Experimental demonstration of phase measurement precision beating standard quantum limit by projection measurement
Abstract
We propose and demonstrate experimentally a projection scheme to measure the quantum phase with a precision beating the standard quantum limit. The initial input state is a twin Fock state N,Nrang proposed by Holland and Burnett (Phys. Rev. Lett., 71 (1993) 1355) but the phase information is extracted by a quantum state projection measurement. The phase precision is about 1.4/N for large photon number N, which approaches the Heisenberg limit of 1/N. Experimentally, we employ a fourphoton state from typeII parametric downconversion and achieve a phase uncertainty of 0.291±0.001 beating the standard quantum limit of 1/\sqrt{N}=1/2 for four photons.
 Publication:

EPL (Europhysics Letters)
 Pub Date:
 April 2008
 DOI:
 10.1209/02955075/82/24001
 arXiv:
 arXiv:0710.2922
 Bibcode:
 2008EL.....8224001S
 Keywords:

 Quantum Physics
 EPrint:
 5 figures