Satoshi Ishizaka

Maximally entangled mixed states under nonlocal unitary operations in two qubits

We propose novel mixed states in two qubits, “maximally entangled mixed states”, which have a property that the amount of entanglement of these states cannot be increased further by applying any unitary operations. The property is proven when the rank of the states is less than 4, and confirmed numerically in the other general cases. The corresponding entanglement of formation specified by its eigenvalues gives an upper bound of that for density matrices with same eigenvalues.

Quantum teleportation scheme by selecting one of multiple output ports

The scheme of quantum teleportation, where Bob has multiple

Asymptotic teleportation scheme as a universal programmable quantum processor.

(N)

Deterministic photon-photon SWAP gate using a Λ system

output ports and obtains the teleported state by simply selecting one of the

Closed formula for the relative entropy of entanglement

N

Comparison of the relative entropy of entanglement and negativity

ports, is thoroughly studied. We consider both the deterministic version and probabilistic version of the teleportation scheme aiming to teleport an unknown state of a qubit. Moreover, we consider two cases for each version: (i) the state employed for the teleportation is fixed to a maximally entangled state and (ii) the state is also optimized as well as Alices measurement. We analytically determine the optimal protocols for all the four cases and show the corresponding optimal fidelity or optimal success probability. All these protocols can achieve the perfect teleportation in the asymptotic limit of

Multiparticle entanglement manipulation under positive partial transpose preserving operations

N\ensuremath{\rightarrow}\ensuremath{\infty}

Binegativity and geometry of entangled states in two qubits

. The entanglement properties of the teleportation scheme are also discussed.

Propagation of solitons of the magnetization in magnetic nanoparticle arrays

We consider a scheme of quantum teleportation where a receiver has multiple (N) output ports and obtains the teleported state by merely selecting one of the N ports according to the outcome of the senders measurement. We demonstrate that such teleportation is possible by showing an explicit protocol where N pairs of maximally entangled qubits are employed. The optimal measurement performed by a sender is the square-root measurement, and a perfect teleportation fidelity is asymptotically achieved for a large N limit. Such asymptotic teleportation can be utilized as a universal programmable processor.

Bound entanglement provides convertibility of pure entangled states.

We theoretically present a method to realize a deterministic photon-photon (SWAP)^{1/2} gate using a three-level lambda system interacting with single photons in reflection geometry. The lambda system is used completely passively as a temporary memory for a photonic qubit; the initial state of the lambda system may be arbitrary, and active control by auxiliary fields is unnecessary throughout the gate operations. These distinct merits make this entangling gate suitable for deterministic and scalable quantum computation.