379 research outputs found
Photon echo quantum RAM integration in quantum computer
We have analyzed an efficient integration of the multi-qubit echo quantum
memory into the quantum computer scheme on the atomic resonant ensembles in
quantum electrodynamics cavity. Here, one atomic ensemble with controllable
inhomogeneous broadening is used for the quantum memory node and other atomic
ensembles characterized by the homogeneous broadening of the resonant line are
used as processing nodes. We have found optimal conditions for efficient
integration of multi-qubit quantum memory modified for this analyzed physical
scheme and we have determined a specified shape of the self temporal modes
providing a perfect reversible transfer of the photon qubits between the
quantum memory node and arbitrary processing nodes. The obtained results open
the way for realization of full-scale solid state quantum computing based on
using the efficient multi-qubit quantum memory.Comment: 13 pages, 5 figure
Photon echo quantum memory with complete use of natural inhomogeneous broadening
The photon echo quantum memory is based on a controlled rephasing of the
atomic coherence excited by signal light field in the inhomogeneously broadened
resonant line. Here, we propose a novel active mechanism of the atomic
rephasing which provides a perfect retrieval of the stored light field in the
photon echo quantum memory for arbitrary initial inhomogeneous broadening of
the resonant line. It is shown that the rephasing mechanism can exploit all
resonant atoms which maximally increases an optical depth of the resonant
transition that is one of the critical parameters for realization of highly
efficient quantum memory. We also demonstrate that the rephasing mechanism can
be used for various realizations of the photon echo quantum memory that opens a
wide road for its practical realization.Comment: 6 pages, 4 figure
Fast and robust two- and three-qubit swapping gates on multi-atomic ensembles in quantum electrodynamic cavity
Creation of quantum computer is outstanding fundamental and practical
problem. The quantum computer could be used for execution of very complicated
tasks which are not solvable with the classical computers. The first prototype
of solid state quantum computer was created in 2009 with superconducting
qubits. However, it suffers from the decoherent processes and it is desirable
to find more practical encoding of qubits with long-lived coherence. It could
be single impurity or vacancy centers in solids, but their interaction with
electromagnetic radiation is rather weak. So, here, ensembles of atoms were
proposed for the qubit encoding by using the dipole blockade mechanism in order
to turn multilevel systems in two level ones. But dipole-dipole based blockade
introduces an additional decoherence that limits its practical significance.
Recently, the collective blockade mechanism has been proposed for the system of
three-level atoms by using the different frequency shifts for the Raman
transitions between the collective atomic states characterized by a different
number of the excited atoms. Here, we propose two qubit gate by using another
collective blockade mechanism in the system of two level atoms based on
exchange interaction via the virtual photons between the multi-atomic ensembles
in the resonator. Also we demonstrate the possibility of three qubit gate
(Controlled SWAP gate) using a suppression of the swap-process between two
multi-atomic ensembles due to dynamical shift of the atomic levels controlled
by the states of photon encoded qubit
Photon echo in ring cavity: pulse area approach
Pulse area approach has been established as a versatile analytical tool for
studying the resonant interaction between the light and the resonant atomic
ensemble. In recent years photon and spin echoes in cavity assisted schemes
become increasingly interesting. In this article we develop the photon echo
pulse area approach to describe primary and multi-pulse echo generation in the
atomic ensemble placed in the ring cavity. We show that the pulse area approach
predicts relative echo magnitudes and whether the system is operating in a
single- or a multi-pulse generation regime. We also analyze the conditions
needed for the realization of these generation regimes. This work develops the
pulse area theorem approach for analytical study of photon/spin echoes in
optical and microwave cavities and echo based protocols of quantum memory.Comment: 8 pages, 4 figure
Rephasing processes and quantum memory for light: reversibility issues and how to fix them
Time reversibility is absent from some recently proposed quantum memory
protocols such as Absorption Frequency Comb (AFC). Focusing on AFC memory, we
show that quantum efficiency and fidelity are reduced dramatically, as a
consequence of non-reversibility, when the spectral width of the incoming
signal approaches the memory bandwidth. Non-reversibility is revealed through
spectral dispersion, giving rise to phase mismatching. We propose a modified
AFC scheme that restores reversibility. This way, signals can be retrieved with
excellent efficiency over the entire memory bandwidth. This study could be
extended to other quantum memory rephasing schemes in inhomogeneously broadened
absorbing media.Comment: 8 pages, 6 figures, was presented in 20th International Laser Physics
Workshop (LPHYS'11), July 11-15, 2011, Sarajevo, Bosnia and Herzegovin
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