International Journal of Quantum Information

We study quantum state transfer through a qubit network modeled by spins with XY interaction, when relying on a single excitation. We show that it is possible to achieve perfect transfer by shifting (adding) energy to specific vertices. This technique appears to be a potentially powerful tool for changing, and in some cases improving, the transfer capabilities of quantum networks. Analytical results are presented for all-to-all networks and for all-to-all networks with a missing link. Moreover, we evaluate the effect of random fluctuations on the transmission fidelity.

This paper studies quantum perfect state transfer on weighted graphs. We prove that the join of a weighted two-vertex graph with any regular graph has perfect state transfer. This generalizes a result of Casaccino et al.¹ where the regular graph is a complete graph with or without a missing edge. In contrast, we prove that the half-join of a weighted two-vertex graph with any weighted regular graph has no perfect state transfer. As a corollary, unlike for complete graphs, adding weights in complete bipartite graphs does not produce perfect state transfer. We also observe that any Hamming graph has perfect state transfer between each pair of its vertices. The result is a corollary of a closure property on weighted Cartesian products of perfect state transfer graphs. Moreover, on a hypercube, we show that perfect state transfer occurs between uniform superpositions on pairs of arbitrary subcubes, thus generalizing results of Bernasconi et al.² and Moore and Russell.³

For a three-qubit Heisenberg XX spin chain with the uniform magnetic field and magnetic impurity, dynamic evolution of pairwise entanglement are studied. We show that the phenomenon of entanglement sudden death (ESD) occurs in the evolution of entanglement for some initial states. We also find that magnetic impurity cannot only eliminate the phenomenon of ESD but also induce the ESD effects, which is different from the case of uniform magnetic field where the ESD can be depressed but cannot be eliminated by introducing the uniform magnetic field.

In this paper, we present a scheme to prepare the W state and the GHZ state of many atomic ensembles based on the dynamics of the atomic system of a single control atom and an atomic ensemble dispersively coupling with a cavity, where the control atom is illuminated by a highly detuned auxiliary classical field at the same time. The dynamics of the atomic system can be described by an effective Jaynes–Cummings model (JCM) with the atomic ensemble as the bosonic mode. The preparation of the entangled states is deterministic. Because the cavity is always in the vacuum state during the whole evolution process, our scheme is less sensitive to the cavity decay.

We propose a novel non-Hermitian adiabatic quantum optimization algorithm. One of the new ideas is to use a non-Hermitian auxiliary "initial" Hamiltonian that provides an effective level repulsion for the main Hamiltonian. This effect enables us to develop an adiabatic theory which determines ground state much more efficiently than Hermitian methods.

We present two robust quantum key distribution protocols against two kinds of collective noise, following some ideas in quantum dense coding. Three-qubit entangled states are used as quantum information carriers, two of which form the logical qubit, which is invariant with a special type of collective noise. The information is encoded on logical qubits with four unitary operations, which can be read out faithfully with Bell-state analysis on two physical qubits and a single-photon measurement on the other physical qubit, not three-photon joint measurements. Two bits of information are exchanged faithfully and securely by transmitting two physical qubits through a noisy channel. When the losses in the noisy channel is low, these protocols can be used to transmit a secret message directly in principle.

In this paper, we revisit the entanglement concentration protocol of Bennett et al. and the entanglement dilution protocol of Lo and Popescu via the method of types and provide a simple upper bound on the coefficient of the bound on the classical communication cost of the Lo-Popescu protocol.

The capability of a one-dimensional four-qubit cluster state for teleportation is extensively investigated in the condition that the four qubits are non-averagely distributed between two locations. Because of the inherent qubit orientation of the cluster state, we found that only in eight distributions can an arbitrary single-qubit state be perfectly teleported from a sender to a receiver. For each case, the necessary local operations and classical communication (LOCC) are explicitly shown.

A new experimental protocol of teleportation is proposed by using hyperentangled photon pairs, and by this protocol the probability approaches unity. This set-up is made of hyper-entangled photon source, linear optical elements and conventional photon detectors.

We present a modified scheme for probabilistic remote preparation of a single qubit when partial classical knowledge of preparing state is available for the receiver. This is in contrast with the previous remote state preparation schemes that the receiver has no classical knowledge of preparing state. It is demonstrated that the total success probability of remote state preparation will be greatly improved when the receiver has partial classical knowledge of preparing state.

In this paper, by constructing a more entangled quantum system, we shorten the adiabatic quantum search algorithm to constant time. On the other hand, we show that the speed-up of adiabatic quantum algorithms by selecting particular adiabatic evolution paths or injecting energy into the quantum system can be explained as a form of entanglement enlargement. These findings suggest that entanglement plays a fundamental role for the efficiency of algorithm performance.

We discuss new aspects of the interaction between a cavity field and Kerr-like medium, focusing on Fisher Information. Here, we provide a new formula for marginal distributions of the Fisher Information and comparison with the Wehrl entropy for the system has been presented. The results show that, it is a correlation measure which is true for any quantum state, provided that it shows the same entropy behaviors of certain reduced states.