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Updated: May 24, 2026

Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators
Published on: May 30, 2014
Procedure for direct measurement of general quantum states using weak measurement
Jeff S Lundeen1, Charles Bamber
1Institute for National Measurement Standards, National Research Council, Ottawa, Ontario, Canada. jeff.lundeen@nrc-cnrc.gc.ca
Abstract:
Recent work by Lundeen et al. [Nature (London) 474, 188 (2011)] directly measured the wave function by weakly measuring a variable followed by a normal (i.e., "strong") measurement of the complementary variable. We generalize this method to mixed states by considering the weak measurement of various products of these observables, thereby providing the density matrix an operational definition in terms of a procedure for its direct measurement. The method only requires measurements in two bases and can be performed in situ, determining the quantum state without destroying it.
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