I didn’t actually plan on writing about quantum physics again, seeing as how I’m pretty much the least qualified person on earth to talk about the subject — but it’s something I take an interest in, and there were three really interesting advancements this week which are worth mentioning, as they bear on the subject I blogged about earlier.  Words like “breakthrough” and “milestone” are being bandied about.

Item No. 1: Scientists, for the first time ever, demonstrably “sent microwave photons, one at a time, into a superconducting microwave resonator.”  This basically means they were able to isolate and control the states of individual quanta inside a special matrix, allowing them to experiment on quanta in oscillation.

The really interesting thing about this is the way it illustrates the wonky behaviour of quanta; quanta come only in pre-determined states, roughly analogous to the way notes on a piano only come in pre-determined tones; they go up by semitones as you ascend key by key.  When nailed down mathematically, quanta are incapable of falling into in-between states.  However, when scientists were able to isolate and control the states of these photons, they were able to manually adjust the states so that they appeared to be oscillating between the usual increments.  But it was only the appearance: it’s the nature of quantum particles to refuse to settle until measured — the reason the particles appeared to be in non-incremental states is because they were in multiple states at once.  Being able to control and measure this effect is an important step on the way towards creating quantum computers.

Further: Scientists in Surrey were, for the first time, able to create one of the elementary components that will, eventually, be used to make quantum computers.  While ordinary computers have transistors that are either “on” or “off,” quantum computers will be exponentially more powerful by relying on analogue rather than binary bit states.  Quantum states hold all sorts of characteristics, meaning the way they store and calculate information is vastly more complex than a simple 1 / 0 dichotomy; they are also able to compute in non-linear ways.*  To create an array of quantum bits, scientists suspended atoms in a silicon crystal, where they could be isolated long enough for their oscillation to be measured — more importantly, they were measured in relation to one another as opposed to individually.  It requires scaling up, but it’s a huge step towards quantum effects being used to achieve actual processing.

Item No. 2: A theory previously thought to be impossible has been proven correct!  The theory in question posited that a partially collapsed quantum particle could be uncollapsed.  Essentially, this relates to the fact that measuring quantum particles affects their state (the Heisenberg Uncertainty Principle is the most famous offshoot of this particular conundrum): a quantum particle, as I said above, can exist in several states at once — measuring the particle forces it to “decide” which state it wants to be in, and “collapse” into a single state.  This is counter-intuitive, of course, because it implies that reality is affected by observation — and we all know that reality exists whether we’re observing it or not.  But on the quantum level, the same is not true, and it requires observation to limit a quantum particle to one state.  Conventionally, it was believed that once observation forced a particle into a single state, the original states would be lost and unmeasurable forever.

But the way this new theory continues is even weirder: the act of measuring can be progressive, and so can the act of collapsing.  To use an analogy: imagine a house with 100 rooms, and a dog which could be in any of the 100 rooms.  As you open one door after another (a “partial measuring” of the location of the dog) the location of the dog is gradually narrowed down until you can deduce the exact room.  In quantum physics, you can likewise take a partial measurement of a quantum particle’s state, which partially eliminates the states which the particle is not in.  It’s not as simple as “the dog is there” or “the dog is not there:” there’s a whole spectrum of certainty that your observations can fall into.

This new study is significant in that it showed that once measurement stopped, the particle could revert to existing in the states which had previously been eliminated — the initial state is not destroyed.  To return to my analogy: once you leave the house, the dog could run from room to room, and eventually you’ll have no idea which room the dog is in again.  The analogy breaks down, of course, when you try to imagine the dog in all 100 rooms simultaneously.  Dogs can’t do that — but quantum particles can.

What does all this have to do with communication?  Measuring quantum particles without destroying their initial states is crucial to getting information from them.  If it were true that observing a particle necessarily changes it, then we would never be certain what effects our observation was having on the information we were receiving.  Being able to measure a particle without destroying its state means measurements can be made — and quantum particles can be used to perform calculations and provide useful information.  The primary uses of quantum computers will be anything that involves crunching huge amounts of data — running complex simulations and encrypting (and decrypting) being the two most obvious examples.

Item No. 3: Perhaps most exciting of all, scientists from New York and Los Alamos have appeared to make a zero-capacity quantum channel that can carry information!  The basic mathematical theory of communication says that any “path” that information can take to get from one point in space to another is quantifiable: this channel has a capacity that can be measured.  A phone line is one example.  A letter is another.  The unit of information depends on the type of communication.  The capacity of the channel is very important in calculating the amount of information a particular channel (or medium, or whatever you want to call it) can send.

What’s the capacity of a quantum information channel?  What is a quantum information channel, for that matter?  A quantum information channel is any channel that transmits quantum information — which sounds ridiculous, but basically, it’s just like a phone line or any other type of classical medium, except instead of words or binary bits, the information it conveys is the mystical, ambiguous type of information that quantum particles exhibit, as well as the more usual type of information we’re able to understand.  Beyond that, any explanation breaks down into math, but basically, after a lot of theorising, nobody really knows what the potential capacity of a quantum information channel might be.  One thing we do know: if a quantum channel has a capacity of zero, it can’t transmit any information at all.

What these scientists have discovered, assuming it holds true, is that two quantum channels with a capacity of zero just might be able to transmit information.  Which, again, defies our intuition: if one dead phone line can’t convey any information, two dead phone lines can’t convey anything either.  Two times zero is still zero. And yet with quantum channels, two zero-capacity channels appear to have to ability to transmit information.  This is huge, because quantum teleportation depends on relaying information through channels that have zero capacity.  While some quantum channels are no big deal, like quantum-information-carrying photons barreling down fibre optic cable, entangled quantum particles are much trickier to use for conveying information, because of the no-communication theory.  But this could be the end-run around that problem; if zero capacity channels can be used to convey information, perhaps the channels that exist between two entangled particles, which essentially teleports information between two distant points, can eventually be used to transmit information faster than the speed of light after all.

I could be way off base here.  I admit I have as much trouble as anyone wrapping my head aroung this stuff … but it sounds to me like being able to measure quantum states without destroying them (thought to be impossible), and relaying information through quantum-entanglement-based zero-capacity quantum channels (also thought to be impossible) could make faster-than-light communication possible.  If anyone out there can point out to me where I’ve gone off the rails here, or any flaws in my reasoning at all, please do!  But it would just figure that the behaviour of quantum particles can defy even their own logic-defying mathematics.