Hyperentangled Photon Pairs Produced
Investigators at the University of Illinois at Urbana-Champaign and at the University of Queensland in Brisbane, Australia, have used paired nonlinear crystals to prepare photon pairs that are entangled in all degrees of freedom: polarization, spatial mode and energy-time. Hyperentanglement may have applications in quantum bits of information to be encoded on a photon pair.
In their experiment, 351-nm radiation from an argon-ion laser pumped contiguous 0.6-mm-thick BBO crystals to produce 702-nm photons by Type I parametric down-conversion. By focusing the pump beam to a waist size of 90 μm at the thin crystals, they maximized polarization and spatial-mode entanglement. Testing against a Bell inequality, they found that the resulting photon pairs exceeded the classical limit by more than 20 standard deviations for each degree of freedom.
A report on the work will appear in an upcoming issue of Physical Review Letters.
- A quantum of electromagnetic energy of a single mode; i.e., a single wavelength, direction and polarization. As a unit of energy, each photon equals hn, h being Planck's constant and n, the frequency of the propagating electromagnetic wave. The momentum of the photon in the direction of propagation is hn/c, c being the speed of light.
- With respect to light radiation, the restriction of the vibrations of the magnetic or electric field vector to a single plane. In a beam of electromagnetic radiation, the polarization direction is the direction of the electric field vector (with no distinction between positive and negative as the field oscillates back and forth). The polarization vector is always in the plane at right angles to the beam direction. Near some given stationary point in space the polarization direction in the beam...
- spatial mode
- Also known as transverse mode. The configurations of energy storage, relative to the structure of a laser resonator, that define the relative intensity distribution of the laser beam.
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