International Journal of Quantum Information

We describe a general quantum computational algorithm that simulates the time evolution of an arbitrary nonrelativistic, Coulombic many-body system in three dimensions, considering only spatial degrees of freedom. We use a simple discretized model of Schrödinger evolution in the coordinate representation and discuss detailed constructions of the operators necessary to realize the scheme of Wiesner and Zalka. The algorithm is simulated numerically for small test cases, and its outputs are found to be in good agreement with analytical solutions.

We present a semiquantum secret sharing protocol by using two-particle entangled states in which quantum Alice shares a secret key with two classical parties, Bob and Charlie. Classical Bob and Charlie are restricted to measuring, preparing a particle in the computational basis, or reflecting the particles. None of them can acquire the secret unless they collaborate. We also show the protocol is secure against eavesdropping.

The protocol of the teleportation of an arbitrary unknown one-qubit state is investigated when the quantum channel is subject to the decoherence from the non-Markovian environments with the memory effects. The quality of the teleportation measured by the average fidelity and minimal fidelity can be enhanced in the non-Markovian channel. The memory effects give rise to the revival of the fidelity which is better than that obtained by the Markovian channel.

A theory of two-photon phase-sensitive amplifier based on two-photon cascade is presented. The atomic coherence is produced by means of two dipole-allowed transitions driven by coherent fields; a practical alternative versus scheme employing coupling between dipole-forbidden levels. The regime of parameters under which a laser signal can be phase locked and amplified is discussed through the corresponding Fokker–Planck equation.

We design a double-slit experimental set-up, realizable at least in principle, for ascertaining three noncommuting quantum observables according to a method alternative to that of the "mean king" problem. Then, we exploit this experimental scheme to identify a physical situation where the known notions of quantum interferometry do not directly apply. A generalization of such notions is proposed that turns out to satisfy the authentic meaning of the interferometric quantum complementarity.

An analytic proof is given which shows that it is impossible to extend any triple of mutually unbiased (MU) product bases in dimension six by a single MU vector. Furthermore, the 16 states obtained by removing two orthogonal states from any MU product triple cannot figure in a (hypothetical) complete set of seven MU bases. These results follow from exploiting the structure of MU product bases in a novel fashion, and they are among the strongest ones obtained for MU bases in dimension six without recourse to computer algebra.

We investigate quantum channels, which after a finite number k of repeated applications erase all input information, i.e. channels whose kth power (but no smaller power) is a completely depolarizing channel. We show that on a system with Hilbert space dimension d, the order is bounded by k ≤ d² - 1, and give an explicit construction scheme for such channels. We also consider strictly forgetful memory channels, i.e. channels with an additional input and output in every step, which after exactly k steps retain no information about the initial memory state. We establish an explicit representation for such channels showing that the same bound applies for the memory depth k in terms of the memory dimension d.

We have verified theoretically, an opportunity for the measurement of a nuclear spin state in a paramagnetic atom with oscillating cantilever-driven adiabatic reversals (OSCAR) technique in magnetic resonance force microscopy (MRFM), which has been applied for a single electron spin detection. We have developed a semi-classical approach, where the electron–nuclear spin system is treated as a quantum mechanical one while the motion of a ferromagnetic particle on the cantilever tip is considered classically. Our computations support the idea of the measurement of a nuclear spin state by detection of a single electron spin. The effect of magnetic noise is also discussed.

The original two-way continuous-variable quantum-key-distribution (CV-QKD) protocols [S. Pirandola, S. Mancini, S. Lloyd and S. L. Braunstein, Nat. Phys. 4 (2008) 726] give the security against the collective attack on the condition of the tomography of the quantum channels. We propose a family of new two-way CV-QKD protocols and prove their security against collective entangling cloner attacks without the tomography of the quantum channels. The simulation result indicates that the new protocols maintain the same advantage as the original two-way protocols whose tolerable excess noise surpasses that of the one-way CV-QKD protocol. We also show that all sub-protocols within the family have higher secret key rate and much longer transmission distance than the one-way CV-QKD protocol for the noisy channel.

The quantum discord is used as measure of quantum correlations for two families of multipartite coherent states. The first family interpolates between generalized GHZ states and generalized Werner states. The second one is an interpolation between generalized GHZ and the ground state of the multipartite quantum system. Two inequivalent ways to split the system in a pair of qubits are introduced. The explicit expressions of quantum quantum discord in multipartite coherent states are derived. Its evaluation uses the Koashi–Winter relation in optimizing the conditional entropy. The temporal evolution of quantum correlations (quantum discord and entanglement) is also discussed.

We proposed a general transformation in probabilistic teleportation, which is based on different entanglement matching coefficients K corresponding to different unitary evolution which provides one with more flexible evolution method experimentally. Through analysis based on the Bell basis and generalized Bell basis measurement for two probabilistic teleportation, we suggested a general probability of successful teleportation, which is not only determined by the entanglement degree of transmission channels and measurement methods, but also related to the unitary transformation in the teleportation process.

We present a scheme for multiparty-controlled remote preparation of an arbitrary m-qudit (d-dimensional quantum system) state via positive operator-valued measurement (POVM) by using nonmaximally entangled states as the quantum channel, not resorting to auxiliary qubits. The sender performs an optimal POVM measurement on her m particles with measurement operators that depend on the original state, the controllers perform generalized X-basis measurement X_d and the receiver can prepare the original state if he cooperates with all the controllers and the sender. The scheme has the advantage of having high success probability for remote preparing an arbitrary m-qudit state and more convenient than others in a practical application. Moreover, it discusses the relationship between the probability that the receiver obtains the originally state and the coefficients of the entangled states.