110 research outputs found
Overcoming Noise in Entanglement Distribution
Noise can be considered the natural enemy of quantum information. An often
implied benefit of high-dimensional entanglement is its increased resilience to
noise. However, manifesting this potential in an experimentally meaningful
fashion is challenging and has never been done before. In infinite dimensional
spaces, discretisation is inevitable and renders the effective dimension of
quantum states a tunable parameter. Owing to advances in experimental
techniques and theoretical tools, we demonstrate an increased resistance to
noise by identifying two pathways to exploit high-dimensional entangled states.
Our study is based on two separate experiments utilising canonical
spatio-temporal properties of entangled photon pairs. Following these different
pathways to noise resilience, we are able to certify entanglement in the
photonic orbital-angular-momentum and energy-time degrees of freedom up to
noise conditions corresponding to a noise fraction of 72 % and 92 %
respectively. Our work paves the way towards practical quantum communication
systems that are able to surpass current noise and distance limitations, while
not compromising on potential device-independence.Comment: 12 pages main text, 7 pages supplementary information, 6 figure
Polarization entanglement by time-reversed Hong-Ou-Mandel interference
Sources of entanglement are an enabling resource in quantum technology, and
pushing the limits of generation rate and quality of entanglement is a
necessary pre-requisite towards practical applications. Here, we present an
ultra-bright source of polarization-entangled photon pairs based on
time-reversed Hong-Ou-Mandel interference. By superimposing four pair-creation
possibilities on a polarization beam splitter, pairs of identical photons are
separated into two spatial modes without the usual requirement for wavelength
distinguishability or non-collinear emission angles. Our source yields
high-fidelity polarization entanglement and high pair-generation rates without
any requirement for active interferometric stabilization, which makes it an
ideal candidate for a variety of applications, in particular those requiring
indistinguishable photons
Photonic entanglement during a zero-g flight
Quantum technologies have matured to the point that we can test fundamental
quantum phenomena under extreme conditions. Specifically, entanglement, a
cornerstone of modern quantum information theory, can be robustly produced and
verified in various adverse environments. We take these tests further and
implement a high-quality Bell experiment during a parabolic flight,
transitioning from microgravity to hypergravity of 1.8 g while continuously
observing Bell violation, with Bell-CHSH parameters between and
, an average of , and average standard
deviation of . This violation is unaffected both
by uniform and non-uniform acceleration. This experiment demonstrates the
stability of current quantum communication platforms for space-based
applications and adds an important reference point for testing the interplay of
non-inertial motion and quantum information.Comment: 10+12 pages, 18 figure
Distribution of genuine high-dimensional entanglement over 10.2 km of noisy metropolitan atmosphere
In a recent quantum key distribution experiment, high-dimensional protocols
were used to show an improved noise resistance over a 10.2 km free-space
channel. One of the unresolved questions in this context is whether the
communicating parties actually shared genuine high-dimensional entanglement. In
this letter we introduce an improved discretisation and entanglement
certification scheme for high-dimensional time-bin setups and apply it to the
data obtained during the experiment. Our analysis answers the aforementioned
question affirmatively and thus the experiment constitutes the first
transmission of genuine high-dimensional entanglement in a single degree of
freedom over a long-range free-space channel.Comment: 6 pages, 3 figure
Cosmic Bell Test using Random Measurement Settings from High-Redshift Quasars
In this Letter, we present a cosmic Bell experiment with
polarization-entangled photons, in which measurement settings were determined
based on real-time measurements of the wavelength of photons from high-redshift
quasars, whose light was emitted billions of years ago, the experiment
simultaneously ensures locality. Assuming fair sampling for all detected
photons and that the wavelength of the quasar photons had not been selectively
altered or previewed between emission and detection, we observe statistically
significant violation of Bell's inequality by standard deviations,
corresponding to an estimated value of . This
experiment pushes back to at least Gyr ago the most recent time by
which any local-realist influences could have exploited the "freedom-of-choice"
loophole to engineer the observed Bell violation, excluding any such mechanism
from of the space-time volume of the past light cone of our experiment,
extending from the big bang to today.Comment: 9 pages, 4 figures, plus Supplemental Material (16 pages, 8 figures).
Matches version to be published in Physical Review Letter
Simultaneous transmission of hyper-entanglement in three degrees of freedom through a multicore fiber
Abstract Entanglement distribution is at the heart of most quantum communication protocols. Inevitable loss of photons along quantum channels is a major obstacle for distributing entangled photons over long distances, as the no-cloning theorem forbids the information to simply be amplified along the way as is done in classical communication. It is therefore desirable for every successfully transmitted photon pair to carry as much entanglement as possible. Spontaneous parametric down-conversion (SPDC) creates photons entangled in multiple high-dimensional degrees of freedom simultaneously, often referred to as hyper-entanglement. In this work, we use a multicore fiber (MCF) to show that energy-time and polarization degrees of freedom can simultaneously be transmitted in multiple fiber cores, even maintaining path entanglement across the cores. We verify a fidelity to the ideal Bell state of at least 95% in all degrees of freedom. Furthermore, because the entangled photons are created with a center wavelength of 1560 nm, our approach can readily be integrated into modern telecommunication infrastructure, thus paving the way for high-rate quantum key distribution and many other entanglement-based quantum communication protocols
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