Measurement of quantum noise in a single-electron transistor near the quantum limit

Abstract

Operating a superconducting single-electron transistor near a double Cooper-pair resonance allows it to achieve a charge-detection sensitivity of just 3.6 times the ultimate quantum limit. Quantum measurement has challenged physicists for almost a century. Classically, there is no lower bound on the noise a measurement may add. Quantum mechanically, however, measuring a system necessarily perturbs it. When applied to electrical amplifiers, this means that improved sensitivity requires increased backaction that itself contributes noise. The result is a strict quantum limit on added amplifier noise1,2,3,4,5,6. To approach this limit, a quantum-limited amplifier must possess an ideal balance between sensitivity and backaction; furthermore, its noise must dominate that of subsequent classical amplifiers7. Here, we report the first complete and quantitative measurement of the quantum noise of a superconducting single-electron transistor (S-SET) near a double Cooper-pair resonance predicted to have the right combination of sensitivity and backaction8. A simultaneous measurement of our S-SET’s charge sensitivity indicates that it operates within a factor of 3.6 of the quantum limit, a fourfold improvement over the nearest comparable results9.

Cite this article

Xue, W., Ji, Z., Pan, F. et al. Measurement of quantum noise in a single-electron transistor near the quantum limit. Nature Phys 5, 660–664 (2009). https://doi.org/10.1038/nphys1339

View full text

>> Full Text:   Measurement of quantum noise in a single-electron transistor near the quantum limit