

















Interdisciplinary research 
Research on SMMs is a multidisciplinary field, which involves close collaboration between Physics and Chemistry. The research objectives of this proposal are focused on the understanding of fundamental aspects of the physicals of these materials, as well as possible applications in information technology. This is a rapidly advancing field with many recent fundamental discoveries. For example, recently a crossover between quantum and thermal regimes of the magnetic relaxation has been observed and studied [9]. Berry phase interference between different quantum tunneling trajectories has also been found [10], with minima in the tunnel rates for discrete values of an external transverse magnetic field. This allows turning on and off the quantum tunneling by slightly varying the magnitude of the applied magnetic field. Moreover, a very recent observation established that quantum magnetic states of neighboring molecules can be quantum entangled [11]. Also, the observation of quantum coherence between superposition states of opposite spin projections has been achieved recently by the PI and collaborators at NYU [12]. These findings led to an extension of the field since 1996, involving more than twenty experimental groups around the world, working with many different measurement techniques. These include dc and ac magnetometry, highfrequency electron paramagnetic resonance (EPR), neutron scattering or calorimetric experiments as well as some new high sensitivity measurement techniques that have been developed in the field (i.e. microHall effect and microSQUID magnetometries). Moreover, magnetic fields are always necessary in the study of magnetic systems. Particularly in these materials, the ability to apply high magnetic fields is a precious tool that can be used to tune the energy scale of the spin system and allows the use of experimental techniques with very different characteristic measuretimes, ranging from d.c. magnetometry to high frequency EPR, NMR or infrared spectroscopy. All these techniques of measurement have led to an increasing number of fundamental physical and chemical properties of SMMs to be examined, providing a better understanding of the principles that govern the quantum behavior of nanoscale magnetic systems. For example, the PI has recently found that the causes and origin of MQT in SMMs are due to changes (disorder) in the symmetry of the molecules and molecular constituents (solvent molecules) of these materials [13,14]. This research answered fundamental questions about the nature of MQT in SMMs that, which remained poorly understood from the beginning of the field, and established that the structural composition and symmetry of SMMs determine the quantum behavior of the magnetization. Therefore, structural characteristics such as symmetry, composition, spin, anisotropy or inter and intramolecule interactions of SMMs can be chemically engineered in order to obtain more appropriate materials for a specific purpose. In general, SMMs allow the study of a number of fundamental phenomena of quantum mechanics in the magnetism of nanostructures and constitutes a bottomup approach to nanomagnetism molecular engineering. 
Applications: Quantum information processes 

Among the proposed applications of SMMs in technology (i.e. magnetic cooling [15], microwave lasers [16], etc…), some suggest that it is possible to use them as magnetic molecular qubits for quantum information and computation processes [7]. For an isolated spin, e.g. initially up, the transverse terms in the Hamiltonian that give rise to QTM would lead to coherent oscillations between the unperturbed up and down spin states at a frequency proportional to the tunnel splitting—this is known as quantum coherence. Coherent oscillations of many periods are necessary for quantum computing with SMMs. However, the electronic spins in SMMs interact with their environment which includes nuclear spins, lattice vibrations and other SMMs in the crystal that introduce decoherence processes. Decoherence is a general problem for quantum computation and must be reduced as much as possible. In SMMs, the degree of decoherence is unknown and has only been indirectly estimated [11,12]. Via the synthesis of new materials and the use of new measurement methods that will be developed in our group, it will be possible to study how decoherence appears and what are the causes of its appearance and its relation to the internal structure and composition of a SMM. An understanding of the dynamics of MQT in SMMs is indispensable to the application of these systems for quantum computing and quantum information process. 

References 

[1]. J. R. Friedman, M. P. Sarachik, J. Tejada and R. Ziolo, Phys. Rev. Lett.76, 3830 (1996); J. M. Hernandez et al., Europhys. Lett. 35, 301 (1996); L. Thomas, F. Lionti, R. Ballou, D. Gatteschi, R. Sessoli and B. Barbara, Nature 383,145 (1996). [2] E. M. Chudnovsky and J. Tejada, Macroscopic Quantum Tunneling of Magnetic Moment. Cambridge University Press, Cambridge, England, (1998) [3] C. H. Van der Val, A. C. J. ter Haar, F. K. Wilhelm, R. N. Schouten, C. J. P. M. Harmans, T. P. Orlando, Seth Lloyd, and J. E. Mooij, Science 290, 773 (2000); I. Chiorescu, Y. Nakamura, C. J. P. Harmans and J. E. Mooij, Science 299, 1869 (2003). [4] Y. Nakamura, Yu. A. Pashkin, J. S. Tsai, Nature 398, 786 (1999); Y. A. Pashkin, T. Yamamoto, O. Astafiev, Y. Nakamura, D. V. Averin, J. S. Tsai, Nature 421, 823 (2003). [5] A. J. Leggett, Prog. Theor. Phys. Suppl. 69, 80 (1980). [6] See, for example, E. M. Chudnovsky, Phys. Rev. Lett. 92, 120405 (2004), and references herein. [7] M. N. Leuenberger and D. Loss, Nature 410, 789 (2001); J. Tejada, E. M. Chudnovsky, E. del Barco and J. M. Hernandez, Nanotechnology 12, 181 (2001). [8] A. J. Tasiopoulos, A. Vinslava, W. Wernsdorfer, K. A. Abboud and G. Christou, arxiv:condmat/0404625 (2004). [9] L. Bokacheva, A. D. Kent, and M. A. Walters, Phys. Rev. Lett. 85, 4803 (2000); A. D. Kent, Y. Zhong, L. Bokacheva, D. Ruiz, D. N. Hendrickson and M. P. Sarachik, Europhys. Lett. 49, 521 (2000). [10] W. Wernsdorfer and R. Sessoli, Science 284, 133 (1999). [11] W. Wernsdorfer, N. AliagaAlcalde, D. N. Hendrickson, G. Christou, Nature 416, 406 (2002); S. Hill, R. S. Edwards, N. AliagaAlcalde and G. Christou, Science 302, 1015 (2003). [12] E. del Barco, A. D. Kent, E. C. Yang and D. N. Hendrickson, arXiv:condmat/0405331 (2004). [13] E. del Barco, A. D. Kent, E. M. Lumberger, D. N. Hendrikson and G. Christou, Phys. Rev. Lett. 91, 047203 (2003). [14] E. del Barco, A. D. Kent, S. Hill, J. M. North, N.S. Dalal, E. M. Rumberger, D. N. Hendrickson, N. Chakov and G. Christou, arXiv:condmat/0404390 (2004). [15] M. Sales, J. M. Hernandez, J. Tejada, and J. L. Martínez, Phys. Rev. B60, 14557 (1999). [16] E. M. Chudnovsky and D. A. Garanin, Phys. Rev. Lett. 89, 157201 (2002). [17] R. S. Edwards, S. Maccagnano, E. C. Yang, S. Hill, W. Wernsdorfer, D. Hendrickson and G. Christou, J. App. Phys. 93, 7807 (2003).. 