1,901 research outputs found
Towards continuous-wave regime teleportation for light matter quantum relay stations
We report a teleportation experiment involving narrowband entangled photons
at 1560 nm and qubit photons at 795 nm emulated by faint laser pulses. A
nonlinear difference frequency generation stage converts the 795 nm photons to
1560 nm in order to enable interference with one photon out of the pairs, i.e.,
at the same wavelength. The spectral bandwidth of all involved photons is of
about 25 MHz, which is close to the emission bandwidth of emissive quantum
memory devices, notably those based on ensembles of cold atoms and rare earth
ions. This opens the route towards the realization of hybrid quantum nodes,
i.e., combining quantum memories and entanglement-based quantum relays
exploiting either a synchronized (pulsed) or asynchronous (continuous- wave)
scenario
PPLN Waveguide for Quantum Communication
We report on energy-time and time-bin entangled photon-pair sources based on
a periodically poled lithium niobate (PPLN) waveguide. Degenerate twin photons
at 1314 nm wavelength are created by spontaneous parametric down-conversion and
coupled into standard telecom fibers. Our PPLN waveguide features a very high
conversion efficiency of about 10^(-6), roughly 4 orders of magnitude more than
that obtained employing bulk crystals. Even if using low power laser diodes,
this engenders a significant probability for creating two pairs at a time - an
important advantage for some quantum communication protocols. We point out a
simple means to characterize the pair creation probability in case of a pulsed
pump. To investigate the quality of the entangled states, we perform
photon-pair interference experiments, leading to visibilities of 97% for the
case of energy-time entanglement and of 84% for the case of time-bin
entanglement. Although the last figure must still be improved, these tests
demonstrate the high potential of PPLN waveguide based sources to become a key
element for future quantum communication schemesComment: 11 pages, 9 figures, submitted to the European Physical Journal D
(special issue of the Quick conference
Toward the multiphoton parametric oscillators
We propose novel types of parametric oscillators generating both three-photon
and four-photon bright light which are accessible for an experiment. The
devices are based on the cascaded down-conversion processes and consist of
second-order media inserted in two-resonant mode cavity. Discussion of
dissipation and quantum features of the system are performed by the
quantum-jump simulation method and concerns to the Wigner functions. The
phase-space multistabilities and critical threshold behavior of three- and
four-photon subharmonics are obtained.Comment: 3 figures, submitted to Physics Letter
Nonlinear interaction between two heralded single photons
Harnessing nonlinearities strong enough to allow two single photons to
interact with one another is not only a fascinating challenge but is central to
numerous advanced applications in quantum information science. Currently, all
known approaches are extremely challenging although a few have led to
experimental realisations with attenuated classical laser light. This has
included cross-phase modulation with weak classical light in atomic ensembles
and optical fibres, converting incident laser light into a non-classical stream
of photon or Rydberg blockades as well as all-optical switches with attenuated
classical light in various atomic systems. Here we report the observation of a
nonlinear parametric interaction between two true single photons. Single
photons are initially generated by heralding one photon from each of two
independent spontaneous parametric downconversion sources. The two heralded
single photons are subsequently combined in a nonlinear waveguide where they
are converted into a single photon with a higher energy. Our approach
highlights the potential for quantum nonlinear optics with integrated devices,
and as the photons are at telecom wavelengths, it is well adapted to
applications in quantum communication.Comment: 4 pages, 4 figure
Realization of a Decoherence-free, Optimally Distinguishable Mesoscopic Quantum Superposition
We report the realization of an entangled quantum superposition of M=12
photons by a high gain, quantum-injected optical parametric amplification. The
system is found so highly resilient against decoherence to exhibit directly
accessible mesoscopic interference effects at normal temperature. By modern
tomographic methods the non-separability and the quantum superposition are
demonstrated for the overall mesoscopic output state of the dynamic ''closed
system''. The device realizes the condition conceived by Erwin Schroedinger
with his 1935 paradigmatic ''Cat'' apologue, a fundamental landmark in quantum
mechanics.Comment: 10 pages, 3 figure
Direct Generation of Tailored Pulse-Mode Entanglement
Photonic quantum technology increasingly uses frequency encoding to enable
higher quantum information density and noise resilience. Pulsed time-frequency
modes (TFM) represent a unique class of spectrally encoded quantum states of
light that enable a complete framework for quantum information processing.
Here, we demonstrate a technique for direct generation of entangled TFM-encoded
states in single-pass, tailored downconversion processes. We achieve
unprecedented quality in state generation---high rates, heralding efficiency
and state fidelity---as characterised via highly resolved time-of-flight fibre
spectroscopy and two-photon interference. We employ this technique in a
four-photon entanglement swapping scheme as a primitive for TFM-encoded quantum
protocols.Comment: 5 pages, 4 figures, 3 pages supplemental materia
Disconnected Elementary Band Representations, Fragile Topology, and Wilson Loops as Topological Indices: An Example on the Triangular Lattice
In this work, we examine the topological phases that can arise in triangular
lattices with disconnected elementary band representations. We show that,
although these phases may be "fragile" with respect to the addition of extra
bands, their topological properties are manifest in certain nontrivial
holonomies (Wilson loops) in the space of nontrivial bands. We introduce an
eigenvalue index for fragile topology, and we show how a nontrivial value of
this index manifests as the winding of a hexagonal Wilson loop; this remains
true even in the absence of time-reversal or sixfold rotational symmetry.
Additionally, when time-reversal and twofold rotational symmetry are present,
we show directly that there is a protected nontrivial winding in more
conventional Wilson loops. Crucially, we emphasize that these Wilson loops
cannot change without closing a gap to the nontrivial bands. By studying the
entanglement spectrum for the fragile bands, we comment on the relationship
between fragile topology and the "obstructed atomic limit" of B. Bradlyn et
al., Nature 547, 298--305 (2017). We conclude with some perspectives on
topological matter beyond the K-theory classification.Comment: 13 pages, 10 figures v2. accepted versio
Interaction of Independent Single Photons based on Integrated Nonlinear Optics
Photons are ideal carriers of quantum information, as they can be easily
created and can travel long distances without being affected by decoherence.
For this reason, they are well suited for quantum communication. However, the
interaction between single photons is negligible under most circumstances.
Realising such an interaction is not only fundamentally fascinating but holds
great potential for emerging technologies. It has recently been shown that even
weak optical nonlinearities between single photons can be used to perform
important quantum communication tasks more efficiently than methods based on
linear optics, which have fundamental limitations. Nonlinear optical effects at
single photon levels in atomic media have been studied and demonstrated but
these are neither flexible nor compatible with quantum communication as they
impose restrictions on photons' wavelengths and bandwidths. Here we use a high
efficiency nonlinear waveguide to observe the sum-frequency generation between
a single photon and a single-photon level coherent state from two independent
sources. The use of an integrated, room-temperature device and telecom
wavelengths makes this approach to photon-photon interaction well adapted to
long distance quantum communication, moving quantum nonlinear optics one step
further towards complex quantum networks and future applications such as device
independent quantum key distribution
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