Improving cold-atom sensors with quantum entanglement: Prospects and challenges

Quantum entanglement has been generated and verified in cold-atom experiments and used to make atom-interferometric measurements below the shot-noise limit. However, current state-of-the-art cold-atom devices exploit separable (i.e. unentangled) atomic states. This Perspective piece asks the question: can entanglement usefully improve cold-atom sensors, in the sense that it gives new sensing capabilities unachievable with current state-of-the-art devices? We briefly review the state-of-the-art in precision cold-atom sensing, focussing on clocks and inertial sensors, identifying the potential benefits entanglement could bring to these devices, and the challenges that need to be overcome to realize these benefits. We survey demonstrated methods of generating metrologically-useful entanglement in cold-atom systems, note their relative strengths and weaknesses, and assess their prospects for near-to-medium term quantum-enhanced cold-atom sensing.Comment: Invited perspective; close to published version. Note the change in title. 19 pages, 7 figure

4-[Bis(4-fluorophenyl)methyl]piperazin-1-ium 2-(2-phenylethyl)benzoate

The asymmetric unit of the title salt, C17H19F2N2 +.C15H13O2 −, derived from a 1,4-diaza­cyclo­hexane derivative and a carb­oxy­lic acid, contains two formula units. The cation is protonated at the secondary amine functionality. The six-membered heterocycles adopt chair conformations. The fluorophenyl rings in the two cations make dihedral angles of 77.21 (19) and 78.8 (2)° while the aromatic rings in the anions enclose angles of 69.5 (2) and 69.9 (2)°. In the crystal, classical N—H⋯O hydrogen bonds as well as C—H⋯F and C—H⋯O contacts connect the entities into layers parallel to ac

3-Chloro-N-(4-meth­oxy­phen­yl)propanamide

The title compound, C10H12ClNO2, is a halogenated derivative of a secondary amide bearing an aromatic substituent. The C(=O)—N(H)—Car—Car torsion angle of −33.70 (18)° rules out the presence of resonance spanning the amide as well as the aromatic system. In the crystal, classical N—H⋯O hydrogen bonds, as well as C–H⋯O contacts connect the mol­ecules into chains propagating along the a axis

Elastic Characterization of Orthotropic Composite Materials from Ultrasonic Inspection through Non-Principal Planes

Transmission of bulk ultrasonic waves through materials immersed in water is a well appropriated method to measure the stiffness matrix of anisotropic composite materials. This matrix can be deduced from velocities measurements by simple [1,2,3] or double transmission [4,5] or from amplitudes of double reflected bulk waves [4]. All these methods are working very well for unidirectional composites when transverse isotropy is assumed and the stiffness matrix has only five independent elastic constants.</p

4-[(1E)-3-(2,6-Dichloro-3-fluoro­phen­yl)-3-oxoprop-1-en-1-yl]benzonitrile

In the title mol­ecule, C16H8Cl2FNO, the benzene rings form a dihedral angle of 78.69 (8)°. The F atom is disordered over two positions in a 0.530 (3):0.470 (3) ratio. The crystal packing exhibits π–π inter­actions between dichloro-substituted rings [centroid–centroid distance = 3.6671 (10) Å] and weak inter­molecular C—H⋯F contacts

(2E)-1-(4,4′′-Difluoro-5′-meth­oxy-1,1′:3′,1′′-terphenyl-4′-yl)-3-(4-fluoro­phen­yl)prop-2-en-1-one

In the title compound, C28H19F3O2, the C=C double bond has an E configuration. In the crystal, C—H⋯F contacts link the mol­ecules into chains along [111]. The shortest centroid–centroid distance between two π systems is 3.8087 (8) Å and is apparent between the para-fluoro­phenyl group attached to the Michael system and its symmetry-generated equivalent

2-(2-Benzyl­phen­yl)propan-2-ol

There are two mol­ecules in the asymmetric unit of the title compound, C16H18O, a tertiary alcohol featuring a 2-benzyl­phenyl substituent. Co-operative O—H⋯O hydrogen bonds connect the mol­ecules into tetra­mers

Cinnarizinium 3,5-dinitro­salicylate

The title compound [systematic name: 4-diphenyl­methyl-1-(3-phenylprop-2-en-1-yl)-piperazin-1-ium 2-carb­oxy-4,6-dinitro­pheno­late], C26H29N2 +·C7H3N2O7 −, is the dinitro­salicylate salt of a tertiary amine. Deprotonation of the carb­oxy­lic acid group occurred on the phenolic hy­droxy group. The diaza­cyclo­hexane ring adopts a chair conformation. Intra­molecular O—H⋯O and inter­molecular C—H⋯O and N—H⋯O hydrogen bonds are observed. The N—H⋯O hydrogen bonds are bifurcated at the H atom and connect the cinnarizinium and 3,5-dinitro­salicylate ions together. Inter­molecular C—H⋯O hydrogen bonds connect the components into layers perpendicular to the crystallographic a axis

(2E)-1-(2,6-Dichloro-3-fluoro­phen­yl)-3-(4-fluoro­phen­yl)prop-2-en-1-one

In the title compound, C15H8Cl2F2O, the C=C double bond is in the E configuration. In the cyrstal, C—H⋯O hydrogen bonds connect the mol­ecules into chains along the c axis. A π–π inter­action of 3.628 (1) Å is also observed between two polyhalogenated benzene rings. The dichloro­substituted ring exhibits partial disorder over two sets of sites, with site-occupancy factors of 0.573 (3) and 0.427 (3)

Vegetation Change from the Euro-American Settlement Era to the Present in Relation to Environment and Disturbance in Southwest Oregon

Faced with landscapes degraded by fire suppression, logging, and grazing, land managers in the interior western US are attempting to restore habitat structure and function. In southwest Oregon, landscape-scale fuels treatments are being implemented with goals including recreating historic vegetation structure, despite poor understanding of the nature of the landscape prior to widespread Euro-American influence, or the patterns and processes of vegetation change over time. We compared a General Land Office-based reconstruction of Euro-American settlement era (1850s) vegetation in southwest Oregon's interior valleys and foothills with modern vegetation interpreted from aerial orthoimages to determine patterns of vegetation distribution in both eras, trajectories of vegetation change, and environmental and disturbance factors related to these themes. We found that this landscape was primarily occupied by closed plant community types in both eras, with a comparatively minor proportion in open types; vegetation was distributed along a dominant environmental gradient that ran from prairies in xeric lowlands to conifer forests in steeper, cooler uplands. Temporal shifts from open to closed vegetation were consistent with expected effects of fire suppression in many cases, but in other cases, the long-term persistence of open vegetation in the absence of recorded fire indicated that other mechanisms were also in operation. Human encroachment into wildlands, particularly in valleys, has also been a major driver of landscape-level change in the past 150 yr. Our results suggest that conservation should focus on lowlands, particularly where uncommon vegetation types such as savanna, shrubland, and prairie still exist.Keywords: vegetation distribution, Klamath-Siskiyou region, General Land Office surveys, southwest Oregon, environmental gradient