677 research outputs found
Impedance-matched cavity quantum memory
We consider an atomic frequency comb based quantum memory inside an
asymmetric optical cavity. In this configuration it is possible to absorb the
input light completely in a system with an effective optical depth of one,
provided that the absorption per cavity round trip exactly matches the
transmission of the coupling mirror ("impedance matching"). We show that the
impedance matching results in a readout efficiency only limited by irreversible
atomic dephasing, whose effect can be made very small in systems with large
inhomogeneous broadening. Our proposal opens up an attractive route towards
quantum memories with close to unit efficiency.Comment: 4 pages, 2 figure
Interpretation of Electron Micrographs
Courses in electron microscopical techniques should include training in the active reading of electron micrographs. The student should be made aware of the fact that every micrograph contains a wealth of information, evident and hidden, and that a careful inspection is required to retrieve the information. More time should normally be spent in scrutinizing the micrograph than in its manufacture. Active reading of the micrograph is aided by a curiosity in the functional significance of the various details of the picture; there has to be a dialogue between the mind and the eye concerning the structural elements and their significance. The investigator also has to be critical with respect to the possibility of technical flaws and should further be on guard against seeing such patterns that others may have seen and have described but which actually do not exist in the micrograph. Among examples given for an analysis in this paper are flaws in the metal shadowing technique and in ultrathin sections that have undergone deformation
Electric control of collective atomic coherence in an Erbium doped solid
We demonstrate fast and accurate control of the evolution of collective
atomic coherences in an Erbium doped solid using external electric fields. This
is achieved by controlling the inhomogeneous broadening of Erbium ions emitting
at 1536 nm using an electric field gradient and the linear Stark effect. The
manipulation of atomic coherence is characterized with the collective
spontaneous emission (optical free induction decay) emitted by the sample after
an optical excitation, which does not require any previous preparation of the
atoms. We show that controlled dephasing and rephasing of the atoms by the
electric field result in collapses and revivals of the optical free induction
decay. Our results show that the use of external electric fields does not
introduce any substantial additional decoherence and enables the manipulation
of collective atomic coherence with a very high degree of precision on the time
scale of tens of ns. This provides an interesting resource for photonic quantum
state storage and quantum state manipulation.Comment: 10 pages, 5 figure
Storage and recall of weak coherent optical pulses with an efficiency of 25%
We demonstrate experimentally a quantum memory scheme for the storage of weak
coherent light pulses in an inhomogeneously broadened optical transition in a
Pr^{3+}: YSO crystal at 2.1 K. Precise optical pumping using a frequency stable
(about 1kHz linewidth) laser is employed to create a highly controllable Atomic
Frequency Comb (AFC) structure. We report single photon storage and retrieval
efficiencies of 25%, based on coherent photon echo type re-emission in the
forward direction. The coherence property of the quantum memory is proved
through interference between a super Gaussian pulse and the emitted echo.
Backward retrieval of the photon echo emission has potential for increasing
storage and recall efficiency.Comment: 5,
Quantum Storage of Photonic Entanglement in a Crystal
Entanglement is the fundamental characteristic of quantum physics. Large
experimental efforts are devoted to harness entanglement between various
physical systems. In particular, entanglement between light and material
systems is interesting due to their prospective roles as "flying" and
stationary qubits in future quantum information technologies, such as quantum
repeaters and quantum networks. Here we report the first demonstration of
entanglement between a photon at telecommunication wavelength and a single
collective atomic excitation stored in a crystal. One photon from an
energy-time entangled pair is mapped onto a crystal and then released into a
well-defined spatial mode after a predetermined storage time. The other photon
is at telecommunication wavelength and is sent directly through a 50 m fiber
link to an analyzer. Successful transfer of entanglement to the crystal and
back is proven by a violation of the Clauser-Horne-Shimony-Holt (CHSH)
inequality by almost three standard deviations (S=2.64+/-0.23). These results
represent an important step towards quantum communication technologies based on
solid-state devices. In particular, our resources pave the way for building
efficient multiplexed quantum repeaters for long-distance quantum networks.Comment: 5 pages, 3 figures + supplementary information; fixed typo in ref.
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