Volume 77, Number 5, March 2007
Article Number 58005
Number of page(s) 4
Section Interdisciplinary Physics and Related Areas of Science and Technology
Published online 22 February 2007
EPL, 77 (2007) 58005
DOI: 10.1209/0295-5075/77/58005

Flux qubit as a sensor of magnetic flux

E. Il'ichev1 and Ya. S. Greenberg2

1  Institute for Physical High Technology - P.O. Box 100239, D-07702 Jena, Germany
2  Novosibirsk State Technical University - 20 K. Marx Ave., 630092 Novosibirsk, Russia

received 17 November 2006; accepted in final form 17 January 2007; published March 2007
published online 22 February 2007

A magnetometer based on the quantum properties of a superconducting flux qubit is proposed. The main advantage of this device is that its sensitivity can be below the so-called "standard quantum limit" (for an oscillator this is half of the Plank constant). Moreover its transfer functions relative to the measured flux can be made to be about $10\,{\rm mV}/\Phi _{0}$, which is an order of magnitude more than the best value for a conventional DC SQUIDs with a direct readout. We analyze here the voltage-to-flux, the phase-to-flux transfer functions and the main noise sources. We show that the experimental characteristics of a flux qubit, obtained in recent experiments, allow the use of a flux qubit as magnetometer with energy resolution close to the Planck constant.

85.25.Cp - Josephson devices.
85.25.Dq - Superconducting quantum interference devices (SQUIDs).
84.37.+q - Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.).

© Europhysics Letters Association 2007