488 research outputs found
Achieving quantum precision limit in adaptive qubit state tomography
The precision limit in quantum state tomography is of great interest not only
to practical applications but also to foundational studies. However, little is
known about this subject in the multiparameter setting even theoretically due
to the subtle information tradeoff among incompatible observables. In the case
of a qubit, the theoretic precision limit was determined by Hayashi as well as
Gill and Massar, but attaining the precision limit in experiments has remained
a challenging task. Here we report the first experiment which achieves this
precision limit in adaptive quantum state tomography on optical polarization
qubits. The two-step adaptive strategy employed in our experiment is very easy
to implement in practice. Yet it is surprisingly powerful in optimizing most
figures of merit of practical interest. Our study may have significant
implications for multiparameter quantum estimation problems, such as quantum
metrology. Meanwhile, it may promote our understanding about the
complementarity principle and uncertainty relations from the information
theoretic perspective.Comment: 9 pages, 4 figures; titles changed and structure reorganise
2-(2-Hydroxy-3-methoxyphenyl)-1H-benzimidazol-3-ium perchlorate
In the title molecular salt, C14H13N2O2
+·ClO4
−, the ring systems in the cation are almost coplanar [dihedral angle = 5.53 (13)°]. Intramolecular N—H⋯O and O—H⋯O hydrogen bonds generate S(6) and S(5) rings, respectively. In the crystal, the two H atoms involved in the intramolecular hydrogen bonds also participate in intermolecular links to acceptor O atoms of the perchlorate anions. A simple intermolecular N—H⋯O bond also occurs. Together, these form a double-chain structure along [101]
Error-compensation measurements on polarization qubits
Systematic errors are inevitable in most measurements performed in real life
because of imperfect measurement devices. Reducing systematic errors is crucial
to ensuring the accuracy and reliability of measurement results. To this end,
delicate error-compensation design is often necessary in addition to device
calibration to reduce the dependence of the systematic error on the
imperfection of the devices. The art of error-compensation design is well
appreciated in nuclear magnetic resonance system by using composite pulses. In
contrast, there are few works on reducing systematic errors in quantum optical
systems. Here we propose an error-compensation design to reduce the systematic
error in projective measurements on a polarization qubit. It can reduce the
systematic error to the second order of the phase errors of both the half-wave
plate (HWP) and the quarter-wave plate (QWP) as well as the angle error of the
HWP. This technique is then applied to experiments on quantum state tomography
on polarization qubits, leading to a 20-fold reduction in the systematic error.
Our study may find applications in high-precision tasks in polarization optics
and quantum optics.Comment: 8 pages, 3 figure
Aquacyanido{6,6′-dimethoxy-2,2′-[1,2-phenylenebis(nitrilomethanylylidene)]diphenolato}cobalt(III) acetonitrile hemisolvate
In the title complex, [Co(C22H18N2O4)(CN)(H2O)]·0.5CH3CN, the CoIII cation is N,N′,O,O′-chelated by a 6,6′-dimethoxy-2,2′-[1,2-phenylenebis(nitrilomethanylylidene)]diphenolate dianion, and is further coordinated by a cyanide anion and a water molecule in the axial sites, completing a distorted octahedral coordination geometry. In the crystal, pairs of bifurcated O—H⋯(O,O) hydrogen bonds link adjacent molecules, forming centrosymmetric dimers. The acetonitrile solvent molecule shows 0.5 occupancy
Poly[tetraaquadi-μ4-oxalato-potassiumytterbium(III)]
In the title compound, [KYb(C2O4)2(H2O)4]n, the YbIII ion lies on a site of symmetry in a dodecahedral environment defined by eight O atoms from four oxalate ligands. The K atom lies on a different axis and is coordinated by four O atoms from four oxalate ligands and four water O atoms. The oxalate ligand has an inversion center at the mid-point of the C—C bond. The metal ions are linked by the oxalate ligands into a three-dimensional framework. O—H⋯O hydrogen bonding is present in the crystal structure
Aqua(cyanido-κC){6,6′-dimethoxy-2,2′-[o-phenylenebis(nitrilomethanylylidene)]diphenolato-κ4 O 1,N,N′,O 1′}cobalt(III) acetonitrile monosolvate
In the title complex, [Co(C22H18N2O4)(CN)(H2O)]·CH3CN, the CoIII ion is six-coordinated in a distorted octahedral environment defined by two N atoms and two O atoms from a salen ligand in the equatorial plane and one O atom from a water molecule and one C atom from a cyanide group at the axial positions. O—H⋯O hydrogen bonds connect adjacent complex molecules into dimers. C—H⋯N hydrogen bonds and π–π interactions between the benzene rings [centroid–centroid distances = 3.700 (2) and 3.845 (2) Å] are also present
[N,N′-Bis(3-methoxy-2-oxidobenzylidene)ethylenediammonium-κ4 O,O′,O′′,O′′′]tris(nitrato-κ2 O,O′)dysprosium(III)
In the title mononuclear Schiff base complex, [Dy(NO3)3(C18H20N2O4)], the DyIII ion is ten-coordinated in a distorted hexadecahedral geometry by six O atoms of three nitrate anions and four O atoms of the Schiff base ligand. An intramolecular N—H⋯O hydrogen bond occurs. The crystal structure is stabilized by intermolecular C—H⋯O hydrogen bonds
{μ-6,6′-Dimethoxy-2,2′-[propane-1,3-diylbis(nitrilomethylidyne)]diphenolato}trinitratocopper(II)europium(III)
In the title complex, [CuEu(C19H20N2O4)(NO3)3], the CuII ion is four-coordinated in a square-planar geometry by two O atoms and two N atoms of the deprotonated Schiff base. The EuIII atom is ten-coordinate, chelated by three nitrate groups and linked to the four O atoms of the deprotonated Schiff base
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