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Quantum computer closer: Optical transistor made from single molecule

By

July 6, 2009

Artist's impression of a molecular transistor. (Photo: Robert Lettow)

Artist's impression of a molecular transistor. (Photo: Robert Lettow)

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Researchers from ETH Zurich have recently managed to create an optical transistor from a single molecule in what is yet another important achievement on the road to quantum computing.

Quantum photonics is a particularly attractive field to scientists and engineers alike in that it could, once some core issues have been resolved, allow for the production of integrated circuits that operate on the basis of photons instead of electrons, which would in turn enable considerably higher data transfer rates as well as dramatically reduced heat dissipation.

Fiber optics are a typical example for the outstanding data transfer rates of light particles when compared to electrons; however, we still need to generate the necessary encoding of the information using electronically controlled switches, which acts as a bottleneck and slows down the process considerably.

But the research group from ETH Zurich has now achieved a decisive breakthrough by successfully creating an optical transistor with a single molecule, which could harness the full potential of quantum optics.

ETH's Martin Pototschnig told us more about the molecule used for the experiments. "It is a small hydrocarbon molecule called dibenzanthanthrene (DBATT). The molecules are doped in n-tetradecane, an organic solvent. So the sample is a pink liquid at room temperature. Then we cryogenically cool the small portion of the sample then the n-tetradecane freezes and forms a molecular crystal."

The molecule itself is about 2 nanometers in size, over ten times smaller than standard transistors, which means that a lot more could be integrated in a single chip.

The reason behind the cooling at the cryogenic temperature of 1.4 K (or -272 °C) is that, under these conditions, quantum mechanical phenomena can be observed much more easily than at room temperature, and particularly to increase a parameter known as coherence time, the time during which the phase between the "0" and the "1" states remain well-defined.

We asked Dr. Hwang, who was part of the research team and lead author of the paper that appeared on the journal Nature detailing the experiment, to give us a sense for how much heat dissipation is affected using these kinds of quantum technologies.

"Our single-molecule optical transistor generates almost negligible amount of heat. When a single molecule absorbs one photon, there is some probability (quantum yield) that the molecule emits a photon out. The rest of the energy absorbed turns into heat in the matrix. For the case of the specific hydrocarbon molecule that we use, the quantum yield is near 100%. So almost no heat is generated."

Determining how a quantum transistor stacks up against a traditional electronic one in terms of performance is however considerably harder because of how the two paradigms differ as its "quantum superposition" can't be directly translated into a precise number of 01 or 10 transactions in standard electronics. Some measure of the performance, Dr. Hwang told us, can still be obtained by analyzing the coherence time, which is about 10 nanoseconds.

By using a laser beam to impose the quantum state of a molecular transistor, the research team demonstrated control of a second laser beam, which reflects the way in which a conventional transistor works.

"The next step is to 'connect' two or more [single-molecule optical transistors]," Pototschnig told us with regard to future areas the team will be focusing on. "In other words, we have to connect two molecules in a way that the quantum mechanical superposition state of each molecule is exchanged in a coherent manner. Only that way the strength of the quantum computing principles can be fully taken advantage of. We are in the middle of coming up with actual ways to implement the connection idea."

About the Author
Dario Borghino Dario studied software engineering at the Polytechnic University of Turin. When he isn't writing for Gizmag he is usually traveling the world on a whim, working on an AI-guided automated trading system, or chasing his dream to become the next European thumbwrestling champion.   All articles by Dario Borghino
6 Comments

"over ten times smaller than standard transistors"?

10 times = 1,000% smaller. 100% smaller = no size at all. Perhaps you mean 90% smaller?

bmwynn
8th July, 2009 @ 09:43 pm PDT

10 times bigger, means 10 times bigger, 10/1 = x10

10 times smaller is bad English but fine in maths, 10 times smaller

1/10 = x0.1 or a tenth of the size

Did you not learn fractions at school.

Philip Mole Rowney
9th July, 2009 @ 03:16 pm PDT

LOL 10x smaller = 10%

100% divided by 10 = 10%, there: ten times smaller is a feasible and possible amount, as is any amount. even 1000x smaller still works, it's just a tiny percentage!

Danny Hodgetts
9th July, 2009 @ 11:21 pm PDT

100% smaller does not mean no size at all...you are just dividing the original size by 10. i't was x meters wide, now it ix x/10 meters wide...

chards
10th July, 2009 @ 05:20 pm PDT

A more correct/concise way of putting it could be, "The molecule itself is about 2 nanometres in size; less than one tenth the size of standard transistors...".

That said, what is a 'standard transistor'? And I personally don't know of any chips in production using a 20nm process.

Intel's very latest desktop chips (Lynnfield and Clarksfield) will still be manufactured using the 45nm process (same as the Core range of chips), when they are launched later in 2009. After that they will move to a 32nm process, but we're still nowhere near 20nm transistors.

So with 45nm being the norm for the best chips currently available to the masses, perhaps the sentence should read, "The molecule itself is about 2 nanometres in size; less than one twentieth the size of today's smallest conventional transistors...".

Stuart Ross
20th July, 2009 @ 02:57 pm PDT

Correct. 10 times snaller means take the original size and divide it by 10.

Chris7527
12th February, 2010 @ 05:29 pm PST
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