Phonon-Assisted Tunneling in the Quantum Regime of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>Mn</mml:mi></mml:mrow><mml:mrow><mml:mn>12</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>Acetate

Chiorescu, Irinel; Giraud, R.; Jansen, A. G. M.; Caneschi, Andréa; Barbara, B.

doi:10.1103/physrevlett.85.4807

Cited by 72 publications

(98 citation statements)

References 26 publications

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“…Fortunately, transverse field is only a prefactor in front of a small term in Eq. (32). This allows one to …”

Section: Distribution Of Tunnel Splittingsmentioning

confidence: 99%

“…This effect is not dramatic since odd and even resonances only differ by a prefactor in front of high power of the small ratio E/D, see Eqs. (30) and (32).…”

Section: Tunnel Splittingsmentioning

confidence: 99%

“…9,11,32 Suggested explanations include collective effects due to dipolar interaction between Mn 12 molecules 43 and fluctuating random noise. 48 The first requires some special initial conditions which are not satisfied in experiment 45,46,47 while the second requires certain assumptions about the spectrum of fluctuations.…”

Section: This Is Because H = −Dsmentioning

confidence: 99%

“…6 There exist two macroscopic experimental approaches to the study of spin tunneling in Mn 12 (see, e.g., Refs. 6,7,8,25,26,27,28,29,10,9,30,11,12,31,32 and references therein). Both clearly demonstrate the effect of resonant spin tunneling.…”

Section: Introductionmentioning

confidence: 99%

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Dislocation-induced spin tunneling inMn12acetate

Garanin

Chudnovsky

2002

Phys. Rev. B

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Comprehensive theory of quantum spin relaxation in Mn12 acetate crystals is developed, that takes into account imperfections of the crystal structure and is based upon the generalization of the LandauZener effect for incoherent tunneling from excited energy levels. It is shown that linear dislocations at plausible concentrations provide the transverse anisotropy which is the main source of tunneling in Mn12. Local rotations of the easy axis due to dislocations result in a transverse magnetic field generated by the field applied along the c-axis of the crystal, which explains the presence of odd tunneling resonances. Long-range deformations due to dislocations produce a broad distribution of tunnel splittings. The theory predicts that at subkelvin temperatures the relaxation curves for different tunneling resonances can be scaled onto a single master curve. The magnetic relaxation in the thermally activated regime follows the stretched-exponential law with the exponent depending on the field, temperature, and concentration of defects.

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“…Fortunately, transverse field is only a prefactor in front of a small term in Eq. (32). This allows one to …”

Section: Distribution Of Tunnel Splittingsmentioning

confidence: 99%

“…This effect is not dramatic since odd and even resonances only differ by a prefactor in front of high power of the small ratio E/D, see Eqs. (30) and (32).…”

Section: Tunnel Splittingsmentioning

confidence: 99%

Section: This Is Because H = −Dsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Dislocation-induced spin tunneling inMn12acetate

Garanin

Chudnovsky

2002

Phys. Rev. B

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“…One way to reduce their effects (apart from going to very low T [23]) would be to go to lower dimensional spin networks; recent progress in attaching and assembling nanomagnets on surfaces [24], or even in chain structures [25] might then yield viable architectures. Designs in which dipolar inter-qubit couplings can be made small -eg., low-spin systems like V 15 or Cr 7 Ni [26] -and where the inter-qubit couplings responsible for information manipulation can be switched on and off, are clearly favored.…”

mentioning

confidence: 99%

Pairwise Decoherence in Coupled Spin Qubit Networks

2006

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Experiments involving phase coherent dynamics of networks of spins, such as echo experiments, will only work if decoherence can be suppressed. We show here, by analyzing the particular example of a crystalline network of Fe8 molecules, that most decoherence typically comes from pairwise interactions (particularly dipolar interactions) between the spins, which cause 'correlated errors'. However at very low T these are strongly suppressed. These results have important implications for the design of quantum information processing systems using electronic spins. [4], are a leading candidate for this. In some of these systems (notably magnetic molecules), the individual qubit properties are controlled by chemistry instead of by nano-engineering (the 'bottom-up' approach [5]), with spin Hamiltonians and inter-molecular spin couplings known and controlled to at least 3 significant figures. Spin also possesses other advantages -information can be encoded in the topological spin phase, with no need to move electrons around. Using spins for quantum information will ultimately require (i) detecting and manipulating single-spins, and (ii) understanding and controlling decoherence.Single spins have been detected in a few ingenious experiments [6], but we don't yet have a general-purpose, single-spin detection/manipulation tool, analogous to single atom STM/AFM. Consider, however, an array of spins, each having a low-energy doublet of states whose splitting is easily controlled by a magnetic field. Even without addressing individual spins, one can still demonstrate coherent qubit operation, using external AC fields to promote resonant transitions between levels, and pulse sequences (e.g. spin echo) to manipulate the phase and measure decoherence rates. This approach is well known for room-temperature bulk NMR quantum computing [7]. Here we treat the case of electronic spins which, unlike nuclei, can be highly polarized at low T . We introduce a formalism allowing the description of any set of spin qubits obtained by truncation to low energy of a larger system, showing how the low-T decoherence rate can be dramatically reduced, even for a network of mutually coupled qubits. To be specific, we treat the case where the qubit is obtained by taking an anisotropic highspin nanomagnet [8] with easy axisẑ, subject to a large transverse field H ⊥ (Fig. 1), giving a low-energy doublet of states with easily controllable energy separation, Fig. 2(a)]. To make quantitative and testable predictions, we then calculate the spin-echo decay rate in a network of Fe 8 molecules. This is a clean, crystalline and stoichiometric chemical compound [8,9], where the inter-qubit and the qubit-environment interactions are known accurately, and it should be a good 'benchmark' for quantitative test of the theory. The resonance experimental set-up and the spin states on the Bloch sphere; (c) At T ≪ ∆o/kB only the lowestenergy eigenstate is populated, |S = 2 −1/2 (|Z+ + |Z− ). A short µwave pulse prepares the system in the |Z+ state (π/2 rotation, correspo...

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Quantum Tunneling of Magnetization in Molecular Complexes with Large Spins – Effect of the Environment

Tupitsyn

Barbara

2001

Magnetism: Molecules to Materials

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The search for quantum effects at the "macroscopic scale" in magnetism started in the early seventies after it was shown that single crystals of rare-earth intermetallics (Dy 3 Al 2 , SmCo 3.5 Cu 1.5 ) exhibit fast magnetic relaxation in the Kelvin range. This phenomenon was interpreted in terms of magnetization reversal by quantum tunneling, below a certain crossover temperature. The magnetization reversal of the bulk crystals being the sum of the elementary reversals of single domain blocks (nucleation of the so-called Barkhausen jumps), this type of study is equivalent to the study of single nanoparticles, but with many complications (size, energy barrier and switching field distributions, effects of domain walls, various dissipation effects…).More recently there have been developments in various disciplines that have led to great progress in the obtention of different types of nanoparticles. In material science, magnetic materials have been produced as isolated aggregates, as deposits of aggregates, as carbon nanotubes and nanocages filled with magnetic material, as electrodeposits of magnetic material in nanoporous polycarbonate membranes, as well as dispersals in polymers. Molecular chemistry has produced molecules with giant spins and colloidal chemistry has used micelles as microreactors to make all sorts of new magnetic nanoparticles. Naturally occurring biological systems have given us ferritin and biochemistry has provided us with their artificial analogues.Among all these systems, an exciting type of material has emerged for the study of macroscopic tunneling in magnetism -namely, molecular crystals with identical magnetic molecules. Despite their relatively large size and the dipolar interactions between their magnetic moments, these molecules clearly exhibit quantum tunneling of magnetization. The focus of this article is on two of these materials (i) the spin cluster system so-called "Mn 12 -ac", which is a Manganese acetate. This system was the first to 3 exhibit what is referred to as "resonant tunneling of magnetization". (ii) Another analogous system is the so-called "Fe 8 ", in which the same phenomenon was observed afterwards, but at lower temperature, which allows easier experimental studies. Mn12 -acetate. 2.1. Experimental results. Over the past years a lot of experimental and theoretical works were performed on molecules of [Mn 12 O 12 (CH 3 COO) 16 (H 2 O) 4 ]. This molecule has a tetragonal symmetry [1] and contains a cluster of twelve Mn ions divided into two shells (four Mn 4+ ions from inner shell with spin S=3/2, surrounded by eight Mn 3+ ions from the outer shell with spin S=2) with strong antiferromagnetic couplings (frustrated triangles, see Figure 1). They form a collective ground state spin S=10 with magnetic moment M=gSµ Β ≈ 20µ B (g ≈ 2 is the Lande factor) [2]. These molecules are chemically identical and form a crystal with an average distance between Mn 12 molecules of the order of 15 ? [1]. Intermolecular exchange interactions are negligible and dipolar interactions are a...

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Phonon-Assisted Tunneling in the Quantum Regime ofMn12Acetate

Cited by 72 publications

References 26 publications

Dislocation-induced spin tunneling inMn12acetate

Dislocation-induced spin tunneling inMn12acetate

Pairwise Decoherence in Coupled Spin Qubit Networks

Quantum Tunneling of Magnetization in Molecular Complexes with Large Spins – Effect of the Environment

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