Mixed Signals
Any sufficiently advanced information is indistinguishable from noise
Monday 22 September 2008, 7:18 PM
More boson goes on - computing with excitons...
A long way away from the LHC, work proceeds on different sorts of bosons to the Higgs type. Bosons are particles - or can be considered as particles, anyway - and some of them are made up of other particles. Or, as is the case with the excitons, a particle and an absence of a particle.
Gotta love the modern physics.
In this case, excitons are electrons and holes - places in a semiconductor lattice where an electron should be, but isn't. When an electron falls into a hole, it gives out energy as a photon - that's how LEDs work - but the prelapsarian state can be considered as a particle in its own right. You can convert a photon back into an exciton too, which is how solar cells work (and yes, an LED can act as a solar cell); the photon impinges on the electron, which grabs the energy and powers away from its old position, leaving a hole.
So far, so pretty. But what researchers at the Universities of California Santa Barbara and San Diego have worked out is how to steer excitons around the place without them doing their recombining trick, by trapping them in quantum wells with a controllable energy barrier between them. It's a bit like sticking two amorous hamsters in adjacent cages - they know each other is there, but can't do much about it. Thus, the excitons can be used within a transistor - and when they get to the circuit output, they recombine and give it up to the aether.
Jolly good - but what's the point? As the researchers point out, it's a lot more efficient to have a logic circuit which automatically converts its own outputs and inputs between electron energy and photons, if you're going to do your computation electronically and your communication photonically. The way things stand at the moment, we spend a lot of time and energy doing that anyway with discrete, inefficient and slow conversion processes.
A compelling argument. Of course, we're ages away from this being useful: it only works in the chilly regions below 40 kelvin, needs mildly exotic materials, has only been demonstrated in simple configurations - all of which is par for the course with new quantum jiggerypokery. You won't catch me predicting whether or when this will change - but it's good to see yet another new idea making it off the blackboard and into the lab.
Gotta love the modern physics.
In this case, excitons are electrons and holes - places in a semiconductor lattice where an electron should be, but isn't. When an electron falls into a hole, it gives out energy as a photon - that's how LEDs work - but the prelapsarian state can be considered as a particle in its own right. You can convert a photon back into an exciton too, which is how solar cells work (and yes, an LED can act as a solar cell); the photon impinges on the electron, which grabs the energy and powers away from its old position, leaving a hole.
So far, so pretty. But what researchers at the Universities of California Santa Barbara and San Diego have worked out is how to steer excitons around the place without them doing their recombining trick, by trapping them in quantum wells with a controllable energy barrier between them. It's a bit like sticking two amorous hamsters in adjacent cages - they know each other is there, but can't do much about it. Thus, the excitons can be used within a transistor - and when they get to the circuit output, they recombine and give it up to the aether.
Jolly good - but what's the point? As the researchers point out, it's a lot more efficient to have a logic circuit which automatically converts its own outputs and inputs between electron energy and photons, if you're going to do your computation electronically and your communication photonically. The way things stand at the moment, we spend a lot of time and energy doing that anyway with discrete, inefficient and slow conversion processes.
A compelling argument. Of course, we're ages away from this being useful: it only works in the chilly regions below 40 kelvin, needs mildly exotic materials, has only been demonstrated in simple configurations - all of which is par for the course with new quantum jiggerypokery. You won't catch me predicting whether or when this will change - but it's good to see yet another new idea making it off the blackboard and into the lab.
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