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Quantum theory predicts that entanglement can also persist in macroscopic physical systems, albeit difficulties to demonstrate it experimentally remain. Recently, significant progress has been achieved and genuine entanglement between up to 2900 atoms was reported. Here, we demonstrate 16 million genuinely entangled atoms in a solid-state quantum memory prepared by the heralded absorption of a single photon. We develop an entanglement witness for quantifying the number of genuinely entangled particles based on the collective effect of directed emission combined with the non-classical nature of the emitted light. The method is applicable to a wide range of physical systems and is effective even in situations with significant losses. Our results clarify the role of multipartite entanglement in ensemble-based quantum memories and demonstrate the accessibility to certain classes of multipartite entanglement with limited experimental control. The presence of entanglement in macroscopic systems is notoriously difficult to observe. Here, the authors develop a witness which allow them to demonstrate entanglement between millions of atoms in a solid-state quantum memory prepared by the heralded absorption of a single photon.

Efficient optical pumping is an important tool for state initialization in quantum technologies, such as optical quantum memories. In crystals doped with Kramers rare-earth ions, such as erbium and neodymium, efficient optical pumping is challenging due to the relatively short population lifetimes of the electronic Zeeman levels, of the order of 100 ms at around 4 K. In this article we show that optical pumping of the hyperfine levels in isotopically enriched 145Nd 3 + :Y2SiO5 crystals is more efficient, owing to the longer population relaxation times of hyperfine levels. By optically cycling the population many times through the excited state a nuclear spin flip can be forced in the ground state hyperfine manifold, in which case the population is trapped for several seconds before relaxing back to the pumped hyperfine level. To demonstrate the effectiveness of this approach in applications we perform an atomic frequency comb memory experiment with 33% storage efficiency in 145Nd 3 + :Y2SiO5, which is on a par with results obtained in non-Kramers ions, e.g. europium and praseodymium, where optical pumping is generally efficient due to the quenched electronic spin. Efficient optical pumping in neodymium-doped crystals is also of interest for spectral filtering in biomedical imaging, as neodymium has an absorption wavelength compatible with tissue imaging. In addition to these applications, our study is of interest for understanding spin dynamics in Kramers ions with nuclear spin.

A quantum computer attains computational advantage when outperforming the best classical computers running the best-known algorithms on well-defined tasks. No photonic machine offering programmability over all its quantum gates has demonstrated quantum computational advantage: previous machines 1 , 2 were largely restricted to static gate sequences. Earlier photonic demonstrations were also vulnerable to spoofing 3 , in which classical heuristics produce samples, without direct simulation, lying closer to the ideal distribution than do samples from the quantum hardware. Here we report quantum computational advantage using Borealis, a photonic processor offering dynamic programmability on all gates implemented. We carry out Gaussian boson sampling 4 (GBS) on 216 squeezed modes entangled with three-dimensional connectivity 5 , using a time-multiplexed and photon-number-resolving architecture. On average, it would take more than 9,000 years for the best available algorithms and supercomputers to produce, using exact methods, a single sample from the programmed distribution, whereas Borealis requires only 36 μs. This runtime advantage is over 50 million times as extreme as that reported from earlier photonic machines. Ours constitutes a very large GBS experiment, registering events with up to 219 photons and a mean photon number of 125. This work is a critical milestone on the path to a practical quantum computer, validating key technological features of photonics as a platform for this goal. Gaussian boson sampling is performed on 216 squeezed modes entangled with three-dimensional connectivity 5 , using Borealis, registering events with up to 219 photons and a mean photon number of 125.

One-way quantum computing requires an entangled multiqubit system. So-called cluster states have been proposed to provide this resource, but they are difficult to generate. An alternative that uses the ground state of a one-dimensional chain of spins is now experimentally realized and used to construct a quantum logic gate. One-way quantum computation proceeds by sequentially measuring individual spins in an entangled many-spin resource state 1 . It remains a challenge, however, to efficiently produce such resources. Is it possible to reduce the task of their production to simply cooling a quantum many-body system to its ground state? Cluster states, the canonical resource for one-way quantum computing, do not naturally occur as ground states of physical systems 2 , 3 , leading to a significant effort to identify alternatives that do appear as ground states in spin lattices  4 , 5 , 6 , 7 , 8 . An appealing candidate is a valence-bond-solid state described by Affleck, Kennedy, Lieb and Tasaki 9 (AKLT). It is the unique, gapped ground state for a two-body Hamiltonian on a spin-1 chain, and can be used as a resource for one-way quantum computing  4 , 5 , 6 , 7 . Here, we experimentally generate a photonic AKLT state and use it to implement single-qubit quantum logic gates.

It is believed that the current approaches to energetic content in gun propellants have reached their limits. Oxidation of molecules with a carbon backbone is the approach that has been in use for decades and has reached its full potential. Strain cage structures like CL-20 provide good energetic content but remain very expensive. Additional challenges in gun propellant design include reduced sensitivity, improved thermal stability, lowered environmental impact and reducing wear of gun systems due to propellants. Nitrogen-rich materials are anticipated to be a solution to these challenges without having to sacrifice performance. However, efforts have mostly been centered on the synthesis of new molecules with little attention paid to their effects in gun propellants. This thesis aims to fill this gap in energetic materials research by measuring the effects of nitrogen-rich materials in gun propellants. More specifically, the properties investigated were the performance, stability and erosivity of nitrogen-rich propellants. A total of four nitrogen-rich materials, 5,5’-hydrazinebistetrazole (HBT), 5,5’-bis-(1H-tetrazolyl)-amine (BTA), 5-aminotetrazolium nitrate (HAT-NO3) and 3,6-dihydrazino-s-tetrazine (DHT) were incorporated at concentrations of 5%, 15%, 25% and 35% (HBT and BTA only) in a modified triple base gun propellant. The triple base was composed of nitrocellulose, trimethylolethane trinitrate and diethylene glycol dinitrate. All nitrogen-rich materials resulted in a burning rate increase regardless of concentration with the burning increase reaching as high as 93% for 5,5’-bis-(1H-tetrazolyl)-amine. Significant changes in burning rate laws also indicated changes in the combustion kinetics of the propellants which were due to the nitrogen-rich materials. The thermal stability, both short-term and long-term, was evaluated for all propellants. BTA and HBT proved to have no significant effect on the long-term stability of the propellants and the short-term thermal stability of the propellants incorporating these materials remained within acceptable levels. Both DHT and HAT-NO3 proved to have poor long-term stability. The decrease of the stability of the propellant incorporating HAT-NO3 is attributed to the salt dissociating into its acid-base precursors which leads to accelerated decomposition of nitrocellulose due to nitric acid. Propellants incorporating DHT exhibited a catastrophic autocatalytic decomposition behavior. This behavior is attributed to the decomposition products of the other materials in the propellant oxidizing DHT which leads to its decomposition and further decomposition of the propellant. The effects of HBT and BTA on the erosivity of gun propellants were characterized, a first for nitrogen-rich materials in propellants. The addition of nitrogen-rich materials significantly lowered the erosivity of the propellants. It also demonstrated that current modeling of erosion may not be adequate for nitrogen-rich materials given their semi-empirical nature and the effects of nitrogen gas diffusing and reacting with the gun steel. Finally, a set of heuristics based on the results obtained is proposed to help formulators with the initial screening of nitrogen-rich materials in gun propellant applications. These heuristics are proposed in lieu of models as it was discovered that such models could only be the result of a complex and important series of experimental works outside of the scope of a single PhD thesis.

Le comité des résidents du Vieux-Québec s’inquiète pour le patrimoine visuel de Québec si un troisième lien devait voir le jour à l’est du centre-ville, tel qu'annoncé par le premier ministre François Legault jeudi. Une citation de Michel Masse, président du comité des résidents du Vieux-Québec Tout sur le 3e lien Québec-Lévis Consulter le dossier complet Tout sur le 3e lien Québec-Lévis Consulter le dossier complet Michel Masse souligne que le gabarit de l’infrastructure sera «immense» puisqu’il faudra permettre le passage des navires sous le pont. À titre d’exemple, le bateau de croisière Queen Mary 2, qui fait parfois escale à Québec, mesure 72 m de haut, dont 62 m au-dessus du niveau de l'eau. La santé publique évite de se prononcer Philippe Robert, médecin spécialisé en santé publique, n’a toutefois pas voulu s’avancer sur la construction d’un éventuel troisième lien, plaidant qu’il n’est pas possible de l’analyser en profondeur à ce stade-ci.

Signaux encourageants Le gouvernement du Québec doit tenir un point de presse d’ici la fin de la semaine pour commenter le plan de mobilité de CDPQ Infra. Dans les couloirs de l’Assemblée nationale mercredi, le ministre des Infrastructures a indiqué que les sommes nécessaires pour réaliser la phase un, soit la ligne de tramway de l’avenue Le Gendre à Charlesbourg et un service rapide par bus sur les deux rives, sont disponibles dans le Plan québécois des infrastructures. «C'est un plan ambitieux qui combine le court, le moyen et le long terme», commente le président Yvon Charest.