10,081 research outputs found
Quantum state estimation with unknown measurements
Improved measurement techniques are central to technological development and
foundational scientific exploration. Quantum optics relies upon detectors
sensitive to non-classical features of light, enabling precise tests of
physical laws and quantum-enhanced technologies such as precision measurement
and secure communications. Accurate detector response calibration for
quantum-scale inputs is key to future research and development in these cognate
areas. To address this requirement quantum detector tomography (QDT) has been
recently introduced. However, the QDT approach becomes increasingly challenging
as the complexity of the detector response and input space grows. Here we
present the first experimental implementation of a versatile alternative
characterization technique to address many-outcome quantum detectors by
limiting the input calibration region. To demonstrate the applicability of this
approach the calibrated detector is subsequently used to estimate non-classical
photon number states.Comment: 7 pages, 3 figure
Some calculations on the ground and lowest-triplet state of the helium isoelectronic sequence with the nucleus in motion
The method described in the preceding paper for the solution of two-electron atoms, which was used to calculate the 1 1S and 2 3S states of helium and heliumlike atoms within the fixed-nucleus approximation, has been applied to the case where all three particles are in relative motion. The solutions in the present case automatically include the effects of the mass polarization term and are compared with the results obtained for the term by using first-order perturbation theory with the fixed-nucleus wave functions. The input data for a particular atom consist of the atomic number, as before, but now the corresponding mass of the nucleus must be given also. Nonrelativistic energies with the nuclear mass included in the calculation have been obtained for the 1 1S and 2 3S states for Z ranging from 1 to 10. The energy with the nucleus in motion can be expressed only to eight significant figures (SF's) given the accuracy with which the relevant physical constants are known at present. All the results given here are computed as if these constants were known to ten SF's so that errors not incurred due to rounding. Convergence of the energies to ten SF's for both the singlet and triplet state was reached with a matrix of size 444 for Z values from 2 to 10. Convergence for the H- ion was a little slower
The cAMP sensors, EPAC1 and EPAC2, display distinct subcellular distributions despite sharing a common nuclear pore localisation signal
We have identified a conserved nuclear pore localisation signal (NPLS; amino acids 764–838 of EPAC1) in the catalytic domains of the cAMP-sensors, EPAC1 and EPAC2A. Consequently, EPAC1 is mainly localised to the nuclear pore complex in HEK293T cells where it becomes activated following stimulation with cAMP. In contrast, structural models indicate that the cAMP-binding domain of EPAC2A (CNBD1) blocks access to the conserved NPLS in EPAC2A, reducing its ability to interact with nuclear binding sites. Consequently, a naturally occurring EPAC2 isoform, EPAC2B, which lacks CNBD1 is enriched in nuclear fractions, similar to EPAC1. Structural differences in EPAC isoforms may therefore determine their intracellular location and their response to elevations in intracellular cAMP
Experimental generation of multi-photon Fock states
We experimentally demonstrate the generation of multi-photon Fock states with
up to three photons in well-defined spatial-temporal modes synchronized with a
classical clock. The states are characterized using quantum optical homodyne
tomography to ensure mode selectivity. The three-photon Fock states are
probabilistically generated by pulsed spontaneous parametric down conversion at
a rate of one per second, enabling complete characterization in 12 hours.Comment: 9 pages, 5 figure
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