Thursday, November 3, 2016

Quantum computing researcher compares two breakthrough experiments

Arne Laucht is a Research Fellow at the School of Electrical Engineering & Telecommunications at the University of New South Wales, in Australia, and the lead author of a paper documenting a breakthrough experiment that involved maintaining “quantum superposition” of an electron spin for ten times longer than ever achieved previously, thereby making it easier to preserve and work with information on the quantum level for longer periods and to use it to perform more calculations using capabilities generated and supported by quantum effects..

You can learn more about this work in “Quantum computers: 10-fold boost in stability achieved."  The work shows how qubits “dressed” with an oscillating electromagnetic field are more stable than “undressed” qubits without one.  “Qubits” are the basic building blocks of quantum computing, and can perform multiple calculations simultaneously, due to the probabilistic nature of atomic structure at the quantum level.

As Laucht says in this article:

“We have now implemented a new way to encode the information: we have subjected the atom to a very strong, continuously oscillating electromagnetic field at microwave frequencies, and thus we have ‘redefined’ the quantum bit as the orientation of the spin with respect to the microwave field.”

Dr. Laucht was kind enough to provide Etopia News with a statement comparing the work being done with quantum computing technology in his lab with related work being done by the Sandia-Harvard team reported on recently by Etopia News here and here.

Here’s what he had to say:

The work done by the Sandia-Harvard team is a very nice demonstration of an all-optical switch using a single SiV [silicon vacancy] centre in diamond integrated in a photonic crystal nanobeam cavity, and the entanglement of two SiV centres via the cavity. Aspects of these experiments have already been demonstrated in other materials using other quantum systems, so the real novelty is the demonstration of all of that within a single chip, with the potential to scale the system to multiple colour centres.

“The physical system that was used by the Sandia-Harvard team is completely different to the one that we are using. They are using excitonic qubits while we are using spin qubits. Their qubits couple directly to the electric field component of light, while our qubits couple to the magnetic field component of microwaves. In principle, it would be possible to demonstrate the entanglement of two spin qubits via a microwave cavity (which would correspond to the measurements from the Sandia-Harvard team in our physical system), however we would have to use special tricks to get the coupling strengths large enough to see these effects. This could possibly be done using the dressed qubits that we have demonstrated, or alternatively using the flip-flop states of the phosphorus donor (see ).

“I hope that helps to clarify the connection between the different experiments.”

Separated as they are by thousands of miles of physical space, these quantum researchers are nevertheless still “entangled” in their efforts to discover and apply quantum mechanical principles that could transform computing and the world.  It’s almost “spooky action at a distance,” in which physically-separated-but-entangled quantum states can function as a single, unitary entity.

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