Quantum Information Processing最新文献

Stabilizer circuits arise in almost every area of quantum computation and communication, so there is interest in studying them from an information-theoretic perspective, i.e. as quantum channels. We consider several natural approaches to what can be called a Clifford channel: the channel that can be realized by a stabilizer circuit without classical control, the channel that sends pure stabilizer states to mixed stabilizer states, the channel with stabilizer Choi state, the channel whose Stinespring dilation can have a Clifford unitary. We show the equivalence of these definitions. Up to unitary encoding and decoding maps any Clifford channel is a product of stabilizer state preparations, qubit discardings, identity channels and full dephasing channels. This simple structure allows to compute information capacities of such channels.

Mode-pairing quantum key distribution (MP-QKD) leverages post-selection pairing strategy to achieve a balance between ease of implementation and high performance, establishing itself as a highly promising protocol in future QKD networks. However, the reliance on pairing strategies causes a considerable number of pulses to be excluded from parameter estimation and key generation, introducing inefficiencies and diminishing overall performance. In this study, we extend the original protocol by incorporating an active pairing strategy. This involves actively pairing clicking events that fall within the same phase slice, thereby generating new successful pairs and enabling the reutilization of previously discarded events. To validate the efficiency of our scheme, we conducted simulations of the three-intensity decoy-state MP-QKD protocol with the double-scanning method. The simulation results demonstrate significant advantages in both parameter estimation and final key generation. Therefore, this study provides valuable insights for advancing future MP-QKD experiments and applications.

In quantum computing theory, the well-known Deutsch’s problem and Deutsch–Jozsa problem can be equivalent to symmetric Boolean functions. Meanwhile, sensitivity of Boolean functions is a quite important complexity measure in the query model. So far, whether symmetry means high-sensitivity problems is still considered as a challenge. In symmetric setting, based on whether all inputs in ({0,1}^{n}) are defined, this paper investigates sensitivity of total and partial Boolean functions, respectively. Firstly, we point out that the computation of sensitivity requires at most (n+1) classical queries or n quantum queries. Secondly, we show that the lower bound of sensitivity is not less than (frac{n}{2}) except for the sensitivity 0. Finally, we discover and prove some non-trivial bounds on the number of symmetric (total and partial) Boolean functions with each possible sensitivity.

Magnon-based quantum state transfer of a qubit is investigated in a one-dimensional Heisenberg model featuring uncorrelated disorder. In the weak coupling regime with respect to the boundaries of the channel, the presence of an anomalous magnon mode with diverging localization length is harnessed to promote high-fidelity state transfer despite the degree of exchange coupling disorder. Under the additional influence of diagonal disorder due to the external magnetic field, we explore ways to optimize the transfer fidelity by navigating through the disordered landscape so as to identify extended states within the channel. Our results are relevant to the design of magnon-based devices for information processing and communication amid the fast-paced progress in the field of magnonics.

In this work, we propose a novel variational quantum approach for solving a class of nonlinear optimal control problems. Our approach integrates Dirac’s canonical quantization of dynamical systems with the solution of the ground state of the resulting non-Hermitian Hamiltonian via a variational quantum eigensolver (VQE). We introduce a new perspective on the Dirac bracket formulation for generalized Hamiltonian dynamics in the presence of constraints, providing a clear motivation and illustrative examples. Additionally, we explore the structural properties of Dirac brackets within the context of multidimensional constrained optimization problems. Our approach for solving a class of nonlinear optimal control problems employs a VQE-based approach to determine the eigenstate and corresponding eigenvalue associated with the ground state energy of a non-Hermitian Hamiltonian. Assuming access to an ideal VQE, our formulation demonstrates excellent results, as evidenced by selected computational examples. Furthermore, our method performs well when combined with a VQE-based approach for non-Hermitian Hamiltonian systems. Our VQE-based formulation effectively addresses challenges associated with a wide range of optimal control problems, particularly in high-dimensional scenarios. Compared to standard classical approaches, our quantum-based method shows significant promise and offers a compelling alternative for tackling complex, high-dimensional optimization challenges.

Consider a one-dimensional spin chain, from spin 1 to spin N, such that each spin interacts with its nearest neighbors. Performing a local operation (measurement) on spin N, we expect from the Lieb–Robinson velocity that, in general, the effect of this measurement achieves spin 1 after some while. But, in this paper, we show that if (a) the measurement on spin N is performed instantaneously and (b) the initial state of the spin chain is chosen appropriately, then the effect of the measurement on spin N never achieves spin 1. In other words, performing or not performing an instantaneous measurement on spin N at (t=0) does not alter the reduced dynamics of spin 1 for all the times (tge 0). We can interpret this as the following: The information of performing an instantaneous measurement on spin N is isolated such that it cannot achieve spin 1.

Boson sampling is one of the main quantum computation models to demonstrate the quantum computational advantage. However, this aim may be hard to realize considering two main kinds of noises, which are photon distinguishability and photon loss. Inspired by the Bayesian validation extended to evaluate whether distinguishability is too high to demonstrate this advantage, the pattern recognition validation is extended for boson sampling, considering both distinguishability and loss. Based on clusters constructed with the K means + + method, where parameters are carefully adjusted to optimize the extended validation performances, the distribution of outcomes is nearly monotonically changed with indistinguishability, especially when photons are close to be indistinguishable. However, this regulation may be suppressed by photon loss. The intrinsic data structure of output events is analyzed through calculating probability distributions and mean 2-norm distances of the sorted outputs. An approximation algorithm is also used to show the data structure changes with noises.

We provide a mathematical framework for identifying the shortest path in a maze using a Grover walk, which becomes non-unitary by introducing absorbing holes. In this study, we define the maze as a network with vertices connected by unweighted edges. Our analysis of the stationary state of the truncated Grover walk on finite graphs, where we strategically place absorbing holes and self-loops on specific vertices, demonstrates that this approach can effectively solve mazes. By setting arbitrary start and goal vertices in the underlying graph, we obtain the following long-time results: (i) in tree structures, the probability amplitude is concentrated exclusively along the shortest path between start and goal; (ii) in ladder-like structures with additional paths, the probability amplitude is maximized near the shortest path.

We investigate the N → M probabilistic quantum cloning of three equidistant states defined by a real number of the overlap among them. We design the most general transformation of probabilistic quantum cloning, which improves the probabilistic quantum cloning proposed in the reference (Duan and Guo. PRL. 80, 4999 (1998)). The success cloning probability of generating M copies out of N original are dependent on the numbers N and M and the sign of the overlaps among three equidistant states. Based on the most general transformation of probabilistic quantum cloning, our result suggests that the measurement operators of the unambiguous state discrimination should include the success operators and the correct operators.

Based on the realignment moments of density matrix, we study parameterized entanglement criteria for bipartite and multipartite states. By adjusting the different parameter values, our criterion can detect not only bound entangled states, but also non-positive partial transpose entangled states for bipartite quantum systems. Moreover, we propose the definition of multipartite realignment moments and generalize the result of bipartite systems to obtain a sufficient criterion to detect entanglement for multipartite quantum states in arbitrary dimensions. And we further improve the conclusion to obtain another new entanglement criterion. The new method can detect more entangled states than previous methods as backed by detailed examples.