum walks-based simple authenticated quantum cryptography protocols for secure wireless sensor networks

Wireless sensor networks (WSNs) play a crucial role in various applications, ranging from environmental monitoring to industrial automation that require high levels of security. With the development of quantum technologies, many security mechanisms may be hacked due to the promising capabilities of quantum computation. To address this challenge, quantum protocols have emerged as a promising solution for enhancing the security of wireless sensor communications. One of the common types of quantum protocols is quantum key distribution (QKD) protocols, which are investigated to allow two participants with fully quantum capabilities to share a random secret key, while semi-quantum key distribution (SQKD) protocols are designed to perform the same task using fewer quantum resources to make quantum communications more realizable and practical. Quantum walk (QW) plays an essential role in quantum computing, which is a universal quantum computational paradigm. In this work, we utilize the advantages of QW to design three authenticated quantum cryptographic protocols to establish secure channels for data transmission between sensor nodes: the first one is authenticated quantum key distribution (AQKD), the second one is authenticated semi-quantum key distribution (ASQKD) with one of the two participants having limited quantum capabilities, and the last one is ASQKD but both legitimate users possess limited quantum resources. The advantages of the proposed protocols are that the partners can exchange several different keys with the same exchanged qubits, and the presented protocols depend on a one-way quantum communication channel. In contrast, all previously designed SQKD protocols rely on two-way quantum communication. Security analyses prove that the presented protocols are secure against various well-known attacks and highly efficient. The utilization of the presented protocols in wireless sensor communications opens up new avenues for secure and trustworthy data transmission, enabling the deployment of resilient WSNs in critical applications. This work also paves the way for future exploration of quantum-based security protocols and their integration into WSNs for enhanced data protection.

Time evolution of quantum correlations induced by atomic state superpositions

In this article, we study the time evolution of Gaussian quantum correlations induced by the superposition of atomic states. Photon-based quantum information and communication are powerful and suitable because the relevant physical mechanisms, the high combination rate of photons, and the sources of coherence can be understood and easily modeled. To this end, coupled photon pairs produced by coherent superposition of atomic states in an atomic laser and influences of spontaneous atomic decay due to vacuum field fluctuations have been considered. The dynamics of the quantum system leads to temporal quantum correlations such as quantum discord, quantum entanglement, and quantum steering, which are treated by the density operator approach. It was found that the generated photon pairs are completely in a separable state in the initial phase of the dynamical processes. The quantum coherences must be given sufficient time to generate quantum correlations that saturate after very short time scales. The strength of these quantum correlations has been improved by increasing the number of superposed atoms per unit of time. In particular, two-way quantum steering, which is a guarantee for the existence of quantum discord and quantum entanglement, can be achieved by increasing the atom injection rate from 10 kHz to 100 kHz when the probability of finding atoms in the excited state is 45%.

Effect of Classical and Quantum Superposition of Atomic States on Quantum Correlations

In this paper, we report the effect of classical and quantum superposition of atomic states on quantum correlations. Coupled photon pairs generated in a ladder quantum beat laser using coherent-induced classical field and atomic state coherent superposition are considered. Once the quantum coherence get sufficient time, it can generate quantum correlations that include quantum discord, quantum entanglement, and quantum steering, which quickly increase with time until they get their maximum strength. Their strength can be improved further by increasing the number of superposed atoms per unit time, selecting an appropriate amplitude of the classical fields, and managing the amount of temperatures and phase fluctuations. In particular, two-way quantum steering, which is a guarantee for the existence of quantum discord and quantum entanglement, can be achieved by increasing the rate of atomic injection from 2 kHz to 25 kHz even if the mean temperature of the heat bath is considered. The maximum achievable strength of quantum correlations is enhanced by increasing the rate of atomic injection and choosing an appropriate parameters of the coherent-induced classical field in the open quantum system which is treated by using the density operator approach.

Https://journals.scholarpublishing.org/index.php/AIVP/issue/view/425

In this paper, we prove the security of the LM05’s two-way quantum key distribution (TWQKD) under the assumption that detector devices in both Alice’s and Bob’s sides are controlled by eavesdroppers. Using a relatively simple method, more practical, we give an analytical proof that LM05’s TWQKD is measurement-device-independent (MDI) security in both the quantum forward channel and the quantum backward channel. This is the first work shows that TWQKD has fully MDI characteristic, thus makes it immune to all possible detector-device-attacks in two-quantum-way in actual implementations.

Simultaneous two-way classical communication and measurement-device-independent quantum key distribution on oceanic quantum channels

Simultaneous two-way classical and quantum (STCQ) communication combines both continuous classical coherent optical communication and continuous-variable quantum key distribution (CV-QKD), which eliminates all detection-related imperfections by being measurement-device-independent (MDI). In this paper, we propose a protocol relying on STCQ communication on the oceanic quantum channel, in which the superposition-modulation-based coherent states depend on the information bits of both the secret key and the classical communication ciphertext. We analyse the encoding combination in classical communication and consider the probability distribution transmittance under seawater turbulence with various interference factors. Our numerical simulations of various practical scenarios demonstrate that the proposed protocol can simultaneously enable two-way classical communication and CV-MDI QKD with just a slight performance degradation transmission distance compared to the original CV-MDI QKD scheme. Moreover, the asymmetric situation outperforms the symmetric case in terms of transmission distance and optical modulation variance. We further take into consideration the impact of finite-size effects to illustrate the applicability of the proposed scheme in practical scenarios. The results show the feasibility of the underwater STCQ scheme, which contributes toward developing a global quantum communication network in free space.

A Hierarchy of Efficient Bounds on Quantum Capacities Exploiting Symmetry

Optimal rates for achieving an information processing task are often characterized in terms of regularized information measures. In many cases of quantum tasks, we do not know how to compute such quantities. Here, we exploit the symmetries in the recently introduced <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {D}^{\#}$ </tex-math></inline-formula> in order to obtain a hierarchy of semidefinite programming bounds on various regularized quantities. As applications, we give a general procedure to give efficient bounds on the regularized Umegaki channel divergence as well as the classical capacity and two-way assisted quantum capacity of quantum channels. In particular, we obtain slight improvements for the capacity of the amplitude damping channel. We also prove that for fixed input and output dimensions, the regularized sandwiched Rényi divergence between any two quantum channels can be approximated up to an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\epsilon $ </tex-math></inline-formula> accuracy in time that is polynomial in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1/\epsilon $ </tex-math></inline-formula> .

基于两光子偏振-空间模超纠缠态的高容量的量子秘密共享协议

<p indent="0mm">This paper proposes a feasible high-capacity tripartite quantum secret sharing protocol based on the two-photon polarization-spatial-mode hyperentangled state. Alice, the secret owner, prepares polarization-spatial-mode hyperentangled photon pairs and distributes them to two agents, Bob and Charlie. Using nonlocal complete Bell state analysis technology assisted by spatial mode entanglement, the two agents can collaborate to distinguish Alice’s Bell state in polarization degree of freedom. Only linear optical elements are needed to construct the agents’ measuring devices, which makes the protocol more feasible in experimental implementation. Compared with the existing quantum secret sharing protocols based on two-photon entanglement, this scheme does not need two-way quantum communication and has high capacity because it can transmit two bits of information with a polarization-spatial-mode hyperentangled photon pair. The proposed quantum secret sharing protocol is secure and reliable due to error correction and privacy amplification technology.

Quantum versus Randomized Communication Complexity, with Efficient Players

We study a new type of separations between quantum and classical communication complexity, separations that are obtained using quantum protocols where all parties are efficient, in the sense that they can be implemented by small quantum circuits, with oracle access to their inputs. Our main result qualitatively matches the strongest known separation between quantum and classical communication complexity Gavinsky (2016) and is obtained using a quantum protocol where all parties are efficient. More precisely, we give an explicit partial Boolean function f over inputs of length N, such that: Items (1), (2) qualitatively match the strongest known separation between quantum and classical communication complexity, proved by Gavinsky (2016). Item (3) is new. (Our result is incomparable to the one of Gavinsky. While he obtained a quantitatively better lower bound of $$\Omega\left(N^{1/2}\right)$$ in the classical case, the referee in his quantum protocol is inefficient). Exponential separations of quantum and classical communication complexity have been studied in numerous previous works, but to the best of our knowledge the efficiency of the parties in the quantum protocol has not been addressed, and in most previous separations the quantum parties seem to be inefficient. The only separations that we know of that have efficient quantum parties are the recent separations that are based on lifting Göös et al. (2017), Chattopadhyay et al. (2019a). However, these separations seem to require quantum protocols with at least two rounds of communication, so they imply a separation of two-way quantum and classical communication complexity, but they do not give the stronger separations of simultaneous-message quantum communication complexity vs. two-way classical communication complexity (or even one-way quantum communication complexity vs. two-way classical communication complexity). Our proof technique is completely new, in the context of communication complexity, and is based on techniques from Raz & Tal (2019). Our function f is based on a lift of the forrelation problem, using xor as a gadget.

Bidirectional quantum operation teleportation with a six-qubit composite Bell-GHZ state

A bidirectional quantum operation teleportation scheme is proposed by utilizing a six-qubit composite Bell-GHZ state. In which, two users Anne and Benson can perform their respective concerned single-qubit operations on each other’s target states. Compared with the other existing schemes of quantum operation teleportation (QOT), the present scheme can realize the remote implement of the positive and negative two-way quantum operations, which not only improves the communication capacity, but also expands the application scenarios of QOT. Additionally, it is deterministic and feasible with the present experimental techniques.

Security of plug-and-play continuous-variable quantum key distribution

Subject of study. Two-way continuous-variable quantum key distribution schemes are studied. Aim. This study aims to prove the security of the plug-and-play continuous-variable quantum key distribution system in the context of the model of trusted noise from legitimate users. Method. Based on an analog of the well-known implementation in the plug-and-play format, the performance of such a system operating under the GG02 protocol is evaluated. The evaluation is conducted in the presence of collective attacks, considering the finite-key effects. Main results. A secure key that satisfies the composability criteria can be distributed with a channel loss of 5 dB, which is expected to be approximately half that in a one-way scheme. Practical significance. Two-way quantum key distribution schemes are more stable than one-way schemes, and hence, their stability requires detailed consideration. This paper is the first, to our knowledge, to propose considering the security of a two-way implementation of continuous-variable quantum key distribution, considering the trusted equipment noise.

Demonstration of 50 Km Fiber-Optic Two-Way Quantum Clock Synchronization

Fiber-optic Quantum clock synchronization has been proposed and experimentally demonstrated for its potential enhancements in precision and better guarantee of security. To further prove its advantage in practical applications, it is necessary to test its synchronization performance between clocks apart for at least intracity optical fiber distance. In this paper, we report a fiber-optic two-way quantum clock synchronization experiment with the distance reaching 50 km. With the common reference clock, a synchronization stability of 54.6 fs at 57300 s and an accuracy of 1.3 ps±36.6 ps have been achieved. With independent reference clocks, comparable performance has also been achieved combined with the microwave frequency transfer technology, which shows a stability of 89.5 fs at 57300 s. These results nicely showcase the feasibility of the two-way quantum clock synchronization to provide femtosecond-scale synchronization precision over intracity optical fiber links.

Exact Affine Counter Automata

We introduce an affine generalization of counter automata, and analyze their ability as well as affine finite automata. Our contributions are as follows. We show that there is a language that can be recognized by exact realtime affine counter automata but by neither 1-way deterministic pushdown automata nor realtime deterministic [Formula: see text]-counter automata. Then, we show that exact realtime affine counter automata can recognize a family of regular languages with a few states but the states required by realtime deterministic [Formula: see text]-counter automata cannot be bounded. We also show that stateless affine increment-only counter automata can recognize some nonregular languages with one-sided bounded-error. Moreover, we show that a promise problem not solved by two-way quantum finite automata in polynomial time can be solved by Las Vegas affine finite automata. Lastly, we present an affine finite automaton algorithm using a counter cleverly to recognize a language, for which we do not know any bounded-error affine finite automata or two-way quantum finite automata recognizing it.

Implementation of field two-way quantum synchronization of distant clocks across a 7 km deployed fiber link.

The two-way quantum clock synchronization has been shown to provide femtosecond-level synchronization capability and security against symmetric delay attacks, thus becoming a prospective method to compare and synchronize distant clocks with enhanced precision and safety. In this letter, a field test of two-way quantum synchronization between a H-maser and a Rb clock linked by a 7 km-long deployed fiber is implemented by using time-energy entangled photon-pair sources. Limited by the intrinsic frequency stability of the Rb clock, the achieved time stability at 30 s is measured as 32 ps. By applying a fiber-optic microwave frequency transfer technology to build frequency syntonization between the separated clocks, the limit set by the intrinsic frequency stability of the Rb clock is overcome. A significantly improved time stability of 1.9 ps at 30 s is achieved, which is mainly restrained by the low number of acquired photon pairs due to the low sampling rate of the utilized coincidence measurement system. Such implementation demonstrates the high practicability of the two-way quantum clock synchronization method for promoting field applications.

An Optimized Bidirectional Quantum Teleportation Scheme with the Use of Bell States

Bidirectional quantum teleportation scheme is a two-way quantum communication process, in which two parties simultaneously receive each other information. Recently, in paper [1] (Zhou et al., IEEE Access, 7, 44269 (2019)), a six-qubit cluster state has been used to teleport three-qubit entangled state (Alice) and arbitrary single-qubit unknown quantum state (Bob) bidirectionally. An experimental point of view, the preparation and the maintenance of cluster type entangled state is very difficult and costly. So, in this paper we have designed an optimal scheme for bidirectional quantum teleportation scheme and shown that proposed scheme requires optimized amount of quantum resources.