Thomas B. Faust

Linking heterometallic rings for quantum information processing and amusement

Linking polymetallic cages can be a method for creating new structures and new properties. In this tutorial review we use heterometallic anti-ferromagnetically coupled rings (AF-rings) as exemplars for three approaches that can be used to link cage compounds. The first of three routes involves an ion-pair interaction supported by hydrogen-bonding interactions, which allows the synthesis of hybrid rotaxanes among other materials. The second route involves functionalising the exterior of the AF-ring so that it will act as a Lewis base; complexes involving coordination of pyridine to bridging monometallic and dimetallic fragments are discussed. The third route involves creating a vacancy on one site of the AF-ring, and then using the ring as a Lewis acid. Di-imine ligands can then be used to link the AF-rings into dimers. A brief discussion of the physical properties of these systems is also included.

Coherent control of a classical nanomechanical two-level system

Coherent control of two flexural modes of a nanoscale oscillator using radiofrequency signals is now demonstrated. This oscillator is analogous to quantum two-level systems such as superconducting circuits and quantum dots, and therefore this technique raises the possibility of information processing using nanomechanical resonators.

Nonadiabatic Dynamics of Two Strongly Coupled Nanomechanical Resonator Modes

The Landau-Zener transition is a fundamental concept for dynamical quantum systems and has been studied in numerous fields of physics. Here, we present a classical mechanical model system exhibiting analogous behavior using two inversely tunable, strongly coupled modes of the same nanomechanical beam resonator. In the adiabatic limit, the anticrossing between the two modes is observed and the coupling strength extracted. Sweeping an initialized mode across the coupling region allows mapping of the progression from diabatic to adiabatic transitions as a function of the sweep rate.

Chemical control of spin propagation between heterometallic rings

We present a synthetic, structural, theoretical, and spectroscopic study of a family of heterometallic ring dimers which have the formula [{Cr(7)NiF(3)(Etglu)(O(2)CtBu)(15)}(2)(NLN)], in which Etglu is the pentadeprotonated form of the sugar N-ethyl-D-glucamine, and NLN is an aromatic bridging diimine ligand. By varying NLN we are able to adjust the strength of the interaction between rings with the aim of understanding how to tune our system to achieve weak magnetic communication between the spins, a prerequisite for quantum entanglement. Micro-SQUID and EPR data reveal that the magnetic coupling between rings is partly related to the through-bond distance between the spin centers, but also depends on spin-polarization mechanisms and torsion angles between aromatic rings. Density functional theory (DFT) calculations allow us to make predictions of how such chemically variable parameters could be used to tune very precisely the interaction in such systems. For possible applications in quantum information processing and molecular spintronics, such precise control is essential.

Signatures of two-level defects in the temperature-dependent damping of nanomechanical silicon nitride resonators

The damping rates of high quality factor nanomechanical resonators are well beyond intrinsic limits. Here, we explore the underlying microscopic loss mechanisms by investigating the temperature-dependent damping of the fundamental and third harmonic transverse flexural mode of a doubly clamped silicon nitride string. It exhibits characteristic maxima reminiscent of two-level defects typical for amorphous materials. Coupling to those defects relaxes the momentum selection rules, allowing energy transfer from discrete long-wavelength resonator modes to the high frequency phonon environment.

Proton NMR Study of Cr-Co Heterometallic Wheel Complexes

(1)H NMR spectra of the paramagnetic heterometallic complexes of general formula [cation][Cr(7)CoF(8)(O(2)C(t)Bu)(16)] have been recorded. The NMR spectra have allowed the investigation of the structure of these complexes in solution. These experiments show that the complexes are stable and maintain the solid state structure in solution, retaining the protonated amine in the cavity of the heterometallic ring.

Controlling magnetic communication through aromatic bridges by variation in torsion angle

A series of heteroaromatic bridging ligands are employed in the synthesis of a family of paramagnetic, heterometallic ring dimers. The extent of spin propagation between the rings via the organic conduit is investigated through micro-SQUID magnetometry and EPR spectroscopy from which conclusions over the mechanism of spin-communication are drawn.

Caesium ion sequestration by a fluoro-metallocrown [16]-MC-8

A fluoro-metallocrown selectively binds caesium, extracting it from aqueous solutions into an organic layer; the binding of Cs is monitored by (1)H-NMR of the paramagnetic complexes.

Classical Stückelberg interferometry of a nanomechanical two-mode system

Suckelberg interferometry is a phenomenon that has been well established for quantum-mechanical two-level systems. Here, we present classical two-mode interference of a nanomechanical two-mode system, realizing a classical analog of Stuckelberg interferometry. Our experiment relies on the coherent energy exchange between two strongly coupled, high-quality factor nanomechanical resonator modes. Furthermore, we discuss an exact theoretical solution for the double-passage Stuckelberg problem by expanding the established finite-time Landau-Zener single-passage solution. For the parameter regime explored in the experiment, we find that the Stuckelberg return probability in the classical version of the problem formally coincides with the quantum case, which reveals the analogy of the return probabilities in the quantum-mechanical and the classical version of the problem. This result qualifies classical two-mode systems at large to simulate quantum-mechanical interferometry.