Fock states could hold clues to quantum memory components

December 23, 2008 By Miranda Marquit, feature

( -- “Fock states will play a role in the future of quantum computing,” Andrew Cleland tells “We have completed the first experimental measurement of the time decay of Fock states in a superconducting quantum circuit, and we believe this will provide useful information as we work toward developing a quantum computer.” Cleland is a professor at the University of California, Santa Barbara, and works with a group headed by John Martinis.

The UC Santa Barbara group used a microwave coplanar waveguide resonator with a superconducting qubit in order to provide the control needed to create, and to measure the decay of, the Fock states. “Learning more about the fundamentals of these states can provide us with some very practical information.” The group’s results are reported in Physical Review Letters: “Measurement of the Decay of Fock States in a Superconducting Quantum Circuit.” Haohua Wang, a postdoctoral scientist in the Martinis group, was the lead researcher on the experiment.

“What we found,” Cleland continues, “is that the time decay of these Fock states follows precisely what is expected in theory. It gives us some good information about how these states work, as well as a foundation on which we can build elements for a quantum computer.”

Cleland also points out that the work done by the Martinis group produced more than one photon for the experiment, and that hadn’t been done before. “Typically experiments use a combination of a zero photon Fock state and a one photon state. No one until now has developed the technology to show that you could controllably create states with more than one photon. We did.” The Martinis group results indicate that it is possible to control Fock states with up to 15 photons.

Because Fock states are the fundamental quantum states of a harmonic oscillator, they are important to study. “These oscillators occur in many natural systems,” Cleland explains. “The electronic versions we studied are known as electromagnetic resonators. These resonators have a number of uses for quantum communications and computing.”

One of the uses that such resonators might have includes memory elements for quantum computing. “Of course,” Cleland qualifies, “no one is close to doing the kinds of computations we’d like to be able to do, but this is a step that could get us there down the road.” The memory elements he refers to need a certain level of control that the Martinis group was able to develop with their present experimental setup.

“The applications associated with having more than one photon – one of the things we showed in our experiment – are not as clear as a one photon memory function,” Cleland admits. But he does believe that there could be uses for such states in quantum simulation. “Right now, simulating the interactions between molecules requires giant computers to work a long time. It’s not very efficient. Quantum simulation could help us more efficiently see accurate interactions with a relatively simple quantum simulator.”

Cleland concedes that the Santa Barbara group is more interested in building a quantum computer, even though he can see other possible uses for the work they have done. “We’ve created a level of control that might make it possible to program quantum memory, and that is exciting itself.”

More Information:
H. Wang, M. Hofheinz, M. Ansmann, R. C. Bialczak, E. Lucero, M. Neeley, A. D. O'Connell, D. Sank, J. Wenner, A. N. Cleland, and John M. Martinis. “Measurement of the Decay of Fock States in a Superconducting Quantum Circuit.” Physical Review Letters (2008). Available online:

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5 / 5 (1) Dec 23, 2008
I can imagine what was said by the guys who discovered Fock states. "Hey, what the fock is this?" "Fock if I know." "Hey, don't Fock with that!"
5 / 5 (1) Dec 23, 2008
Fock states! Title doesn't make sense to anyone without a PhD in physics :D
5 / 5 (1) Dec 24, 2008
Fock states! Title doesn't make sense to anyone without a PhD in physics :D

So only the Fockers wil get it. And only those who are really smart get to be a Focker. Tht's why there aren't many Fockers walking around. You would think the Fockers would be smart enough to choose a different name for Fock states. Because immature and unintelligent people will think that the Fockers are refering to a verb instead of a noun. those poor, misunderstood Fockers.
Dec 27, 2008
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not rated yet Dec 27, 2008
it's a sort of manipulation of publicity, analogous to behavior of medicinemanns of ancient era.

Except now the medicine men don't have to spit on the ground twice, do the hokey pokey, eat a lizard, and sacrifice a small cat to get anything done. Now they just spend years staring at the same three equations until they figure out something to do with them. Yay progress.
4 / 5 (4) Dec 28, 2008
I believe, this article will make a much easier to understand, what these guys are dealing with for most readers...
not rated yet Dec 28, 2008
and they never once mentioned a qubit !!!!!
not rated yet Jan 03, 2009
Hmmm, new and mysterious, wonder when it will be used with Global Warming.

"Global Warming is a Fock State and the debate is over."
not rated yet Jan 09, 2009
Hmmm, new and mysterious, wonder when it will be used with Global Warming.

"Global Warming is a Fock State and the debate is over."

I love how the first people to bring up global warming are the ones who complain about every article being tied into global warming. Oh, the hillarity.
5 / 5 (1) Jan 11, 2009
The usage of special term "Fock state" just makes the whole thing mysterious, new and apparently worth to research - and money spending. I.e. it's a sort of manipulation of publicity, analogous to behavior of medicinemanns of ancient era.

If thats the case, pity the poor researcher who decides to submit his grant proposal on Monte Carlo simulation of Fock states - why the reviewers might think the guy is going off to the brothel and gambling!

BTW - usually those who are reviewing these things are well aware of meanings and ramifications of the words used in the proposal, and those researchers that add too much BS are often left oscillating in a virtual Fock state.

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