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Technological challenges

  • Is the DBT robust to temperature-cycling?
  • Can you encapsulate the anthracene in a way that is robust to temperature cycling? If you do the sealed-volume approach, will the crystal eventually disappear?
  • Can we make crystals that are consistently the same thickness for integration consistency?
  • Can we invert the emitter using a waveguide (cross-excitation or through the bus waveguide) and collect a single photon without getting laser noise?
  • Precisely what indistinguishability can you get with DBT? Has it even been measured? What is the indistinguishability of photons from a cavity? Basically, we want to make the case that coupling efficiency is ourmain challenge.

Photon efficiency limit

It will probably be difficult to get photons off the chip with 90% efficiency. It will be difficult to get a $\beta>90\%$. That puts our total collection efficiency at $\eta \approx 80\%$. The good news is that, in order to get $\beta \approx 90\%$, we only need to improve our demonstrated Purcell factor by a factor of 10. That's actually not so bad. Our demonstrated device had $Q=8,600$ and a mode volume of $V\sim (\lambda/n)^3$. The equivalent ring resonator with a diameter of $D=30\,\mu\mathrm{m}$ would have $Q \approx 7\times 10^5$. Commercial vendors quote ring resonators with $Q\sim10^7$. So improving our Purcell factor by 10 is very doable, even if we did it commercially. Granted, the $Q$ would not be $10^7$ after integration in all likelihood. So our best bet is to stick with photonic crystal cavities.

Synthesis

Integration

Cryocooling

We may be able to buy a 3rd-party cryocooler or contract this part out. The product will be much cheaper if we can make do with a 4 K cooler instead of 2-3 K.

  • It may be possible to get a relatively inexpensive 3 K cryostat. [iceoxford]
  • It is likely the case that SNSPD companies contract the cryostats to other manufacturers. ChatGPT says that SNSPDs typically need to be $<4$ K. We should talk to these companies and get their advice on what companies to contract for photonic integration and cryostat manufacturing. A single photon source would be good for business so they may be willing to help us.

Cavity

This could be contracted out, but likely only if we can accomplish the coupling with a ring resonator. If we need a photonic crystal cavity, we will likely need to do it in-house.

Fiber integration

This can be contracted out to one of many photonics companies