Monday, February 20, 2012

One atom transistor

ScienceDaily reports:
The smallest transistor ever built -- in fact, the smallest transistor that can be built -- has been created using a single phosphorus atom by an international team of researchers at the University of New South Wales, Purdue University and the University of Melbourne. ...

"This is a beautiful demonstration of controlling matter at the atomic scale to make a real device," Simmons says. "Fifty years ago when the first transistor was developed, no one could have predicted the role that computers would play in our society today. As we transition to atomic-scale devices, we are now entering a new paradigm where quantum mechanics promises a similar technological disruption. It is the promise of this future technology that makes this present development so exciting." ...

The single-atom transistor does have one serious limitation: It must be kept very cold, at least as cold as liquid nitrogen, or minus 391 degrees Fahrenheit (minus 196 Celsius). ...
This is not a new paradism. Quantum mechanics has always been used to make transistors. We have no other understanding of them. But the real hype here is not smaller or faster computers, but the holy grail of quantum computers.
The single-atom transistor could lead the way to building a quantum computer that works by controlling the electrons and thereby the quantum information, or qubits. Some scientists, however, have doubts that such a device can ever be built.

"Whilst this result is a major milestone in scalable silicon quantum computing, it does not answer the question of whether quantum computing is possible or not," Simmons says. "The answer to this lies in whether quantum coherence can be controlled over large numbers of qubits. The technique we have developed is potentially scalable, using the same materials as the silicon industry, but more time is needed to realize this goal."
This is where quantum computing research has been stuck for 30 years. Physicists can find more and cleverer ways of demonstrating quantum phenonema, but they cannot show that scalable qubits are possible. I am betting that scalable qubits are impossible.

Wired explains:
This means a quantum computer could do things a classical machine never could, letting you, say, crack today’s most complex encryption algorithms in relatively short order. But physicists still can’t agree on whether a quantum computer can actually be built. The rub is that if you interact with a quantum system, it “decoheres,” collapsing into a single state. In other words, the qubit turns into an ordinary bit. If you want to build a quantum computer, you have to — among other things — isolate its qubits from their surrounding environment.

The new research from Purdue and New South Wales does not demonstrate a quantum bit. But in placing a single-atom transistor on a silicon crystal — and carefully isolating it from the surrounding substrate — it provides a clearer path to a working quantum computer.
Note the admission that no one has a qubit yet, in spite of all the hype.


  1. While it's refreshing to find someone as skeptical of scientific hype as you, I think you have done too far with the claim that "no one has a qubit yet". Reasonable people can argue about how useful the qubits are that have been produced, but there are multiple examples of small numbers of qubits (with reasonable definitions of "qubit").

  2. So who invented the qubit? And why didn't he get a Nobel Prize for it?