g‐Engineering in Hybrid Rotaxanes To Create AB and AB₂ Electron Spin Systems: EPR Spectroscopic Studies of Weak Interactions between Dissimilar Electron Spin Qubits

Abstract

Hybrid [2]rotaxanes and pseudorotaxanes are reported where the magnetic interaction between dissimilar spins is controlled to create AB and AB2 electron spin systems, allowing independent control of weakly interacting S=${{ 1/2 }}$ centers.

Cr7Ni Wheels: Supramolecular Tectons for the Physical Implementation of Quantum Information Processing

“…The requirement of ammonium cations that template the formation of {Cr7Ni} wheels have also been exploited by Winpenny's group to create hybrid inorganic-organic rotaxanes [53][54][55][56][57]. They have shown that it is possible to obtain in high yields [2]-and [3]-rotaxanes from the reaction in pivalic acid of chromium(III) trifluoride, a nickel(II) pivalate salt, and a thread with one or two amines, respectively, that would be protonated during the reaction and then act as template cations.…”

Measuring Spin⋅⋅⋅Spin Interactions between Heterospins in a Hybrid [2]Rotaxane

“…Recently,A rdavan et al have shown using double electronelectron resonance (DEER) spectroscopy that the interaction between electron spins in {Cr 7 Ni}r ings can be controlled to fall within the range needed for two qubit gates.[3] These studies were performed on dimers of {Cr 7 Ni}rings [4] where the S = 1/2 spins in each half are identical.Systems containing different spins also have great potential for QIP as there is then the possibility of manipulating each spin separately.T his underpins the g-engineering idea proposed by Takui and co-workers for organic radicals [5] and work employing heterometallic lanthanide dimers.[6] Large differences in g-values could also be used as am eans to implement entangling two qubit gates.[7] Quantifying weak interactions between very different spins is challenging.I n cases where the interaction can easily be measured, for example by magnetometry or continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy, [8] the interaction will be too large to permit implementation of both one-and two-qubit gates in the same molecule.[3] CW EPR spectroscopy can still be au seful tool to investigate dipolar interactions;byobserving the line broadening of aN triplet in at wo-qubit structure,Z hou et al showed the existence of ad ipolar interaction that they could estimate in conjunction with spin density calculations.[9] On the other hand, DEER spectroscopy, [10] while ap owerful tool to measure weak interactions by directly manipulating two weakly interacting spins with specific microwave pulses,i s limited as the bandwidth of the microwave source must encompass the resonant frequency of both electron spins.Here we report at wo-qubit assembly comprising an organic radical within the thread of ah ybrid [2]rotaxane containing a{Cr 7 Ni}ring:this is aheterospin system where the constituent spins possess vastly different g-values.T oquantify the weak interaction between the spins we use "Relaxation Induced Dipolar Modulation" (RIDME) spectroscopy, [11] which has been developed in structural biology to measure distances between dissimilar spins. [12] To make the [2]rotaxane an organic thread was synthesized containing as econdary amine and terminating in an aldehyde (see the Supporting Information for details).…”

“…[7] Quantifying weak interactions between very different spins is challenging.I n cases where the interaction can easily be measured, for example by magnetometry or continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy, [8] the interaction will be too large to permit implementation of both one-and two-qubit gates in the same molecule.…”

“…[6] Large differences in g-values could also be used as am eans to implement entangling two qubit gates. [7] Quantifying weak interactions between very different spins is challenging.I n cases where the interaction can easily be measured, for example by magnetometry or continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy, [8] the interaction will be too large to permit implementation of both one-and two-qubit gates in the same molecule. [3] CW EPR spectroscopy can still be au seful tool to investigate dipolar interactions;byobserving the line broadening of aN triplet in at wo-qubit structure,Z hou et al showed the existence of ad ipolar interaction that they could estimate in conjunction with spin density calculations.…”

“…)a nd D para = À18(3) MHz (0.0006 cm À1 ), respectively.I np revious work where we looked at the interaction between ar ing and as ingle Cu II center [8] an exchange interaction of around 0.02 cm À1 was Figure 2. 33.823 GHz FSED spectra at 5Kon af rozen toluene solution.…”