The h Bar

heather

22:00

one of the things i think i need (a quarter wave quartz wave plate) is $430

there's no way i can pay for that

Mithrandir24601

@heather Just wait until you start pricing crystals, single photon detectors and coincidence counters :P

heather

yep =/

also, can i just point out that while the polarizer i need is $35, the rotation mount for it is $125...

Mithrandir24601

@heather When they do a chip run here, it's ~£20k per run. Lasers tend to be at least that amount as well... Yeah, experimental physics is expensive

heather

yeah, but it's also pretty cool =)

anyway, i'll try to get some of the equipment donated; i've had success with that before.

Mithrandir24601

I mean, we get to work with lasers

heather

22:05

yeah =D

Mithrandir24601

@heather word of advice: don't break the crystal... Be careful with it. Be so unbelievably careful that everything else feels totally careless in comparison, despite 'everything else' involving extreme levels of precision

heather

i will hold it more carefully than a baby.

my book says you need to keep them in a bag with a "desiccator"?

Mithrandir24601

If you can avoid it, don't even touch the crystal. No, that's not good enough - don't even think of touching the crystal

heather

what if you have gloves on?

Mithrandir24601

@heather Those things they put in things to help keep moisture out

heather

22:08

oh, right.

makes sense.

Mithrandir24601

@heather If you have gloves on, then you're allowed to pick up the things you're going to use to clean the crystal

heather

oh geesh

what do you use to clean the crystal?

Mithrandir24601

Seriously, we had a broken crystal - the level of care after that was insane

So you need a bottle of compressed air so that no dust gets on whatever the crystal's on top of - this is the most important thing (a bit of dust can crack the crystal)

heather

okay, compressed air

do i need to do anything to isolate the experiment area (cleanroom style)?

Mithrandir24601

And something clean and reasonably soft to put it on so it doesn't get scratched. That's pretty much it actually :P

heather

22:11

okay, i can handle that =)

how is one to move the crystal/mount it?

Mithrandir24601

@heather Our lab's got some sort of seal on the windows to keep dust out and light in

@heather You might want some sort of crystal oven

heather

and is it okay to have just a desiccant, or do you need a desiccator?

Mithrandir24601

It doesn't actually matter if the sides of the crystal are perfectly clean (so long as they're dust, dirt etc. free so they don't crack), so long as the bit that the light's going through is clean

(if that makes sense?)

@heather Hmm... We just keep them in the small plastic boxes they come in

heather

@Mithrandir24601 yeah, that makes sense

hopefully my crystal comes in a small plastic box =P

let's see, what else...hmm, should the storage area be cool/dry/anything like that?

akinuri

I have a simple question about bending of space. Anyone's interested?

heather

22:17

@akinuri you don't need to ask to ask; just ask =)

Mithrandir24601

Yeah, there's also a difference between keeping something in a box in a cupboard that's rarely opened in a well sealed physics lab in a physics department and keeping it in your house :P

heather

heh, yeah.

akinuri

@heather Alright :D I know that mass bends the space. It is usually depicted as wtamu.edu/~cbaird/sq/images/spacetime_curvature.png or qph.ec.quoracdn.net/…

Mithrandir24601

@heather Physics lab conditions? :P I don't actually know at this point, other than to say that the exact properties of the crystal vary with temperature, which is another experimental parameter, although the crystal itself is unharmed between at least around 10-100 (ish) degrees C

@akinuri The 3D one looks pretty decent in terms of realism :)

heather

well, in terms of temperature i should be fine then. i'll make sure windows are kept shut while the crystals are out.

Mithrandir24601

22:20

@heather Yes. Definitely a good idea

heather

there's a closet in the lab that i'll maybe store the crystals in, and i'll make sure they're wrapped in a soft cloth, probably in the box they're sent. i might as well get a simple desiccant too, just to be safe.

akinuri

@heather From a graphical perspective, this effect is called pinch. What I'm wordering is does mass also twirl space? I mean, the sun for example. It bends the space around it, but it also spins. Does this spin (besides its mass) also affect the space? A twirl example: i.sstatic.net/OTofy.png

heather

is there such a thing as "drying out" the crystals too much @Mithrandir24601?

Mithrandir24601

@heather Any bog standard cheap one is fine

@heather Doubt it, but I don't see the point in going overboard...

heather

sweet, McMaster Carr has a pack of two silica gel desiccants for ~$8

@Mithrandir24601 sure, that was more of a "let's make sure heather doesn't do anything stupid" than a "permission to go overboard"

=)

Mithrandir24601

22:24

@heather If you've got any of the really small packets that occasionally comes with stuff (I get some with tea), even that's perfectly fine

heather

we usually just throw those right out, so i don't have any.

Mithrandir24601

To be honest, I don't even think we actually use any for the crystals - the box they come in might be good enough, or the lab might be good enough... (we do use them for other stuff though)

heather

sure, but as you said, there's a difference between a physics lab and a home =)

tyger2020

Hi...can I ask a question about a particular physics problem I am having?

akinuri

Any ideas?

heather

22:29

@akinuri I don't, but someone else might.

@tyger2020 yes, of course.

Mithrandir24601

@akinuri I'm not sure what this graphic means any more - the thing you're referring to is called the Kerr metric

There's an effect known as frame dragging...

dmckee

@Mithrandir24601 Not really. The primary effect of mass stationary on space-time is on the time-like component. This diagram continue the incorrect impression that it is the space-like part bends.

Mithrandir24601

@dmckee Well... It's both on the time-like and space-like components...

DanielSank

McMaster Carr is amazing.

Mithrandir24601

I do agree it's not fully accurate... But it's a lot better than most

akinuri

22:45

I've been checking the pages related to "Kerr metric" and "Frame dragging". I suppose these from wiki confirm that rotation affects the distortion.

"A stationary field is one that is in a steady state, but the masses causing that field may be non-static, rotating for instance."

"They predicted that the rotation of a massive object would distort the spacetime metric, making the orbit of a nearby test particle precess. This does not happen in Newtonian mechanics for which the gravitational field of a body depends only on its mass, not on its rotation."

Mithrandir24601

@DanielSank According to Wiki: "The site ranked third in a 2002 study performed at Stanford University about trust and credibility, just behind Amazon and Barnes & Noble", so fair enough I suppose...

tyger2020

Here's the question: A baseball and a ball of clay are approaching each other. The mass of the baseball is 145 g and it is moving due west 5 m/s at 180 degrees. The ball of clay is 290 g and it is moving northwest at 135 degrees at 4 m/s. What is the magnitude of their combined velocity after they collide and stick together?

I first tried to find velocity in the x direction, then velocity in the y direction, and use the Pythagorean theorem to find total magnitude. I got 1.71 m/s. Why is this wrong? What should I be doing instead?

Mithrandir24601

It must be physics Saturday :P

tyger2020

The only practice I've done is going straight up...do I need to do anything about the angles or treat it regularly?

heather

@DanielSank hello =)

DanielSank

23:03

@heather haiza

I'm practicing Rust.

Whatcha doing?

Mithrandir24601

oh, also @DanielSank - I tried getting the audio fixed earlier today... It can be done, but it would take me many tens of hours :/ and it would sound utterly horrible, so I had to give up on it :/ Lesson learned for the future...

DanielSank

Not a problem. Thank you for looking into it.

I hope you'll continue your series and I'm always happy to return.

In my dreams I do a more public set of things like this in the future.

Mithrandir24601

@DanielSank Thanks! :D I do want to hear more... Most of us will be away until October, but we're definitely interested :)

@DanielSank If the echo had a lower volume it might have been more doable, but alas

DanielSank

@Mithrandir24601 Don't worry about it.

@Mithrandir24601 Ok, this time if you could get an idea of what people want to hear about, I will be happy to try to fill the request.

So yeah, @heather Rust is cool.

Mithrandir24601

23:26

@DanielSank Sure! It'll probably be to slightly different people (new cohort in, half the cohort I'm in won't be in Bristol any more) and it might take me a few weeks, but it'll happen! Of course, if you ever find yourself in Bristol...

CooperCape

@Mithrandir24601 are you a PhD student at bristol?

Mithrandir24601

Or even the UK... (the Uni is happy to pay a limited amount of travel expenses, but unfortunately can't afford to bring someone all the way from America)

@CooperCape yeah :)

CooperCape

I'm applying for physics there this year :p

heather

@DanielSank trying to find components =)

Mithrandir24601

@CooperCape Oh, nice! As a PhD student? In the physics department?

CooperCape

23:29

Oooh I wish... undergraduate MSc

DanielSank

@Mithrandir24601 I will try to find myself in Bristol.

Mithrandir24601

@CooperCape Well, you have to start somewhere :P Bristol's actually a really nice city :)

DanielSank

We get invited to conferences all the time. I've been declining for a while because I was tired of travel, but if Bristol comes up I'll take it.

Often, John gets an invite and forwards to the rest of the group to spread out the responsibility and experience.

CooperCape

Yeah I went on an open day earlier this year... Looked pretty awesome :p

DanielSank

@heather McMaster has all the things.

...and Digi-Key has the rest.

and then if you still can't find it, ask ThorLabs.

Mithrandir24601

23:32

@DanielSank Does this count?: quantumlab.info

heather

very true.

those are basically the three sites i'm looking at, plus Edmund Optics, which is so expensive it should be ashamed of itself.

but thankfully, i think my dad might have the wave plate i need somewhere.

DanielSank

@Mithrandir24601 Is that an invitation?

lol. Your dad randomly has wave plates.

That's funny/awesome/nerdy.

Mithrandir24601

@DanielSank Why yes, yes it is - I can get someone to properly send you a more 'formal' invite if you're interested?

DanielSank

Kinda like how my dad used to go get random transistors from the basement.

@Mithrandir24601 Yeah go for it.

That's not too long after the APS March meeting, so I might not do it.

heather

@DanielSank yeah - we actually have a room in our apartment that's lab space =D

i spent part of today helping my dad organize it.

DanielSank

23:36

@heather o_O

Mithrandir24601

@DanielSank If it doesn't work out, it doesn't work out and that's not a problem, but if it works out, we'd definitely be very happy to have you :)

DanielSank

That is so cool.

@Mithrandir24601 Thanks much.

Y'all have some ion trappers, yeah?

heather

@DanielSank ::giant grin::

my dad promised me some space for my experiment so i'm rather excited.

he's also got some optical components i need to go through tonight.

DanielSank

I'm really happy for you. You have your own lab teacher!

Right at home.

Mithrandir24601

@DanielSank I've sent one of the people organising it a message, so you'll get an e-mail in a couple of days :)

Mohamed Ziad

23:39

hello guys, I have a question:
-- for a 13 sided regular polygon with 13 equal charges (q) on each vertex what is the net force on a charge (Q) placed at the center of the shape?
I've learned that it would be zero, but why is that? can I come to this conclusion without vector addition of the forces?

Mithrandir24601

@heather you are extremely lucky to have your own physics lab at home :o

heather

@DanielSank yeah, it's really amazing!

DanielSank

@Mithrandir24601 Thank you.

@heather what are you working on?

heather

this probably won't work, but i'm trying to create a quantum computer with SPDC for the nonlinear optical component.

sort of like theoretically, you can use Kerr media to build a cnot gate, but the effect with a single photon is so small it's useless.

you can build a cnot gate with enough beamsplitters/mirrors/linear optical components, but it's really inefficient.

Mithrandir24601

@heather <.< >.> <.< You're not the only one with this idea... I never told you that :P >.> <.< >.>

DanielSank

23:44

@heather I'm kinda curious, if you expect it to not work, why do that particular project?

heather

well, i'm kind of hoping it will work =)

DanielSank

Any idea how well you expect it to work based on back-of-the-envelope calculation?

heather

well, you'll need to send a lot of photons through to get the result, just because of the limited number of photons the crystals will down convert.

DanielSank

@Mithrandir24601 I have a possible offensive question, but I promise it's just my ignorance: I keep hearing that optical quantum computing is really hard and inefficient. Are there any outstanding problems that appear solvable that would make the field less scary?

heather

and setting it up to do multiple qubits will be difficult, i think.

the short answer is, i couldn't really tell you how well it will work.

i'm still trying to figure out the mathematical operation SPDC performs on the polarization of a photon.

that's really why i think it probably won't work - i'm really inexperienced in experimental physics and quantum computing and optics and quantum mechanics (i.e., all the things).

when i figure out the mathematical representation for SPDC, i can start figuring out how to construct gates, how to create a certain circuit, and so forth.

Mithrandir24601

23:49

@DanielSank So, if someone could build a good, deterministic single photon source that can be multiplexed or is easily copyable (to get exactly the same wavelength photons), that would pretty much be problem solved. Alternatively, we need a few more dB of squeezing to do continuous variable...

DanielSank

Thanks for explaining that.

I'm really in my little superconducting qubit bubble.

So..... is everyone and their dog working on that?

Mithrandir24601

@heather first hint: optical QC has lots of loss involved. Gates make loss issues even worse, so why would you want to implement lots of gates? Is there an alternative model that doesn't use as many gates, yet is equivalent? (hint: I'm asking the question, so...)

heather

the fabry-perot cavity system? that's the most commonly used, right?

Mithrandir24601

@DanielSank Not everyone, just nearly everyone - some of us are beginning to look into simulating on quantum chips e.g. I'll be doing a little bit on lossy systems in the hope we get some insight that helps chip design (and other, less relevant things)

@heather Ah, sorry - I'm asking: Is there an alternative to the gate model of quantum computing that's entirely equivalent, yet easier to implement in photonics?

heather

hmm, well, what types are there - there's gate based, adiabatic, cluster state.

Mithrandir24601

23:56

@heather Cluster state might be worth looking in to :P

heather

oh.

Mithrandir24601

To be fair, if you're just planning on implementing a single gate, there's not really going to be any difference

And you're just moving the difficulty from getting photons to interact (good luck!) to entangling lots of photons at once...

heather

@Mithrandir24601 i was hoping to implement a couple.

Mithrandir24601

@heather Not much difference really

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