Quantum entanglement by the means of beam splitters

[sciencejournalist00]

Yes, no one is disputing that for polarization entangled states. As I say, you are mixing and matching ideas that you are reading that have similar words. You must realize that each experiment is unique and presents its own elements. You can't take one from column A and one from column B like a menu. There are literally thousands of entanglement experiments, and they each explore a different idea around entanglement. So you must be specific to make good sense.

http://www.nature.com/news/diamond-shows-promise-for-a-quantum-internet-1.12870
To entangle qubits in separate pieces of diamond, the team uses lasers to entangle each qubit with a photon at temperatures of 10 kelvin. The photons meet midway through a fibre-optic cable, where they are themselves entangled.

A quantum Internet would use entangled photons traveling down fibre-optic cables to in turn entangle qubits, with the aim of one day providing super-secure communications, or delivering software and data to future quantum computers

 

[DrChinese]

Experimental set-up. Each nitrogen–vacancy (NV) centre resides in a synthetic ultrapure diamond oriented in thedirection. The two diamonds are located in two independent low-temperature confocal microscope set-ups separated by 3 m. The NV centres can be individually excited resonantly by red lasers and off-resonantly by a green laser. The emission (dashed arrows) is spectrally separated into an off-resonant part (phonon sideband, PSB) and a resonant part (zero-phonon line, ZPL). The PSB emission is used for independent single-shot readout of the spin qubits9. The ZPL photons from the two NV centres are overlapped on a fibre-coupled beamsplitter. Microwave pulses for spin control are applied via on-chip microwave striplines. An applied magnetic field of 17.5 G splits the mS = ±1 levels in energy. The optical frequencies of NV B are tuned by a d.c. electric field applied to the gate electrodes (inset, scanning electron microscope image of a similar device). To enhance the collection efficiency, solid immersion lenses have been milled around the two NV centres. (Credit: H. Bernien et al./Nature)

And after reviewing the above diagram, your conclusion is that the PBS is the only thing necessary to create entanglement. I am sure that would be news to a few scientists.

 

[DrChinese]

A quantum Internet would use entangled photons traveling down fibre-optic cables to in turn entangle qubits, with the aim of one day providing super-secure communications, or delivering software and data to future quantum computers

I think this general concept is known to quite a few people. I would again ask: what is your remaining question? Everything else you have has been answered.

 

[sciencejournalist00]

Why do you bother buying expensive nonlinear crystals with very low conversion efficiency when you can use beam splitters and when momentum conservation which leads to pair production is found in very many phenomena? Even collisions will make the direction and momentum of one particle depend on the other particle, you do not need actual particle decay in radioactivity and spontaneous parametric down conversion

Why choose expensive ways instead of cheap ways?

 

[Nugatory]

Why choose expensive ways instead of cheap ways?

There are two plausible answers to that question.
1) The scientists doing the experiment are stupid.
2) The cheap way that you're thinking of doesn't work because quantum mechanics doesn't work the way you think it does.

In this case, the answer is #2. If you want to learn QM, Physics Forums is one of the places outside of an academic setting where you can find expert help... But arguing is an ineffective way of learning, so this thread is closed.