Quantum filtering one bit at a time

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Update (2011-12-22): Our paper has now been published in Physical Review Letters here: 10.1103/PhysRevLett.107.260503.

Update (2011-11-11): Our paper has been accepted for publication in Physical Review Letters.

Today we submitted a paper on quantum filtering using a digitized weak measurement record:

“Quantum filtering one bit at a time” Jason F. Ralph and Neil P. Oxtoby (read the abstract and download from arXiv:1108.0823)

Overview: The classical analogue signal originating from diffusive weak measurement of a qubit (or two) is digitized into a single bit based on its sign (+/-).  We show that such a one-bit record (OBR) can be used to purify a single- or double-qubit, both with and without feedback control.  Quantum discord and classical correlations between a pair of qubits are also very well reproduced by the OBR.

The bottom line: we have made a significant reduction in the data required to accurately reconstruct a quantum state with only minor reduction in the filter performance.