Phase damping is the main decoherence in the evolution of quantum states. In
most of the known quantum computing and quantum information processing,
devices have amplitude damping times that are around 1-2 orders of magnitude
larger than the corresponding dephasing times. For lossy optical fibre as a
quantum channel, the quantum capacity is well known. The channel is
degradable. We know that dephasing channel is also degradable, thus it can
be anticipate that the channel capacity is available. We calculate the
capacity with various methods in this paper.
We analyze the entanglement condition of a new kind of non-Gaussian quantum
state, which is prepared by photon number subtraction from a two mode
Gaussian state. Fock space criterion and Shchukin-Vogel criterion are
applied and the results are compared. Two kinds of the original Gaussian
states are utilized. Their photon subtracted states have different
We consider the time evolution of the tripartite three mode
Gaussian state which is initially prepared in genuine entangled
pure state. The state undergoes parametric amplification and
amplitude damping as well as thermal noise. The correlation matrix
of the evolved state is studied in the symmetrical case. The
separability conditions are given.
We consider the entanglement transformations of the protocols that convert quantum qubit system to continuous variable system and convert it back. Here the quantum D/A conversion protocol maps finite-dimensional input states onto continuous variable states while the quantum A/D conversion protocol maps two mode squeezed state onto entangled state in 2x2 dimensions. Quantum carrier is investigated when pure qubit state interacts with coherent state.
Multipartite entanglement is quite difficult to deal with. In this paper, I will consider a particular kind of tripartite Gaussian states, which can be produced as the initial pure tripartite states undergo different noise for each party. I will make use of the relative entropy of entanglement to evaluate the entanglement properties of the states based on the fact that the separability of tripartite Gaussian states is well known. In addition, the procedure of calculating the relative entropy between Gaussian states have developed recently. All these make the evaluating the relative entropy of entanglement of tripartite Gaussian states possible.
The entanglement of formation of bipartite quantum Gaussian state is investigated by means of local operation, which maps continuous variable state to a bipartite qubits system. A two parameters quantum Guassian state is introduced, the concurrence of its mapped qubits state is calculated to characterize the entanglement of the original state.
In this paper, we analyze the performance of error probability of amplitude shift keying (ASK) system of coherent state signals and phase shift keying (PSK) system of squeezed state signals, in which we use a quantum receiver called square root measurement.