Quantum noise in SQUIDS

Journal Article · Sun May 01 04:00:00 EDT 1983 · IEEE Trans. Magn.; (United States)

DOI:https://doi.org/10.1109/TMAG.1983.1062489· OSTI ID:5483240

Danilov, V; Likharev, K; Zorin, A

The sensitivity limitations due to thermal, quantum and shot noise are calculated for dc and ac SQUIDs. Two approximations are used for the Josephson junctions: RSJ model with the equilibrium source of thermal-and quantum fluctuations and microscopic theory of the tunnel junctions with small capacitance (the latter theory takes into account the shot noise as well). The ultimate ''output'' sensitivity epsilon /SUB V/ is shown to be substantially less than the Planck's constant h, for the both types of SQUIDs. This result does not contradict to the uncertainty principle, because the ''total'' sensitivity epsilon rather than epsilon /SUB V/ is an adequate figure of merit of SQUID as a linear amplifier. The total sensitivity is shown to be, in fact, limited by the quantum fluctuations, epsilon>h/2. These fluctuations originate in the shunting resistances of the dc SQUID, while in the ac SQUID they are due to quantum noise of the following stage of amplification. Nevertheless, even the total sensitivity epsilon can be made less than h/2, if the ''degenerate'' type of SQUID is used, being sensitive to the only one of the quadrature components of the input signal.

• Research Organization: Dept. of Physics, Moscow State Univ., Moscow 117234
• OSTI ID: 5483240
• Journal Information: IEEE Trans. Magn.; (United States), Journal Name: IEEE Trans. Magn.; (United States) Vol. 19:3; ISSN IEMGA
• Country of Publication: United States
• Language: English

Related Subjects

420201* -- Engineering-- Cryogenic Equipment & Devices
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AMPLIFIERS
ELECTRONIC EQUIPMENT
EQUIPMENT
FLUXMETERS
JOSEPHSON JUNCTIONS
JUNCTIONS
MEASURING INSTRUMENTS
MECHANICS
MICROWAVE EQUIPMENT
NOISE
QUADRATURES
QUANTUM MECHANICS
SENSITIVITY
SIGNALS
SQUID DEVICES
SUPERCONDUCTING DEVICES
SUPERCONDUCTING JUNCTIONS
TUNNEL EFFECT
UNCERTAINTY PRINCIPLE