Abstract We propose an efficient, measurement-based quantum dialogue protocol through non-destructive discrimination (NDD) of cluster state. We use ancilla-based measurements that allow the state to be reused without destroying its entanglement. The initial state is a local unitary equivalent of the five-qubit cluster state, which significantly reduces the state components from 32 to 4, simultaneously allowing one to write its different subspaces using two different bases. The protocol utilizes single qubit unitaries from the Pauli group to encode the messages, thus preserving the stabilizer nature of the initial state throughout. We demonstrate that the proposed protocol is secure under common quantum attacks and outlining the procedure for the scalability of the scheme to transmit an n -bit message. The proposed protocol has been experimentally verified using IBM quantum backend ‘IBM-Torino’ as a proof of concept. Using the stabilizer nature of the state, we further introduce a single-qubit error correction mechanism that enhances robustness against noise without requiring any additional qubits. Further, the use of NDD allows one to reuse the quantum resources in advancing the two-way dialogue, marking the importance and novelty of the proposed scheme over preexisting methods.
Abstract We propose an efficient, measurement-based quantum dialogue protocol through non-destructive discrimination (NDD) of cluster state. We use ancilla-based measurements that allow the state to be reused without destroying its entanglement. The initial state is a local unitary equivalent of the five-qubit cluster state, which significantly reduces the state components from 32 to 4, simultaneously allowing one to write its different subspaces using two different bases. The protocol utilizes single qubit unitaries from the Pauli group to encode the messages, thus preserving the stabilizer nature of the initial state throughout. We demonstrate that the proposed protocol is secure under common quantum attacks and outlining the procedure for the scalability of the scheme to transmit an n -bit message. The proposed protocol has been experimentally verified using IBM quantum backend ‘IBM-Torino’ as a proof of concept. Using the stabilizer nature of the state, we further introduce a single-qubit error correction mechanism that enhances robustness against noise without requiring any additional qubits. Further, the use of NDD allows one to reuse the quantum resources in advancing the two-way dialogue, marking the importance and novelty of the proposed scheme over preexisting methods.
Efficient generation of cluster states is crucial for engineering large-scale measurement-based quantum computers. Hybrid matter-optical systems offer a robust, scalable path to this goal. Such systems have an ancilla which acts as a bus connecting the qubits. Ancilla-driven schemes are important for chip-based quantum computing architectures, where the flying ancilla mediates between static qubits. Hybrid architectures form a natural substrate for measurement-based quantum computing (MBQC) [1], one type of which (the topological model) has the best error threshold for quantum computing [2]. In this type of processing a highly-entangled cluster state is generated, and then computation performed by sequential qubit measurements. The quantum processing task is to generate the cluster state, after which it becomes a matter of measurement and classical communication. In physically-realizable implementations the cluster is prepared dynamically, a few layers at a time. As the cluster state is the fundamental quantum resource of a measurement-based computation, it becomes extremely important to make it as error-free as possible. Errors in constructing the cluster can propagate rapidly through a computation because of the highly-entangled nature of the state, leading to failure of the computation. Hybrid systems are susceptible to specific error types that other systems are not, because of the use of the mediating ancilla. In cases where the ancilla is not destroyed after each gate there is a nonzero probability of errors propagating through ancilla reuse. FIG. 1: A cluster of 4 bricks of length b = 5 qubits, each made using a different bus. We present the optimal scheme for dynamic fault-tolerant 2-D cluster state generation in hybrid systems where the mediating system can be used for more than a single gate operation without being reset. We divide the cluster state into “Lego bricks”, each of which uses a single bus. We give the optimal method for constructing the bricks, reducing the number of system-bus entanglements. We then show how to determine the block size based on the error threshold of the system being used. We find that, even when the probability of error in the system is high, this scheme can still deliver significant efficiency savings through bus reuse, enabling a larger cluster to be generated. By reducing the time required to prepare sections of the cluster, bus reuse more than doubles the size of the computational workspace that can be used before decoherence effects dominate [3]. A simple example of the bricks is shown in figure 1. They are always the same height (m direction), but have length b (n direction) determined by [3] 1 ¡1 − exp[−(6b + 4)γτ − 16bηβ2]¢ ≤ ε. (1) 2 For a given set of experimental parameters γ, τ, η and β, and desired dephasing limit to ε, this determines b. If we use one bus per CPhase gate to generate a brick, we have 1 ¡1 − exp[−16bγτ − 4ηβ2]¢ ≤ ε. (2) 2 Comparing equations (1) and (2), we find our Lego scheme produces less qubit dephasing than using one bus per CPhase gate provided ηβ2 < ∼ γτ/2. Compared with 8mn − 4(m + n) bus operations with no bus reuse, for large clusters, the Lego scheme uses less than half for b > 2. And even for b = 1, the reduction is O(5mn) compared to O(8mn), equivalent to the method of [4] for five qubits per bus. This will thus be the method of choice for any ancilla-based cluster generation that allows bus reuse. Our results are directly applicable to bus-based experimental production of cluster states, enabling the same FIG. 2: Dynamic generation using multiple ancillas. resources to produce dynamically-generated cluster states of twice the size compared to single-gate bus use, see fig. 2. For multi-bus dynamic schemes, fully scalable operation can be achieved with half the coherence time compared to single-gate buses, needing as few as 20 CPhase gates per bus. We thank Aram Harrow, Ashley Stephens and Simon Devitt for useful discussions. CH was supported by EU project QAP and the Bristol Centre for Nanoscience and Quantum Information. KLB is supported by a UK Engineering and Physical Sciences Research Council industrial CASE studentship from Hewlett-Packard, VMK is supported by a UK Royal Society University Research Fellowship and WJM acknowledges partial support from the EU project HIP and MEXT in Japan.
Discrimination of Bell states plays an important role in a number of quantum computational protocols such as teleportation and secret sharing. However, most of the protocols dealing with Bell state discrimination in the literature either involve performing correlated measurements or destroying the entanglement of the system. Here, we demonstrate an NMR-based experimental realization of a protocol for Bell state discrimination, following a scheme proposed by Gupta et al (quant-ph/0504183v1, 23 April 2005), which does not destroy the Bell state under consideration. Using the proposed protocol, one can deterministically distinguish the Bell states, without performing a measurement using the entangled basis. State discrimination is performed through two independent measurements on one ancilla qubit, which leaves the Bell states unchanged.
Cluster state quantum dialogue is proposed,which enables both legitimate parties to exchange their 4 bit secret messages in a direct way.Compared with the there-particle W states,the shemes have following advantages.After two-step security check,four-bit secret message can be transmitted to each other by transmitting of single particle with the aid of two-bit classical information.The scheme can discard the drawback of the intercept-resend attack,the entangle-measure attack,and the optimal incoherent attack.
By designing two-step transmissions, this paper presents two quantum dialogue (QD) protocols that can resist different types of collective noise in the quantum channel. The message carrier of the proposed scheme utilizes decoherence-free subspaces to remain invariant under the impact of collective noise. We employ combinations of these quantum states to form decoy photon pairs, ensuring secure transmission and preventing message distortion. Based on the principle that a single photon in an EPR pair reveals no information about its actual state, an EPR pair requires only one photon for protection during transmission. This property effectively reduces the number of decoy photons needed to ensure the security of quantum transmission, which can also be applied to the logical EPR pair consisting of logical qubits. A quantum logic circuit is also designed to demonstrate the practical implementation of shuffling the logical qubits within each logical EPR pair. Therefore, the proposed two-step QD protocols require only half as many decoy photons to achieve the same security level as other state-of-the-art QD schemes. The significant reduction in the utilization of decoy photons improves the qubit efficiency of the proposed QD protocols compared to other existing works in the field. Additionally, the security analysis of the proposed QD schemes ensures the absence of information leakage and resistance to common quantum attacks.
In this paper, two robust quantum dialogue (QD) protocols over collective-dephasing noise channel and collective- rotation noise channel are proposed, respectively, by using three-qubit entangled states as the initial quantum resource. Alice generates a series of three-qubit entangled states and divides them into a physical qubit sequence and a logical qubit sequence. Then, Alice sends the logical qubit sequence to Bob. Afterward, Alice and Bob measure the physical qubit sequence and the logical qubit sequence, respectively. According to his measurement result, Bob generates a new logical qubit sequence with no measurement performed. Then, Bob encodes his secret messages on the new logical qubit sequence by performing logical unitary operations on it. Afterward, Bob sends the encoded logical qubit sequence back to Alice. Finally, Alice encodes her secret messages on the encoded logical qubit sequence from Bob by performing logical unitary operations on it and publishes her measurement. As a result, Alice and Bob can decode out each other's secret messages. By virtue of the measurement correlation of three-qubit entangled states, two participants share the initial states of message logical qubits privately. In this way, the information leakage problem is overcome. The proposed protocols only need the single-photon measurements. Compared with previous QD protocols workable over collective noise channels, the proposed protocols have the highest information-theoretical efficiency.