Are Expectation Values Measured for Coupled Photons from SPDC?

In summary, entangled photons are created through parametric down conversion, with one beam having a polarization of 0° and the other having a polarization of 90°. The photons are emitted in two intersecting cones of light, with each beam containing a mix of horizontally and vertically polarized photons. However, if the photons are distinguishable, they will not be entangled and will act independently in terms of polarization. The measurement of expectation values for this case is not yet known.
  • #1
emuc
31
2
Entangled photons are generated, for example, by parametric down conversion (SPDC). The ordinary photon beam has polarization 0° and the extraordinary photon beam comes with the polarization 90°. Each photon leaves the source in a cone of light. Both cone shells intersect in two beams, which are thus each a mixture of horizontally and vertically polarized photons in equal share.

My question is how are photons related, which do not emerge on the line of intersection of the cone shells but are each clearly assigned to one of the two cone shells.

Does anybody know if this is measured already?
 
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  • #2
emuc said:
My question is how are photons related, which do not emerge on the line of intersection of the cone shells but are each clearly assigned to one of the two cone shells.
If the photons are distinguishable - as they would be in this case - they will not be entangled. One will be V, the other H. This is for what is called Type II SPDC. Not being entangled, they act independently as to polarization.
 
  • #3
Do you know about measurements of expectation values for this case?
 

1. What is SPDC and how does it produce coupled photons?

SPDC stands for Spontaneous Parametric Down-Conversion, which is a process in which a single photon is split into two lower energy photons. These two photons are called "signal" and "idler" photons, and they are entangled, meaning that their properties are linked. This entanglement is what allows them to be considered "coupled" photons.

2. What is the significance of coupled photons from SPDC?

Coupled photons from SPDC have many potential applications in quantum information processing, such as quantum cryptography and quantum teleportation. They can also be used in quantum computing and quantum communication, as their entanglement allows for faster and more secure data transmission.

3. How do scientists control the properties of coupled photons from SPDC?

The properties of coupled photons from SPDC, such as their polarization and wavelength, can be controlled by adjusting the parameters of the SPDC process, such as the type of crystal used and the angle of the laser beam. Additionally, specialized optical elements can be used to manipulate the photons after they are generated.

4. Are there any challenges in working with coupled photons from SPDC?

One of the main challenges in working with coupled photons from SPDC is maintaining their entanglement over long distances and in different environments. The photons can also be easily affected by external factors, such as noise and interference, which can disrupt their entanglement and affect their properties.

5. What advancements have been made in the field of coupled photons from SPDC?

Recent advancements in technology have allowed for the production of highly efficient and high-quality coupled photons from SPDC. Scientists have also been able to extend the range of entanglement between these photons, making them more practical for use in various quantum applications. Additionally, research is ongoing to find ways to overcome the challenges associated with working with coupled photons from SPDC.

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