12,467 research outputs found
Revealing the Exciton Fine Structure in PbSe Nanocrystal Quantum Dots
We measure the photoluminescence (PL) lifetime, , of excitons in
colloidal PbSe nanocrystals (NCs) at low temperatures to 270~mK and in high
magnetic fields to 15~T. For all NCs (1.3-2.3~nm radii), increases
sharply below 10~K but saturates by 500~mK. In contrast to the usual picture of
well-separated ``bright" and ``dark" exciton states (found, e.g., in CdSe NCs),
these dynamics fit remarkably well to a system having two exciton states with
comparable - but small - oscillator strengths that are separated by only
300-900 eV. Importantly, magnetic fields reduce below 10~K,
consistent with field-induced mixing between the two states. Magnetic circular
dichroism studies reveal exciton g-factors from 2-5, and magneto-PL shows
10\% circularly polarized emission.Comment: To appear in Physical Review Letter
Simple scheme for expanding a polarization-entangled W state by adding one photon
We propose a simple scheme for expanding a polarization-entangled W state. By
mixing a single photon and one of the photons in an n-photon W state at a
polarization-dependent beam splitter (PDBS), we can obtain an (n+1)-photon W
state after post-selection. Our scheme also opens the door for generating
n-photon W states using single photons and linear optics.Comment: 3 pages, 2 figure
Single-qubit rotations in two-dimensional optical lattices with multiqubit addressing
Published versio
Lattice paramenter, lattice disorder and resistivity of carbohydrate doepd MgB2 and their correlation with the transition temperature
The change in the lattice parameters or the lattice disorder is claimed as a
cause of the slight reduction in the transition temperature by carbon doping in
MgB2. In this work, an extensive investigation on the effects of carbohydrate
doping has been carried out. It is found that not only the a-axis but also the
c-axis lattice parameter increases with the sintering temperature. A linear
relation between the unit cell volume and the critical temperature is observed.
Compared with the well known correlation between the lattice strain and the
critical temperature, the X-ray peak broadening itself shows a closer
correlation with the transition temperature. The residual resistivity and the
critical temperature are linearly correlated with each other as well and its
implication is further discussed.Comment: 3 pages. Accepted by Jouranl of nanoscience and Nanotechnology (JNN
- …