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Old 10-04-05, 10:27 AM   #1
timmhaan
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step toward quantum computing - slowing down light

if you're interested in things like this, check out the article. it's pretty amazing.

"Physicists in Australia have slowed a speeding laser pulse and captured it in a crystal, a feat that could be instrumental in creating quantum computers."

http://wired.com/news/technology/0,1...w=wn_tophead_1
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Old 10-04-05, 04:05 PM   #2
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Great.

As if traffic on LA wasn't slow enough, the Australians have figured out how to slow light down.

So, if the speed of light is constant under all conditions, does this mean time inside the crystal has to slow down too (based on our frame of reference)?

We have the speed of light, c in m/s. This is constant under all conditions within the frame of reference.

But now we have a new speed of light, v which is less than c.

The length of the crystal, L, is assumed to be constant.

And we have a new time for the light to pass through the crystal, t.

So v = L/t

but v < c from our frame of reference.

Therefore time must slow down relative to our frame of reference, because from a frame of reference within the crystal v = c.

Cool. My quantum computer will last longer.
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Old 10-04-05, 04:15 PM   #3
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Originally Posted by eubi
So, if the speed of light is constant under all conditions, does this mean time inside the crystal has to slow down too (based on our frame of reference)?
That's something that was assumed.....IIRC there have been a number of theories (maybe its even been proven) in the last 10 years or so that the speed of light is not constant.
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Old 10-04-05, 06:22 PM   #4
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Originally Posted by eubi
...So, if the speed of light is constant under all conditions, does this mean time inside the crystal has to slow down too (based on our frame of reference)?...
Uh nope. The speed of light varies based upon the medium it's passing through. In an absolute vacuum it has maximum speed. But when it hits the atmosphere it goes slower. It also goes slower through water as well. It goes at different speeds in different types of glass. That's how diffraction in lenses work...
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Old 10-04-05, 07:13 PM   #5
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Originally Posted by DannoXYZ
Uh nope. The speed of light varies based upon the medium it's passing through. In an absolute vacuum it has maximum speed. But when it hits the atmosphere it goes slower. It also goes slower through water as well. It goes at different speeds in different types of glass. That's how diffraction in lenses work...
Doesn't it mean that the speed of light is not any slower in various mediums, but that it just takes longer to get where it is going?
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Old 10-04-05, 08:59 PM   #6
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Doesn't it mean that the speed of light is not any slower in various mediums, but that it just takes longer to get where it is going?
If you've got a 10cm piece of vacuum, a 10cm piece of air, a 10cm piece of water, a 10cm piece of glass placed next to each other, and you send a wide beam of light through all of them at once. The time it takes the light to traverse the samples and come out on the back sides will be different. In all cases, the light has traveled the same 10cm through different materials. The different amounts of time it takes to travel the same distance can be plugged into this equation:

V = d/t

If V is different for each sample, what does that indicate? Velocity or speed is covering a certain distance in a certain amount of time. If you cover the same distance in different times, that's different velocities right?

This discussion reminds of the speed of free-falling objects. Sure on an academic school-book sense, we're taught that ALL objects fall at the same rate, 9.8m/s/s acceleration. However, in real life, there are other variables such as surface-area and wind-resistance that needs to be accounted for. Anyone who've ever dropped a bowling ball on their feet can probably tell you that it certainly falls faster than a feather or leaf.

Same issue with speed-of-light. Those with textbook knowledge will not have experience with real-world applications. Any telecommunications engineer will tell you that speed-of-light through fibre-optics is about 0.6c, or 0.6 times the speed of light in a vacuum.

The effect that's happening to the photons in the beam is that they are absorbed and re-emitted by the material with a certain frequency based upon their wavelength. There appears to be a delay between the absorption and emission of the photos along the way. Here a table of the refractive index (N) of various materials:

Air 1.0003
Water 1.33
Glycerin 1.47
Immersion Oil 1.515
Glass 1.52
Flint 1.66
Zircon 1.92
Diamond 2.42
Lead Sulfide 3.91

where N = c/V ; with c = native unimpeded speed of light and V = actual speed through material.

An interesting phenomenon is Cherenkov radiation where particles exist that will actually move through various materials faster than the speed of light.

Last edited by DannoXYZ; 10-05-05 at 01:27 AM.
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Old 10-04-05, 10:08 PM   #7
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I only hope that when quantum computers come out, they have pentagonal keyboards.
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Old 10-04-05, 11:26 PM   #8
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Diamond slows light way down, something like 40-odd percent.
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Old 10-05-05, 06:03 AM   #9
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Quote:
Originally Posted by DannoXYZ
Uh nope. The speed of light varies based upon the medium it's passing through. In an absolute vacuum it has maximum speed. But when it hits the atmosphere it goes slower. It also goes slower through water as well. It goes at different speeds in different types of glass. That's how diffraction in lenses work...
Hahaha.

Let me adjust my glasses so I can see better. You are absolutely correct about the lenses. I do enjoy your technical posts. You know what you are talking about.

Of course, my tongue was firmly in cheek when I wrote this.

The slowing down of light in that crystal was extreme: 300,000 km/sec to about 700 m/s? Wow. That's only about .00023% of its normal speed!

As a side - and off topic - note, how do I post quotes from multiple posters? For instance, If I wanted to include quotes from King Termite AND DannoXYZ in my post how do I do that? I've tried to figure it out and nothing works. Thanks!

Last edited by eubi; 10-05-05 at 09:40 AM.
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Old 10-05-05, 06:24 AM   #10
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I usually have a second browser tab open and do the old c&p, framing things with the [ quote = whoever ] C&P here [ / quote ] tags. Just take out the spaces so the code will work properly.
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Old 10-05-05, 07:14 AM   #11
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Quote:
Originally Posted by eubi
As a side - and off topic - note, how do I post quotes from multiple posters? For instance, If I wanted to include quotes from King Termite AND DannoXYZ in my post how do I do that? I've tried to figure it out and nothing works. Thanks!
I just use Reply w/ Post, copy the text, go back and reply to another post, and past the copied text back in. Quite simple, really.

Or you could just type the other's post, but there's a greater risk of misquoting them...
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Old 10-05-05, 09:41 AM   #12
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I usually have a second browser tab open and do the old c&p, framing things with the [ quote = whoever ] C&P here [ / quote ] tags. Just take out the spaces so the code will work properly.
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Originally Posted by Nicodemus
I just use Reply w/ Post, copy the text, go back and reply to another post, and past the copied text back in. Quite simple, really.

Or you could just type the other's post, but there's a greater risk of misquoting them...

OK, thanks!
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Old 10-06-05, 07:22 AM   #13
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The japanese and russians and Israelis have been doing crap with light for almost 3 decades now. Despite all the technological "advances" nothing that can be more then perceived as being fruitful has really yet to come of either and I severely doubt that anything will come close to this. It would be intreresting to see if computers that were built solely with light would advance from a bit being on or a bit being off since light can have numerous colors. Could a computer operate at 255- 16million bits in a single instance.
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Old 10-06-05, 07:26 AM   #14
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It would be intreresting to see if computers that were built solely with light would advance from a bit being on or a bit being off since light can have numerous colors. Could a computer operate at 255- 16million bits in a single instance.
Not sure that would do much either...they have been building "Analog Computers" for years as well, and have never offered enough of a benefit to go mainstream with them. Same idea as what you are saying...using as precise a voltage level as you wish to instrument to in order to have many different "states" (other than just 0 or 1).
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Old 10-06-05, 07:34 AM   #15
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Not sure that would do much either...they have been building "Analog Computers" for years as well, and have never offered enough of a benefit to go mainstream with them. Same idea as what you are saying...using as precise a voltage level as you wish to instrument to in order to have many different "states" (other than just 0 or 1).
Well thanks for spoilin it for everybody else
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Old 10-06-05, 07:36 AM   #16
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Well thanks for spoilin it for everybody else
Sorry...ya forgot to give me the "heads up" this time.

But...the idea of having a rainbow in the coputer is kinda cool...maybe you could have a virtual leprechaun at the end.
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