Quantum Information Processing最新文献

In this paper, a new scheme for asymmetric cyclic controlled teleportation of arbitrary three-dimensional unknown quantum states is proposed by performing three-dimensional Bell-state measurements and three-dimensional Hadamard transformation. The entangled state of thirteen-qutrit acts as the quantum channel to connect senders and receivers, which is constructed by a three-qutrit entangled state and five two-qutrit entangled states. In this scheme, Alice wants to transmit an arbitrary unknown single-qutrit state to Bob, at the same time, Bob wants to transmit an arbitrary unknown two-qutrit entangled state to Charlie and Charlie wants to transmit an arbitrary unknown three-qutrit entangled state to Alice under the control of the supervisor David. Participants can reconstruct the original states and make the scheme perfectly by performing appropriate unitary operation. Then, the scheme can be generalized to realize the asymmetric cyclic controlled quantum teleportation of N (N > 3) participants in the three-dimensional system, and come up with two universal schemes are determined by the parity of the participant. Furthermore, the scheme is investigated in two different noisy channels: amplitude-damping noise and phase-damping noise, and calculated the fidelities of the output states. It is demonstrated that the fidelities only depend on the coefficients of the initial state and the decoherence noisy rate. The security of the scheme is briefly analyzed and compares with the previous schemes in terms of efficiency. The proposed scheme contributes to advancing understanding of high-dimensional quantum teleportation.

We study the ground-state entanglement between two atoms in a two-dimensional isotropic harmonic trap. We consider a finite-range soft-core interaction that can be applied to simulate various atomic systems. We provide detailed results on the dependence of the correlations on the parameters of the system. Our investigations show that in the hardcore limit, the wave function can be approximated as the product of the radial and angular components regardless of the interaction range. This implies that the radial and angular correlations are independent of one another. However, correlations within the radial and angular components persist and are heavily influenced by the interaction range. The radial correlations are generally weaker than the angular correlations. When soft-core interactions are considered, the correlations exhibit more complex behavior.

Orthogonal frequency-division multiplexing (OFDM) is a crucial modulation method used in contemporary digital communication systems for its significant spectral efficiency, low latency, and robustness in challenging environments. This work examines the novel use of OFDM in quantum communication, an area that offers exceptional security and efficiency in information transfer using quantum mechanics principles. In the rapidly evolving field of quantum computing, understanding, and mitigating quantum bit errors is paramount. This paper presents a rigorous analysis of bit error rates (BER) in quantum circuits, focusing on the impact of the quantum Fourier transform and its inverse, contrasted against quantum circuits employing dynamic gate sequences. Our research methodology encompasses simulations over a diverse set of parameters, including varying qubit counts ranging from 2 to 8 and theta angles (15, 30, 45, and 60°), as well as random theta values, utilizing the advanced capabilities of the Qiskit framework. Our findings indicate that quantum OFDM substantially improves quantum communication, lowering errors and boosting security. The quantum model outperforms the reference model in BER, with further enhancements as qubits increase.

This paper presents a hybrid variational quantum algorithm that finds a random eigenvector of a unitary matrix with a known quantum circuit. The algorithm is based on the SWAP test on trial states generated by a parametrized quantum circuit. The eigenvector is described by a compact set of classical parameters that can be used to reproduce the found approximation to the eigenstate on demand. This variational eigenvector finder can be adapted to solve the generalized eigenvalue problem, to find the eigenvectors of normal matrices and to perform quantum principal component analysis on unknown input mixed states. These algorithms can all be run with low-depth quantum circuits, suitable for an efficient implementation on noisy intermediate-scale quantum computers and, with some restrictions, on linear optical systems. In full-scale quantum computers, where there might be optimization problems due to barren plateaus in larger systems, the proposed algorithms can be used as a primitive to boost known quantum algorithms. Limitations and potential applications are discussed.

Quantum error correction techniques are important for implementing fault-tolerant quantum computation, and topological quantum error correcting codes provide feasibility for implementing large-scale fault-tolerant quantum computation. Here, we propose a deep reinforcement learning framework for implementing quantum error correction algorithms for errors on heavy hexagonal codes. Specifically, we construct the double deep Q learning model with policy reuse method, so that the decoding agent does not have to explore the learning from scratch when dealing with new error syndrome, but instead reuses past policies, which can reduce the computational complexity. And the double deep Q network can avoid the problem of threshold being overestimated and get the true decoding threshold. Our experimental results show that the error correction accuracy of our decoder can reach 91.86%. Different thresholds are obtained according to the code distance, which is 0.0058 when the code distance is 3, 5, 7, and 0.0065 when the code distance is 5, 7, 9, both higher than that of the classical minimum weight perfect matching decoder. Compared to the threshold of the MWPM decoder under the depolarizing noise model, the threshold of our decoder is improved by 32.63%, which enables better fault-tolerant quantum computation.

A quantum conference key agreement (QCKA) protocol based on differential-phase-shift quantum key distribution is presented, which provides a common secret key for secure communication between more than two parties. In the proposed protocol, one party simultaneously broadcasts a weak coherent pulse train with {0, π} phases to multiple parties that measure the phase differences between adjacent pulses using a delay interferometer followed by photon detectors, and the transmitter and receivers share secret key bits from the coincident counts in the receivers. The system setup and operation are simpler than those of conventional QCKA schemes that use a multipartite quantum entanglement state. The key creation performance is evaluated by considering the eavesdropping probability. The results indicate that the proposed scheme offers better performance than the conventional entanglement-based QCKA system.

Uncertainty principle is one of the most fundamental features in quantum mechanics and plays a significant role in quantum information processing. We establish tighter summation form of the uncertainty relations based on metric-adjusted skew information via operator representation of observables, which improves the existing results. By employing the methodologies of sampling coordinates of observables, we also present tighter product form of the uncertainty relations. Detailed examples are given to illustrate the advantages of our uncertainty relations.

The sharing of quantum nonlocality has been the subject of much recent research for two-qubit and three-qubit entangled systems. In this paper, we discuss nonlocality sharing with unsharp measurement based on Mermin–Ardehali–Belinskii–Klyshko (MABK) inequality for the N-qubit generalized Greenberger–Horne–Zeilinger (GHZ) system. In the one-sided sequential measurements scenario, we determine a state range associated with k within which ( k+1 ) independent observers can share the standard N-partite nonlocality with the other ((N-1)) sides, as well as a state range where arbitrarily many independent observers can do the same. Similarly, as to the m-sided sequential measurements scenario, we also identify a state range influenced by k within which ( k+1 ) independent observers in each of m sides can share the standard N-partite nonlocality with the other ((N-m)) sides, and a state range where arbitrarily many independent observers can do so. Crucially, all of our nonlocality sharing findings result from a measurement strategy in which every sequential observer employs unequal sharpness measurements. As a special case, for the three-qubit maximally entangled GHZ state, we demonstrate that an unbounded number of observers can share the nonlocality in the one-sided sequential measurements scenario. This outcome further underscores the importance of unequal sharpness measurements in recycling qubits for generating quantum nonlocality.

Quantum circuits are one of the best platforms to implement quantum algorithms. Concerning fault-tolerant quantum circuit, the Clifford + T gate set supports quantum circuits against decoherence error. However, they cause physical resource overheads like many qubits and the use of T gates as a high-cost computing element. This work focuses on low T-cost fault tolerant quantum ALU implementation using Clifford + T gate set. Three new different designs of quantum ALU are proposed by introducing a new quantum logic unit, and new low-cost fault tolerant implementations of full adder and subtractor circuits. We present a novel lemma in synthesizing quantum NCV-based circuits to Clifford + T quantum circuits. This lemma shows how an NCV-based structure with less CNOT layer can lead to an improvement in T-count and T-depth criteria in Clifford + T equivalent circuit. We analyze the effect of applying our proposed lemma in implementing low-cost fault tolerant Clifford + T circuits by some examples on adder and subtractors and ALUs. Comparison of the designs shows 50%, 40%, 36%, and 69% superior functionality of our proposed ALU module in terms of T-count, T-depth, number of qubits, and number of calculated operations compared to the existing counterpart, respectively. The proposed lemma can be used as a simplification step in quantum circuit synthesis algorithms and can be extended to use in quantum synthesis tools.

In this paper, we examine how finite time disentanglement can be manipulated for the quantum system out of thermal equilibrium. To this aim, we employ the Markovian master equation approach to find the rate equations and Wootter’s concurrence to analyze out of thermal equilibrium entanglement dynamics for Dicke bases. The effect of super- and sub-radiant rates on entanglement sudden death is examined for different classes of X-states. It is found that the shorter dark period is achieved at a higher transition rate of a super-radiant state. This approach allows us to analyze the further applications of quantum information technologies.