Generalized quantum measurements (also known as positive operator-valued measures or POVMs) are of great
importance in quantum information and quantum foundations, but often difficult to perform. We present an
experimental approach which can in principle be used to perform arbitrary POVMs in a linear-optical context.
One of the most interesting POVMs, the symmetric, informationally complete-POVM (or SIC-POVM), is the
most compact set of measurements that can be used to fully describe a quantum state. We use our technique
to carry out the first experimental characterization of the state of a qutrit using SIC-POVMs. Because of the
highly symmetric nature of this measurement, such a representation has the unique property that it permits all
other measurement outcomes to be predicted by a simple extension of the classical Bayesian sum rule, making
no use of complex amplitudes or Hilbert-space operators. We demonstrate this approach on several qutrit states
encoded in single photons.
The demand for ever-increasing system performance- channel count, bit rate and span length- is driving the development of higher-performance erbium doped fiber amplifiers (EDFAs) and the deployment of distributed Raman amplification. This in turn has driven requirements for increasing output power from the highly reliable 1420nm to 1510nm laser diodes used in the power amplifier stage(s) of EDFAs and as the basis for C- and L-band Raman amplification. Wavelength division multiplexing (WDM) of pump lasers for higher-power EDFAs and control of the gain spectrum in Raman amplification have also driven the increased need for wavelength stabilization of these devices. At the same time, tight system space constraints have driven the need for improved efficiency and thermal management as the operating currents of these devices have increased. This paper reports progress at Agere Systems in the development and manufacture of extremely high-reliability, high-power laser diode pump sources, including >300mW Fiber Bragg Grating (FBG) -stabilized and Distributed FeedBack (DFB) -based wavelength stabilized modules, for current and future-generation telecommunications systems.
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