**Administration**

Happy birthday to

**malver**!

Hello to new readers

**sand_l**,

**siepie**,

**stephanieburgis**!

Administration-related thingie that's annoying me - some of y'all are leaving LJ due to the Strikethrough '07 crap. Some of you are keeping accounts around, or creating new accounts to read your friendslists. I would like to keep you in the loop. But I'd also like to add new readers. So. If you have multiple accounts for this, please just tell me which one I should keep friended and which one I can drop to make room for more people. Thanks!

**Medical**

Yesterday was a bad breathing day. Fortunately, today is Allergist Day! We're doing environmental-allergen testing first; I've been reacting to new foods, yes, but it's something airborne that's made my lung capacity half normal on the good days and scary on the bad days. I'm hoping I can get some treatment started today. I don't remember how this goes... I haven't had allergy testing since I was 12.

**National Invisible Chronic Illness Week, cont'd.**

This is a repost, but I have new readers since then: The top ten sites for chronic pain.

**Husband!**

Adam's off work today! I get a weekday with my husband! *boogies down* We're going to go into town together this morning because he has something to do and I have to shop for my BPAL Switch Witch (I know the perfect store, and it's only one bus ride away!), and otherwise... maybe a movie,if we can fit one in before the allergist? Yay. :)

**Link Soup**

* Animated Knots by Grog: Learn to tie knots the fun and easy way! I must study this before Thanksgiving.. :)

* A Four-Dimensional Tribute to the Late Madeleine L'Engle.

**Daily Science**

*The basic idea of this paper is that they prepare a quantum system in a superposition of several different states, and then use an ingenious measurement technique to make repeated measurements of the state of the system. This lets them follow the state as it moves from a quantum superposition of several different states to a more classical state where it has one and only one value. As they say in the abstract, the experiment "illustrates all the postulates of quantum measurement (state collapse, statistical results, and repeatability)," making it a really impressive piece of work.*

So, how do they do this?

...

This is the ingenious part of their experiment:

...

They load the cavity up, and then they start sending atoms in. But this is a quantum system, so the initial state of the system isn't exactly three, or five, or seven photons, but a superposition of all the photon numbers from 0 to 7 (and beyond, though the probability of 8 or more is very small) at the same time. There is no definite photon number in the cavity at the start of the experiment, so when they send the first atom in, they get an indeterminate answer-- the most probable number is three, say, but there's a pretty good chance of it being two or four, or even six. This produces the large, spread-out initial distribution seen in the figure at left (cropped from Figure 2b of the Nature paper).When they send in a second atom, though, they get a bit more information about the state, and the distribution gets a little narrower. A third atom gets still more information, and a fourth, a fifth, and so on. What they see is that, as time goes on, the system evolves from a superposition of lots of different photon numbers into a single definite number-- by the time they've sent 50 atoms through, the state has pretty much converged to a single number, say five photons, as seen in the figure. And they can track the evolution of the state by looking at each of the individual atoms as it comes out.

...

They can also follow the state after the "collapse" to a single value, and what they see there is pretty cool, as well: the number of photons in the cavity decreases through discrete and random jumps, as individual photons slowly leak out of the cavity, over a few tenths of a second. The transition from, say, five photons to four happens very quickly, in a hundredth of a second or so, and then the cavity will sit at that state for a short time before dropping to three photons, and so on. They tracked 2000 states, and from that can put together a nice description of the photon lifetime, including some odd states where photons hang around for anomalously long times, or where thermal fluctuations cause the number to actually increase for a short time.

So, how do they do this?

...

This is the ingenious part of their experiment:

**they have a way to detect the presence of photons in the cavity without destroying the photons**. They do this by passing the atoms from an atomic clock through the center of the cavity. The photons in the cavity aren't at the right frequency to be absorbed by the atoms, but they do shift the energy levels of the atoms by a tiny amount, causing the clock to run a tiny bit faster....

They load the cavity up, and then they start sending atoms in. But this is a quantum system, so the initial state of the system isn't exactly three, or five, or seven photons, but a superposition of all the photon numbers from 0 to 7 (and beyond, though the probability of 8 or more is very small) at the same time. There is no definite photon number in the cavity at the start of the experiment, so when they send the first atom in, they get an indeterminate answer-- the most probable number is three, say, but there's a pretty good chance of it being two or four, or even six. This produces the large, spread-out initial distribution seen in the figure at left (cropped from Figure 2b of the Nature paper).When they send in a second atom, though, they get a bit more information about the state, and the distribution gets a little narrower. A third atom gets still more information, and a fourth, a fifth, and so on. What they see is that, as time goes on, the system evolves from a superposition of lots of different photon numbers into a single definite number-- by the time they've sent 50 atoms through, the state has pretty much converged to a single number, say five photons, as seen in the figure. And they can track the evolution of the state by looking at each of the individual atoms as it comes out.

...

They can also follow the state after the "collapse" to a single value, and what they see there is pretty cool, as well: the number of photons in the cavity decreases through discrete and random jumps, as individual photons slowly leak out of the cavity, over a few tenths of a second. The transition from, say, five photons to four happens very quickly, in a hundredth of a second or so, and then the cavity will sit at that state for a short time before dropping to three photons, and so on. They tracked 2000 states, and from that can put together a nice description of the photon lifetime, including some odd states where photons hang around for anomalously long times, or where thermal fluctuations cause the number to actually increase for a short time.

Keen!

**Daily Scent-Stuff**

BPAL: Got my Click & Ship!

Droplettes:

**Therapy**:

*Coffee ice cream with soft squishy brownies mixed in.*

In bottle: Wow. It really is. Sweet creamy coffee with a bit of chocolate.

On me: Hm. Something overly sweet about it, but it may die down.

**White Pumpkin**:

*The ghostly vegetable in your garden! Pumpkin with white tea and coconut.*

In bottle: I'm getting the white tea more than anything else.

On me: Ah, there's the pumpkin! This is nice and delicate.

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