15,721 research outputs found
Non-classical correlations between a C-band telecom photon and a stored spin-wave
Future ground-based quantum information networks will likely use single
photons transmitted through optical fibers to entangle individual network
nodes. To extend communication distances and overcome limitations due to photon
absorption in fibers the concept of quantum repeaters has been proposed. For
that purpose, it is required to achieve quantum correlations between the
material nodes and photons at telecom wavelengths which can be sent over long
distances in optical fibers. Here we demonstrate non-classical correlation
between a frequency converted telecom C-band photon and a spin-wave stored in
an atomic ensemble quantum memory. The photons emitted from the ensemble and
heralding the spin-waves are converted from 780 nm to 1552 nm by means of an
all-solid-state integrated waveguide non-linear device. We show ultra-low noise
operation of the device enabling a high signal to noise ratio of the converted
single photon, leading to a high spin-wave heralding efficiency. The presented
work is an enabling step towards the practical entanglement of remote quantum
memories and the entanglement of quantum systems operating at different
wavelengths.Comment: 9 pages, 5 figure
Long-lived non-classical correlations for scalable quantum repeaters at room temperature
Heralded single-photon sources with on-demand readout are promising
candidates for quantum repeaters enabling long-distance quantum communication.
The need for scalability of such systems requires simple experimental
solutions, thus favouring room-temperature systems. For quantum repeater
applications, long delays between heralding and single-photon readout are
crucial. Until now, this has been prevented in room-temperature atomic systems
by fast decoherence due to thermal motion. Here we demonstrate efficient
heralding and readout of single collective excitations created in warm caesium
vapour. Using the principle of motional averaging we achieve a collective
excitation lifetime of ms, two orders of magnitude larger than
previously achieved for single excitations in room-temperature sources. We
experimentally verify non-classicality of the light-matter correlations by
observing a violation of the Cauchy-Schwarz inequality with .
Through spectral and temporal analysis we identify intrinsic four-wave mixing
noise as the main contribution compromising single-photon operation of the
source.Comment: 21 pages total, the first 17 pages are the main article and the
remaining pages are supplemental materia
Narrowband frequency tunable light source of continuous quadrature entanglement
We report the observation of non-classical quantum correlations of continuous
light variables from a novel type of source. It is a frequency non-degenerate
optical parametric oscillator below threshold, where signal and idler fields
are separated by 740MHz corresponding to two free spectrum ranges of the
parametric oscillator cavity. The degree of entanglement observed, - 3.8 dB, is
the highest to-date for a narrowband tunable source suitable for atomic quantum
memory and other applications in atomic physics. Finally we use the latter to
visualize the Einstein-Podolsky-Rosen paradox.Comment: 11 pages, 9 figures, LaTe
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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Multi-mode and long-lived quantum correlations between photons and spins in a crystal
The realization of quantum networks and quantum repeaters remains an
outstanding challenge in quantum communication. These rely on entanglement of
remote matter systems, which in turn requires creation of quantum correlations
between a single photon and a matter system. A practical way to establish such
correlations is via spontaneous Raman scattering in atomic ensembles, known as
the DLCZ scheme. However, time multiplexing is inherently difficult using this
method, which leads to low communication rates even in theory. Moreover, it is
desirable to find solid-state ensembles where such matter-photon correlations
could be generated. Here we demonstrate quantum correlations between a single
photon and a spin excitation in up to 12 temporal modes, in a Eu
doped YSiO crystal, using a novel DLCZ approach that is inherently
multimode. After a storage time of 1 ms, the spin excitation is converted into
a second photon. The quantum correlation of the generated photon pair is
verified by violating a Cauchy - Schwarz inequality. Our results show that
solid-state rare-earth crystals could be used to generate remote multi-mode
entanglement, an important resource for future quantum networks
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