15 research outputs found
Stable control of 10 dB two-mode squeezed vacuum states of light
Continuous variable entanglement is a fundamental resource for many quantum
information tasks. Important protocols like superactivation of zero-capacity
channels and finite-size quantum cryptography that provides security against
most general attacks, require about 10 dB two-mode squeezing. Additionally,
stable phase control mechanisms are necessary but are difficult to achieve
because the total amount of optical loss to the entangled beams needs to be
small. Here, we experimentally demonstrate a control scheme for two-mode
squeezed vacuum states at the telecommunication wavelength of 1550 nm. Our
states exhibited an Einstein-Podolsky-Rosen covariance product of 0.0309 \pm
0.0002, where 1 is the critical value, and a Duan inseparability value of 0.360
\pm 0.001, where 4 is the critical value. The latter corresponds to 10.45 \pm
0.01 dB which reflects the average non-classical noise suppression of the two
squeezed vacuum states used to generate the entanglement. With the results of
this work demanding quantum information protocols will become feasible.Comment: 8 pages, 4 figure
Experimental analysis of Einstein-Podolsky-Rosen steering for quantum information applications
[no abstract
Experimental entanglement distribution by separable states
The distribution of entanglement between macroscopically separated parties
represents a crucial protocol for future quantum information networks.
Surprisingly, it has been theoretically shown that two distant systems can be
entangled by sending a third mediating system that is not entangled with either
of them. Such a possibility seems to contradict the intuition that to
distribute entanglement, the transmitted system always needs to be entangled
with the sender. Here, we experimentally distribute entanglement by exchanging
a subsystem and successfully prove that this subsystem is not entangled with
either of the two parties. Our implementation relies on the preparation of a
specific three-mode Gaussian state containing thermal noise that demolishes the
entanglement in two of the three bipartite splittings. After transmission of a
separable mode this noise can be removed by quantum interference. Our work
demonstrates an unexpected variant of entanglement distribution and improves
the understanding necessary to engineer multipartite quantum information
networks.Comment: 9 pages, 6 figure
Strong Einstein-Podolsky-Rosen entanglement from a single squeezed light source
Einstein-Podolsky-Rosen (EPR) entanglement is a criterion that is more
demanding than just certifying entanglement. We theoretically and
experimentally analyze the low resource generation of bi-partite continuous
variable entanglement, as realized by mixing a squeezed mode with a vacuum mode
at a balanced beam splitter, i.e. the generation of so-called vacuum-class
entanglement. We find that in order to observe EPR entanglement the total
optical loss must be smaller than 33.3 %. However, arbitrary strong EPR
entanglement is generally possible with this scheme. We realize continuous wave
squeezed light at 1550 nm with up to 9.9 dB of non-classical noise reduction,
which is the highest value at a telecom wavelength so far. Using two phase
controlled balanced homodyne detectors we observe an EPR co-variance product of
0.502 \pm 0.006 < 1, where 1 is the critical value. We discuss the feasibility
of strong Gaussian entanglement and its application for quantum key
distribution in a short-distance fiber network.Comment: 4 pages, 4 figure
Implementation of Quantum Key Distribution with Composable Security Against Coherent Attacks using Einstein-Podolsky-Rosen Entanglement
Secret communication over public channels is one of the central pillars of a
modern information society. Using quantum key distribution (QKD) this is
achieved without relying on the hardness of mathematical problems which might
be compromised by improved algorithms or by future quantum computers.
State-of-the-art QKD requires composable security against coherent attacks for
a finite number of samples. Here, we present the first implementation of QKD
satisfying this requirement and additionally achieving security which is
independent of any possible flaws in the implementation of the receiver. By
distributing strongly Einstein-Podolsky-Rosen entangled continuous variable
(CV) light in a table-top arrangement, we generated secret keys using a highly
efficient error reconciliation algorithm. Since CV encoding is compatible with
conventional optical communication technology, we consider our work to be a
major promotion for commercialized QKD providing composable security against
the most general channel attacks.Comment: 7 pages, 3 figure
Efficient information reconciliation for Continuous-Variable QKD using Non-Binary Low-Density Parity-Check Codes
We present here an information reconciliation method and demonstrate for the first time that it can achieve efficiencies close to 0.98. This method is based on the belief propagation decoding of non-binary LDPC codes over finite (Galois) fields. In particular, for convenience and faster decoding we only consider power-of-two Galois fields
Quantum Enhancement of the Zero-Area Sagnac Interferometer Topology for Gravitational Wave Detection
Only a few years ago, it was realized that the zero-area Sagnac
interferometer topology is able to perform quantum nondemolition measurements
of position changes of a mechanical oscillator. Here, we experimentally show
that such an interferometer can also be efficiently enhanced by squeezed light.
We achieved a nonclassical sensitivity improvement of up to 8.2 dB, limited by
optical loss inside our interferometer. Measurements performed directly on our
squeezed-light laser output revealed squeezing of 12.7 dB. We show that the
sensitivity of a squeezed-light enhanced Sagnac interferometer can surpass the
standard quantum limit for a broad spectrum of signal frequencies without the
need for filter cavities as required for Michelson interferometers. The Sagnac
topology is therefore a powerful option for future gravitational-wave
detectors, such as the Einstein Telescope, whose design is currently being
studied.Comment: 4 pages, 4 figure
Ab-initio Quantum Enhanced Optical Phase Estimation Using Real-time Feedback Control
Optical phase estimation is a vital measurement primitive that is used to
perform accurate measurements of various physical quantities like length,
velocity and displacements. The precision of such measurements can be largely
enhanced by the use of entangled or squeezed states of light as demonstrated in
a variety of different optical systems. Most of these accounts however deal
with the measurement of a very small shift of an already known phase, which is
in stark contrast to ab-initio phase estimation where the initial phase is
unknown. Here we report on the realization of a quantum enhanced and fully
deterministic phase estimation protocol based on real-time feedback control.
Using robust squeezed states of light combined with a real-time Bayesian
estimation feedback algorithm, we demonstrate deterministic phase estimation
with a precision beyond the quantum shot noise limit. The demonstrated protocol
opens up new opportunities for quantum microscopy, quantum metrology and
quantum information processing.Comment: 5 figure
Observation of one-way Einstein-Podolsky-Rosen steering
The distinctive non-classical features of quantum physics were first
discussed in the seminal paper by A. Einstein, B. Podolsky and N. Rosen (EPR)
in 1935. In his immediate response E. Schr\"odinger introduced the notion of
entanglement, now seen as the essential resource in quantum information as well
as in quantum metrology. Furthermore he showed that at the core of the EPR
argument is a phenomenon which he called steering. In contrast to entanglement
and violations of Bell's inequalities, steering implies a direction between the
parties involved. Recent theoretical works have precisely defined this
property. Here we present an experimental realization of two entangled Gaussian
modes of light by which in fact one party can steer the other but not
conversely. The generated one-way steering gives a new insight into quantum
physics and may open a new field of applications in quantum information.Comment: 4 pages, 4 figure