Kuang Le-Man

QUANTUM STATISTICAL PROPERTIES OF PHOTONS AND ATOMS IN INTERACTION OF AN ATOMIC BOSE-EINSTEIN CONDENSATE WITH LASERS

In this paper, we study quantum statistical properties of atoms and photons in interaction of -atomic Bose–Einstein condensate in the ground-state hyperfine sublevels with laser fields. We investigate not only quantum conversions between atoms in the condensate and photons in the quantized laser field, but also transfer of nonclassical characteristics of atoms and photons between input states and output states when the atom field is initially in a number state and the quantized laser field is in the even coherent state and the odd coherent state, respectively. We find various conditions to realize these quantum conversions. We also study atom-photon quantum correlations and their input-output conversions. It is indicated that there are atom-field nonclassical correlations.

Even and odd coherent states of a harmonic oscillator in a finite-dimensional Hilbert space and their squeezing properties

Abstract The even and odd coherent states (CSs) of a finite-dimensional Hilbert space harmonic oscillator (FDHSHO) are constructed and some properties of these states are studied. Their quadrature squeezing and amplitude-squared squeezing are investigated in detail. It is shown that, while the squeezing behavior of the even and odd CSs of the FDHSHO approaches that of the even and odd CSs of the usual harmonic oscillator as the dimension of the Hilbert space tends to infinity, this behavior is nontrivally different if the dimension of the Hilbert space is finite. In the latter case, it is found that the even and odd CSs exhibit both amplitude-squared squeezing and quadrature squeezing.

Generation of High-Dimensional Photon Entangled Coherent States in Double Electromagnetically Induced Transparency System

We present an approach to generate high-dimensional entangled coherent states between photons by using a dense atomic system in a double electromagnetically induced transparency state. The system under our consideration involves an atomic configuration with six internal states, two weak quantized probe lasers, and two strong classical coupling lasers. We show how to generate high dimensional entangled coherent states between the two probe lasers.

Entanglement-Enhanced Two-Photon Delocalization in a Coupled-Cavity Array

We study the transport properties of two entangled photons which are initially injected into two nearest-neighbor coupling cavities in an one-dimensional coupled-cavity array (CCA). It is found that photonic transport dynamics in the two-photon CCA exhibits the entanglement-enhanced two-photon delocalization phenomenon. It is shown that the CCA can realize the localization-to-delocalization transition for two entangled photons.We study transport properties of two entangled photons whic h are initially injected into two nearest-neighbor coupling cavities in a one-dimensional coupled-cavity arr ay (CCA). It is found that photonic transport dynamics in the two-photon CCA exhibits entanglement-enhanced twoph ton delocalization (TPD) phenomenon. It is shown that the CCA can realize the localization-to-delocal ization transition for two entangled photons.

Broadcasting of Entanglement in Three-Particle Greenberger-Horne-Zeilinger State via Quantum Copying

We introduce entanglement measures to describe entanglement in a threeparticle system and apply it to studying broadcasting of entanglement in three-particle GHZ state. We show that entanglement of three-qubit GHZ state can be partially broadcasted with the help of local or non-local copying processes. It is found that non-local cloning is much more efficient than local cloning for the broadcasting of entanglement. PACS number(s): 03.75.Fi, 03.65Bz; 32.80.Pj, 74.20.De Typeset using REVTEX 1 Quantum entanglement, first noted by Einstein-Podolsky-Rosen and Schrödinger [1], is one of the essential features of quantum mechanics. It has been well known that quntum entanglement plays a key role in many such applications like quantum teleportation [2], super-dense coding [3], quantum error correction [4], and quantum computational speedups [5]. Recently, maximally entangled states of three particles, i.e., three-particle GHZ states, have been produced experimentally [6]. Usually, it is difficult to obtain ideal entangled multi-particle state. An interesting question is: whether there are ways which can broadcast the entanglement of correlated systems? The answer is ok. Masiak and Knight [7] have shown that copies of entangled pair of qubits can be genetated through using a universal quantum cloning machine (UQCM) [8] , although the degree of entanglement of the resultant copies is substantially reduced due to a residual entanglement between the copied output and the copying machine. On the other hand, up to now there is not an appropriate measure to describe quantatively the entanglement of three and more subsystems due to the high complexity of entanglement in multi-particle system [9]. The purpose of this paper is to propose measures of entanglement in three qubit system in terms of the entanglement tensor approach [10], and use these measures to investigate broadcasting of entanglement [11] in three-particle GHZ state. Consider a system consisting of three qubits. The density operator of the system can be expanded as a sum of tensor products in terms of Puali matrices, ρ̂ = 1 8 [1̂ ⊗ 1̂ ⊗ 1̂ + 3We introduce entanglement measures to describe entanglement in a three-particle system and apply it to studying broadcasting of entanglement in the three-particle Greenberger-Horne-Zeilinger (GHZ) state. The results show that the entanglement of the three-qubit GHZ state can be partially broadcasted with the help of local or non-local copying processes. It is found that non-local cloning is much more efficient than local cloning for the broadcasting of entanglement.

Quantum Dynamics of Entanglement and Single Excitation Transfer in LH1-RC-Type Trimer

In this paper, we study quantum dynamics of entanglement and single excitation transfer (SET) in an LH1-RC-type trimer which can describe a basic unit cell in the LH1-RC complex in the photosynthetic process. It is shown that there exists a sudden change of entanglement at the critic point of quantum phase transition (QPT) of the system at low temperatures, the entanglement sudden change caused by the QPT is suppressed at higher temperatures. We investigate the influence of environment on entanglement and SET. We show the generation of the dephasing-assisted entanglement between a donor and an acceptor and the existence of the steady-state entanglement, and demonstrate the entanglement transfer from donor-donor entanglement to donor-acceptor entanglement in the dynamic evolution. We reveal the close relation between the SET probability and donor-acceptor entanglement. Especially, we find that the SET probability is proportional to the amount of donor-acceptor entanglement under certain conditions.

Entanglement Preserving in Quantum Copying of Three-Qubit Entangled State*

We study the degree to which quantum entanglement survives when a three-qubit entangled state is copied by using local and non-local processes, respectively, and investigate iterating quantum copying for the three-qubit system. There may exist inter-three-qubit entanglement and inter-two-qubit entanglement for the three-qubit system. We show that both local and non-local copying processes degrade quantum entanglement in the three-particle system due to a residual correlation between the copied output and the copying machine. We also show that the inter-two-qubit entanglement is preserved better than the inter-three-qubit entanglement in the local cloning process. We find that non-local cloning is much more efficient than the local copying for broadcasting entanglement, and output state via non-local cloning exhibits the fidelity better than local cloning.

Squeezing Properties of Even Coherent States in a Finite-Dimensional Hilbert Space

Even coherent states (ECSs) of a finite-dimensional Hilbert space harmonic oscillator (FDHSHO) are constructed explicitly. Some properties of them are discussed. The quadrature squeezing and the amplituded-squared squeezing of these states are investigated in detail. It is found that ECSs of the FDHSHO exhibit not only the quadrature squeezing but also the amplituded-squeezing.

Even and Odd Q-coherent State Representations of the Q-deformed Heisenberg-Weyl Algebra

We construct explicitly even and odd q-coherent states. These q-coherent states are introduced in terms of the q-functions defined in the paper. It is shown that the even and odd q-coherent states form a kind of representations of the q-deformed Heisenberg-Weyl algebra which is realized in the form of matrix q-differential operators in the even and odd q-coherent state space. We also analyse some different between the even and odd q-CSs and the usual even and odd CSs.

Quantum Dynamics of Two Capacitively Coupled Superconducting Islands via Josephson Junctions

In this paper, we consider a system consisting of two capacitively coupled superconducting islands via Josephson junctions. We show that it can be reduced to two coupling harmonic oscillators under certain conditions, and can be solved exactly in terms of a displacing transformation, a beam-splitter-like transformation, and a squeezing transformation. It is found that the system evolves by a rotated-squeezed-coherent state when the system is initially in a coherent state. Quantum dynamics of the Cooper pairs in the two superconducting islands are investigated. It is shown that the number of the Cooper pairs in the two islands evolves periodically.