34,947 research outputs found
Microscopic interface phonon modes in structures of GaAs quantum dots embedded in AlAs shells
By means of a microscopic valence force field model, a series of novel
microscopic interface phonon modes are identified in shell quantum dots(SQDs)
composed of a GaAs quantum dot of nanoscale embedded in an AlAs shell of a few
atomic layers in thickness. In SQDs with such thin shells, the basic principle
of the continuum dielectric model and the macroscopic dielectric function are
not valid any more. The frequencies of these microscopic interface modes lie
inside the gap between the bulk GaAs band and the bulk AlAs band, contrary to
the macroscopic interface phonon modes. The average vibrational energies and
amplitudes of each atomic shell show peaks at the interface between GaAs and
AlAs. These peaks decay fast as their penetrating depths from the interface
increase.Comment: 13 pages, 4 figure
Time-resolved measurement of photon states using two-photon interference with photons from short-time reference pulses
To fully utilize the energy-time degree of freedom of photons for optical
quantum information processes, it is necessary to control and characterize the
quantum states of the photons at extremely short time scales. For measurements
beyond the time resolution of available detectors, two-photon interference with
a photon in a short time reference pulse may be a viable alternative. In this
paper, we derive the temporal measurement operators for the bunching statistics
of a single photon input state with a reference photon. It is shown that the
effects of the pulse shape of the reference pulse can be expressed in terms of
a spectral filter selecting the bandwidth within which the measurement can be
treated as an ideal projection on eigenstates of time. For full quantum
tomography, temporal coherence can be determined by using superpositions of
reference pulses at two different times. Moreover, energy-time entanglement can
be evaluated based on the two-by-two entanglement observed in the coherences
between pairs of detection times.Comment: 6 pages, including 3 figure
Clock synchronization using maximal multipartite entanglement
We propose a multi party quantum clock synchronization protocol that makes
optimal use of the maximal multipartite entanglement of GHZ-type states. To
realize the protocol, different versions of maximally entangled eigenstates of
collective energy are generated by local transformations that distinguish
between different groupings of the parties. The maximal sensitivity of the
entangled states to time differences between the local clocks can then be
accessed if all parties share the results of their local time dependent
measurements. The efficiency of the protocol is evaluated in terms of the
statistical errors in the estimation of time differences and the performance of
the protocol is compared to alternative protocols previously proposed
- …