Switching qubits with a terahertz source?

March 2, 2011

(PhysOrg.com) -- Rotational transitions induced in molecules on a chip could have important applications in quantum computing.

Scientists in Germany and the USA have been able to induce rotational transitions in trapped at a close distance above a chip using a terahertz source. The new results, which are published in ChemPhysChem, could have interesting applications in quantum computing.

Polar molecules in selected quantum states can be guided, decelerated and trapped using electric fields created by microstructured on a chip. One of the possible applications of such molecules on a chip is their use in future quantum computers. However, to achieve this, researchers must be able to drive transitions from a certain to another one, that is, they should to be able "to switch a (or quantum bit)". A transition between two rotational levels in a molecule is very well suited for this, and that is the reason why Gabriele Santambrogio and co-workers at the Fritz Haber Institute of the Max Planck Society in Berlin and Liam Duffy of the University of North Carolina at Greensboro decided to use a rather uncommon narrowband terahertz (THz) source to induce rotational transitions in laser-prepared metastable CO molecules. The researchers coupled the source to a chip setup that had been previously developed by them and studied the transitions between two quantum states in polar molecules trapped on the chip.

According to co-author Gerard Meijer, both the experimental approach and the results of this work are unique. The combination of laser-prepared molecules in a single rotational level, tunable narrow-band mm-wave radiation that can transfer the population to another rotational level, and state-selective detection of the molecules at a known delay and position, offers many interesting possibilities. With this approach, the research team has not only been able to trap the polar molecules on a chip but has also played further games with them—like inducing the rotational transitions. Meijer believes that these results could find important applications in : "In the future, it is conceivable that compact THz sources are integrated on a chip, and that one can use this to switch between qubits in a routine fashion", he says.

Explore further: Quantum dots as midinfrared emitters

More information: Gabriele Santambrogio, Driving Rotational Transitions in Molecules on a Chip, ChemPhysChem 2011, 12, No. 10, dx.doi.org/10.1002/cphc.201001007

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not rated yet Mar 02, 2011
What is this THz source, I wonder. Also, I don't understand how controlling rotational transitions (changing energy states of molecules) contributes to quantum computing.
not rated yet Mar 03, 2011
What is this THz source, I wonder. Also, I don't understand how controlling rotational transitions (changing energy states of molecules) contributes to quantum computing.

Well, theoretically, if we can manipulate molecules in most of the ways permitted by the laws of physics, then it should be possible to store a "information" in the physical orientation of the molecules.

I don't think this is necessarily useful for a "quantum processor," but perhaps useful for the "quantum RAM" or "cache".

Anyway, theoretically, you should be able to store more than one "bit" just by manipulating and measuring the physical orientation of a molecule.

If it is oriented along the x-axis, that might be a "0".
If it is oriented along the y-axis, that might be a "1".
If it is oriented along the z-axis, that would be a "2".

So you could maybe make an analog computer, or make a computer which is "digital," but not necessarily "Binary Digits".
not rated yet Mar 03, 2011
Instead of a "Qubit" - Quantum Binary Digit, you might have a "Qutrit" - Quantum Trinary Digit.

This could also work, because certain quantum properties can occur in "fractional" values, or more than one property of the atom or molecule could be manipulated. Either way, you can theoretically store MORE than one Bit or even one Qubit in a single molecule.

By manipulating more than one property, it should be possible to store both a "Qubit" and a classical binary (or trinary) data value in the same molecule or atom simultaneously, because you can theoretically manipulate both the magnetism, or "spin", and the classical, physical "rotation" or "orientation" as seperate data units.

Again, at the molecular level, it theoretically should be possible to store both a "Qubit" and a "trinary digit" in each and every molecule, just using the scheme above. Actually designing a device capable of doing this is probably incredibly hard.

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