Effective multi-mode photon echo based quantum memory on multi-atomic ensemble in the QED cavity is proposed. Analytical solution is obtained for the quantum memory efficiency that can be equal unity when optimal relations for the cavity and atomic parameters are held. Numerical estimation for realistic atomic and cavity parameters demonstrates the high efficiency of the quantum memory for optically thin resonant atomic system. 42.50.Ct, 42.50.Md Quantum communications and quantum computation require an effective quantum memory (QM) that should possess a multi-mode and high fidelity character [1][2][3][4][5]. Most well-known QM based on electromagnetically induced transparency effect [6] demonstrates an efficient storage and retrieval only for a specific single temporal mode regime [7][8][9]. Photon echo QM [10-14] offers most promising properties for realization of the multi-mode QM [15][16][17]. However, the quantum efficiency of all discussed multi-mode variants of the photon echo QM tends to unity for infinite optical depth αL as [1 − exp(−αL)] 2 , where α and L are resonant absorption coefficient and length of the medium along the light field propagation [18,19]. It imposes a fundamental limit for the QM efficiency so it is necessary to increase either the atomic concentration or the medium length. However, the QM device should be compact and the large increase of the atomic concentration gives rise to atomic decoherence due to the dipole-dipole interactions limiting thereby a storage time. So, using the free space QM scheme is quite problematic for practical devices. Efficient photon echo QM with controlled reverse of inhomogeneous broadening (CRIB) have been studied recently in ideal cavity [20] and in bad cavity [21] where high QM efficiency has been demonstrated only for a specific optimal single mode regime. Here, we propose a general approach for multi-mode photon echo type of QM in QED cavity (single mode resonator). We demonstrate a high efficiency of the QM for the optimized system of atoms and QED cavity at arbitrary temporal shape of the stored field modes. We find a simple analytical solution for QM efficiency and the optimal conditions for matching of the atomic and cavity parameters where the QM efficiency can reach unity even for small optical depth of the medium loaded in the cavity. Basic equations:We analyze resonant multi-atomic system in a single mode QED cavity coupled with signal and bath fields. By following to the cavity mode formalism [22], we use a Tavis-Cumming Hamiltonian [23]Ĥ =Ĥ o +Ĥ 1 , for N atoms, field modes and their interactions taking into account the inhomogeneous and homogeneous broadenings of the atomic frequencies and continuous spectral distribution of the field modes wherêare main energies of atoms (S j z is a z-projection of the spin 1/2 operator), energy of cavity field (â + andâ are arising and decreasing operators), energies of signal (l=1) and bath (l=2) fields (b + l and b l are arising and decreasing operators of the field modesThe first term in (2) compr...

In this paper we present universal broadband multi-resonator quantum memory (MR-QM) based on the spatial-frequency combs of the microresonators coupled with a common waveguide. Here we found new Bragg-type impedance matching condition for the coupling of the microresonators with a waveguide field which provides an efficient broadband quantum storage. The obtained analytical solution for the microresonator fields enables sustainable parametric control of all the memory characteristics.

The first realization of solid state quantum computer was demonstrated recently by using artificial atoms -transmons in superconducting resonator. Here, we propose a novel architecture of flexible and scalable quantum computer based on a waveguide circuit coupling many quantum nodes of controlled atomic ensembles. For the first time, we found the optimal practically attainable parameters of the atoms and circuit for 100% efficiency of quantum memory for multi qubit photon fields and confirmed experimentally the predicted perfect storage. Then we revealed self modes for reversible transfer of qubits between the quantum memory node and arbitrary other nodes. We found a realization of iSWAP gate via direct coupling of two arbitrary nodes with a processing rate accelerated proportionally to number of atoms in the node. A large number of the two-qubit gates can be simultaneously realized in the circuit for implementation of parallel quantum processing. Dynamic coherent elimination procedure of excess quantum state and collective blockade mechanism are proposed for realization of iSW AP and √ iSW AP quantum gates.