Distinguishing N Photons in an Entangled State from N Separate Photons

최유준, 권오성, 문성욱 +2 more

Harald Weinfurter

J. C. Garrison, R. Y. Chiao

A state of two distinguishable particles is “separable” if the wavefunction is a product of single-particle wavefunctions. Schrödinger introduced the term “entangled” to describe a two-particle state that is not separable. This notion is extended to all pairs of distinguishable quantum systems by using tensor products of Hilbert spaces and the Schmidt decomposition. Equivalent operational definitions are expressed in terms of correlation functions representing measurements. A state of two indistinguishable particles is kinematically separable if the product function satisfies Bose or Fermi statistics, otherwise it is kinematically entangled. Alternatively, a two-particle state is dynamically separable if the wavefunction has the minimal form required by Bose or Fermi statistics, and dynamically entangled otherwise. For photons, the role of the missing position-space wave function is played by a detection amplitude directly related to counting rates.

B. C. Sanctuary

Disentanglement refers to decoherence that destroys the quantum interference terms between particles as they separate. This process reduces the pure isotropic entangled EPR state to a mixed anisotropic state. Averaging over the ensemble of states leads to correlations between separated particles that satisfies Bell's inequalities. Applying disentanglement to EPR pairs of photons shows that entanglement is characterized by various two-particle symmetry properties. These symmetry properties are destroyed by disentanglement but photon helicity is conserved. This is sufficient to account for the correlations needed to resolve the EPR paradox. Apart from a numerical factor, the functional form for the correlations due to entanglement and disentanglement is identical, thereby making it difficult to distinguish between the two in the current experiments.

秀治 三上

Minyi Huang, Ray-Kuang Lee

Uncertainty and entanglement are both profound and key concepts in quantum theory. For three observables, the tightest uncertainty constants for both product and summation forms are revealed. In this work, we give an alternative proof for three observables, also with a physical interpretation of the uncertainty constants. Our results show that such constants are intimately connected with the distinguishment between separable and entangled states.