by
Prof.Gunnar Björk(Schol of Information and Communication technology, KTH)
→
Europe/Stockholm
112:028
112:028
Description
In quantum information a, or perhaps the, fundamental information-containing system is the qubit. A measurement of a single qubit can at most yield one classical bit of information or randomness. However, a dichotomous measurement of an unknown qubit will yield much less information about the qubit state. We use Baysian inference to compute how much information one progressively gets by making sucessive, individual measurements on an ensemble of identically prepared qubits. Perhaps surprisingly, even if the measurements are arranged so that each measurement yields one classical bit, that is, the two possible measurement outcomes are a priori equiprobable, it takes almost a handful of measurements before one has gained one bit of information about the gradually concentrated qubit probability density. We also show that by following a strategy that reaps the maximum information per measurement, we are first led to a mutually unbiased basis as our measurement bases, but eventually to a adaptive measurement strategy. This is a pleasing, although not entirely surprising result.
