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Science 16 October 1992:
Vol. 258. no. 5081, pp. 414 - 421
DOI: 10.1126/science.258.5081.414
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Articles

Macroscopic Quantum Effects in Nanometer-Scale Magnets

David D. Awschalom 1, David P. DiVincenzo 2, and Joseph F. Smyth 1

1 Department of Physics, University of California, Santa Barbara, CA 93106
2 IBM Research Division, Thomas J. Watson Research Center, Yorktown Heights, NY 10598

Quantum tunneling, the passage of a microscopic system from one state to another by way of a classically forbidden path, is theoretically possible in the macroscopic world. One can now make direct observations of such macroscopic quantum tunneling in very small magnetic structures. This is possible because of significant advances both in the ability to obtain magnetic systems of almost any desirable size, shape, and composition and in the development of superconducting instrumentation for the detection of extremely weak magnetic signals. As an example, measurements on magnetic horse spleen ferritin proteins with the predictions of quantum tunneling theory are discussed and shown.


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