22 research outputs found
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
In-field entanglement distribution over a 96 km-long submarine optical fibre
Techniques for the distribution of quantum-secured cryptographic keys have
reached a level of maturity allowing them to be implemented in all kinds of
environments, away from any form of laboratory infrastructure. Here, we detail
the distribution of entanglement between Malta and Sicily over a 96 km-long
submarine telecommunications optical fibre cable. We used this standard
telecommunications fibre as a quantum channel to distribute
polarisation-entangled photons and were able to observe around 257 photon pairs
per second, with a polarisation visibility above 90%. Our experiment
demonstrates the feasibility of using deployed submarine telecommunications
optical fibres as long-distance quantum channels for polarisation-entangled
photons. This opens up a plethora of possibilities for future experiments and
technological applications using existing infrastructure.Comment: 6 pages, 4 figure
Passively stable distribution of polarisation entanglement over 192 km of deployed optical fibre
Quantum key distribution (QKD) based on entangled photon pairs holds the
potential for repeater-based quantum networks connecting clients over long
distance. We demonstrate long-distance entanglement distribution by means of
polarisation-entangled photon pairs through two successive deployed 96 km-long
telecommunications fibres in the same submarine cable. One photon of each pair
was detected directly after the source, while the other travelled the fibre
cable in both directions for a total distance of 192 km and attenuation of 48
dB. The observed two-photon Bell state exhibited a fidelity 85% 2% and
was stable over several hours. We employed neither active stabilisation of the
quantum state nor chromatic dispersion compensation for the fibre.Comment: 7 pages, 3 figure
Cosmic Bell Test: Measurement Settings from Milky Way Stars
Bell’s theorem states that some predictions of quantum mechanics cannot be reproduced by a local-realist theory. That conflict is expressed by Bell’s inequality, which is usually derived under the assumption that there are no statistical correlations between the choices of measurement settings and anything else that can causally affect the measurement outcomes. In previous experiments, this “freedom of choice” was addressed by ensuring that selection of measurement settings via conventional “quantum random number generators” was spacelike separated from the entangled particle creation. This, however, left open the possibility that an unknown cause affected both the setting choices and measurement outcomes as recently as mere microseconds before each experimental trial. Here we report on a new experimental test of Bell’s inequality that, for the first time, uses distant astronomical sources as “cosmic setting generators.” In our tests with polarization-entangled photons, measurement settings were chosen using real-time observations of Milky Way stars while simultaneously ensuring locality. Assuming fair sampling for all detected photons, and that each stellar photon’s color was set at emission, we observe statistically significant ≳7.31σ and ≳11.93σ violations of Bell’s inequality with estimated p values of ≲1.8×10[superscript -13] and ≲4.0×10[superscript -33], respectively, thereby pushing back by ∼600 years the most recent time by which any local-realist influences could have engineered the observed Bell violation.Austrian Academy of SciencesAustrian Science Fund (Projects SFB F40 (FOQUS) and CoQuS W1210-N16)Austria. Federal Ministry of Science, Research, and EconomyNational Science Foundation (U.S.) (INSPIRE Grant PHY-1541160 and SES-1056580)Massachusetts Institute of Technology. Undergraduate Research Opportunities Progra
Scalable Authentication and Optimal Flooding in a Quantum Network
The global interest in quantum networks stems from the security guaranteed by the laws of physics. The deployment of quantum networks means facing the challenges of scaling up the physical hardware and, more importantly, of scaling up all other network layers and optimally utilizing network resources. Here, we consider two related protocols and their experimental demonstrations on an eight-user quantum network test bed, and discuss their usefulness with the aid of example use cases. First, we consider an authentication-transfer protocol to manage a fundamental limitation of quantum communication—the need for a preshared key between every pair of users linked together on the quantum network. By temporarily trusting some intermediary nodes for a short period of time (<35 min in our network), we can generate and distribute these initial authentication keys with a very high level of security. Second, when end users quantify their trust in intermediary nodes, our flooding protocol can be used to improve both end-to-end communication speeds and increase security against malicious nodes
Unconditionally secure digital signatures implemented in an eight-user quantum network
The ability to know and verifiably demonstrate the origins of messages can often be as important as encrypting the message itself. Here we present an experimental demonstration of an unconditionally secure digital signature (USS) protocol implemented for the first time, to the best of our knowledge, on a fully connected quantum network without trusted nodes. We choose a USS protocol which is secure against forging, repudiation and messages are transferrable. We show the feasibility of unconditionally secure signatures using only bi-partite entangled states distributed throughout the network and experimentally evaluate the performance of the protocol in real world scenarios with varying message lengths
Efficient cavity-assisted storage of photonic qubits in a solid-state quantum memory
We report on the high-efficiency storage and retrieval of weak coherent
optical pulses and photonic qubits in a cavity-enhanced solid-state quantum
memory. By using an atomic frequency comb (AFC) memory in a
crystal embedded in a low-finesse impedance-matched cavity, we stored weak
coherent pulses at the single photon level with up to 62% efficiency for a
pre-determined storage time of 2 s. We also confirmed that the
impedance-matched cavity enhances the efficiency for longer storage times up to
70 s. Taking advantage of the temporal multimodality of the AFC scheme, we
then store weak coherent time-bin qubits with (51+-2)% efficiency and a
measurement-device limited fidelity over (94.8+-1.4)% for the retrieved qubits.
These results represent the most efficient storage in a single photon level AFC
memory and the most efficient qubit storage in a solid-state quantum memory
up-to-date.Comment: 7 pages, 5 figure, 1 tabl
Simulation as a tool to improve wave heating in fusion plasmas
Équipe 107 : Physique des plasmas chaudsInternational audienceFirstly, a brief overview will be given on different models that are able to describe the behaviour of wave propagation as a function of specific frequency ranges. Each range corresponds to different heating systems, namely, 20-100 MHz for the ion cyclotron resonant heating, 2-20 GHz for lower-hybrid heating or current drive, and 100-250 GHz for electron cyclotron resonant heating or current drive systems. The specification of every system will be explained in detail, including the typical set of equations and the assumptions needed to describe the properties of these heating or current drive systems, as well as their specific domains of validity. In these descriptions, special attention will be paid to the boundary conditions. A review of specific physical problems associated with the wave heating systems will also be provided. The review will detail the role of simulation in answering questions that arise from experiments on magnetized plasma devices devoted to fusion. A few examples that will be covered are the impact of edge turbulence on wave propagation and its consequences on heating system performance, the effects of fast particles and ponderomotive effects, among others. A study that is more focused on radio-frequency sheath effects will also be discussed. It shows that such simulations require very sophisticated tools to gain a partial understanding of the observations undertaken in dedicated experiments. To conclude this review, an overview will be given about the requirements and progress necessary to obtain relevant predictive simulation tools able to describe the wave heating systems used in fusion devices