2 a pproximately resonant transition from | e 〉 to | g 〉 ; the o ther is an exact classical field with Rabi frequency Ω to le ad the transition from | e 〉 to | m 〉 . The quantum dy- n amics of the total system is described by the following Hamiltonian in the interaction picture [5] H = ga N ∑ j =1 exp ( i K$_{ge}$ · j ) σ j $_{ge}$+ Ω N ∑ j =1 exp ( i K$_{me}$ · j ) σ j me + h.c., (3) H | d$_{n}$ ( θ ) 〉 = 0 , (4) D $^{†}$( θ ) = a $^{†}$cos θ − C $^{†}$sin θ, (5) C † = 1 √$_{N}$ N ∑ j =1 exp ( i K · j ) σ j $_{mg}$. (6) | d$_{n}$ ( θ ) 〉 = A ( n, N, θ ) √$_{n}$$_{!}$ [ D $^{†}$( θ ) ] $^{n}$| 0 〉 , (7) A ( n, N, θ ) = √ ( N − n )! N n N ! sin 2 $^{n}$2 θ × [ $_{1}$F$_{1}$ ( − n ; N − n + 1; − N cot $^{2}$θ ) ] − 1 2 (8) | 0 〉 = | 0 〉 ⊗ |↓〉 (9) II. ADIABATICALLY CREATING SQUEEZING IN DARK STATES A. Dark states w here K$_{ge}$ and K$_{me}$ are, respectively, the wave vectors of the quantum and the classical light fields. We have in- tr oduced the quasi-spin operators σ j αβ ≡ | α 〉 jj 〈 β | ( α, β = e, g, m ) for α = β in above Hamiltonian to describe the tr ansitions among the levels of | e 〉 , | g 〉 and | m 〉 . For EIT, to find the degenerate class of the eigenstates | d$_{n}$ ( θ ) 〉 satisfying FIG. 1: (Color online) Schematic illustration of the atomic ensemble interacting with two light fields: the classical light field (denoted by the blue arrow) with Rabi frequency Ω and the wave vector K me and the quantum light field (denoted by the red arrow) with the coupling constant g and the wave vector K ge . Each Λ − type atom confined in the rectangular container has the same excited state | e 〉 , the relative ground state | g 〉 and the metastable state | m 〉 . w e introduce the dark state polariton operator w hich obviously mix the electromagnetic field with cre- a tion operator a † and the quasi-spin wave with corre- s p onding operator the multipartite correlations characterized by the atomic squeezing beyond the pairwise entanglement in the dark states. In Sec. II, we study the relationship between the concurrence and the spin squeezing under adiabatic ma- nipulation, and indicate that the photon statistics varies in the same way of the spin squeezing. In Sec. IV, the sudden death of the atomic squeezing and the pairwise entanglement are considered by introducing three typical decoherence channels. The optimal times for generating the atomic squeezing and the pairwise entanglement are obtained in Sec. V. We conclude in Sec. V. The angle tan θ = $_{g}$√$_{n/}$$_{Ω}$ can be adiabatically manip- ulated in the quantum storage process, and K = K$_{ge}$ − K$_{me}$ is the wave vector difference between the quantum and the classical fields. We construct the degenerate class of the eigenstates | d$_{n}$ ( θ ) 〉 as where the normalization constant reduces to 1 when the atom number N is much larger than n . Here, n is the excitation number of the atomic ensemble, the vacuum state As shown in Fig. 1, the model we consider consists of atomic ensemble with N Λ − type atoms, which have the excited state | e 〉 , the relative ground state | g 〉 and the metastable state | m 〉 . For convenience we assume all the atoms have the same energy spacings for the above three atomic states. For the cold atomic ensemble, the Doppler width broadening of the atoms can be depressed effectively. These atoms interact with two single-mode light fields: one is quantized radiation mode (with cou- pling constant g and annihilation operator a ) to lead the is the direct product of the photonic vacuum state | 0 〉 and the quasi-spin ground state |↓〉 ≡ ∏ N j = 1 | g 〉 $_{j}$.