August 4, 2004

I'm published

Posted by Arcane Gazebo at August 4, 2004 2:06 PM

in the August issue of Review of Scientific Instruments.

Review of Scientific Instruments -- August 2004 -- Volume 75, Issue 8, pp. 2541-2544

Low-noise computer-controlled current source for quantum coherence experiments

S. Linzen, T. L. Robertson, T. Hime, B. L. T. Plourde, P. A. Reichardt, and John Clarke
Department of Physics, University of California, Berkeley, California 94720-7300

(Received 10 February 2004; accepted 2 May 2004; published online 26 July 2004)

We describe a dual current source designed to provide static flux biases for a superconducting qubit and for the Superconducting QUantum Interference Device (SQUID) which measures the qubit state. The source combines digitally programmable potentiometers with a stabilized voltage source. Each channel has a maximum output of ±1  mA, and can be adjusted with an accuracy of about ±1  nA. Both current supplies are fully computer controlled and designed not to inject digital noise into the quantum bit and SQUID during manipulation and measurement of the flux. For a 275  µA setting, the measured noise current is 2.6 parts per million (ppm) rms, in a bandwidth of 0.0017–10  Hz, from which we estimate dephasing times of hundreds of nanoseconds in the particular case of our own qubit design. By resetting the current every 10  min, we are able to reduce the drift to no more than 5  ppm at a current of 750  µA over a period of 3 days. The current source has been implemented without thermal regulation inside a radiofrequency-shielding room, and is used routinely in our quantum coherence experiments. ©2004 American Institute of Physics.


*holding my spinning head*

Um...congratulations? Wow. Um. Someday will you explain it to me?

Posted by: Tracy | August 4, 2004 3:34 PM


Our experiment is a study of quantum bits ("qubits") which perform the same function in a quantum computer as bits in a classical computer. For purposes of explaining this paper, never mind the details of what qubits are or how they work. The important thing is that to perform operations on a qubit we irradiate it to microwaves, but for this to work the qubit has to be tuned to the frequency of radiation we're using. We also use a SQUID (superconducting quantum interference device, a magnetic field detector) to detect the magnetic field from the qubit, but this device needs to be tuned as well to be sensitive to the qubit state. We accomplish both tunings by applying magnetic fields, and the easiest way to produce magnetic fields is by generating electric currents. The paper describes a circuit we built to generate these currents for tuning the device, which had to be very accurate, very stable, and computer controlled; it's more of an engineering result than a scientific one. Much of the abstract consists of various specifications of the circuit's stability.

Posted by: Arcane Gazebo | August 4, 2004 4:53 PM

That's just what I would have said.

Posted by: Dad | August 4, 2004 5:03 PM

Being published is cool---of course, that's not one of the journals I read. :)


The feeling of publishing one's first paper is a very good one indeed.

Now you just need to do some theory so there's aren't so many authors on the paper... :P

Posted by: Mason Porter | August 5, 2004 4:42 PM

Hey, you're published! Too bad scientists don't get publicity budgets and tour schedules though...

Posted by: Sarah | August 8, 2004 7:17 AM
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