Volume 82, Number 2, April 2008
|Number of page(s)||5|
|Section||Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics|
|Published online||26 March 2008|
Experimental demonstration of phase measurement precision beating standard quantum limit by projection measurement
Key Laboratory of Quantum Information, University of Science and Technology of China (CAS) - Hefei 230026, PRC
2 Department of Physics, Indiana University-Purdue University Indianapolis - 402 N. Blackford Street, Indianapolis, IN 46202, USA
Corresponding author: email@example.com
Accepted: 18 February 2008
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,N 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 for large photon number N, which approaches the Heisenberg limit of . Experimentally, we employ a four-photon state from type-II parametric down-conversion and achieve a phase uncertainty of 0.291±0.001 beating the standard quantum limit of = 1/2 for four photons.
PACS: 42.50.Dv – Quantum state engineering and measurements / 03.65.Ta – Foundations of quantum mechanics; measurement theory / 07.60.Ly – Interferometers
© EPLA, 2008
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