id: 05904348
dt: j
an: 05904348
au: Frey, Michael; Collins, David; Gerlach, Karl
ti: Probing the qudit depolarizing channel.
so: J. Phys. A, Math. Theor. 44, No. 20, Article ID 205306, 16 p. (2011).
py: 2011
pu: IOP Publishing, Bristol
la: EN
cc: 
ut: 
ci: 
li: doi:10.1088/1751-8113/44/20/205306
ab: Summary: For the quantum depolarizing channel with any finite dimension, we
    compare three schemes for channel identification: unentangled probes,
    probes maximally entangled with an external ancilla, and maximally
    entangled probe pairs. This comparison includes cases where the ancilla
    is itself depolarizing and where the probe is circulated back through
    the channel before measurement. Compared on the basis of (quantum
    Fisher) information gained per channel use, we find broadly that
    entanglement with an ancilla dominates the other two schemes, but only
    if entanglement is cheap relative to the cost per channel use and only
    if the external ancilla is well shielded from depolarization. We arrive
    at these results by a relatively simple analytical means. A separate,
    more complicated analysis for partially entangled probes shows for the
    qudit depolarizing channel that any amount of probe entanglement is
    advantageous and that the greatest advantage comes with maximal
    entanglement.
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