330 research outputs found
Single-Quadrature Continuous-Variable Quantum Key Distribution
Most continuous-variable quantum key distribution schemes are based on the
Gaussian modulation of coherent states followed by continuous quadrature
detection using homodyne detectors. In all previous schemes, the Gaussian
modulation has been carried out in conjugate quadratures thus requiring two
independent modulators for their implementations. Here, we propose and
experimentally test a largely simplified scheme in which the Gaussian
modulation is performed in a single quadrature. The scheme is shown to be
asymptotically secure against collective attacks, and considers asymmetric
preparation and excess noise. A single-quadrature modulation approach renders
the need for a costly amplitude modulator unnecessary, and thus facilitates
commercialization of continuous-variable quantum key distribution.Comment: 13 pages, 7 figure
Continuous Variable Quantum Key Distribution with a Noisy Laser
Existing experimental implementations of continuous-variable quantum key
distribution require shot-noise limited operation, achieved with shot-noise
limited lasers. However, loosening this requirement on the laser source would
allow for cheaper, potentially integrated systems. Here, we implement a
theoretically proposed prepare-and-measure continuous-variable protocol and
experimentally demonstrate the robustness of it against preparation noise
stemming for instance from technical laser noise. Provided that direct
reconciliation techniques are used in the post-processing we show that for
small distances large amounts of preparation noise can be tolerated in contrast
to reverse reconciliation where the key rate quickly drops to zero. Our
experiment thereby demonstrates that quantum key distribution with
non-shot-noise limited laser diodes might be feasible.Comment: 10 pages, 6 figures. Corrected plots for reverse reconciliatio
Super sensitivity and super resolution with quantum teleportation
We propose a method for quantum enhanced phase estimation based on continuous
variable (CV) quantum teleportation. The phase shift probed by a coherent state
can be enhanced by repeatedly teleporting the state back to interact with the
phase shift again using a supply of two-mode squeezed vacuum states. In this
way, both super resolution and super sensitivity can be obtained due to the
coherent addition of the phase shift. The protocol enables Heisenberg limited
sensitivity and super- resolution given sufficiently strong squeezing. The
proposed method could be implemented with current or near-term technology of CV
teleportation.Comment: 5 pagers, 3 figure
Electrophysiological evidence for differences between fusion and combination illusions in audiovisual speech perception
Accepted manuscript online: 4 October 2017Incongruent audiovisual speech stimuli can lead to perceptual illusions such as fusions or combinations. Here, we investigated
the underlying audiovisual integration process by measuring ERPs. We observed that visual speech-induced suppression of P2
amplitude (which is generally taken as a measure of audiovisual integration) for fusions was similar to suppression obtained with
fully congruent stimuli, whereas P2 suppression for combinations was larger. We argue that these effects arise because the phonetic
incongruency is solved differently for both types of stimuli.MB was supported by the Spanish Ministry of Economy and Competitiveness
(MINECO grant FPDI-2013-15661) and the Netherlands Organization
for Scientific Research (NWO VENI grant 275-89-027)
Quantum cryptography with an ideal local relay
We consider two remote parties connected to a relay by two quantum channels.
To generate a secret key, they transmit coherent states to the relay, where the
states are subject to a continuous-variable (CV) Bell detection. We study the
ideal case where Alice's channel is lossless, i.e., the relay is locally
situated in her lab and the Bell detection is performed with unit efficiency.
This configuration allows us to explore the optimal performances achievable by
CV measurement-device-independent (MDI) quantum key distribution (QKD). This
corresponds to the limit of a trusted local relay, where the detection loss can
be re-scaled. Our theoretical analysis is confirmed by an experimental
simulation where 10^-4 secret bits per use can potentially be distributed at
170km assuming ideal reconciliation.Comment: in Proceedings of the SPIE Security + Defence 2015 conference on
Quantum Information Science and Technology, Toulouse, France (21-24 September
2015) - Paper 9648-4
MDI-QKD: Continuous- versus discrete-variables at metropolitan distances
In a comment, Xu, Curty, Qi, Qian, and Lo claimed that discrete-variable (DV)
measurement device independent (MDI) quantum key distribution (QKD) would
compete with its continuous-variable (CV) counterpart at metropolitan
distances. Actually, Xu et al.'s analysis supports exactly the opposite by
showing that the experimental rate of our CV protocol (achieved with practical
room-temperature devices) remains one order of magnitude higher than their
purely-numerical and over-optimistic extrapolation for qubits, based on
nearly-ideal parameters and cryogenic detectors (unsuitable solutions for a
realistic metropolitan network, which is expected to run on cheap
room-temperature devices, potentially even mobile). The experimental rate of
our protocol (expressed as bits per relay use) is confirmed to be two-three
orders of magnitude higher than the rate of any realistic simulation of
practical DV-MDI-QKD over short-medium distances. Of course this does not mean
that DV-MDI-QKD networks should not be investigated or built, but increasing
their rate is a non-trivial practical problem clearly beyond the analysis of Xu
et al. Finally, in order to clarify the facts, we also refute a series of
incorrect arguments against CV-MDI-QKD and, more generally, CV-QKD, which were
made by Xu et al. with the goal of supporting their thesis.Comment: Updated reply to Xu, Curty, Qi, Qian and Lo (arXiv:1506.04819),
including a point-to-point rebuttal of their new "Appendix E: Addendum
Distributed quantum sensing in a continuous variable entangled network
Networking plays a ubiquitous role in quantum technology. It is an integral
part of quantum communication and has significant potential for upscaling
quantum computer technologies that are otherwise not scalable. Recently, it was
realized that sensing of multiple spatially distributed parameters may also
benefit from an entangled quantum network. Here we experimentally demonstrate
how sensing of an averaged phase shift among four distributed nodes benefits
from an entangled quantum network. Using a four-mode entangled continuous
variable (CV) state, we demonstrate deterministic quantum phase sensing with a
precision beyond what is attainable with separable probes. The techniques
behind this result can have direct applications in a number of primitives
ranging from biological imaging to quantum networks of atomic clocks
The early maximum likelihood estimation model of audiovisual integration in speech perception
- …