Nanotechnology White Papers
On the Measurement of Qubits
Overview We describe in detail the theory underpinning the measurement of density matrices of a pair of quantum two-level systems ("qubits"). Our particular emphasis is on qubits realized by the two polarization degrees of freedom of a pair of entangled photons generated in a down-conversion experiment; however the discussion applies in general, regardless of the actual physical realization. Two techniques are discussed, namely a tomographic reconstruction (in which the density matrix is linearly related to a set of measured quantities) and a maximum likelihood technique which requires numerical optimization (but has the advantage of producing density matrices which are always non- negative definite). In addition a detailed error analysis is presented, allowing errors in quantities derived from the density matrix, such as the entropy or entanglement of formation, to be estimated.
| Publisher | HP Labs | File Format | PDF, requires Acrobat Rdr 5 |
|---|---|---|---|
| Date Published | June 2001 | Downloads | 108 |
| Format | White Papers | ||
| Topics | |||
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