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Quantum computing in molecular magnets


Shor and Grover demonstrated that a quantum computer can outperform any classical computer in factoring numbers1 and in searching a database2 by exploiting the parallelism of quantum mechanics. Whereas Shor's algorithm requires both superposition and entanglement of a many-particle system3, the superposition of single-particle quantum states is sufficient for Grover's algorithm4. Recently, the latter has been successfully implemented5 using Rydberg atoms. Here we propose an implementation of Grover's algorithm that uses molecular magnets6,7,8,9,10, which are solid-state systems with a large spin; their spin eigenstates make them natural candidates for single-particle systems. We show theoretically that molecular magnets can be used to build dense and efficient memory devices based on the Grover algorithm. In particular, one single crystal can serve as a storage unit of a dynamic random access memory device. Fast electron spin resonance pulses can be used to decode and read out stored numbers of up to 105, with access times as short as 10-10 seconds. We show that our proposal should be feasible using the molecular magnets Fe8 and Mn12.

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Figure 1: Double well potential seen by the spin due to magnetic anisotropies in Mn12.
Figure 2: Feynman diagrams F that contribute to S(5)m,s for s = 10 and m0 = 5 describing transitions (of 5th order in V) in the left well of the spin system (see Fig. 1).


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We thank G. Salis and J. Schliemann for useful comments. This work has been supported in part by the Swiss NSF and by the European Union Molnanomag network.

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Correspondence to Daniel Loss.

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Leuenberger, M., Loss, D. Quantum computing in molecular magnets. Nature 410, 789–793 (2001).

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